Abstract
To elucidate the role of growth hormone (GH)-releasing hormone (GRH) and somatostatin (SRIH) in the regulation of the growth hormone (GH) secretory pattern, we collected portal blood from five unanesthetized ovariectomized ewes for repeated measurements of GRH and SRIH simultaneous with those of peripheral GH. Hormones were measured at 10-min intervals for 5.5 h and their interrelationships analyzed. Mean portal GRH was 20.4 +/- 6.7 (SD) pg/ml and the estimated overall secretion rate was 13 pg/min. GRH secretion was pulsatile with peaks of 25-40 pg/ml and a mean pulse interval of 71 min. Mean portal SRIH was 72 +/- 33 pg/ml and the estimated overall secretion rate was 32 pg/min. SRIH secretion was also pulsatile with peaks of 65-160 pg/ml and a mean pulse interval of 54 min. The GH pulse interval was 62 min. A significant association was present between GRH and GH secretory peaks though not between GRH and SRIH or SRIH and GH. Insulin hypoglycemia resulted in a rapid and brief stimulation of SRIH secretion followed by a decline in GH levels. No effect was observed on GRH secretion until 90 min, when a slight increase occurred. The results suggest (a) the presence of an independent neural rhythmicity of GRH and SRIH secretion with a primary role of GRH in determining pulsatile GRH secretion, and (b) that the inhibitory effects of insulin hypoglycemia on GH in this species are attributable to a combination of enhanced SRIH secretion and possibly other factors, though without significant inhibition of GRH.
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Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Berelowitz M., Dudlak D., Frohman L. A. Release of somatostatin-like immunoreactivity from incubated rat hypothalamus and cerebral cortex. Effects of glucose and glucoregulatory hormones. J Clin Invest. 1982 Jun;69(6):1293–1301. doi: 10.1172/JCI110569. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Berelowitz M., Szabo M., Frohman L. A., Firestone S., Chu L., Hintz R. L. Somatomedin-C mediates growth hormone negative feedback by effects on both the hypothalamus and the pituitary. Science. 1981 Jun 12;212(4500):1279–1281. doi: 10.1126/science.6262917. [DOI] [PubMed] [Google Scholar]
- Brazeau P., Guillemin R., Ling N., van Wyk J., Humbel R. Inhibition par les somatomédines de la sécrétion de l'hormone de croissance stimulée par le facteur hypothalamique somatocrinine (GRF) ou le peptide de synthèse hpGRF. C R Seances Acad Sci III. 1982 Nov 29;295(11):651–654. [PubMed] [Google Scholar]
- Clarke I. J., Cummins J. T. The temporal relationship between gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH) secretion in ovariectomized ewes. Endocrinology. 1982 Nov;111(5):1737–1739. doi: 10.1210/endo-111-5-1737. [DOI] [PubMed] [Google Scholar]
- Clarke I. J., Thomas G. B., Yao B., Cummins J. T. GnRH secretion throughout the ovine estrous cycle. Neuroendocrinology. 1987 Jun;46(1):82–88. doi: 10.1159/000124800. [DOI] [PubMed] [Google Scholar]
- Engler D., Pham T., Fullerton M. J., Funder J. W., Clarke I. J. Studies of the regulation of the hypothalamic-pituitary-adrenal axis in sheep with hypothalamic-pituitary disconnection. I. Effect of an audiovisual stimulus and insulin-induced hypoglycemia. Neuroendocrinology. 1988 Nov;48(5):551–560. doi: 10.1159/000125062. [DOI] [PubMed] [Google Scholar]
- Ferland L., Labrie F., Jobin M., Arimura A., Schally A. V. Physiological role of somatostatin in the control of growth hormone and thyrotropin secretion. Biochem Biophys Res Commun. 1976 Jan 12;68(1):149–156. doi: 10.1016/0006-291x(76)90022-x. [DOI] [PubMed] [Google Scholar]
- Frohman L. A., Downs T. R. Measurement of growth hormone-releasing factor. Methods Enzymol. 1986;124:371–389. doi: 10.1016/0076-6879(86)24029-x. [DOI] [PubMed] [Google Scholar]
