We used ultrastructural morphometric methods to study the in vivo regulation of secretion in bronchiolar Clara cells of rats. The Clara cells studied were located in airways with an internal diameter of 0.21 +/- 0.06 mm (mean +/- SD) at a transpulmonary pressure of 20 cm H2O. We found that pilocarpine caused a 50% decrease in the volume density of secretory granules of Clara cells in 60 min and that atropine blocked this effect. Isoproterenol produced a similar fall in volume density and this was blocked by propranolol. Propranolol also blocked the effect of pilocarpine. The fall in volume density of the secretory granules produced by pilocarpine and by isoproterenol occurred without any change in the surface-to-volume ratio of the granules. This indicates the change in volume density reflected a decrease in number rather than in size of the secretory granules. The observation that propranolol blocks the secretory response to pilocarpine as well as the response to isoproterenol suggests a dual in series cholinergic adrenergic regulation of secretion in bronchiolar Clara cells in rats.
G D Massaro, M Paris, L A Thet
Serial microscopic immunodiffusion assays of F cells, i.e., erythrocytes that contain fetal hemoglobin (HbF), in four individuals recovering from anemia demonstrate initial increases in the percentage of circulating reticulocytes that contain HbF (F reticulocytes) and subsequent increases in the percentage of mature erythrocytes that contain HbF (F erythrocytes). In one individual responding to therapy for iron-deficiency anemia, the average percentage of F reticulocytes increased from 4.8±1.1 to 16.0±2.8% (mean±SD), while the mean level of F erythrocytes increased from 3.5±0.7 to 7.2±0.6%. Two normal children with transient erythroblastopenia exhibited F reticulocyte percentages of 71.3±6.7 and 41.5±1.5%, respectively, when erythropoiesis resumed. With recovery these values fell to finally measured values of 33.7±4.7 and 12.6±1.1%, respectively. In an adolescent with sickle cell anemia, F-reticulocyte percentages fluctuated between 0.6±1.1 and 34.0±2.8% and paralleled the rise and fall of total reticulocytes associated with therapy for a nasopharyngeal carcinoma.
George J. Dover, Samuel H. Boyer, William H. Zinkham
The ability of the neutrophil myeloperoxidase-hydrogen peroxide-halide system to induce the release of human platelet constituents was examined. Both lytic and nonlytic effects on platelets were assessed by comparison of the simultaneously measured release of a dense-granule marker, [3H]serotonin, and a cytoplasmic marker, [14C]adenine. Incubation of platelets with H2O2 alone (20 μM H2O2 for 10 min) resulted in a small, although significant, release of both serotonin and adenine, suggesting some platelet lysis. Substantial release of these markers was observed only with increased H2O2 concentrations (>0.1 mM) or prolonged incubation (1-2 h).
Robert A. Clark
The mechanisms responsible for altered adrenergic tone in hyperthyroidism and hypothyroidism are not fully understood. To investigate these mechanisms, the β-adrenergic receptor-cyclic AMP complex of the turkey erythrocyte was studied among groups of normal, hyperthyroid, and hypothyroid turkeys. In erythrocytes obtained from hypothyroid turkeys, there were fewer β-adrenergic receptors than in normal cells as determined by the specific binding of [125I]iodohydroxybenzylpindolol, as well as associated decreases both in catecholamine-responsive adenylate cyclase activity and in cellular cyclic AMP content. In contrast, erythrocytes obtained from hyperthyroid turkeys contained the same number of β-receptors and had the same catecholamine-responsive adenylate cyclase activity as cells from normal birds. Other characteristics of the β-receptors in cells from hyperthyroid birds were indistinguishable from those present in normal erythrocytes. However, within the range of circulating catecholamine concentrations, 5-50 nM, the erythrocytes of the hyperthyroid turkeys generated substantially more cyclic AMP after exposure to isoproterenol than did normal cells. These results suggest that thyroid hormone affects β-receptor-cyclic AMP interrelationships in the turkey erythrocyte by two distinct mechanisms: (a) In hypothyroidism, both β-receptors and catecholamine-dependent cyclic AMP formation are coordinately decreased; (b) in hyperthyroidism, β-receptors are unchanged but there is an amplification of the hormonal signal so that occupation of a given number of receptors at physiological concentrations of catecholamines leads to increased levels of cyclic AMP.
