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

Intravital microscopy of the hamster cheek pouch microvasculature was used for in vivo studies of the effects of diltiazem (calcium antagoni st, 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 isop roterenol (beta-adrenergic receptor agonist, group IX) in a concentrat ion range of 10(-9)-10(-5) M and their combination with 10(-7) M of bu flomedil (groups II, IV, VI, VIII and X) on mean arteriolar internal d iameter and spontaneous vasomotion. All drugs were applied topically. Vasomotor activity was studied in 270 arterioles (internal diameter ra nge 20.0-75.0 mu m) of 60 preparations. Diltiazem dose dependently inc reased the microvascular diameter and reduced and ultimately abolished the vasomotion frequency and amplitude. Addition of buflomedil did no t significantly change the vasodilation evoked by diltiazem and potent iated its depressive effect on vasomotion frequency and amplitude. Pra zosin dose-dependently increased the arteriolar diameter and reduced t he vasomotion frequency and amplitude. Addition of buflomedil potentia ted both the vasodilation elicited by prazosin and the reduction in va somotion frequency and amplitude. Rauwolscine tended to elicit vasocon striction at lower concentrations (10(-9) and 10(-8) M) and vasodilati on at higher concentrations (10(-5) M) and significantly reduced the v asomotion frequency and amplitude. Addition of buflomedil potentiated both the vasodilation and the reduction in vasomotion frequency, but t ended to increase the vasomotion amplitude. Phenylephrine significantl y decreased the mean arteriolar internal diameter, moderately decrease d the vasomotion frequency and did not significantly change the vasomo tion amplitude. Addition of buflomedil totally blocked the vasoconstri ction elicited by phenylephrine, potentiated the reduction in vasomoti on 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 phenylephrin e (10(-6) and 10(-5) M). Isoproterenol significantly increased the mea n arteriolar diameter and reduced the vasomotion frequency and amplitu de. Addition of buflomedil did not significantly change either the vas odilation or the reduction in vasomotion frequency and amplitude. The effects observed with buflomedil on the hamster cheek pouch microcircu lation further support its properties as a competitive inhibitor of cx -adrenergic receptors, not selective for either the alpha(1)- or alpha (2)-adrenergic receptor subtype, and as a weak calcium antagonist.