Issue published January 1, 1967

T he clearance of radioiron from plasma and its appearance in circulating erythrocytes in normal subjects are studied. The importance of correcting for plasma iron fluctuations and for mean body hematocrit is illustrated. The data are analyzed by probability theory to determine relationships between intravascular and extravascular iron. Two refluxes are described, one of about 7 particles of every 100 leaving the plasma, and the second of about 23. The return times of these are about 5 hours and 8 days, respectively.

C eruloplasmin labeled with ⁶⁷copper and administered intravenously to dogs, control human subjects, and patients with excessive gastrointestinal loss was shown to fulfill the requirements for a label for quantification of gastrointestinal protein loss. The radiocopper moiety was poorly absorbed from the gastrointestinal tract, not actively secreted into the intestinal tract, and did not alter significantly the metabolism of ceruloplasmin. Approximately 70% of the body pool of ceruloplasmin in both dog and man was within the intravascular space. In control human subjects the mean ceruloplasmin concentration was 30 mg per 100 ml with total circulating and total body ceruloplasmin pools of 15.5 and 22 mg per kg, respectively. In patients with excessive gastrointestinal protein loss secondary to intestinal lymphangiectasia, the serum ceruloplasmin concentration was reduced to 16 mg per 100 ml with a comparable reduction in the total circulating and total body ceruloplasmin pools to 8.8 and 12 mg per kg.The survival half-time of ceruloplasmin was 6.1 days in normal human subjects and 4.5 days in normal dogs. From 1.0 to 1.9% of the intravascular pool of ceruloplasmin was lost into the gastrointestinal tract of the dog per day, representing less than 11% of the over-all metabolism of this protein. In control human subjects from 1.9 to 3.9% of the intravascular pool was lost into the gastrointestinal tract each day, representing a maximum of from 11 to 22% of the over-all metabolism of this molecule. In contrast, patients with intestinal lymphangiectasia had a markedly shortened ceruloplasmin survival of 3.1 days, with from 15 to 40% of the intravascular pool of ceruloplasmin cleared into the gastrointestinal tract daily. This represented 76% of the over-all metabolism of this protein. Thus, although bulk loss of serum proteins into the gastrointestinal tract does not normally appear to be a significant factor in protein metabolism in normal dogs and men, such loss is a major factor in the pathogenesis of the hypoceruloplasminemia noted in patients with intestinal lymphangiectasia.

S tool carrier rates of Escherichia coli serogroups 4, 6, and 75 were determined on admission and discharge for 190 patients. Persons who were in the hospital 3 weeks or longer had an intestinal carrier rate of 46% compared to a rate of 28% in individuals who had no recent hospital contact. Treatment with broad spectrum antibiotics increased the susceptibility for acquisition of certain specific serologic groups. This was apparently not related to replacement of sensitive E. coli by drug-resistant forms. Studies were made to determine the environmental source for colonization of hospitalized patients and the risk of urinary infection in stool carriers of these strains. A survey of inanimate objects of medical and urological wards demonstrated infrequent isolation of 04, 06, and 075, indicating that extraintestinal foci were an unlikely source for hospital-acquired E. coli. Hemagglutination titers with determination of group-specific O antibody failed to demonstrate any deficiency in hospitalized patients who became colonized with certain coliforms. Similarly, no significant deficit in group-specific serum antibody was found in patients who were community carriers of E. coli 04, 06, or 075. Despite a high rate of acquisition of E. coli serogroups 4, 6, and 75 in the stools of hospitalized patients, only those patients undergoing urinary tract manipulation developed bacteriuria.

C ystine and cysteine are transported by energy-dependent, mediated processes in human gut. When either of these amino acids is transported, only cysteine is recovered intracellularly, indicating that cystine is reduced to cysteine after achieving an intracellular location. In contrast to results with cystine, cysteine uptake is not defective in gut from cystinuric patients, nor do lysine and arginine compete with cysteine for transport. It is, therefore, concluded that cystine and cysteine are transported by different mechanisms, and that only the cystine transport mechanism is defective in cystinuria.

