Issue published May 1, 1970

S tudies of the possibility that thyroxine (T4) is converted to 3.5,3′-triiodo-L-thyronine (T3) in the extrathyroidal tissues in man have been conducted in 13 patients, all but two of whom were athyreotic or hypothyroid, and all of whom were receiving at least physiological replacement doses of synthetic sodium-L-thyroxine.T3 was found in the sera of all patients, in concentrations ranging between 243 and 680 ng/100 ml (normal range 170-270 ng/100 ml). These concentrations were far in excess of those which would have been expected on the basis of the T3 contamination of the administered T4, as measured by the same technique employed in the analysis of serum. When oral medication was enriched with ¹²⁵I-labeled T4 for 8 or more days, labeled T3 and tetraiodothyroacetic acid (Tetrac or TA₄) were found in the serum to the extent of approximately 2-5% of total radioactivity, as assessed by unidimensional paper chromatography. The same results were obtained with a specially purified lot of radioactive T4 containing less than 0.1% T3 as a contaminant. The identities of the ¹²⁵I-labeled T3 and TA₄ were verified by two-dimensional chromatography as well as by specific patterns of binding in serum. The labeled T3 isolated was bound by albumin and by T4-binding globulin (TBG), but not by T4-binding prealbumin (TBPA): in contrast the labeled TA₄ was bound by albumin and TBPA, but not by TBG.To exclude the possibility that the conversion of T4 to T3 was a peculiarity of the oral route of administration, the sera of two additional patients were obtained 48 hr after 7-day courses of daily intravenous injections of a mixture of stable and ¹²⁵I-labeled T4. Both stable and labeled T3 were likewise found in these sera.In contrast to earlier experiments in humans in which ¹³¹I-labeled T3 was not definitively demonstrated in serum after a single intravenous injection of ¹³¹I-labeled T4, the present findings are taken to provide conclusive evidence of the extrathyroidal conversion of T4 to T3 in man. These results raise once again the question of the extent to which the metabolic effect of T4 is mediated through the peripheral generation of T3.

P olymorphonuclear leukocytes from patients with chronic granulomatous disease (CGD) exhibit metabolic and bactericidal deficiencies that may be the result of inadequate production of H₂O₂. A hydrogen peroxide-generating system was, therefore, inserted into CGD leukocytes. This was accomplished by allowing the cells to phagocytize latex spherules coated with glucose oxidase. This produced an amelioration in the known metabolic deficiencies of these cells during phagocytosis: (a) intracellular (catalatic) formate oxidation dependent upon hydrogen peroxide production was enhanced fourfold; and (b) hexose monophosphate shunt activity, which other workers have shown to be at least partially dependent upon the availability of H₂O₂, was markedly stimulated. These data strengthen the evidence that the fundamental metabolic lesion in CGD cells during phagocytosis is indeed deficient production of hydrogen peroxide, probably, as previously shown, due to diminished oxidase for reduced nicotinamide adenine dinucleotide.

O bservations were made on the relation of the renin-angiotensin-aldosterone system and renal hemodynamic function to sodium balance in 43 pregnant dogs. Daily balance studies revealed that about 30-40% of ingested sodium was retained during the last half of pregnancy; during the same period, potassium balance was also positive but to a lesser extent. For groups of pregnant dogs, plasma renin activity (n = 14) and aldosterone secretion (n = 19) were significantly higher than normal; however, in some animals one or both functions were normal even though sodium retention was present. In contrast, plasma renin substrate concentration was consistently elevated during pregnancy in seven dogs. In a group of nine dogs in which both aldosterone secretion and plasma renin activity were measured, aldosterone secretion was elevated in the three dogs with the highest values for plasma renin activity; in two of the remaining six animals aldosterone secretion was elevated but plasma renin activity was normal or only slightly increased. The sequestration of sodium and water into the uterine contents was defined quantitatively in this study but evidence was lacking to support the idea that such changes led to renin release. The glomerular filtration rate (GFR) was significantly elevated throughout pregnancy but a significant decrease from the high level of mid-pregnancy occurred during the last half of pregnancy; this decrease in GFR probably contributed to the sodium retention. Administration of a large dose of deoxycorticosterone acetate (DOCA) to dogs in late pregnancy produced marked sodium retention but “escape” from the sodium-retaining steroid occurred. The data demonstrate that although increased activity of the renin-angiotensin-aldosterone system was frequently present during pregnancy, a normal rate of aldosterone secretion occurred. This finding and the observed “escape” from DOCA suggest the existence of sodium-retaining mechanisms other than the mechanism provided by a high plasma level of aldosterone.

