Hypothalamic Secretion of Somatostatin and Growth Hormone-Releasing Factor into the Hypophysial-Portal Circulation Is Reduced in Streptozotocin Diabetic Male Rats

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Abstract
Growth hormone (GH) secretory patterns are disrupted in streptozotocin (STZ) diabetic rats. Alterations in hypothalamic growth hormone-releasing factor (GRF) or hypothalamic somatostatin (SRIF) secretion, increased systemic SRIF secretion, and changes in somatotroph sensitivity to these hypothalamic factors have been advanced as potential underlying mechanisms for the observed attenuation of GH secretion after STZ treatment. Two weeks after STZ treatment, the mean circulating GH level was attenuated by 58%, plasma glucose concentration was 4-fold higher, and systemic SRIF concentration was elevated 6.8-fold with respect to vehicle (VEH)-treated rats. The hypothalamic content of neither SRIF nor GRF was significantly different between VEH and STZ groups. Total hypophysial-portal SRIF concentration, which represents the sum of both peripheral and hypothalamic SRIF contributions, was significantly elevated in the STZ versus VEH group (p

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