T he nature of the gastrointestinal absorptive defect for triglyceride in three subjects with abetalipoproteinemia has been investigated by studying peroral biopsies of the gastrointestinal mucosa. The following conclusions were reached.1) In confirmation of other studies, the abnormal vacuoles within the duodenal absorptive cells of these individuals were lipophilic.2) On chemical analysis there was significantly more mucosal lipid than found in normal fasting specimens, and almost the entire increase was due to triglyceride.3) This excess mucosal lipid was reduced by a low fat diet, but even after 34 days on such a diet there was still an excess of lipophilic material near the villus tip and increased quantities of total lipid and triglyceride when compared with material from normal subjects similarly treated.4) Although there are demonstrable qualitative changes in mucosal and plasma lipids after an acute fat load, they are not quantitatively as great as in normal individuals. Fat balance studies and the qualitative changes in plasma and tissue lipids that do occur after more extended periods on different types of dietary fat do indicate that a considerable percentage of the dietary fat is assimilated. The route by which it is absorbed remains to be clarified.

T he mechanism by which expansion of extracellular fluid volume with isotonic saline suppresses reabsorption in the proximal tubule was studied in rats by examining the relations among glomerular filtration rate (GFR), absolute and fractional reabsorption of filtrate, intrinsic reabsorptive capacity (rate of reabsorption per unit tubular volume), transit time, and tubular volume.Saline infusions reduced the per cent of the glomerular filtrate reabsorbed in the proximal tubule from 50% during antidiuresis to 25% during saline diuresis. The suppression of proximal reabsorption was the result of two factors: 1) a 30% reduction of intrinsic reabsorptive capacity, and 2) a 26% reduction of tubular volume per unit GFR.GFR invariably rose during saline diuresis. However, prevention of the rise in GFR by aortic clamping had no effect on either the inhibition of intrinsic reabsorptive capacity or the reduction in tubular volume per unit GFR produced by saline infusions. Expansion of extracellular fluid volume with isotonic saline, therefore, depressed intrinsic reabsorptive capacity and tubular volume per unit GFR by some mechanism completely independent of GFR.The effects of furosemide administration were contrasted with those of saline infusions. Furosemide inhibited intrinsic reabsorptive capacity by 40% but had no significant effect on proximal fractional reabsorption. The failure to suppress fractional reabsorption was the consequence of a disproportionate rise in tubular volume (relative to GFR) that was sufficient to completely overcome the inhibition of intrinsic reabsorptive capacity. Inhibition of intrinsic reabsorptive capacity alone, therefore, will not result in a net suppression of reabsorption of filtrate in the proximal tubule. We concluded that, although intrinsic reabsorptive capacity was inhibited during saline diuresis, the critical factor responsible for translating this inhibition into effective net suppression of proximal reabsorption was the observed reduction in tubular volume per unit GFR.

< i>1) In the absence of the thyroid gland, the infusion of parathyroid hormone leads to a prompt rise in plasma calcium and to prompt increase in the rate of excretion of calcium in the urine.2) In the presence of the thyroid gland, the parathyroid hormone-induced rise in plasma calcium is less marked; the rate of urinary calcium excretion falls initially and rises only after 20 to 30 hours of continuous parathyroid hormone infusion.3) The infusion of exogenous thyrocalcitonin along with the parathyroid hormone into a thyroparathyroidectomized animal leads to a pattern of response similar to that seen in the animal with an intact thyroid gland.4) Thyrocalcitonin has little apparent effect upon the immediate changes in renal function induced by parathyroid hormone.5) We conclude that bone is a major site of action of thyrocalcitonin and that it probably inhibits bone resorption.

T he relation between the active potassium influx in the human red blood cell and the extracellular potassium concentration does not appear to be consistent with the Michaelis-Menten model, but is adequately described by a model in which two potassium ions are required simultaneously at some site or sites in the transport mechanism before transport occurs. The same type of relation appears to exist between that portion of the sodium outflux that requires the presence of extracellular potassium and the extracellular potassium concentration. Rubidium, cesium, and lithium, which are apparently transported by the same system that transports potassium, stimulate the potassium influx when both potassium and the second ion are present at low concentrations, as is predicted by the two-site model.

