The effects of alpha- or beta-adrenergic receptor agonists and antagonists and calcium entry blockers on the spontaneous vasomotion.

The effects of systemic injections of vasoactive substances were studied in the micro-circulation of the hamster skin fold window preparation, which can be observed without anesthesia, exposure, and acute surgical procedures. The effects were characterized by the continuous measurement of the diameter of the arterial microvessels ranging from 100 to 8 micron. Power spectrum analysis was utilized to determine the frequency and the amplitude of the fundamental component of spontaneous diameter changes. Epinephrine and norepinephrine increased the frequency of vasomotion and reduced mean diameter at low dosages. Phentolamine reduced the frequency of vasomotion and increased mean diameter. Propranolol increased the frequency of vasomotion and did not significantly change mean diameter. Adenosine and verapamil suppressed vasomotion and increased mean diameter. These results are explained by postulating that low-dosage alpha-adrenergic receptor stimulation facilitates the spontaneous discharge of smooth muscle cells; beta-adrenergic receptor stimulation has the opposite effect, whereas beta-adrenergic receptor inhibition also enhances the vasomotor effect. Calcium entry blockers abolish the rhythmic discharge. This explanation of the activity of the various substances supports the hypothesis that the spontaneous vasomotion of the arterial microvessels is related to the intrinsic property of smooth muscle cells.