Phentolamine suppresses the increase in arteriolar vasomotion frequency due to systemic hypoxia in hamster skeletal muscle microcirculation

Systemic hypoxia (8%, 11% and 15% oxygen gas mixture inspiration) has been shown to increase the frequency of arteriolar rhythmic diameter changes in hamster skeletal muscle microcirculation. The effects of phentolamine on va somotion frequency during systemic hypoxia were studied in Syrian hamsters implanted with a plastic chamber in the dorsum skin. Phentolamine(50 mug/10 0 g body wt.) was injected intravenously before the 20-min exposure to 11% oxygen gas mixture. The microvessels were studied with a fluorescent micros copy technique, using fluorescein isothiocyanate bound to dextran (mol. wt. 150,000) as a tracer. Vessel diameters were measured with a: shearing meth od. Fourier transform and autoregressive modeling were used to assess the t ime variant features of diameter changes. Under baseline conditions, the arterioles were characterized by rhythmic di ameter changes with fundamental frequency related to vessel size. The termi nal branchings were dominated by order 3 vessel activity (frequency: 0.08-0 .16 Hz) spreading downstream to all daughter arterioles. Systemic hypoxia c aused an increase in vasomotion frequency of order 3 arterioles up to 0.3-0 .5 Hz (average: 0.40 +/- 0.06 Hz) and a significant decrease in mean diamet er(-28 +/- 5%). Phentolamine completely suppressed the rhythmic changes in diameter of order 3 arterioles that dilated significantly (+30 +/- 4%). Therefore, the effects of systemic hypoxia on arteriolar vasomotion appear to be triggered by an increase in sympathetic nervous discharge that induce s a rise in frequency up to 0.3-0.5 Hz. (C) 2001 Elsevier Science B.V. All rights reserved.