I n 17 healthy men, beta-adrenergic blockade reduced significantly the tachycardia and the elevation of cardiac output associated with inhalation of 7.5% oxygen for 7 to 10 minutes.Hypoxia did not increase plasma concentrations of epinephrine or norepinephrine in six subjects. Furthermore, blockade of alpha and beta receptors in the forearm did not modify the vasodilation in the forearm induced by hypoxia, providing pharmacologic evidence that hypoxia of the degree and duration used was not associated with an increase in the concentrations of circulating catecholamines in man.Part of the increase in cardiac output and heart rate during acute hypoxia in man is produced by stimulation of beta-adrenergic receptors, probably by cardiac sympathetic nerves. The mechanism of the vasodilation in the forearm during hypoxia remains uncertain.

N ormal adult men and women have been infused with epinephrine, 6 μg per minute, during lipolytic blockade with nicotinic acid, beta-adrenergic blockade with propranolol and Butoxamine, and alpha-adrenergic blockade with phentolamine. Epinephrine infusion was associated with low serum levels of immunoreactive insulin (IRI) except when phentolamine was given simultaneously. These findings are compatible with an alpha receptor mechanism for the epinephrine inhibition of insulin release. Phentolamine had no blocking effects on the tachycardia and widened pulse pressure or lipolytic stimulation by epinephrine, whereas both propranolol and Butoxamine blocked lipolysis, tachycardia, and widened pulse pressure. These findings are consistent with an alpha receptor blocking action for phentolamine and beta receptor blocking action for propranolol and Butoxamine. Inhibition of lipolysis by nicotinic acid did not alter IRI or glucose responses to epinephrine. It is concluded that the lipolytic effect of epinephrine is unrelated to its effects on IRI release. Lipolytic blockade by nicotinic acid also did not change IRI or glucose in fasting subjects or their responses to a glucose infusion, 300 mg per minute. These observations appear to conflict with the Randle hypothesis (the glucose-fatty acid cycle) and raise some doubt as to whether plasma FFA concentrations are direct determinants of glucose or IRI concentrations in normal man.

I n order to determine whether HCO₃^- gains access to the proximal tubular lumen from a source other than the glomerular filtrate, we carried out microperfusion experiments on isolated segments of rat proximal tubules in vivo. The perfusion fluid was essentially free of HCO₃^- and of a composition that prevented net absorption of sodium and water.It was found that when plasma HCO₃^- concentration and CO₂ tension (PCO₂) were normal, the HCO₃^- concentration in the collected perfusate rose to about 3 mEq per L. Inhibition of renal carbonic anhydrase did not produce an appreciable change in this value in normal rats, but when the enzyme was inhibited in acutely alkalotic rats, a mean concentration of 15 mEq per L was recovered in the perfusate. Addition of HCO₃^- to the tubular lumen might occur by either intraluminal generation of HCO₃^- from CO₂ and OH^- or by influx of ionic bicarbonate from the plasma or tubular cells. Because of the marked increase in HCO₃^- found when intraluminal carbonic anhydrase was inhibited, generation of new HCO₃^- from CO₂ and OH^- seems unlikely. We conclude, therefore, that influx of ionic bicarbonate occurred, either across the luminal membrane or through extracellular aqueous channels. These observations suggest that the proximal epithelium has a finite degree of permeability to HCO₃^- and that influx of this ion may be a component of the over-all handling of HCO₃^- by the kidney.

T he acute metabolic effects and disposition of human placental lactogen (HPL) have been studied in 15 men and 8 women during continuous intravenous infusions. The mean plasma half-life, metabolic pool size, and turnover rate of HPL are comparable to the values previously reported for human growth hormone (HGH). From the data presented, we calculate that the placenta secretes approximately 290 mg HPL daily at term.After 12-hour infusions of HPL in physiologic amounts, impairment of glucose tolerance despite increased plasma insulin responses to glucose was observed in 7 of 8 subjects tested. However, HPL, unlike HGH, did not produce significant changes in blood glucose, plasma insulin, or plasma free fatty acid concentrations in fasting subjects before glucose administration or in carbohydrate tolerance or plasma insulin responses to glucose during 5-hour infusions. These findings are compatible with the thesis that HPL is a physiologic antagonist to insulin during pregnancy.

