Effects of calcitonin gene-related peptide and substance P on regional blood flow in the cat eye.

The effects of calcitonin gene-related peptide (CGRP) and substance P (SP) on the regional blood flow of the eye were studied in cats. The animals were anaesthetized and the eyes were cannulated for intracameral administration of the test substances and intraocular pressure measurement. Regional blood flow was determined using the radioactively labelled microsphere method. Intracameral injection of 1.3 x 10(-9) mol of CGRP increased markedly the blood flow of the iris, the ciliary body, and the sclera. There was no clear-cut effect in the choroid or in the retina. Intracameral administration of 1.3 x 10(-9) mol of SP had no clear-cut effect on the blood flow of any of the ocular tissues studied. In addition, CGRP reduced the intraocular pressure statistically significantly, whereas SP had no effect. The results of the present study indicate that CGRP is a potent vasodilator in the anterior uvea of the cat eye when administered from the adventitial side, whereas SP seems to have little or no effect.