T he present studies were performed to elucidate the mechanisms responsible for the impairment of glucose-stimulated insulin secretion observed in fasting. Rats fasted for 48 hr displayed marked impairment in their insulin secretory response to both oral and intravenous glucose. Glucose-stimulated insulin secretion was restored within 24 hr by refeeding; actinomycin D given before refeeding blocked the expected return of normal glucose-stimulated insulin secretion despite adequate food intake. Fasted rats refed a diet devoid of carbohydrate failed to display a return of normal insulin secretory responsiveness to oral glucose in contrast to rats fed isocalorically a high carbohydrate diet. Differences in insulin secretion in fed, fasted, and fasted-refed rats could not be attributed to changes in pancreatic insulin content. There was no significant difference in the insulin secretory response to aminophylline of fed, fasted, or fasted-refed rats. The intermittent pulsing of fasted rats with hyperglycemic episodes by the injection of small amounts of glucose (500 mg) intraperitoneally every 8 hr ameliorated the impairment of glucose-stimulated insulin secretion characteristic of the fasting state. These results suggest that the impairment of glucose-stimulated insulin secretion during fasting and its restoration by refeeding are regulated by changes in a glucose-inducible enzyme system in the pancreatic beta cell.

T he rate of eccrine sweating has been studied by collecting samples in unventilated capsules from human subjects following subdermal or intradermal injections of acetyl-β-methylcholine and under moderate total body heat exposure. The rate of sweating in a given area of skin could increase by recruitment of fresh glands, enhanced output of the already active glands, or some combination of both.A theoretical analysis shows how recruitment and enhancement can be calculated separately, assuming the existence of a maximal rate of sodium reabsorption by eccrine sweat glands, a sodium concentration of 145 μEq/ml in the precursor fluid, the absence of significant water reabsorption, and the absence of back-diffusion of sodium. The results indicate that, depending on the experimental conditions, an increased rate of sweating can be attributed mainly to recruitment, to enhancement, or to a combination of both.

T his study sought to elucidate the mechanism by which human red cells, in a variety of clinical settings, become coated in vivo with autologous complement components in the absence of anti-red cell autoantibodies demonstrable by standard methods. By means of a newly developed complement-fixing antibody consumption test, previously undetectable red cell-bound γG globulin could be detected and quantified. By this technique, the complement-coated red cells of 13 of 16 patients were shown to carry abnormally high numbers of γG molecules per cell, which were nevertheless below the level for detection by the direct antiglobulin test. Eluates were made from the red cells of seven of these patients and each eluate, when sufficiently concentrated, was capable of sensitizing normal human red cells (with γG antibodies) to give a positive indirect antiglobulin test with anti-γG serum. In the presence of fresh normal serum, six of the eluates so tested were capable of fixing complement to normal human red cells. The antibodies in the red cell eluates did not exhibit Rh specificity and did not react with nonprimate red cells. When studied by sucrose gradient ultracentrifugation, the γG antibodies to human red cells in these eluates sedimented in the 7S region. It is concluded that in many patients in whom direct antiglobulin tests reveal only cell-bound complement, the complement fixation is mediated in vivo by small quantities of “warm-reacting” erythrocyte autoantibodies of the γG class.

