Central effects of dopamine and bromocriptine on vasopressin release and blood pressure

In order to investigate the role of central dopaminergic receptors in the control of vasopressin release and in cardiovascular regulation, the effects of intracerebroventricular administration of dopamine (DA) and bromocriptine (BC), a specific DA agonist, were compared in the anesthetized dog. The drugs were infused over a 20-min period into a lateral ventricle. DA brought about a transient decrease in mean arterial blood pressure, a slight increase in heart rate toward the end of the experiment, and a suppression of vasopressin release. BC increased heart rate and decreased blood pressure to a greater extent than did DA, and doubled the plasma vasopressin concentration. The increase in vasopressin secretion preceded the fall in blood pressure, ans was, therefore, due to a direct central action of BC. Although in these circumstances it is difficult to determine the role of dopaminergic neurons in the control of vasopressin release, there is some reason to believe that this role may be expressed by the actions of BC under the present experimental conditions.