EFFECTS OF CENTRAL AND PERIPHERAL ADMINISTRATION OF ARGININE VASOTOCIN AND RELATED NEUROPEPTIDES ON BLOOD-PRESSURE AND HEART-RATE IN THE CONSCIOUS TROUT

The cardiovascular activity of neurohypophyseal peptides has been inve stigated in conscious trout bearing an intracerebroventricular guide c annula and a permanent intraarterial catheter. Changes in diastolic pr essure, systolic pressure and heart rate were monitored during the 25- min period following intracerebroventricular or intraarterial administ ration of arginine vasotocin and related neuropeptides, including argi nine vasopressin, oxytocin, hydrin-2, mesotocin, isotocin and conopres sin-S. Intracerebroventricular injection of increasing doses of argini ne vasotocin (0.62-5 pmol) induced a dose-dependent increase of diasto lic and systolic pressures. The onset of the response occurred within 3-5 min after intracerebroventricular administration of arginine vasot ocin and the maximal increase was reached at 10-15 min. Central admini stration of vasopressin and oxytocin induced a significant rise in dia stolic and systolic pressures at a dose of 5 pmol while hydrin-2 only caused a significant elevation of blood pressure at a dose of 50 pmol. Central administration of mesotocin, isotocin and conopressin-S (5-50 0 pmol each) had no significant effect on blood pressure. No changes i n heart rate occurred after intracerebroventricular injection of any o f the seven neuropeptides tested. Intraarterial injection of arginine vasotocin (50 pmol) induced a significant rise in blood pressure and b radycardia. Peripheral injection of the other neuropeptides did not ca use any modification of the cardiovascular activity, whatever the dose s administered (5-500 pmol). The VIA receptor antagonist [d(CH2)5, Tyr (OMe)2]arginine vasopressin had no intrinsic effect on blood pressure and heart rate when injected centrally (50 pmol) or in the peripheral circulation (200 pmol). At the same doses. [d(CH2)5, Tyr(OMe)2]arginin e vasopressin reduced by 50 and 66%, respectively, the increase in blo od pressure evoked by intracerebroventricular (5 pmol) or intraarteria l (50 pmol) injections of arginine vasotocin. These data indicate that arginine vasotocin acts centrally to increase blood pressure in consc ious trout through activation of receptors related to the mammalian VI receptor type.