The present investigation assessed the ability of the neurohypophysial nonapeptide arginine vasotocin (AVT) to centrally regulate the cardiovascular activity in fish. Intracerebroventricular (ICV) injection of AVT (0.4 to 50 ng/kg b.wt.) in anesthetized trout resulted in a dose-related increase in blood pressure (BP) without any consistent changes in heart rate. For doses of AVT ranging from 2 to 50 ng/kg b.wt., BP remained elevated during at least 25 min after ICV injection. Systemic (intraarterial) administration of the same doses of AVT appeared to be less efficient than ICV injection, except for the highest dose (50 ng/kg) which evoked a similar rise in BP as that observed after ICV administration. In contrast to AVT, a high concentration of neuropeptide Y (10 μg/kg b.wt., ICV) caused only a slight increase of BP. The results suggest that AVT acts centrally to regulate BP in fish. These data, together with the widespread distribution of AVT-immunoreactive fibers and AVT binding sites in the brain, support the notion that, in fish, AVT may play neuromodulator and/or neurotransmitter functions. © 1991.
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