John P. Bilezikian, John N. Loeb, Donald E. Gammon
Reports by a number of investigators have described the thymus-derived (T)-cell dependence of immunoglobulin synthesis by pokeweed mitogen (PWM) stimulated human peripheral blood bone marrow-derived (B) cells. Because of the cooperative nature of this in vitro system, it was chosen for examination of the differential effects of low density lipoprotein inhibitor (LDL-In) on B- and T-cell functions. Supernates from 7-d cultures that contained either peripheral blood mononuclear cells (PBM) or combinations of isolated lymphocyte populations were assayed for immunoglobulin (Ig)G by competitive inhibition radio-immunoassay. LDL-In suppression of whole PBM IgG synthesis occurred at 5-20 μg protein/ml and was independent of PWM concentration. Maximal suppression required preincubation of cells with LDL-In before stimulation. Suppression was also observed when B cells alone were exposed for 24 h to LDL-In before PWM stimulation; these suppressed B cells were not rescued by normal T cells. Exposure of T cells alone to low doses of LDL-In for 24 h augmented, but high doses suppressed, IgG synthesis, suggesting a differential effect on T-helper vs T-suppressor cell populations. Independent LDL-In exposure of T-helper or T-suppressor cell enriched populations, separated by rosetting with IgG- or IgM-coated ox erythrocytes, identified the T-suppressor cell populations as the most sensitive of the lymphocyte populations tested. The sensitivities of lymphocyte subpopulations to LDL-In, relative to PBM, were 2.8, 1.2, and 0.3 for the T-suppressor cells, B cells and T-helper cells, respectively. Thus, both B and T lymphocytes are sensitive to and can be regulated by LDL-In. In addition, the biologic activity observed when unseparated PBM are exposed to LDL-In appears to represent a composite of the sensitivity of each of the lymphocyte subpopulations.
Linda K. Curtiss, Thomas S. Edgington
The high incidence of fatal septicemia associated with severe thermal injury is believed to result from a loss of immunocompetence. To detect burn-mediated immune defects, lymphocyte function in peripheral blood leukocytes from 18 individuals sustaining 20-80% full thickness thermal burns was investigated. We examined the kinetics of the mitogen responses, the development of suppressive activity, and the correlation of mononuclear cell functional abnormalities with the incidence of sepsis. Patients were divided into three groups corresponding to their clinical course. The phytohemagglutinin responses of Ficoll-Hypaque purified leukocytes from eight of these patients (group III) were normal at day 1-2 after injury, but were significantly depressed (mean 16% of normal) at days 5-10 after injury. All of these group III patients experienced multiple, severe, septic episodes, and septic mortality was 75%. The other 10 burned individuals showed either augmented (group II) or unaltered (group I) mitogen responsiveness.
Carol L. Miller, Christopher C. Baker
In vitro studies of isolated, perfused, cortical collecting tubules have demonstrated that prior chronic deoxycorticosterone acetate (DOCA) treatment increases sodium reabsorption in this nephron segment, yet sodium balance in vivo is maintained. To evaluate the effect of chronic DOCA treatment on collecting duct sodium reabsorption in vivo, we compared fractional sodium delivery (FDNa%) out of the superficial late distal tubule with the fraction of sodium remaining at the base and the tip of the papillary collecting duct during extracellular fluid volume expansion in untreated, salt-treated, and DOCA-salt-treated rats. In untreated rats, FDNa% to the distal tubule was 6.5±1.0%, and to the base was 8.7±1.6% (Δ2.2±0.9%, P < 0.05). FDNa% to the tip was 4.9±1.1%, significantly less than FDNa% to the base (Δ3.7±1.1%, P < 0.01). In salt-treated rats, FDNa% to the distal tubule was 8.3±0.8%, and to the base was 10.4±1.1%. FDNa% to the tip was 5.9±0.6%, significantly less than FDNa% to the base (Δ 4.6±1.0%, P < 0.005). In DOCA-salt-treated rats, FDNa% to the distal tubule was 16.1±2.6% and to the base was 9.5±1.9% (Δ 6.6±1.7%, P < 0.005). FDNa% to the tip was 5.9±1.2%, also significantly less than FDNa% to the base (Δ 3.6±1.1%, P < 0.01). We conclude that (a) in DOCA-salt-treated rats, sodium delivery to the end of the superficial distal tubule is greater than in untreated or salt-treated rats; (b) in DOCA-salt-treated rats, sodium delivery to the end of the superficial distal tubule is greater than to the base of the papillary collecting duct, suggesting stimulation of sodium reabsorption in the cortical and(or) outer medullary collecting duct; and (c) sodium reabsorption by the papillary collecting duct is unaffected by chronic DOCA-salt treatment in the volume-expanded rat.
