Stimulation of arteriolar number by salbutamol in spontaneously hypertensive rats

Experiments were performed to study beta2-adrenergic involvement in arteriolar development in spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. Newly weaned 20-day WKY and SHR rats were injected with salbutamol, a selective beta2-agonist (50 microgram/day sc, plus 5 mg/100 ml in drinking water), for 20 days. At 40 days, under 2% chloralose-7.5% urethan anesthesia (6 ml/kg), either the cremaster muscle was prepared for in vivo microscopy to estimate the number and diameter of open arterioles or the arterioles were injected with latex to determine the total number of arterioles and their maximal diameters. Control SHRs had 62% (P less than 0.01) fewer open arterioles and a 32% (P less than 0.001) reduction in the total number of arterioles compared to WKY controls. Salbutamol stimulated 67% (P less than 0.001) and 22% (P less than 0.05) increases in total number of the smallest arterioles in the SHR and the WKY, respectively. Salbutamol also significantly reduced the maximum diameter of latex-injected arterioles. These results suggest that the decreased arteriolar density in the cremaster muscle of SHR rats may result from differences in the beta-adrenergic mechanism.