MODIFICATION OF ALPHA-ADRENERGIC RESPONSES OF SMALL ARTERIES BY ALTERED PCO2 AND PH

Closed-circuit television microscopy was used to measure in vivo small artery (75-140 μ) and vein (105-230 μm) diameters to determine if changes in tissue PCO2 and/or pH would alter the microvascular responses to norepinephrine. Sprague-Dawley rats were anesthetized with a combination of urethane (800 mg/kg) and α-chloralose (60 mg/kg). The cremaster muscle with intact circulation and inervation was suspended by sutures in a 60-ml bath which contained and mofified Krebs solution (31°C) that was buffered by Tris of bicarbonate. There were four groups of animals with different combintions of bath PCO2 and pH: (1) PCO2 < 10 mm Hg and pH = 7.2, PCO2 < 10 mm Hg and pH = 6.9, (3) PCO2 = 60-70 mm Hg and pH = 6.9. The maximal responses of the small artery and vein to norepinephrine were similar for the four groups. The artery sensitivity to norepinephrine was signficantly lower for group 4 when compared to groups 1, 2 and 3, but there was no effect on small vein sensitivity. This, the combination of decreased pH and increased PCO2 reduces small artery sensitivity to norepinephrine in the cremaster muscle of the rat. © 1979.