John A. Haas, Theresa J. Berndt, Stephen P. Youngberg, Franklyn G. Knox
Prostacyclin (PGI2) is the most potent, naturally occurring inhibitor of platelet aggregation known. To determine whether PGI2 is bound by platelets, high specific activity [9-3H]PGI2 was synthesized by iodination and subsequent base treatment of the labeled precursor [9-3H]prostaglandin (PG)F2α methyl ester. Binding experiments were performed at room temperature with normal citrated human platelet-rich plasma that contained [14C]sucrose or [14C]PGF1α as an internal marker for the extracellular space. Binding of [3H]PGI2 plateaued within 2 min and this bond radioactivity could be displaced rapidly by excess nonradioactive PGI2. Scatchard analysis of concentration-dependent binding yielded a hyperbolic plot which appeared to be caused by the existence of two classes of binding sites. The higher affinity class has a dissociation constant of 12.1±2.7 nM and a capacity of 93 (±21)sites per platelet. The lower affinity class had a dissociation constant of 0.909±.236 μM and a capacity of 2,700±700 sites per platelet. The relative ability of PGI2, PGE1, PGE2, and 6-keto-PGF1α to displace [3H]PGI2 initially bound to the higher affinity class of sites were 100:5:<0.3: <0.3. These relative abilities parallel the relative potencies of these compounds as inhibitors of ADP-induced platelet aggregation in vitro. However PGD2, which is more potent than PGE1 as an inhibitor of aggregation, did not displace bound [3H]PGI2. The higher affinity binding site for PGI2 appears to be the specific receptor through which PGI2 exerts its effect on platelets.
Adelaide M. Siegl, J. Bryan Smith, Melvin J. Silver
Human peripheral blood neutrophils (PMN) obtained from healthy adults were examined in vitro with techniques adapted to assess the effects of chemotactic factors (CF) on cellular configuration and adhesiveness. The results were compared with those that use certain conventional techniques for assessing chemotaxis and chemokinesis. Exposure of PMN to N-formyl-l-methionyl-l-phenylalanine (f-Met-Phe), zymosan-activated serum, bacterial chemotactic factor, or a low molecular weight chemotactic factor from activated serum (C5a) in the absence of a gradient resulted in a change in cellular shape from a spherical to a polarized configuration in a high percentage of cells. This occurred rapidly in suspension, under conditions designed to exclude a role for cell adhesiveness, and was reversible upon removal of the CF. Restimulation of cells with the CF resulted in reappearance of the polarized configuration to the same extent as on initial stimulation with one exception: f-Met-Phe pretreated cells failed to respond to f-Met-Phe, though they responded fully to the other CF. Each CF caused a significant increase in PMN attachment to protein-coated glass. This enhanced adhesiveness was not reversible upon removal of the CF when the cells were treated under conditions shown to produce chemotactic deactivation. Cells treated under these conditions also exhibited significantly reduced motility on glass and in micropore filters in the absence of a gradient of CF. Bacterial chemotactic factor, even at high concentrations, failed to produce deactivation and did not cause a sustained enhancement of adhesiveness.
C. Wayne Smith, James C. Hollers, Richard A. Patrick, Clare Hassett
The effects of adrenergic substances on pancreatic insular secretions were studied in a completely isolated canine pancreas with exclusion of the duodenum from the perfusion circuit. To ensure adequate blockade, blockers were infused before agonists. A dose range of β-receptor blockade was tested, and putative α-adrenergic effects were confirmed by combined α- and β-adrenergic receptor blockade.