A fter administration of the coumarin anticoagulant racemic warfarin to normal humans, seven fluorescent compounds were chromatographically separated from extracts of their urine. Four of these were identified using mass spectrometry, thin-layer chromatography, and ultraviolet absorption spectroscopy. One metabolic pathway, reduction of the acetonyl side chain of warfarin, resulted in the formation of a second asymmetric carbon atom, and two diastereoisomer alcohols were identified. These warfarin alcohols are structurally similar to pharmacologically active coumarin derivatives. They have not been reported in animal studies. In addition, 6- and 7-hydroxywarfarin were identified. These are the first studies to document the metabolic fate of warfarin in the normal human.

T he quantitative relationship between the catabolism of heme and the formation of bilirubin and carbon monoxide (CO) was studied in untreated rats and in animals treated with phenobarbital or the porphyrogenic drug, allylisopropylacetamide (AIA). A novel metabolic chamber permitting continuous collection of the bile and breath was utilized for quantitation of bilirubin-¹⁴C and ¹⁴CO after the administration of hematin-¹⁴C or glycine-¹⁴C.After intravenous infusion of hematin-¹⁴C, control and phenobarbital-treated rats produced equimolar amounts of labeled bilirubin and CO; a minor fraction of the infused radioactivity appeared in the bile in other metabolites. The equimolar relationship in the formation of bilirubin and CO was also observed after pulse-labeling with glycine-2-¹⁴C; in phenobarbital-treated rats both metabolites were formed at an increased rate as compared to controls. By contrast, AIA treatment reduced the fractional conversion of hematin-¹⁴C to bilirubin and CO; a major fraction of the infused radioactivity appeared in the bile in metabolites other than bilirubin. In addition, in AIA-treated animals the molar CO/bilirubin recovery ratio was consistently greater than 1.0. Comparable results were obtained in AIA-treated rats after pulse-labeling with glycine-2-¹⁴C.These findings suggest that (a) in control and phenobarbital-treated rats infused hematin and heme formed in the liver are converted predominantly to bilirubin and CO, appearing in equimolar amounts; only a minor fraction of the hematin is degraded to other metabolites; (b) treatment with phenobarbital results in a proportional increase in the formation of both bilirubin and CO, reflecting increased heme synthesis and degradation in the liver; and (c) treatment with the porphyrogenic drug AIA shifts the CO/bilirubin ratio in favor of the gas, and enhances the formation of nonbilirubin metabolites.

I n order to obtain direct evidence for the existence of a natriuretic hormone, dialysates and ultrafiltrates of plasma of dogs expanded with saline were tested for effects on sodium transport by the toad urinary bladder. Dialysate was obtained by dialysis of blood in vivo in a clinical dialyzer and by dialysis in vitro of small volumes of blood using a miniature model of the clinical dialyzer. Ultrafiltrates were prepared using selective molecular filters which permit passage of substances on the basis of molecular weight and three dimensional configuration.Dialysates and ultrafiltrates of hydropenic dogs caused a change in toad bladder potential difference of + 1% and in short circuit current of - 5%. In contrast, dialysates and ultrafiltrates from expanded dogs caused a change in potential difference of - 23% and in short circuit current of - 32%, a highly significant difference. Onset of reduction of short circuit current occurred within 3-5 min, reaching a maximum in 10-20 min. The effect was rapidly reversible, was specific for the serosal surface of the bladder, and could not be explained on the basis of nonspecific alterations in ionic composition or by dilutional effects. Ultrafiltrates of jugular vein plasma caused significantly more reduction of short circuit current than ultrafiltrates of femoral vein plasma. The data indicate the presence in plasma of saline-loaded dogs of a dialyzable inhibitor of toad bladder sodium transport. Ultrafiltrate studies using membranes of appropriate selectivity suggest the factor has a molecular weight of less than 3000.

