Acute effects of salbutamol on arteriolar vasodilatation and blood pressure in spontaneously hypertensive rats

The acute effects of salbutamol, a β₂ agonist, on arteriolar vasodilatation and blood pressure were studied in WKY and SHR rats. The cremaster muscle was prepared for in vivo microscopy and the femoral artery cannulated for administration of salbutamol (0.001- to 4.0-μg doses). Systemic mean arterial pressures were measured from the carotid artery. Changes in arteriolar diameter were recorded on videotape and analyzed using variable resistance calipers to trace the changes in diameter. In both WKYs and SHRs salbutamol induced dose-dependent vasodilatations, the magnitudes of which were inversely related to the resting diameter. Among arterioles 35 μm or less in diameter, the SHRs exhibited significantly greater percentage vasodilatations. Vasodilatation among arterioles greater than 35 μm was strongly attenuated at all doses in both WKYs and SHRs. These vasodilatory responses were accompanied by dose-dependent decreases in the mean arterial pressure. At all doses the absolute pressure drop was greater in the SHR, although the percentage decreases were similar. Both the vasodilatations and blood pressure decreases were blocked by propranolol. This enhanced vasodilatory capacity to β₂ stimulation by the smaller SHR arterioles may serve as part of a compensatory mechanism to maintain sufficient blood flow regulation in the face of a reduced vascular density.