Intravital microscopy of the hamster cheek pouch microvasculature was used for in vivo studies on the effects of buflomedil, phentolamine (α-adrenergic receptor antagonist) and norepinephrine on the mean internal arteriolar diameter and spontaneous vasomotion. All drugs were applied topically. The vasomotor activity was studied in 125 arterioles (internal diameter range 18.0–62.0 µm) of 34 preparations. Addition of buflomedil (10–9 to 10–5M) 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 µm), respectively. Phentolamine (10–9 to 10–5M) 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 µm, respectively). Addition of buflomedil (10–7M) reduced the vasodilation evoked by phentolamine (from 103.3 ± 0.7 to 127.0 ± 1.5%) and potentiated its depressive effect on vasomotion 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 µm, respectively). Norepinephrine (10–9 to 10–5M) 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 emp and from 8.7 ± 0.2 to 0.5 ± 0.4 µm, 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 µm, 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 α-adrenergic receptors and as a weak calcium antagonist.

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