A decrease in the amount and function of inhibitory GTP-binding protein inthe resistance small artery from spontaneously hypertensive rats

The inhibitory GTP-binding protein (Gi protein) plays an important role in regulation of vascular tone. Many studies have implicated the role of Gi pr otein in conduit vessels. However, the physiological role of Gi protein in the control of peripheral microvascular tone in hypertension has not been e stablished yet. Therefore, we investigated the concentration of Gi protein in the peripheral resistance arteries and aorta in the spontaneously hypert ensive rats (SHR), normotensive Wistar-Kyoto rats (WKY) and renovascular hy pertensive rats (RHR), using immunohistochemical methods semiquantitatively . Changes in the function of Gi protein in relation to alpha(2)-adrenocepto r were also investigated by microcannulation techniques. We have shown that the amount of alpha(2) subunits of Gi protein in the cremaster small arter y was significantly lower in SHR aged 4 weeks and older than in age-matched WKY and that there were no significant differences between RHR and WKY. We also demonstrated that the function of Gi protein in relation to alpha(2)- adrenoceptor was already lower in SHR before the onset of hypertension. The quantitative and functional decline in Gi protein in the smooth muscle cel ls of peripheral small arteries were observed in SHR even before the onset of hypertension, whereas rats with secondary hypertension did not exhibit t his finding.