Neural and local control of arterioles in SHR

This study sought to determine if neural influences and/or alterations in arteriolar responses to oxygen could contribute to an elevated microvascular resistance in spontaneously hypertensive rats (SHR). Diameters of third-order arterioles (3A) and fourth-order arterioles (4A) were measured in the cremaster muscle of 12- to 15-week-old SHR and normotensive Wistar-Kyoto (WKY) controls anesthetized with pentobarbital. The preparation was suffused with physiological salt solution (PSS) equilibrated with various concentrations of oxygen (0% O2, 5% O2, or 10% O2) with and without local neural blockade with 10(-7) g/ml tetrodotoxin (TTX). Total active tone was assessed with 10(-4) M adenosine. SHR 3A (but not 4A) exhibited a smaller resting diameter than WKY, and larger dilations in response to TTX and adenosine. When suffusion solution PO2 was elevated in the presence or absence of TTX, SHR arterioles constricted more than did those of WKY, and SHR 4A exhibited a higher incidence of complete closure. Therefore, both neural influences and local vascular control mechanisms may contribute to an elevated microvascular resistance in SHR.