Ellis Samols, Gordon C. Weir
Adipocyte size and number were determined in 288 subjects ranging in age from 4 mo to 19 yr. The study was performed in 110 obese and 178 non-obese subjects. 4-yr, longitudinal, follow-up studies were also performed in 132 subjects. The results demonstrate that the contribution of cell number and size to the growth of the fat depot in nonobese children varies with age. Deviations from this normal development were observed in obese children shortly after 1 yr of age. By 11 yr of age obese children exceeded the mean cell number found in nonobese adults. Indeed, obese subjects displayed more rapid and earlier elevations in both cell number and size, which were maintained throughout the study. Thus obese children display both quantitative and qualitative differences in fat tissue development when compared to nonobese children. The data indicate that the rate and type of adipose tissue cellular development one encounters in children may play a role in the development of the enlarged fat depots found in obese subjects.
J L Knittle, K Timmers, F Ginsberg-Fellner, R E Brown, D P Katz
Recent work suggests the existence of a dual corticosteroid feedback mechanism of stress-induced ACTH secretion in the rat. This possibility led us to study the kinetics of suppression of ACTH levels by corticosteroid administration in patients with nonstress ACTH hypersecretion secondary to hypoadrenocorticism. Cortisol was administered according to different protocols, which were chosen to provide extreme variations of the input signal. By this means, two phases of suppression of ACTH levels could be differentiated. A first decrease occurred without latency whenever, and as long as, plasma cortisol levels were rising. There was a linear regression between the logarithm of the increments in cortisol concentrations and the decrease in ACTH levels per minute (r = 0.951) (differential or rate-sensitive feedback mechanism). Neither the absolute doses of cortisol, nor plasma cortisol concentrations were closely correlated with the degree of suppression of ACTH by this rapid mechanism. A second decrease in ACTH levels began ≅30 min after corticosteroid administration. In this case there was a significant linear regression between the degree of inhibition of ACTH levels and the cortisol doses (r = 0.997) (integral or dose-sensitive feedback mechanism).
H. L. Fehm, K. H. Voigt, G. Kummer, R. Lang, E. F. Pfeiffer
Endotoxin has been shown to induce amyloidosis in mice and to result in the appearance in serum of large amounts of amyloidrelated protein (SAA). After injection of 300 μg lipopolysaccharide Escherichia coli, SAA behaves as an acute phase reactant with levels reaching a peak of >600 μg/ml at 18-22 h and returning to base line (<50 μg/ml) by 48 h in each of four strains tested; only the endotoxin-resistant C3H/HeJ strain showed a smaller response. Lesser, though significant, elevations were also found after subcutaneous injection of 25 mg of casein, bovine serum albumin, ovalbumin, or monomeric immunoglobulin G, whereas pyrogen-free human serum albumin/U. S. Pharmacopeia failed to raise SAA levels. SAA generation may thus be a result of endotoxin contamination of these protein preparations.
Peter D. Gorevic, Yoram Levo, Prem C. Chatpar, Blas Frangione, E. C. Franklin
The influence of testosterone on gonadotropin-releasing hormone (GnRH) secretion was assessed indirectly by altering the serum testosterone concentration of male rats and measuring GnRH release from their incubated hypothalami 1 wk later.
Robert S. Rudenstein, Homayoon Bigdeli, Maureen H. McDonald, Peter J. Snyder
A further study of the Tgamma-chain in a variety of conditions has revealed its presence in the cord bloods of ethnic groups previously unstudied. Heterozygous newborn average 17-19% Tgamma-chain while the mean value in four presumed homozygotes was 31%. The Tgamma-chain is readily detectable in beta-thalassemia of various ethnic groups (although infrequent in Blacks) as well as in deltabeta-thalassemia. Studies of a few families have provided an opportunity to determine whether or not certain individuals are heterozygous or homozygous for the Tgamma-gene. The Tgamma-chain has not been detected in the human fetal hemoglobin that is synthesized in increased amounts in persons with the hereditary persistence of fetal hemoglobin. Although the Tgamma-chain is detectable in sickle cell anemia, its frequency appears to be lower than in normal individuals. By focusing upon the relationship of the percentage of Tgamma-chain to the sources of human fetal globulin from determinants in cis and in trans, the conclusion has been reached that the Tgamma-chain is the product of a mutant Agamma-locus which should be named the TAgamma-chain.
