EFFECTS OF BUFLOMEDIL ON SPONTANEOUS VASOMOTION AND MEAN ARTERIOLAR INTERNAL DIAMETER IN THE HAMSTER-CHEEK POUCH

Intravital microscopy of the hamster cheek pouch microvasculature was used for in vivo studies on the effects of buflomedil, phentolamine (alpha-adrenergic receptor antagonist) and norepinephrine on the mean internal arteriolar diameter and spontaneous vasomotion. All drugs were applied topically. The vaso-motor activity was studied in 125 arterioles (internal diameter range 18.0-62.0 mu m) of 34 preparations. Addition of buflomedil (10(-9) to 10(-5) M) did not affect the arteriolar diameter significantly(from 100.7 +/- 3.5 to 106.4 +/- 1.8%, values expressed in percent of the initial diameter as mean +/- SE), but increased the vasomotion frequency and amplitude by approximately 20% (from 7.5 +/- 0.3 to 9.2 +/- 0.2 cpm) and 30% (from 7.3 +/- 0.3 to 10.0 +/- 0.5 mu m), respectively. Phentolamine (10(-9) to 10(-5) M) dose-dependently increased the microvascular diameter (from 102.3 +/- 1.2 to 139.1 +/- 4.3%) and reduced the vasomotion frequency and amplitude (from 8.0 +/- 0.3 to 1.9 +/- 0.5 cpm and from 9.0 +/- 2.1 to 3.1 +/- 0.2 mu m, respectively). Addition of buflomedil (10(-7) M) reduced the vasodilation evoked by phentolamine (from 103.3 +/- 0.7 to 127.0 +/- 1.5%) and potentiated its depressive effect on vaso-motion frequency and amplitude (from 7.6 +/- 0.1 to 1.0 +/- 0.3 cpm and from 9.0 +/- 0.3 to 1.9 +/- 0.6 mu m, respectively). Norepinephrine (10(-9) to 10(-5) M) dose-dependently decreased to arteriolar diameter (from 102.3 +/- 0.7 to 69.6 +/- 1.6%) and the vasomotion frequency and amplitude (from 8.4 +/- 0.2 to 0.4 +/- 0.3 cmp and from 8.7 +/- 0.2 to 0.5 +/- 0.4 mu m, respectively). Addition of buflomedil (10(-7) M) reduced the vasoconstriction elicited by norepinephrine (from 103.2 +/- 0.9 to 82.9 +/- 3.9%) and restored the vasomotion frequency and amplitude (from 8.4 +/- 0.3 to 7.8 +/- 0.4 cpm and from 8.6 +/- 0.2 to 7.8 +/- 0.3 mu m, respectively). The effects observed with buflomedil on the hamster cheek pouch microcirculation suggest a direct action on the smooth muscle excitability and further support its properties as a competitive inhibitor of alpha-adrenergic receptors and as a weak calcium antagonist.