Alpha 2-adrenergic stimulation within the nucleus tractus solitarius attenuates vasopressin release induced by depletion of cardiovascular volume.

The functional role of the nucleus tractus solitarius (NTS) in the regulation of arginine-vasopressin (AVP) release mediated by baroreceptor activation was investigated by examining the effects induced by the presynaptic alpha-adrenergic agonist clonidine. The present data show that microinjection of clonidine into NTS resulted in a significant attenuation of AVP secretion induced by hypovolemia in the rat. This effect produced by NTS injection of 8 and 10 nmol clonidine was prevented by NTS pretreatment with the alpha-2-adrenoceptor blocker, yohimbine (10 nmol), indicating alpha-2-adrenergic receptors were required for the biological response. These findings suggest that catecholaminergic projections from NTS to hypothalamic vasopressinergic neurons play a facilitatory role in controlling AVP secretion.