Growth Hormone Output Research Articles

Effect of sulphydryl reagents on the release o ox growth hormone in vitro

1. 1. The release of ox growth hormone from pituitary slices in vitro was increased by p-chloromercuribenozate (PCMB), 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB), and N-ethylmaleimide in a dose-dependent manner, the lowest effective concentrations being: PCMB, 2 μM, DTNB, 8 μM, and N-ethylmaleimide, 250 μM. Stimulation of release by PCMB decreased in successive incubation periods. 2. 2. Neither dithiothreitol nor glutathione had any affect on basal growth hormone release. Stimulation of release of PCMB was reversed by 2-mercaptoethanol. 3. 3. Exposure to PCMB (8 μM) did not change the tissue ATP concentration and had no effect on oxygen uptake or glucose oxidation rates, suggesting that cell metabolism was not altered. 4. 4. Ouabain (10 −5 M) increased pituitary Na + and decreased pituitary K + contents, and stimulated growth hormone output; however, PCMB (8 μM) had no effect on tissue Na + or K + concentrations, indicating that it did not act through the Na + pump. 5. 5. Stimulation of release by PCMB was not inhibited by trichloromethoxycarbonylcyanide phenyl hydrazone (40 μg/ml), tetracaine (0.5 mM0, Mg 2+ (12.5 mM), depletion of pituitary calcium, or colchicine (5 mM), and exposure to PCMB (8 μM) did not alter the Ca 2+ content of slices incubated in the presence or absence of Ca 2+. This suggests that stimulation of release by PCMB involves neither ATP nor changes in Ca 2+ concentrations. 6. 6. Replacement of Na + by choline did not alter intracellular Na + or K + concentrations, while replacement of Na + by Li + resulted in a fall in both Na + and K + concentrations. Stimulation of release of PCMB was not altered by these substitutions, but when Na + was replaced by choline, stimulation of release by DTNB was inhibited.

Studies on growth hormone secretion. I. Effects of dibutyryl cyclic AMP, theophylline, epinephrine, ammonium ion, and hypothalamic extracts on the release of growth hormone from rat anterior pituitaries in vitro.

The release of immunoreactive growth hormone (GH) from male rat anterior pituitary explants was measured under a variety of experimental conditions. After a somewhat higher initial level, secretory rates remained essentially constant during a five-hour incubation period. Theophylline and dibutyryl cyclic AMP alone and in combination significantly stimulated GH secretion. Ammonium acetate and ammonium chloride (25 mM/L) also increased GH output by two-threefold. Unlike theophylline which increased both pituitary cyclic AMP levels and GH content of the medium, ammonium ion stimulated GH release was not accompanied by increased concentrations of intracellular cyclic AMP. Beef hypothalamic extracts, crude and purified, failed to stimulate GH release. Cerebral cortex extract and synthetic lysine vasopressin were also without effect. Epinephrine exhibited an inhibitory tendency on theophylline and cyclic AMP stimulated GH secretion. The results, which support the “second messenger” concept, are discussed in rel...

The regulation of growth hormone secretion from the isolated rat anterior pituitary in vitro. The role of adenosine 3':5'-cyclic monophosphate.

1. The release of growth hormone from isolated fragments of rat anterior pituitary tissue incubated in vitro was studied by employing a double-antibody radioimmunoassay. 2. In the absence of added stimuli, two phases of hormone release could be distinguished, an early phase of 2h duration and a subsequent late phase. In the early phase, hormone release was rapid but could be significantly decreased by calcium depletion and by 2,4-dinitrophenol whereas the rate of release in the late phase was uninfluenced by these incubation conditions. These results have been interpreted as indicating the existence of a secretory component in the early phase of release. 3. In subsequent experiments, the effects of various agents on the rate of hormone output during the late phase of incubation were investigated. Hormone release was increased by theophylline and by dibutyryl cyclic AMP (N(6)-2'-O-dibutyryl-adenosine 3':5'-cyclic monophosphate), the response to both of these agents being related to the concentration of the stimulant employed. 4. The stimulation of growth hormone output by theophylline was significantly decreased by calcium deprivation and by 2,4-dinitrophenol. The response to dibutyryl cyclic AMP was diminished by 2,4-dinitrophenol, iodoacetate and 2-deoxyglucose but not by malonate or colchicine. 5. Arginine, beta-hydroxybutyrate, albumin-bound palmitate and variation in the glucose concentration of the incubation medium over a wide range were without any statistically significant effect on the rate of hormone release from either control pituitary fragments or those subject to secretory stimulation by dibutyryl cyclic AMP. 6. It is suggested that the regulation of growth hormone secretion is mediated by cyclic AMP (adenosine 3':5'-cyclic monophosphate). The secretion observed in response to cyclic AMP requires the presence of ionized calcium and a source of metabolic energy but is independent of pituitary protein synthesis de novo. The integrity of the glycolytic pathway of glucose metabolism appears to be essential for cyclic AMP-stimulated growth hormone secretion to occur.

Measurement of growth hormone released by ox anterior-pituitary slices in vitro.

1. A method has been developed for the iodination of ox growth hormone by using iodine monochloride, giving a product which is 93+/-4% bindable to antiserum. 2. The (131)I- or (125)I-labelled growth hormone obtained has been used in the development of an immunological assay for growth hormone. 3. The assay could be applied to the measurement of growth-hormone output by pituitary slices in vitro. 4. On incubation ox-pituitary slices liberate 8.1% of their growth-hormone content in the first hour and 4.5% in the second hour. 5. The amount of growth hormone liberated into the medium is greater if the tissue is frequently transferred than if it is incubated in the same medium. 6. The output is stimulated by a hypothalamic extract but inhibited by high concentrations of posterior-lobe powder: a stalk-median-eminence extract had no effect. 7. The output is lowered by temperature reduction, beta-hydroxybutyrate, acetoacetate, and pyruvate, glutamate and fumarate. Palmitoylcarnitine stimulates growth-hormone output. 8. Anoxia and 2,4-dinitrophenol have no effect on output.

Effect of chronic tolbutamide administration on growth and carbohydrate metabolism in weanling rats.

ABSTRACT In the present study the chronic administration of tolbutamide to weanling rats was associated with evidence of accelerated skeletal growth as shown by increased tibial epiphyseal cartilage width and tail length. It is proposed that tolbutamide-induced hyperinsulinism may have augmented daily growth hormone output in the treated rats secondary to recurring hypoglycaemia and that increased growth hormone output may also have contributed to transient glucose intolerance observed in these animals.