Central somatostatin: a re-examination of its effects on feeding.

Previous investigations of centrally administered somatostatin (SRIF) have tended to employ pharmacological (nmol and greater) doses of the peptide. Under this protocol contradictory findings of feeding effects have been reported. There is evidence that the use of physiological doses can induce a completely distinct response from that obtained with pharmacological doses. In order to discern whether physiological doses of centrally administered somatostatin have any effect on feeding. SRIF in doses ranging from 0.4 pmol to 3 nmol were administered into the lateral ventricles of rats. Low pmol doses (0.4-40) administered during the light photoperiod increased 1 h feeding whereas 3 nmol decreased 1 h feeding. None of the doses tested during the dark photoperiod significantly altered 1 h food intake. Similarly, no significant change in 24-h food intake was observed following injections of any of the doses tested, whether in the light or dark. A dose of SRIF that increased feeding (1 pmol) did not significantly alter 1 h water intake when applied centrally in the light nor did it alter spontaneous locomotor activity. Furthermore, when applied peripherally it did not change 1 h food intake. These studies suggest that SRIF may work centrally to regulate food intake. A similarity exists between SRIF's feeding effects and the feeding effects we have previously described following central injections of growth hormone-releasing factor (GRF), both in terms of dose-response and photosensitivity. This suggests that these 2 peptides may act via a common mechanism to regulate food consumption; possibly in co-ordination with their regulation of growth hormone release. The possibility that such feeding regulation occurs as part of a short intrahypothalamic feedback loop is discussed.