Active tone and arteriolar responses to increased oxygen availability in the mesoappendix of spontaneously hypertensive rats.

The goal of this study was to determine if active tone and arteriolar constriction in response to increased PO2 are enhanced in the mesenteric microcirculation of spontaneously hypertensive rats (SHR) relative to normotensive Wistar-Kyoto (WKY) controls. Diameters of arterioles, metarterioles, and precapillary arterioles were measured in the mesoappendix of anesthetized 12-15 week old SHR and WKY rats during superfusion with physiological salt solution equilibrated with either 0%, O2, 5% O2 or 10% O2, with 5% CO2-balance N2. Active tone was assessed by superfusion with 10(-4) M adenosine. Metarterioles of SHR constricted significantly more than those of WKY when superfusion solution PO2 was elevated, but vessel closure did not occur in response to elevated PO2 in either SHR or WKY. Arteriolar dilation in response to 10(-4) M adenosine was not significantly different in hypertensive and normotensive animals, suggesting that resting tone is not elevated in mesoappendix arterioles of SHR. Although metarterioles of SHR constricted significantly more than those of WKY in response to elevated PO2, an enhanced response of arterioles to increased oxygen availability does not appear to contribute to functional rarefaction (i.e., active vessel closure) of small arterioles in the mesenteric microcirculation of SHR.