T he activity and properties of cholinesterase of the motor end plate in human intercostal muscle were studied in the isolated muscle membrane. This preparation was used because cholinesterase activity of the membrane preparation was localized in the motor end plate without contamination of cholinesterase of other muscle components. Under the experimental conditions, cholinesterase in a human end plate hydrolyzed 1.21 × 10⁸ molecules of acetylcholine per msec, which is smaller than hydrolysis of 2.69 × 10⁸ by a motor end plate of rat intercostal muscle. Studies with cholinesterase inhibitors and specific substrates indicated that about 90% of cholinesterase of human motor endplates is acetylcholinesterase, and about 10% is pseudocholinesterase. The end plate cholinesterase had an optimal pH of 7.8 and a Michaelis-Menten constant of 4.15 mmoles/liter, and was stable at 4°C for at least 4 wk. Motor end plates were estimated to contain only about 2% of the total cholinesterase activity of human intercostal muscle, compared with about 20% in rat tibialis anterior muscle. The difference is due to the lower cholinesterase activity of the motor end plate and higher cholinesterase activity of non-end plate components in human muscle than in rat muscle. The isolated muscle membrane provides a useful preparation for the study of the properties of motor end plate in human skeletal muscle.

T he early renal metabolic response was studied in rats made acidotic by oral feeding of ammonium chloride. 2 hr after feeding of ammonium chloride there was already significant acidosis. Urinary ammonia also increased after ammonium chloride ingestion and at 1½ hr was significantly elevated. In vitro gluconeogenesis by renal cortical slices was increased at 2 hr and thereafter increased steadily. Ammonia production by the same slices was also increased at 2 hr, but thereafter fell and at 6 hr had decreased to levels which, although higher than those of the control, were lower than those obtained from the rats acidotic for only 2 hr. There was no correlation between in vitro gluconeogenesis and ammonia production by kidney slices from rats during the first 6 hr of acidosis, but after 48 hr of ammonium chloride feeding, these two processes were significantly correlated. The early increase in renal gluconeogenesis was demonstrable with both glutamine and succinate as substrates.The activity of the enzyme phosphoenolpyruvate carboxykinase was increased after 4-6 hr of acidosis. During this time there was a decrease in renal RNA synthesis as shown by decreased uptake of orotic acid-⁵H into RNA.Metabolic intermediates were also measured in quick-frozen kidneys at varying times after induction of acidosis. There was an immediate rise in aspartate and a fall in α-ketoglutarate and malate levels. There was never any difference in pyruvate or lactate levels or lactate:pyruvate ratios between control and acidotic rats. Phosphoenolpyruvate rose significantly after 6 hr of acidosis.All the data indicate that increased gluconeogenesis is an early response to metabolic acidosis and will facilitate ammonia production by utilization of glutamate which inhibits the glutaminase I enzyme. The pattern of change in metabolic intermediates can also be interpreted as showing that there is not only enhanced gluconeogenesis, but also that there may be significant increase of activity of glutaminase II as part of the very early response to metabolic acidosis.

T he metabolism of β-sitosterol was compared to that of cholesterol in 12 patients. Sterol balance methods were supplemented by radiosterol studies, with the following results. (a) Plasma concentrations of β-sitosterol ranged from 0.30 to 1.02 mg/100 ml plasma in patients on intakes of β-sitosterol typical of the American diet. Plasma levels were raised little when intakes were increased greatly, and on fixed intakes they were constant from week to week. On diets devoid of plant sterols, the plasma and feces rapidly became free of β-sitosterol. (b) The percentage of esterified β-sitosterol in the plasma was the same as for cholesterol. However, the rate of esterification of β-sitosterol was slower than that for cholesterol. (c) Specific activity-time curves after simultaneous pulse labeling with β-sitosterol-³H and cholesterol-¹⁴C conformed to two-pool models. The two exponential half-lives of β-sitosterol were much shorter than for cholesterol, and pool sizes were much smaller. Values of turnover for β-sitosterol obtained by the sterol balance method agreed closely with those derived by use of the two-pool model. There was no endogenous synthesis of β-sitosterol in the patients studied; hence, daily turnover of β-sitosterol equaled its daily absorption. Absorption of β-sitosterol was 5% (or less) of daily intake, while cholesterol absorption ranged from 45 to 54% of intake. (d) About 20% of the absorbed β-sitosterol was converted to cholic and chenodeoxycholic acids. The remainder was excreted in bile as free sterol; this excretion was more rapid than that of cholesterol. (e) The employment of β-sitosterol as an internal standard to correct for losses of cholesterol in sterol balance studies is further validated by the results presented here.

