Angiotensin II does not contract bovine retinal resistance arteries in vitro

The effect of angiotensin II was studied in vitro on ring segments of bovine retinal resistance arteries (i.d. 126-271 microns) and posterior ciliary arteries (i.d. 207-1153 microns). Although the retinal resistance arteries were responsive to 5-hydroxytryptamine, prostaglandin F2 alpha, and changes in extracellular K(+)-concentration, they did not, in contrast to the posterior ciliary arteries, contract to cumulative or single doses of angiotensin II. In the latter arteries, angiotensin II induced a small concentration dependent contraction, 5% of maximal 125 mM K(+)-induced response, with a pD2-value of 9.3. The single addition of 10(-6) M angiotensin II increased the maximal vessel response of the posterior ciliary arteries three times to angiotensin II. Tachyphylaxis was pronounced in the posterior ciliary arteries, in which the response to angiotensin II could not be repeated. Indomethacin (10(-5) M), methylene blue (3 x 10(-6) M), or removal of endothelium did not make the retinal resistance arteries responsive to angiotensin II. Retinal arteries precontracted with 30 mM potassium did not respond to angiotensin II. Angiotensin II did not potentiate the 5-hydroxytryptamine- and noradrenaline concentration-response characteristics of both retinal resistance and posterior ciliary arteries. Although angiotensin II-receptors have been detected in bovine retinal vascular smooth muscle using radioligand-binding technique, the present results suggest that these receptors are non-functional in respect to regulation of retinal resistance artery tone.