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  • Title: A possible role of hypothalamic somatostatin in the maintenance of rat pituitary responsiveness to growth hormone-releasing factor.
    Author: Soya H, Suzuki M.
    Journal: Endocrinology; 1990 Jan; 126(1):285-91. PubMed ID: 1967163.
    Abstract:
    To characterize the role of hypothalamic somatostatin (SRIF) in regulating pituitary responsiveness to GH-releasing factor (GRF) in vitro, we reduced SRIF input to the rat anterior pituitary through the portal vessels. Three different paradigms were used as follows: 1) anterolateral hypothalamic deafferentation, 2) electrolytic lesions of the periventricular nucleus, and 3) passive immunization with SRIF antiserum. Rat CRF content in the stalk-median eminence markedly decreased to 19% and 57% of that of sham-operated controls 10 days after the deafferentation and the lesions, respectively. In contrast, rat GRF content was unchanged by either operation. SRIF content markedly decreased to 78%, 12%, and 2% of the control level 1, 3, and 10 days after deafferentation, respectively, and to 48% and 8%, 1 and 10 days after the lesions, respectively. The serum GH concentration was significantly increased 1 and 3 days after the deafferentation (P less than 0.01) and also 1 day after the lesions (P less than 0.01), followed by no increase 10 days after either operation. Anterior pituitary weight and GH content markedly decreased 3 and 10 days and 10 days after the deafferentation and the lesions, respectively. The human GRF (0.1 microM)-induced GH release response of anterior pituitaries removed from these treated rats was examined in an in vitro perifusion system. Even 1 day after these treatments, GH responsiveness was clearly attenuated by anterolateral hypothalamic differentiation (8.61 +/- 0.78 vs. 3.62 +/- 0.54 micrograms GH/h; P less than 0.01), periventricular nucleus lesions (6.52 +/- 1.07 vs. 3.20 +/- 0.53 micrograms GH/h; P less than 0.01) and passive immunization with SRIF antiserum (5.80 +/- 0.43 vs. 2.54 +/- 0.16 micrograms GH/h; P less than 0.01). This attenuated responsiveness gradually deteriorated 3 and 10 days after the surgical operations. These results indicate that SRIF neurons in the anterior periventricular nucleus play a role in maintaining the pituitary responsiveness to GRF, in addition to the original action of inhibiting GH release.
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