C ertain gouty subjects with excessive de novo purine synthesis are deficient in hypoxanthineguanine phosphoribosyltransferase (HG-PRTase [EC 2.4.2.8]). The mechanism of accelerated uric acid formation in these patients was explored by measuring the incorporation of glycine-¹⁴C into various urinary purine bases of normal and enzyme-deficient subjects during treatment with the xanthine oxidase inhibitor, allopurinol.In the presence of normal HG-PRTase activity, allopurinol reduced purine biosynthesis as demonstrated by diminished excretion of total urinary purine or by reduction of glycine-¹⁴C incorporation into hypoxanthine, xanthine, and uric acid to less than one-half of control values. A boy with the Lesch-Nyhan syndrome was resistant to this effect of allopurinol while a patient with 12.5% of normal enzyme activity had an equivocal response. Three patients with normal HG-PRTase activity had a mean molar ratio of hypoxanthine to xanthine in the urine of 0.28, whereas two subjects who were deficient in HG-PRTase had reversal of this ratio (1.01 and 1.04). The patterns of ¹⁴C-labeling observed in HG-PRTase deficiency reflected the role of hypoxanthine as precursor of xanthine. The data indicate that excessive uric acid in HG-PRTase deficiency is derived from hypoxanthine which is insufficiently reutilized and, as a consequence thereof, catabolized inordinately to uric acid. The data provide evidence for cyclic interconversion of adenine and hypoxanthine derivatives. Cleavage of inosinic acid to hypoxanthine via inosine does not contribute significantly to the formation of uric acid in either normal man or in patients with HG-PRTase deficiency.HG-PRTase was not completely absent in red blood cells from a boy with the Lesch-Nyhan syndrome; with hypoxanthine as substrate, the activity in erythrocyte hemolysates was 0.64% of normal values.

T he recently discovered hormone precursors, pork and beef proinsulins, their respective connecting peptides, and beef proinsulin intermediates have been compared to insulin in their ability to stimulate the conversion of glucose-U-¹⁴C to ¹⁴CO₂ and lipids in isolated fat cells. The concentrations of beef and pork proinsulins required to achieve the same biological effect were respectively, 15 and 10 times that of insulin. Beef proinsulin intermediates required only 2.6 times the concentration of insulin for the same effect. Pork and beef connecting peptides in high or low concentrations alone or in combination with proinsulin, insulin, or proinsulin intermediates showed no biological effect on the isolated fat cell system. The insulin-like activity of beef and pork proinsulins on the isolated fat cell system was not abolished with pancreatic trypsin or kallikrein inhibitors. Pork insulin antiserum inhibited the biological activity of pork insulin and proinsulin as well as that of beef insulin or proinsulin. Pork proinsulin antiserum also inhibited the insulin-like activity of both pork insulin and proinsulin. By the radioimmunoassay method, pork insulin antiserum bound only ¼ to [unk] as much proinsulin as insulin. Beef proinsulin intermediates, on the other hand, were found to react with the pork insulin antiserum to an extent nearly equal to that of insulin. These data suggest that (a) proinsulin exhibits its effect on the isolated fat cells independent of its conversion to insulin, (b) connecting peptides have no biological effect under present experimental conditions, and (c) in comparison to insulin, immunological reactivity of proinsulin is greater than its biological activity using our pork insulin antiserum; thus, the comparison of antibody specificity with the fat cell receptor specificity suggests that the biological site of action is different from the immunologic site.