W A Schroeder, T H Huisman, G D Efremov, J R Shelton, J B Shelton, R Phillips, A Reese, M Gravely, J M Harrison, H Lam
Serum antibodies to exotoxin A and type-specific lipopolysaccharide were measured by passive hemagglutination in 52 patients with Pseudomonas aeruginosa septicemia. Their comparative protective activities were evaluated by relating the titers of each at the onset of bacteremia to subsequent outcome. High acute serum antitoxin and antilipopolysaccharide titers (log2 reciprocal mean titers greater than 5) were associated with survival (76% of 17 with high vs. 46% of 24 with low antitoxin titers, P = 0.05; 85% of 13 with high vs. 48% of 29 with low antilipopolysaccharide titers, P = 0.03). In contrast, neither antibody titer was significantly associated (P less than or equal to 0.05) with patients' age or sex, severity of underlying disease, presence of leukopenia, steroid or immunosuppressive therapy. Despite a correlation between acute titers of the two antibodies (r = 0.33, P = 0.06), they appeared to protect independently and additively. Whereas 75% of 8 patients with high antitoxin titers and only 38% of 16 with low titers survived with low antilipopolysaccharide titers (P = 0.10), 100% (6/6), 73% (8/11), and 38% (6/16) survived, respectively, when both, one, or neither antibody was present in high titer (P = 0.01). Furthermore, the association between high acute serum antitoxin titers and survival was more pronounced in patients with rapidly fatal underlying disease (P = 0.06) and leukopenia (P = 0.12) than in more favorable prognostic and immune categories. These data indicate that serum antibodies to exotoxin A and lipopolysaccharide are found in most patients with P. aeruginosa septicemia and both are protective. Both antibodies may have therapeutic or prophylactic potential, whereas serum antiexotoxin A antibodies may be particularly beneficial in compromised hosts.
M Pollack, L S Young
The effect of furosemide on plasma renin, vasopressin (AVP), and aldosterone concentrations was studied in 10 control and 6 nephrectomized lambs during the 1st 2 wk of life. In a separate study in 10 newborn lambs, 1-sarcosine-8-alanine-angiotensin II (saralasin acetate, 5 μg/kg per min) was infused alone for 40 min, after which furosemide 2 mg/kg i.v. was injected in association with continuing saralasin acetate infusion.
Sharon R. Siegel, Richard E. Weitzman, Delbert A. Fisher
We studied the effect of several doses of atropine on the serum gastrin and pancreatic polypeptide responses to vagal stimulation in healthy human subjects. Vagal stimulation was induced by sham feeding. To eliminate the effect of gastric acidity on gastrin release, gastric pH was held constant (pH 5) and acid secretion was measured by intragastric titration. Although a small dose of atropine (2.3 μg/kg) significantly inhibited the acid secretory response and completely abolished the pancreatic polypeptide response to sham feeding, this dose of atropine significantly enhanced the gastrin response. Higher atropine doses (7.0 and 21.0 μg/kg) had effects on gastrin and pancreatic polypeptide release which were similar to the 2.3-μg/kg dose. Atropine (0.78 and 2.3 μg/kg) without sham feeding significantly inhibited basal acid secretion and also led to significant increases in serum gastrin above basal levels. The gastrin response to sham feeding with 2.3 μg/kg atropine was significantly greater than the sum of the gastrin responses to sham feeding alone and to 2.3 μg/kg atropine alone, indicating potentiation of vagal gastrin release by atropine. We conclude: (a) Unlike vagally mediated gastric acid secretion and pancreatic polypeptide release which can be blocked by atropine, vagal gastrin release is potentiated by atropine. This observation suggests the existence of a vagal-cholinergic pathway which normally (i.e., in the absence of atropine) inhibits gastrin release. (b) Because atropine (without sham feeding) increased basal gastrin levels, it is likely that the cholinergic pathway which inhibits gastrin release is active even when the vagus nerve is not stimulated by sham feeding.
