Role of central vasopressin in cardiovascular regulation in rats

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1. Vasopressin (AVP) receptor subtypes in rat brain :To determine the subtype (s) of the AVP receptor in the brain, we examined the inhibitions of specific binding of [^3H] -AVP by the V1 antagonist OPC-21268 and V2 antagonist OPC-31260. [^3H] -AVP binding to rat hippocampal membranes was strongly inhibited by the V1 antagonist, OPC-21268. In this study, we tested for AVP V1a-and V2-receptor mRNAs in the hippocampus of adult rats by a reverse transcription-polymerase chain reaction (RT-PCR) method. PCR product of the V2 receptor mRNA was detected in the hippocampus, but that of V1a receptor mRNA was not. We do not know why V1a receptor mRNA was not detected in the hippocampus 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.Role of vasopressin in the area postrema in regulation of baroreceptor reflex.We examined the involvements of vasopressin and its receptors in the sensitivity of the baroreceptor reflex in hypertension. The sensitivity of baroreceptor reflex was remarkably increased via V2 receptor in the area postrema in the initial stage of one-kidney, one clip hypertensive rats, but not in the other hypertensive models. And this period, V2 receptor mRNA was expressed temporarily at the area postrema. These results suggested that vasopressin in the area postrema have very important roles of baroreceptor reflex and development of a kind of hypertension.