Vasopressin and oxytocin in the neural control of the circulation.

Catecholamine innervation originating in dorsal medial and ventral lateral medulla terminates on parvocellular and magnocellular subnuclei, respectively, of the paraventricular nucleus of the hypothalamus. In turn, parvocellular pathways terminate in brain stem and spinal cord, whereas magnocellular pathways terminate in median eminence and posterior pituitary. Consistent with the neuroanatomy, we find that baroreceptor regulation of neuroendocrine (plasma vasopressin) and autonomic (blood pressure) functions can be dissociated. Further, studies indicate that sympathetic vasomotor pathways are activated by injections of vasopressin and oxytocin into the nucleus tractus solitarii and vasopressin into the lateral cerebral ventricles. Also, parasympathetic pathways to the heart and baroreflex function are activated and augmented, respectively, by i.v. administered vasopressin. These results are consistent with at least three central sites of action and suggest a complex role of vasopressin (and possibly oxytocin) in the central neural regulation of the heart and circulation.