Effects of a calcium antagonist and of the adrenergic system on spontaneous vasomotion and mean arteriolar diameter in the hamster cheek pouch: influence of buflomedil.

Abstract

Intravital microscopy of the hamster cheek pouch microvasculature was used for in vivo studies of the effects of diltiazem (calcium antagonist, group I), prazosin (alpha 1-adrenergic receptor antagonist, group III), rauwolscine (alpha 2-adrenergic receptor antagonist, group V), phenylephrine (alpha-adrenergic receptor agonist, group VII) and isoproterenol (beta-adrenergic receptor agonist, group IX) in a concentration range of 10(-9)-10(-5) M and their combination with 10(-7) M of buflomedil (groups II, IV, VI, VIII and X) on mean arteriolar internal diameter and spontaneous vasomotion. All drugs were applied topically. Vasomotor activity was studied in 270 arterioles (internal diameter range 20.0-75.0 microns) of 60 preparations. Diltiazem dose dependently increased the microvascular diameter and reduced and ultimately abolished the vasomotion frequency and amplitude. Addition of buflomedil did not significantly change the vasodilation evoked by diltiazem and potentiated its depressive effect on vasomotion frequency and amplitude. Prazosin dose-dependently increased the arteriolar diameter and reduced the vasomotion frequency and amplitude. Addition of buflomedil potentiated both the vasodilation elicited by prazosin and the reduction in vasomotion frequency and amplitude. Rauwolscine tended to elicit vasoconstriction at lower concentrations (10(-9) and 10(-8) M) and vasodilation at higher concentrations (10(-5) M) and significantly reduced the vasomotion frequency and amplitude. Addition of buflomedil potentiated both the vasodilation and the reduction in vasomotion frequency, but tended to increase the vasomotion amplitude. Phenylephrine significantly decreased the mean arteriolar internal diameter, moderately decreased the vasomotion frequency and did not significantly change the vasomotion amplitude. Addition of buflomedil totally blocked the vasoconstriction elicited by phenylephrine, potentiated the reduction in vasomotion frequency and amplitude when combined with lower concentrations of phenylephrine (10(-9)-10(-7) M) and restored the vasomotion frequency and amplitude when combined with higher concentrations of phenylephrine (10(-6) and 10(-5) M). Isoproterenol significantly increased the mean arteriolar diameter and reduced the vasomotion frequency and amplitude. Addition of buflomedil did not significantly change either the vasodilation or the reduction in vasomotion frequency and amplitude. The effects observed with buflomedil on the hamster cheek pouch microcirculation further support its properties as a competitive inhibitor of alpha-adrenergic receptors, not selective for either the alpha 1- or alpha 2-adrenergic receptor subtype, and as a weak calcium antagonist.