T he patterns of bicarbonate reabsorption during increasing plasma concentrations were studied in subjects with a range of glomerular filtration rates (GFR) from 170 to 2 ml/min. In a group of five subjects with GFR values above 30 ml/min, paired bicarbonate titration studies were performed first under conditions which minimized extracellular fluid (ECF) volume expansion, and second under conditions which were conducive to exaggerated expansion of ECF volume. In patients with GFR values below 30 ml/min, a single protocol was employed. Studies also were performed on two patients with far advanced renal disease who were nephrotic and exhibited a sodium-retaining state. When ECF volume expansion was minimized in the nonuremic subjects, values for bicarbonate reabsorption were well in excess of the usually accepted Tm level and over the range of plasma bicarbonate concentrations employed, no evidence of a Tm phenomenon was observed. A similar pattern emerged in the two nephrotic patients despite the presence of uremia. However, with both exaggerated expansion of ECF volume (GFR greater than 30) and in patients with advanced renal disease in the absence of exaggerated ECF volume expansion a tendency towards saturation kinetics for bicarbonate reabsorption was demonstrable. In comparing the minimized with the exaggerated expansion studies, evidence emerged for a decrease in both bicarbonate reabsorption per unit of GFR and the absolute rate of bicarbonate reabsorption. When ECF volume expansion was exaggerated in uremic patients after stable rates of bicarbonate reabsorption had been achieved, a decrease in reabsorption per unit of GFR and in absolute bicarbonate reabsorption occurred. The possible relationship of the factors controlling sodium excretion to the observed patterns of bicarbonate reabsorption is considered in the text.

A lthough glucagon exerts positive inotropic effects in patients with no or mild impairment of cardiac function, similar effects are not consistently observed in patients with chronic heart failure. Accordingly, the inotropic effects of glucagon on papillary muscles from normal cats and cats in which right ventricular failure had been produced for 4-145 days by pulmonary artery banding were compared. At the peak of the concentration-response curve, glucagon increased peak isometric tension (T) in normal muscles from 4.4±0.4 to 6.6±0.5 g/mm² (P <0.001), and maximum rate of tension development (dT/dt) from 16.9±0.9 to 25.1±1.6 g/sec per mm² (P < 0.001). In contrast, glucagon produced no significant increases in T or dT/dt in failure muscles. The percentage increases in T and dT/dt caused by norepinephrine were the same in muscles from normal and failing hearts. Since the cardiac effects of glucagon and norepinephrine may be mediated by adenyl cyclase, responsiveness of adenyl cyclase was determined in particulate fractions of the right ventricle. Glucagon activated adenyl cyclase in normal, but had no effect in failure preparations. Norepinephrine-induced activation of adenyl cyclase, however, was unaltered by failure. Thus, in contrast to norepinephrine, glucagon loses the capacity to augment myocardial contractility and activate adenyl cyclase in hearts derived from cats in chronic failure.

T he purpose of this study was to determine the effect of familial hyperlipoproteinemia (HLP) on peripheral vascular disease (PVD) and the extent to which the vascular disease (PVD) and the extent to which the vascular disease is modified by treatment of the lipoprotein disorder. PVD was detected plethysmographically by observing a diminished peak reactive hyperemia blood (PRHBF) following ischemia. The value for PRHBF in the extremity demonstrating the lowest response in 32 normal subjects (age 19-50 yr) was 39.6±1.5 SEM, ml/min per 100 g. Patients with untreated HLP. who had PRHBF below the lower limit of normal, were 2 of 11 type II, 9 of 12 type III, 1 of 10 type IV. As a group, patients with type III HLP showed diminished PRHBF (26.6 ±3.0 ml/min per 100 g, P <0.01). In view of the high incidence of PVD and the striking reduction in serum lipids and complete resorption of xanthomas observed in type III HLP with therapy, six patients were studied before and after 3-6 months of treatment with a therapeutic diet and clofibrate. PRHBF in the most severely affected extremity increased markedly, from 20.4 ±1.6 to 31.9 ±1.8 ml/min per 100 g (P<0.01), indicating a dramatic increase in maximum blood flow to this extremity. In two type III patients with PVD not treated, no change in PRHBF occurred over 5 months. In two other type III patients the PRHBF increased 17% during the first 25 days of therapy concomitant with a 30% reduction in whole blood viscosity. Over the next 120 days, blood viscosity decreased only an additional 4.6% whereas the PRHBF increased 57%, indicating that the observed changes seen in the PRHBF with therapy of type III patients can be only minimally accounted for by changes in the viscosity of the blood. Thus, patients with type III HLP are particularly susceptible to the development of PVD and objective improvement of PVD can occur with medical treatment of this lipid transport disorder.