T richloroacetic acid extracts of plasma were fractionated on a CG-50 resin column and the 50% acetic acid eluents chromatographed on silicic acid-impregnated glass paper in butanol-acetic acid-water. The specific arginine vasopressin (AVP) zone was eluted and assayed for antidiuretic activity in the diuretic rat. Thioglycolate inactivation was used to confirm AVP activity. Recovery of as little as 4 μU AVP per ml plasma ranged between 80 and 90%. In normal subjects after an overnight fast, plasma AVP ranged between 2.5 and 10.0 μU per ml. AVP secretion was inhibited by hemodilution and stimulated with nicotine and hypertonic saline. Plasma AVP was absent in patients with diabetes insipidus even after neurohypophyseal stimulation. Plasma AVP was abnormally elevated during mild dehydration and remained above the normal range despite hemodilution in patients with untreated adrenocortical insufficiency demonstrating a delayed water diuresis. Glucosteroid therapy lowered plasma AVP to normal in dehydrated patients. A normal diuretic response to hydration was accompanied by a fall in plasma AVP to zero in steroid-treated patients. These findings suggest that hypersecretion of AVP may play an important role in the abnormal water metabolism of adrenocortical insufficiency and that the glucosteroids promote normal water diuresis by inhibiting the secretion of AVP from the neurohypophysis.

< i>1) The effect of hemin on heme synthesis was studied in vivo. Heme synthesis was measured by determining red cell ⁵⁹Fe uptake and glycine-2-¹⁴C incorporation into red cell hemin in normal CF₁ female mice.2) Both bovine and human hemin significantly decreased red cell ⁵⁹Fe uptake 48, 72, and 96 hours after hemin injection.3) Glycine-2-¹⁴C incorporation into red cell hemin was decreased to 50% of control values after the administration of hemin (90 μmoles per kg).4) There was no significant difference between the plasma iron of mice injected with hemin and the values in control groups.5) Protoporphyrin decreased the inhibitory effect of hemin on red cell ⁵⁹Fe uptake by 64%.6) There was no measurable effect of δ-aminolevulinic acid on hemin inhibition of red cell ⁵⁹Fe uptake.7) Data are presented to show that the effect of hemin is not by a dilution mechanism nor by a decrease in red cell maturation and subsequent release of reticulocytes into the peripheral blood. The findings are discussed in regard to the possible site of a negative feedback control of heme synthesis by heme.

< i>1) Measured during spontaneous breathing in ten patients with diffuse interstitial lung disease, total pulmonary resistance averaged 3.53 ± 1.56 cm H₂O per L per second; airway resistance, 1.63 ± 0.79 cm H₂O per L per second; and lung tissue resistance, 1.90 ± 0.95 cm H₂O per L per second (range, 0.89 to 3.96). The lung tissue resistance was on an average about four times higher in patients with lung fibrosis than in ten healthy persons of the same age. No significant difference in airway resistance was found between healthy subjects and patients.2) In three patients the lung tissue resistance was measured during spontaneous breathing and during panting. Much higher values were found during spontaneous breathing.3) In patients with lung fibrosis and also in healthy subjects, there seems to have been an inverse correlation between the vital capacity, or the compliance, on the one hand, and the lung tissue resistance on the other. Nevertheless, in patients with lung fibrosis the lung tissue resistance was more increased than could be attributed to the loss of normally compliant lung tissue only.4) No correlation was found between the lung tissue resistance and severity of impairment of pulmonary gas exchange; especially no relationship appeared to exist between the lung tissue resistance and the alveolar-end capillary PO₂ gradient during hypoxia. This result indicates that the pathological alterations producing a measurable end gradient in hypoxia may be independent of the augmentation of the fibrous framework responsible for the stiffening of the lung.