Contractile and relaxing effects of arachidonic acid derivatives on isolated bovine retinal resistance arteries.

The reactivity of isolated ring segments (i.d. ca. 200 microns) of calf retinal resistance arteries to arachidonic acid derivatives were studied in vitro. Prostaglandin F2 alpha (PGF2 alpha) prostaglandin E2 (PGE2), and a thromboxane A2 analogue, 9,11-dideoxy-9 alpha,11 alpha-epoxymethane-prostaglandin F2 alpha, (TX2 alpha), induced a concentration dependent contraction with the order of potency: Tx2 alpha greater than PGE2 greater than PGF2 alpha with pD2-values (-log[EC50(M)]) of 6.88, 6.19 and 5.20, respectively. The maximal active tension development of the vessels induced by Tx2 alpha, PGE2 and PGF2 alpha, were 1.57 N m(-1), 1.05 N m(-1) and 1.19 N m(-1), corresponding to 94%, 57% and 67% of Emax, respectively. The active pressure development, and estimate of the maximum pressure which the vessels may be able to contract against in vivo, was 18 kPa, 12 kPa and 14 kPa (138, 89 and 110 mmHg) for Tx2 alpha, PGE2 and PGF2 alpha, respectively. Prostaglandin I2 (prostacyclin, PGI2) induced a concentration-dependent relaxation of retinal resistance arteries precontracted with 10(-5) M PGF2 alpha. The maximal relaxation induced by PGI2 amounted to 65% of the control vessel response induced by PGF2 alpha (1.27 N m(-1] with a -log[EC50(M)] value of 6.51. The results indicate that arachidonic acid derivatives are potent and effective agents capable of regulating bovine retinal resistance artery smooth muscle tension in vitro.