Acute elevations in salt intake and reduced renal mass hypertension compromise arteriolar dilation in rat cremaster muscle

Alterations in arteriolar reactivity to dilator agonists were assessed in the skeletal muscle microcirculation of normotensive male Sprague-Dawley rats fed either high- (4% NaCl; HS) or low- (0. 4% NaCl; LS) salt diets and in reduced renal mass hypertensive rats (RRM-HT) on a high-salt diet for 3 days. An in situ cremaster muscle preparation was superfused with physiological salt solution, transilluminated, and viewed via television microscopy. A videomicrometer was used to measure changes in diameter of distal arterioles in response to increasing concentrations of acetylcholine (ACH), iloprost (ILO), cholera toxin (CT), forskolin (FOR), and sodium nitroprusside (SNP). Arteriolar dilation in response to ACH, ILO, and CT was significantly reduced in both HS and RRM-HT rats, while responses to FOR and SNP were decreased in RRM-HT rats only. The maximum dilation of the arterioles (determined during superfusion of the muscle with Ca2+-free solution containing 10(-4) M adenosine) was similar in the normotensive control animals on LS and HS diets, but was reduced in the RRM-HT rats, suggesting that early anatomic remodeling of the vessel wall may be occurring with RRM-HT. We conclude that arteriolar reactivity to endothelium-dependent and -independent vasodilator agonists is impaired as early as 3 days after the development of RRM hypertension or commencement of a high-salt diet in normotensive rats. Structural remodeling of the arteriolar wall, although becoming evident in the hypertensive rats, takes longer to develop than the impaired vasodilator reactivity.