Angiotensin II-induced contractions of rabbit splenic capsular strips and release of prostaglandins. Use of radioimmunoassays for prostaglandins E1 and E2.

Rabbit splenic capsular strips contract in response to angiotensin II and simultaneously release prostaglandins E and F into the bath fluid. Contractions, though not sustained, and prostaglandin release are dependent on the concentrations of angiotensin II. Addition of indometacin to the bath fluid inhibits prostaglandin release and potentiates the angiotensin II-induced contractions. Similarly, 5,8,11,14-eicosatetraynoic acid, another blocker of prostaglandin synthesis, potentiates contractions elicited by angiotensin II. Exogenous prostaglandin E1 (300 ng/ml) tends to decrease angiotensin II-induced contractions, while prostaglandin E2 (300 ng/ml) as well as prostaglandin F2alpha (300 ng/ml) significantly increase the contractions produced by angiotensin II. The prostaglandin endoperoxide analogues (15S)-hydroxy-9alpha,11alpha-(epoxymethano)prosta-5Z,13 E-dienoic acid and (15S)-hydroxy-11alpha,9alpha-(epoxymethano)-prosta-5Z,13 E-dienoic acid in concentrations of 300 ng/ml are either without effect or weak smooth muscle stimulants of their own, but do not influence the effect of angiotensin II. By the simultaneous use of sensitive and specific radioimmunoassays for prostaglandins E1 and E2 the prostaglandin E-like substance released by the rabbit splenic capsular strips was found to resemble serologically much more the dienoic prostaglandin E2 than prostaglandin E1. The potentation of the effect of angiotensin II by indometacin and 5,8,11,14-eicosatetraynoic acid might be caused by inhibition of synthesis of prostaglandins or related compounds in the splenic tissue. However, an undefined sensitizing effect of indometacin and 5,8,11,14-eicosatetraynoic acid, not related to their effect on prostaglandin synthetase, on the smooth muscle preparation cannot be excluded.