Abstract

Arg8-vasotocin (AVT), oxytocin and Arg8-vasopressin (AVP) were injected into the i.c.v. space and/or the hypothalamus of awake, freely moving rats in order to investigate the potential role of these neuropeptides in central cardiovascular control. AVT (0.015-10 nmol) injected i.c.v. caused dose-dependent pressor responses; low doses also elicited tachycardia, whereas the higher doses (1 and 10 nmol) produced bradycardia. In contrast, oxytocin injections into the lateral ventricle (0.015-100 nmol) had no significant cardiovascular effects. Plasma vasopressin was not affected by i.c.v. administration of oxytocin or AVT except at the highest dose of AVT. AVT (0.1 or 1 nmol) and AVP (0.015 or 0.1 nmol) injected into the hypothalamic nucleus preopticus medialis (POM) increased blood pressure and heart rate; these changes were much greater than with comparable doses of AVT injected i.c.v. Plasma levels of norepinephrine and epinephrine, but not vasopressin, were significantly elevated during the pressor period induced by 1 nmol of AVT injected into the POM. The pressor and cardiac accelerating effects of AVT (1 nmol) injected into the POM were significantly diminished in bilaterally adrenal demedullated, bretylium-treated rats. These data suggest a role for AVT, but not oxytocin, in central cardiovascular control through activation of the sympathoadrenomedullary axis. The anteroventral hypothalamus might play a central role in these autonomic effects of vasotocin. It is also suggested that AVP and AVT share some central autonomic effects due to similarities in the side-chain of their molecules.