Mark Feldman, Charles T. Richardson, Ian L. Taylor, John H. Walsh
For plethysmographic studies of lung mechanics and measurement of pulmonary diffusing capacity, 62 subjects were drawn from a randomly selected population sample. Data obtained from the 24 subjects of heterozygous phenotype for alpha-1-antitrypsin deficiency (PiMZ) were compared by age group with data from 38 normal (PiM) subjects matched for sex, age, and smoking history. Comparison of mean values by age group for lung volumes, diffusing capacity, lung elastic recoil, maximum expiratory flow, and the occurrence of frequency dependence of dynamic compliance revealed no differences between phenotype groups. There was no evidence of an accelerated effect of aging among PiMZ subjects when compared with normal counterparts nor was there evidence of an increased effect of smoking. From these data it appears that the PiMZ phenotype per se is not a risk factor in the development of emphysema.
D J McDonagh, S P Nathan, R J Knudson, M D Lebowitz
We studied the contribution of α- and β-adrenergic receptor activation to the cardiovascular, metabolic, and hormonal effects of dopamine. At a concentration of 1.5 μg/kg·min, the infusion of dopamine in 12 normal volunteers was associated with a transient but significant rise in pulse rate, which was prevented by propranolol. Venous plasma glucose did not change throughout the experiments, and a mild increase in plasma free fatty acid levels observed during the administration of dopamine alone was antagonized by propranolol. In contrast, neither the β-adrenergic blocker, propranolol, nor the α-adrenergic blocker, phentolamine, was effective in inhibiting the dopamine-induced rise in plasma glucagon (from 82±9 to 128±14 pg/ml; P < 0.005) and serum insulin (from 7.5±1 to 13±1.5 μU/ml; P < 0.005) or its suppression of plasma prolactin (from 8.5±1 to 5.2±0.8 ng/ml; P < 0.001). Although serum growth hormone levels did not change during the infusion of dopamine alone, an obvious rise occurred in three subjects during the combined infusion of propranolol and dopamine.
Mara Lorenzi, John H. Karam, Eva Tsalikian, Nancy V. Bohannon, John E. Gerich, Peter H. Forsham
Human α1-microglobulin was isolated from the urine of patients with tubular proteinuria, and its molecular weight was established by sodium dodecyl sulfate-polyacrylamide gel electrophoresis at 33,000 daltons. The carbohydrate content was 21.7%. Anti-α1-microglobulin serum was prepared and observed to react monospecifically in gel diffusion to purified α1-microglobulin, as well as to normal human serum and urine. Sera from the domestic chicken, mouse, rat, rabbit, dog, calf, cow, goat, sheep, and horse, however, did not react to anti-α1-microglobulin serum in immunodiffusion. The lymphocyte culture supernate was found to contain α1-microglobulin. Both thymus-derived(T)- and bone marrow-derived(B)-lymphocyte culture media clearly displayed a specific precipitin line against anti-α1-microglobulin serum when tested with the Ouchterlony immunodiffusion method. The tissue distribution of α1-microglobulin was studied under immunofluorescence, and a positive staining was recognized on the lymphocyte surface. Identical staining patterns were noted on both T and B lymphocytes, though B lymphocytes took a more intense stain. It would thus seem quite possible that lymphocytes are the primary source of α1-microglobulin and that this is filtered through the glomerular basement membrane and partly reabsorbed by the renal tubules. This, then, would suggest the possibility that α1-microglobulin shares some immunological role in vivo with lymphocytes and(or) is one of the membrane proteins of lymphocytes.
Kimiteru Takagi, Kohjin Kin, Yoshihisa Itoh, Tadashi Kawai, Tadashi Kasahara, Toshihiko Shimoda, Toshio Shikata
Heat-labile opsonic activity was measured simultaneously in serum and pleural fluid of patients with transudates, infectious exudates (with positive or negative bacterial culture) and neoplastic exudates, using two different complement-dependent phagocytic tests: the killing of Staphylococcus aureus Wood 46 variant strain (K50 opsonic titers) and the assessment of ingestion rate of endotoxin-coated paraffin particles (Oil Red 0 uptake test). K50 opsonic titers were lower in culture-positive pleural effusions as compared to culture-negative (P < 0.002) or neoplastic effusions (P < 0.002). These results were corroborated by the Oil Red 0 uptake test. The data obtained with the two assays showed a significant correlation (P < 0.001).