- Gordon K., Renfree M. B., Short R. V., Clarke I. J. Hypothalamo-pituitary portal blood concentrations of beta-endorphin during suckling in the ewe. J Reprod Fertil. 1987 Mar;79(2):397–408. doi: 10.1530/jrf.0.0790397. [DOI] [PubMed] [Google Scholar]
- Guardabasso V., De Nicolao G., Rocchetti M., Rodbard D. Evaluation of pulse-detection algorithms by computer simulation of hormone secretion. Am J Physiol. 1988 Dec;255(6 Pt 1):E775–E784. doi: 10.1152/ajpendo.1988.255.6.E775. [DOI] [PubMed] [Google Scholar]
- Kashio Y., Chihara K., Kita T., Okimura Y., Sato M., Kadowaki S., Fujita T. Effect of oral glucose administration on plasma growth hormone-releasing hormone (GHRH)-like immunoreactivity levels in normal subjects and patients with idiopathic GH deficiency: evidence that GHRH is released not only from the hypothalamus but also from extrahypothalamic tissue. J Clin Endocrinol Metab. 1987 Jan;64(1):92–97. doi: 10.1210/jcem-64-1-92. [DOI] [PubMed] [Google Scholar]
- Katakami H., Downs T. R., Frohman L. A. Inhibitory effect of hypothalamic medial preoptic area somatostatin on growth hormone-releasing factor in the rat. Endocrinology. 1988 Aug;123(2):1103–1109. doi: 10.1210/endo-123-2-1103. [DOI] [PubMed] [Google Scholar]
- Kelijman M., Frohman L. A. Discordant effects of insulin-hypoglycemia on growth hormone (GH)-releasing hormone-stimulated GH and thyrotropin (TSH)-releasing hormone-stimulated TSH secretion. J Clin Endocrinol Metab. 1988 Apr;66(4):872–875. doi: 10.1210/jcem-66-4-872. [DOI] [PubMed] [Google Scholar]
- Kronheim S., Berelowitz M., Pimstone B. L. The characterization of somatostatin-like immunoreactivity in human serum. Diabetes. 1978 May;27(5):523–529. doi: 10.2337/diab.27.5.523. [DOI] [PubMed] [Google Scholar]
- Liposits Z., Merchenthaler I., Paull W. K., Flerkó B. Synaptic communication between somatostatinergic axons and growth hormone-releasing factor (GRF) synthesizing neurons in the arcuate nucleus of the rat. Histochemistry. 1988;89(3):247–252. doi: 10.1007/BF00493148. [DOI] [PubMed] [Google Scholar]
- Oliver C., Mical R. S., Porter J. C. Hypothalamic-pituitary vasculature: evidence for retrograde blood flow in the pituitary stalk. Endocrinology. 1977 Aug;101(2):598–604. doi: 10.1210/endo-101-2-598. [DOI] [PubMed] [Google Scholar]
- Patel Y. C., Srikant C. B. Somatostatin mediation of adenohypophysial secretion. Annu Rev Physiol. 1986;48:551–567. doi: 10.1146/annurev.ph.48.030186.003003. [DOI] [PubMed] [Google Scholar]
- Plotsky P. M., Vale W. Patterns of growth hormone-releasing factor and somatostatin secretion into the hypophysial-portal circulation of the rat. Science. 1985 Oct 25;230(4724):461–463. doi: 10.1126/science.2864742. [DOI] [PubMed] [Google Scholar]
- ROTH J., GLICK S. M., YALOW R. S., BERSONSA Hypoglycemia: a potent stimulus to secretion of growth hormone. Science. 1963 May 31;140(3570):987–988. doi: 10.1126/science.140.3570.987. [DOI] [PubMed] [Google Scholar]
- Tannenbaum G. S., Ling N. The interrelationship of growth hormone (GH)-releasing factor and somatostatin in generation of the ultradian rhythm of GH secretion. Endocrinology. 1984 Nov;115(5):1952–1957. doi: 10.1210/endo-115-5-1952. [DOI] [PubMed] [Google Scholar]
- Wehrenberg W. B., Brazeau P., Luben R., Böhlen P., Guillemin R. Inhibition of the pulsatile secretion of growth hormone by monoclonal antibodies to the hypothalamic growth hormone releasing factor (GRF). Endocrinology. 1982 Dec;111(6):2147–2148. doi: 10.1210/endo-111-6-2147. [DOI] [PubMed] [Google Scholar]
- Williams T. C., Kelijman M., Crelin W. C., Downs T. R., Frohman L. A. Differential effects of somatostatin (SRIH) and a SRIH analog, SMS 201-995, on the secretion of growth hormone and thyroid-stimulating hormone in man. J Clin Endocrinol Metab. 1988 Jan;66(1):39–45. doi: 10.1210/jcem-66-1-39. [DOI] [PubMed] [Google Scholar]