A dministration of phenobarbital, which acts exclusively on cellular sites, results in an augmentation of the liver/plasma concentration ratio of L-thyroxine (T4) in rats but no change in the liver/plasma concentration ratio of L-triiodothyronine (T3). Whereas phenobarbital stimulates the fecal clearance rate both of T3 and T4, it increases the deiodinative clearance rate of T4 only. These findings suggest basic differences in the cellular metabolism of T3 and T4. Further evidence pointing to cellular differences was obtained from a comparison of the distribution and metabolism of these hormones with appropriate corrections for the effect of differential plasma binding. The percentage of total exchangeable cellular T4 within the liver (28.5) is significantly greater than the corresponding percentage of exchangeable cellular T3 within this organ (12.3). Extrahepatic tissues bind T3 twice as firmly as T4. The cellular metabolic clearance rate (= free hormone clearance rate) of T3 exceeds that of T4 by a factor 1.8 in the rat. The corresponding ratio in man, 2.4, was determined by noncompartmental analysis of turnover studies in four individuals after the simultaneous injection of T4-¹²⁵I and T3-¹³¹I. The greater cellular metabolic clearance rate of T3 both in rat and man may be related to the higher specific hormonal potency of this iodothyronine.

T he formation of bilirubin-¹⁴C was measured in rats given transfusions of red blood cells containing ¹⁴C-labeled hemoglobin heme. Per cent conversion of hemoglobin-¹⁴C to bilirubin was 4 times greater with transfusion of “stress” reticulocytes from rats responding to hemorrhage than with normal reticulocytes from unstimulated donors. When the increased number of labeled reticulocytes produced by hemorrhaged donors was also considered, the total magnitude of labeled bilirubin formation was almost 20 times higher with stress as compared to normal reticulocytes. The findings were not influenced by splenectomy of either donor or recipient rats, iron loading of donors, or bleeding of recipients. However, bilirubin-¹⁴C formation fell off progressively as studies were performed at longer intervals after erythroid stimulation.Total bilirubin-¹⁴C formation in rats transfused with stress reticulocytes was compared to the production of early-labeled bilirubin from all potential sources in intact rats bled according to the same schedule used in the transfusion experiments. It is estimated that degradation of hemoglobin from sress reticulocytes accounts for virtually the entire rise in erythropoietic bilirubin formation from 24 to 96 hr after glycine-2-¹⁴C administration, but that additional sources make a major contribution before that time. These findings are consistent with the concept that destruction of immature erythroid cells in the peripheral blood, and probably in the bone marrow, accompanies the physiologic response to erythroid stimulation.

T he fetal hemoglobin in the affected members of three Greek families with the hereditary persistence of fetal hemoglobin has only γ-chains of the type with alanine in position 136. Although certain Negro families had been considered to have only this type of γ-chains in their fetal hemoglobin, further studies required that they be reclassified. Consequently, the Greek cases are the sole examples of this class among the heterozygotes for the hereditary persistence of fetal hemoglobin. In Greek double heterozygotes for β-thalassemia and the hereditary persistence of fetal hemoglobin, fetal hemoglobin is increased above the level of hemoglobin F in simple heterozygotes and γ-chains with glycine in position 136 become apparent. In these individuals, γ-chains with alanine in position 136 apparently derive from the chromosome for the hereditary persistence of fetal hemoglobin and are present in the hemoglobin F with γ-chains of both types from the chromosome for β-thalassemia. When these data are correlated with earlier knowledge of the genetic state of the Greek individuals, modifications of our previous ideas about deletions as the genetic basis of the hereditary persistence of fetal hemoglobin must be considered.