Evidence for a common neural mechanism mediating growth hormone-releasing factor-induced and somatostatin-induced...

We have previously reported that the somatotropin regulatory peptides, growth hormone-releasing hormone (GRF) and somatostatin (SS) increase feeding when applied centrally in low picomole-range doses. The similarity between the dose-response characteristics and photoperiod sensitivities of these two peptide's feeding effects, together with indirect evidence suggesting that these peptides interact functionally within the hypothalamus, suggests that GRF and SS may induce feeding via a common neural mechanism. The present studies sought to investigate this possibility. In the first experiment combined intracerebroventricular (icv) injections of optimal doses of GRF and SS were found to be less potent than icv injections of GRF or SS alone, suggesting that the mechanisms mediating GRF-induced and SS-induced feeding are not totally independent. In further studies, icv injections of antiserum raised against SS blocked GRF-induced feeding. In contrast, icv injections of antiserum raised against GRF were ineffective in blocking SS-induced feeding. These results suggest that SS may act downstream to GRF in a putative neural feeding mechanism which utilizes both peptides. The possible anatomical basis for such a feeding mechanism involving GRF and SS is discussed.