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Regulation of growth hormone release from the pituitaries of rats in vitro


, : Regulation of growth hormone release from the pituitaries of rats in vitro. Endocrinology 108(3): 1071-1080

In vitro studies were performed to investigate the regulation of GH [growth hormone] release from the pituitary of rats using the synthetic pentapeptides, Tyr-DTrp-Gly-Phe-Met-NH2 (DTrp2) or Tyr-Ala-DTrp-Phe-Met-NH2 (DTrp3), and the synthetic tetradecapeptide somatostatin (SRIF). DTrp2/3 act directly on the pituitary to specifically release GH and presumably mimic the action of the putative hypothalamic native GH-releasing hormone. The GH release induced by DTrp2/3 was dose related, occurred within 5 min, and was inhibited by small amounts (10-30 ng/ml incubation medium) of SRIF. Particular emphasis was given to the possibility that GH from the pituitary of immature rats and mature rats may be influenced differently at the pituitary level. This latter conclusion was supported by the finding that the GH released by DTrp2/3 from the pituitary of the mature rat compared to that released in the immature rat was greater in magnitude but more easily inhibited by SRIF. Other differences included: progressively decreasing GH release from the pituitary of the mature, but not the immature rat on repeated stimulation with DTrp2/3; the addition of glucose to the incubation medium caused a partial decrease of the GH response to DTrp2/3 from the pituitary of the mature and immature rat but only inhibited the unstimulated release of GH from the pituitary of the mature rat and temporary inhibition of the DTrp2/3 pituitary GH response of SRIF of the immature compared to the mature rat was more readily reversible. For comparison, some of the above studies were also performed using the GH-releasing agents prostaglandin [PG] E1 and theophylline (Theo) with and without DTrp2/3 and/or SRIF. Repeated stimulation with PGE1 and Theo, but not DTrp2/3 elicited a sustained release of GH from the pituitary of the mature rat; adding PGE1 or Theo with DTrp2/3 elicited a greater release of GH when the DTrp2/3 GH response alone was usually decreased during the last 2 h of a 6 h incubation. In contrast to the DTrp2/3 GH response, the PGE1 and Theo GH responses were immediately reversible after temporary inhibition with SRIF. DTrp2/3 may be unique pentapeptides for learning more about the function and behavior of the putative GH-releasing hormone receptor of the pituitary somatotrophs; the dual effects of SRIF plus DTrp2/3 rather than the effect of SRIF alone appear to produce an irreversible inhibition of the stimulated release of GH at the putative GH-releasing hormone-SRIF receptor(s) and studies on the regulation of GH release in vitro from the pituitaries of immature and mature rats may reveal certain unique differences which have important physiological implications in vivo.

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Related references

Bowers, C.Y.; Reynolds, G.A.; Chang, D.; Hong, A.; Chang, K.; Momany, F., 1981: A study on the regulation of growth hormone release from the pituitaries of rats in vitro. Endocrinology 108(3): 1071-1080

Smith, M.S., 1982: Effect of pulsatile gonadotropin-releasing hormone on the release of luteinizing hormone and follicle-stimulating hormone in vitro by anterior pituitaries from lactating and cycling rats. Hemipituitaries from Sprague-Dawley females were exposed to GnRH for 6 min during each hour of incubation. Compared with LH release by anterior pituitaries from dioestrous females in response to pulsatile exposure to GnRH, the LH release was signi...

Hall T.R.; Chadwick A., 1976: Effects of growth hormone inhibition factor somatostatin on the release of growth hormone and prolactin from pituitaries of the domestic fowl in vitro. Journal of Endocrinology 68(1): 163-164

Hall, T.R.; Chadwick, A., 1976: Effects of growth hormone inhibiting factor (somatostatin) on the release of growth hormone and prolactin from pituitaries of the domestic fowl in vitro. Journal of Endocrinology 68(1): 163-164

Hertlelendy, F.; Todd, H.; Peake, G.T.; Machlin, L.J.; Johnston, G.; Pounds, G., 1971: 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. Endocrinology 89(5): 1256-1262

Krulich L.; Mccann S.M., 1969: Effect of growth hormone releasing factor and growth hormone inhibiting factor on the release and concentration of growth hormone in pituitaries incubated in vitro rat. Endocrinology 85(2): 319-324

Sato, K.; Yamamoto, Y., 1977: Effects of actinomycin D on the release of prolactin and growth hormone from rat pituitaries in vitro by thyrotropin releasing hormone. Nihon Funin Gakkai Zasshi 22(2): 33-38

Uehara T.; Arimura A.; Schally A.V., 1974: Influence of previous cooling of rat pituitaries on the release of growth hormone luteinizing hormone and prolactin in vitro. Neuroendocrinology 13(4-5): 278-283

Hertelendy F.; Todd H.; Peake G.T.; Machlin L.J.; Johnston G.; Pounds G., 1971: Studies on growth hormone secretion part 1 effects of di butyryl cyclic amp theophylline epinephrine ammonium ion and hypothalamic extracts on the release of growth hormone from rat anterior pituitaries in vitro. Endocrinology 89(5): 1256-1262

Smith M.S., 1982: Effect of pulsatile gonadotropin releasing hormone on the release of luteinizing hormone and fsh in vitro by anterior pituitaries from lactating and cycling rats. The ability of pituitaries from lactating animals to secrete LH [luteinizing hormone] and FSH in response to gonadotropin-releasing hormone (GnRH) was studied in vitro using a pituitary incubation system. Hemipituitaries were exposed to GnRH for 6...