Effect of alpha-1 and beta agonists on contraction of bovine retinal resistance arteries in vitro.

Contractile responses of bovine retinal arteries (BRA) (diameter: 179 +/- 9 micron, n = 25) to high K+, circumferential stretch and adrenergic stimulation were studied in vitro. BRA could be activated by rapid circumferential stretch. Under resting conditions, phenylephrine consistently activated BRA at the highest dose of the drug used (10(-5) M). During K+- and stretch-induced activation, significant contractile responses to phenylephrine appeared at lower doses (respectively, 3.10(-8) and 10(-6) M). Isoproterenol did not relax K+- and stretch-induced contractions. Therefore, (1) BRA probably can autoregulate through a myogenic mechanism on the basis of stretch; (2) during alpha 1 adrenergic stimulation, myogenic autoregulatory responses probably increase; (3) contractile responses to alpha 1 adrenergic stimulation are masked under resting conditions; and (4) BRA may not possess functional beta adrenergic receptors.