Differential effects of passive immunization with somatostatin antiserum on adenohypophysial hormone secretions in starved rats

Abstract

The role of somatostatin (SRIF) on adenohypophysial hormone secretion in starved rats was reassessed by passive immunization. Because of the absence of pulsatile GH secretion in starved rats, the effects of the injection of SRIF antiserum on GH levels can be clearly demonstrated. To determine whether starvation modifies the sensitivity of the adenohypophysis to SRIF, we measured 125I-labelled iodo-N-Tyr-SRIF binding. There was no difference in the dissociation constant (Kd) nor in the maximal binding capacity (Bmax) in fed (n = 15) and starved (n = 15) animals (Kd = 0.38 +/- 0.09 (S.E.M.) and 0.45 +/- 0.09 nmol; Bmax = 204 +/- 39 and 205 +/- 30 fmol/mg protein respectively). Administration of SRIF antiserum resulted in a dose-dependent increase in plasma concentrations of GH, TSH and prolactin. The minimal effective dose of SRIF antiserum was 50 microliters for GH, 100 microliters TSH and 200 microliter for prolactin. Our results show that: starvation does not modify adenohypophysial SRIF-binding sites, in starved male rats endogenous SRIF exerts a negative control on prolactin secretion in vivo and sensitivity to endogenous SRIF seems to be different for each hypophysial cell type.

Acute Hyperglycemia and Activation of the .BETA.-Adrenergic System do not Exhibit Synergistic Inhibitory Actions on Thyrotropin-releasing Hormone (TRH)-induced Thyroid Stimulating Hormone (TSH) Secretion

“…Williams et al [29] also reported more potent inhibitory effect of SRIH on GH compared to TSH secretion in men. Other supporting evidence has been reported by several investigators, where treatment of animals with SRIF antiserum increases both GH and TSH levels [30][31][32]. However, more marked stimulatory effects of SRIH antiserum on GH compared to TSH levels were observed [31,32].…”

“…Other supporting evidence has been reported by several investigators, where treatment of animals with SRIF antiserum increases both GH and TSH levels [30][31][32]. However, more marked stimulatory effects of SRIH antiserum on GH compared to TSH levels were observed [31,32]. Another explanation of the discrepancy between GH and TSH responses is the very weak degree of suppression by isoproterenol on TSH secretion.…”

Differential Response of Lactotrophs and Somatotrophs to a Joint Application of Vasoactive Intestinal Peptide and Thyrotrophin‐Releasing Hormone in the Rat

“…In our study TRH-and VIP-induced G H secretion shows a higher sensitivity to the hypothalamic lesion, an effect which parallels the high sensitivity of somatotrophs to SRIF in vivo (22) as well as in vitro (23,24), as compared to that of the other cell types.…”

Hypothalamic signaling in anorexia induced by indispensable amino acid deficiency

“…Also consistent with this report, we observed an increase in hypothalamic SS expression in VDD animals. This finding likely reflects the enhanced somatostatinergic tone underlying the decrease in growth hormone in starved animals (22). Cumulatively, these data show that IAADA does not result from a disordered response to negative energy balance but rather to increased activity of inhibitory networks functionally similar to those found in dehydration-induced anorexia (42).…”