Regional differences of vascular sensitivities in canine long posterior ciliary arteries

Abstract

Information is needed with regard to the vascular reactivities of ophthalmic and ciliary arteries in order to provide rational medical treatment of ocular disease by systemic administration of drugs. In the present study, vascular reactions of isolated proximal and distal portions of dog long posterior ciliary arteries (LPCAs) to norepinephrine (NE), prostaglandin F_2α (PGF_2α) and KCl were examined using the arterial-perfusion method, in the presence and absence of 2 kinds of antagonists, bunazosin (a selective alpha-1 adrenoceptor antagonist) and diltiazem (a calcium antagonist). In the present study, the proximal LPCA is defined as the region of LPCA on the optic nerve, and the distal one the region along the sclera except the anterior uvea. Each drug was injected by a microinjector into the endothelial side of an artery through a cannulated rubber tubing. Responses were recorded as changes in perfusion pressure. Results were as follows: 1) Three agents produced temporal vasoconstrictions, and the rank order of potency for inducing a vasoconstriction was NE>PGF_2αKl in each portion. 2) In these two regions or LPCAs, the maximum increase in perfusion pressure and the threshold dose for KCL were almost the same. 3) The maximum increase in perfusion pressure by PGF_2α was the same in these regions, but the threshold dose on proximal vessels was significantly larger than that on distal ones, indicating that the distal LPCAs were more sensitive to PGF_2α than the proximal ones. 4) The threshold dose for NE in the distal LPCAs was significantly greater than that in the proximal ones. In the proximal LPCAs the maximum response was about 60 mmHg, but in the distal ones it was only about 20 mmHg. 5) The dose response curves for KCl were shifted to the right by diltiazem (1–100 μg) in a dose dependent manner, but those for NE were slightly affected only by a large dose of 100 μg of diltiazem. 6) Bunazosin (0.1–10 μg) blocked the NE-induced constrictions of both regions of LPCAs in a dose dependent manner, although 10 μg of bunazosin did not inhibit the KCl-induced responses. From these results, it is suggested that proximal LPCAs contain more alpha-1 adrenoceptors than distal LPCAs.