Effects of calcium channel blockers on the response to endothelin-1, bradykinin and sodium nitroprusside in porcine ciliary arteries.

Calcium channel blockers are increasingly used in ophthalmology, for instance in patients with visual field defects caused by vasospasm. Endothelin is a new vasoactive peptide which also has been implicated in hypoperfusion of the ophthalmic circulation. This study investigated the effects of the calcium channel blockers on the response to endothelin-1, bradykinin and sodium nitroprusside in isolated porcine ciliary arteries (diameter 200-250 microns). Isolated porcine ciliary arteries were suspended in myograph systems filled with modified Krebs-Ringer solution (37 degrees C; 95% O2/5% CO2) for isometric tension recording. Endothelin-1 (10(-12) -10(-7) M) induced potent concentration-dependent contractions of porcine ciliary arteries (PD50 = 8.3 +/- 0.1; n = 7). Lacidipine (10(-5) -10(-7) M) and nifedipine (10(-5) M) significantly reduced the contractions and decreased the sensitivity to endothelin-1 as compared to control (P < 0.03). On the other hand, endothelium-dependent relaxations to bradykinin (10(-10) -10(-6) M) and endothelium-independent relaxations to sodium nitroprusside (10(-10) -10(-4) M) remained unaffected by the calcium channel blocker. These findings demonstrate that in porcine ciliary arteries, the calcium channel blockers selectively inhibit endothelin-1-induced contractions, while leaving endothelium-dependent and endothelium-independent relaxations unaffected. This property of calcium channel blockers may contribute to the clinical efficacy of this class of drugs in patients with ocular vasospasms.