Hypoxia influences somatostatin release in rats

The impact of hypoxia on somatostatin (SS) secretion from the median eminence (ME) of the hypothalamus and the possible glucocorticosteroid involvement in modulating secretion, were investigated in adult male rats exposed to hypoxia. SS levels were measured by specific radioimmunoassay during acute and prolonged hypoxia as well as after bilateral adrenalectomy (ADX) with or without a replacement with dexamethasone (DEX). The results were as follows: (a) acute hypoxia (5 km altitude, 10.8% O(2)) for 2 and 24 h markedly increased SS content in ME, but acute severe hypoxia (7 km, 8.2% O(2) for 24 h) markedly decreased SS level in ME. (b) Chronic hypoxia (10.8% O(2)) from 5 to 25 days exposure did not significantly affect SS content of ME. (c) ADX alone increased SS content of ME and this increase was further enhanced after 2 h exposure to hypoxia. (d) The increased SS in ME of ADX rats was blocked by replacement with DEX (500 microg/rat i.p.). The data presented suggest that acute hypoxia stress may increase or decrease SS content of ME in rats, depending on the severity and duration of the hypoxia and that the stimulatory action of hypoxia on SS content of ME be may in part mediated by the increased corticosterone levels during hypoxia.