Responses of isolated canine ophthalmic and ciliary arteries to vasoactive substances

The effects of 11 vasoactive substances were compared on the isolated and perfused canine internal and external ophthalmic and ciliary arteries. The vessels were isolated with the optic nerve, and perfused independently with Tyrode solution under a constant flow rate at 37 degrees C and a perfusion pressure of 40-80 mmHg. Drugs used were 5-hydroxytryptamine (5-HT), epinephrine (EPI), norepinephrine (NE), phenylephrine (PHE), prostaglandin F2 alpha (PGF2 alpha), ATP, dopamine (DA), tyramine (TYR), KCl, xylazine (XYL) and clonidine (CLO). Each drug solution was administered by a microinjector into the endothelial side of an artery through a cannula. Responses were obtained as changes in perfusion pressure. Results were as follows: 1) The rank order of potency for inducing a vasoconstriction in external ophthalmic arteries (EOA) was 5-HT greater than or equal to EPI greater than NE greater than PHE much greater than ATP greater than or equal to DA greater than KCl much much greater than TYR, XYL, CLO. Since PGF2 alpha induced only a slight vasoconstriction, it was omitted from the order. 2) In internal ophthalmic arteries (IOA), the responses were similar to those in EOA, although EPI, NE and PHE induced a relatively smaller response. The order was 5-HT greater than EPI = NE greater than PHE much greater than DA = ATP greater than KCl much much greater than TYR, XYL, CLO. 3) In ciliary arteries, the order was EPI greater than NE greater than PHE greater than PGF2 alpha greater than DA greater than ATP greater than KCl much much greater than TYR, XYL, CLO. It was found that 5-HT induced a slight vasoconstriction and the efficacy was low. PGF2 alpha induced a greater response in ciliary arteries than in EOA or IOA. 4) In all three arteries, alpha-2 adrenoceptor agonists, XYL and CLO did not produce significant changes in perfusion pressure. These three arteries might be rich in alpha-1 adrenoceptors but poor in alpha-2 adrenoceptors.