Characteristics of a novel vasopressin receptor in the cardiovascular system

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1. Vasopressin (AVP) receptor subtypes in rat brain :High-affibity [_3H]-AVP binding sites have been identified in both the nucleus tractus solitarius (NTS) and the area postrema (AP). In addition, we examined the subtype (s) of the AVP receptor in the NTS and the AP.The binding study showed that AVP receptor in these areas is the V1 subtype. Next, we tested for AVP A1a-and V20receptor mRNAs in the NTS and AP of adult rats. PCR product of the V1a and V2 receptor mRNA was detected in the NTS,but not in the AP.We do not know why V1a receptor mRNA was not detected in the Apa in this study. Possible explanations are that the sequence of the AVP receptor mRNA in the brain may not completely consistent with that of V1a receptor mRNA in peripheral tissues.2. Roles of AVP receptors in cardiovascular regulation :The role of AVP in regulation of the baroreceptor reflex in the AP was examined in anesthetized hypertensive rats. The sensitivity of the baroreceptor reflex in a one-kidney one clip (1 … More K1C) hypertensive rats was increased in only the initial stage (2 weeks), in association with increase in blood pressure, and then returned to the normal level. This increase in the sensitivity of the baroreceptor reflex in the initial stage was reversed by microinjection of a V1 or V2 antagonist into the AP.AVP V2 receptor mRNA was expressed temporarily in the AP in this period.3. Electrophysiological studies :We found the functional relationship between the area postrema and NTS in the physiological experiments in vitro. Stimulating electrodes were set on the AP and/or solitary tract (ST), and spikes were recorded from the NTS neuron. Most of neurons in the AP and NTS showed spontaneous firings, and some of neurons in the NTS received the neuronal inputs from both the AP and ST.AVP caused inhibitory (24.3%) and excitatory efects (24.7%) on sponteous firings of the of the AP neurons. The rest of neurons (51.3%) were no effect. These results suggest that there are two types of AVP sensitive neuron and that the AP neurons responding to the endogenous AVP send the information into the NTS neurons and modify arterial baroreceptor reflex. Less