Augmented vascular responses to ouabain in SHRSP during salt loading.

It is not known whether high salt diet alters the sarcolemmal Na-K pump activity of resistance vessels in stroke-prone spontaneously hypertensive rats (SHRSP). We examined hindquarters vascular responses to ouabain 10(-3) M in the isolated hindquarters perfused with the Krebs-Henseleit solution in SHRSP and in normotensive Wistar-Kyoto rats (WKY) after two weeks of either normal (0.3% NaCl) or high (8% NaCl) salt diet. Salt loading increased arterial pressure (P less than 0.05) and augmented ouabain-induced vasoconstriction (P less than 0.01) in SHRSP. In WKY, salt loading did not alter arterial pressure or vascular responses to ouabain. Neither hindquarters vascular resistance during maximal vasodilatation produced by nitroprusside nor hindquarters vascular responses to norepinephrine were different between the two groups of SHRSP, which suggested that augmented response to ouabain in SHRSP on high salt diet could not be explained by structural vascular changes. Vasodilatation by phentolamine during maximal vasoconstriction induced by ouabain was also not different between two groups of SHRSP, which suggested that ouabain-induced release of norepinephrine from nerve endings was not different between the two groups of SHRSP. These results suggest that salt loading might augment the sarcolemmal Na-K pump activity of hindquarters resistance vessels in SHRSP but not in WKY. The augmented sarcolemmal Na-K pump activity of resistance vessels may act against salt-induced vasoconstriction in SHRSP.