Pablo D. Lew, Rudolf Zubler, Pierre Vaudaux, Jean J. Farquet, Francis A. Waldvogel, Paul-Henri Lambert
To evaluate the role of vitamin D in the physiologic response to phosphorus depletion (P depleton) and the response to vitamin D administration in P depletion, we studied vitamin D-deficient (−D) rats, fed either a normal or low phosphorus diet and then injected intraperitoneally on alternate days with replacement vitamin D3, 1.25 μg qod (D3); 1.25-dihydroxy-vitamin D3[1,25(OH)2D3] in physiologic, 54 ng qod (LD), and pharmacologic doses, 400 ng qod (HD); or vehicle alone (−D). The following results were obtained: (a) With P depletion, urinary excretion of inorganic phosphorus (Pi) fell to almost undetectable levels in −D rats, and two physiologic features of P depletion a calcemic effect and hypercalciuria, ensued. (b) With administration of vitamin D3 or 1,25(OH)2D3 in either doses to P-depleted rats, the renal retention of Pi was unaltered despite a significant elevation of serum Pi. (c) The calcemic response to P depletion was accentuated by vitamin D sterols, and the hypercalciuria of P depletion was reduced by 1,25(OH)2D3, HD > LD > D3. (d) In −D animals receiving normal Pi (+P), D3, and 1,25(OH)2D3, both LD and HD produced a significant calcemic and phosphatemic effect. (e) Urinary Pi excretion in +P animals was reduced slightly by vitamin D3 whereas 1,25(OH)2D3, both LD and HD, lowered urinary Pi markedly despite an increased serum Pi. (f) The serial values of serum Ca and Pi and urinary Ca in PD rats and the sequential values for urinary and serum Pi in +P rats indicated more rapid effects of 1,25(OH)2D3, both HD and LD, compared with D3. We conclude that: (a) The renal adaptation and physiologic response to PD does not require the presence of vitamin D. (b) 1,25(OH)2D3 may directly enhance the renal tubular reabsorption of Pi even as serum Pi rises. (c) A hypocalciuric action of 1,25(OH)2D3 in rats on low phosphorus diet could be direct or occur as a consequence of an increase in serum Pi produced by 1,25(OH)2D3. The different sequential renal response to D3 compared with 1,25-(OH)2D3 raises the possibility that other natural forms of vitamin D3 [i.e., 25(OH)D3, 24,25(OH)2D3, etc.] which may be present in vitamin D-fed rats but not those given only 1,25(OH)2D3, could modify the actions of 1,25(OH)2D3.
Nachman Brautbar, Marlin W. Walling, Jack W. Coburn, John O. Steppe
Plasma 1,25-dihydroxyvitamin D levels are elevated in early pregnancy and continue to increase throughout pregnancy. They remain elevated postpartum in lactating women. The elevated levels probably represent a physiological response to increased calcium requirements.
R Kumar, W R Cohen, P Silva, F H Epstein
Exogenous arachidonate addition to intact platelets, in the absence or the presence of blood vessel microsomes, results in the production of thromboxane B2 (the stable degradation product of thromboxane A2) only. Prostaglandin (PG) endoperoxides are released from intact platelets only when thromboxane synthetase is inhibited. Thus, addition of exogenous arachidonate to imidazole-pretreated platelets in the presence of bovine aorta microsomes (source of prostacyclin synthetase) results predominantly in the synthesis of 6-keto-PGF1α (the stable degradation product of prostacyclin). Strips of intact aorta were removed from aspirin-treated rabbits, thus the isolated blood vessels were unable to convert endogenous or exogenous arachidonate to prostacyclin. Human platelets, with [14C]arachidonate-labeled phospholipids, adhered to the blood vessel segments and released some thromboxane B2. The subsequent addition of thrombin facilitated the release of endogenous arachidonate and thromboxane, but no labeled 6-keto-PGF1α was detectable. There is therefore no direct chemical evidence of PG-endoperoxide release from human platelets during either aggregation or adhesion, which therefore precludes the possibility that blood vessels use platelet PG-endoperoxide for prostacyclin synthesis. Imidazole inhibited the thromboxane synthetase in the labeled platelets, and thereafter thrombin stimulation resulted in the release of platelet-derived, labeled PG-endoperoxides that were converted to labeled prostacyclin by the vascular prostacyclin synthetase. The latter result suggests a potential antithrombotic therapeutic benefit might be achieved using an effective thromboxane synthetase inhibitor.
Philip Needleman, Angela Wyche, Amiram Raz