VASCULAR ACTIONS OF VASOACTIVE INTESTINAL POLYPEPTIDE AND BETA-ENDORPHIN IN ISOLATED PERFUSED GILLS OF THE BROWN TROUT, SALMO-TRUTTA-L

Vasoactive intestinal polypeptide (VIP) produced a concentration-dependent vasodilation in isolated rainbow trout gill arches perfused through the arterio-arterial circulation from a constant head apparatus. Pre-incubation with noradrenaline [norepinephrine, NE] increased the sensitivity of the gills to VIP. The vasodilatory action of VIP was abolished by indomethacin, suggesting a possible involvement of prostaglandins, but was not antagonized by propranolol, suggesting that .beta.-adrenergic receptors were not involved. .beta.-Endorphin increased the sensitivity of the preparation to NE-induced vasodilation. This effect was completely abolished by the opiate antagonist naloxone. Receptors for VIP and .beta.-endorphin evidently exist in the arterio-arterial circulation of trout gills. The possibility of a physiological role for peptides in the regulation of branchial blood flow is suggested.