Evidence for an antihypertensive factor from the adrenal medulla of SHR modulating neurogenic vasoconstriction

The aim of this study is to investigate some vasoactive properties of the b lood of spontaneously hypertensive rats (SHR). Isolated segments of rat tai l arteries obtained from normotensive rats (Wistar-Kyoto (WKY) and Wistar) were perfused with blood from conscious donor rats (WKY, Wistar or SHR). Al terations of the neurogenic constrictor responses (NCR) of the isolated seg ments evoked by electrical stimulation were studied. The amplitude of NCR o f the isolated arteries was studied during perfusion with blood according t o the perfusion scheme WKY1(1)-SHR1(2)-WKY1(3) and WKY1(1)-WKY2(2)-WKY1(3). The release of H-3-noradrenaline ([H-3]-NA) from vascular sympathetic fibr es was measured. The influence of adrenal demedullation on NCR was estimate d. We have shown that NCR of isolated arteries decreased by 28.3 +/- 7.9% ( P < 0.05 vs. WKY1(1)) during perfusion with blood from SHR (scheme WKY1(1)- SHR1(2)-WKY1(3)). In these experiments, release of [H-3]-NA from sympatheti c fibres of the artery segments decreased by 39.9 +/- 9.6% during the perfu sion with blood from SHR vs. WKY1(1) (P < 0.05). Adrenal demedullation prev ented the decrease of NCR during perfusion of the arteries with blood from SHR. In conclusion, the blood of SHR has some antihypertensive factor(s), w hich causes decrease of NCR in the tail artery from normotensive rats. This decline is accompanied by the decrease of release in [H-3]-NA from the tra nsmural sympathetic fibres and is abolished after adrenal demedullation of blood donor rats.