PROSTAGLANDIN INTERACTION WITH THE RENAL EFFECTS OF PLASMA ANGIOTENSIN-II IN THE PEKIN DUCK

The present study was designed to determine whether the responses of t he avian kidney to circulating angiotensin II, under different osmotic conditions, involve an interaction with prostaglandins. The renal eff ects of i.v. infusions of angiotensin II at 10, 30 and 90 ng . kg . mi n(-1) for 30 min were compared in Pekin ducks given maintenance infusi ons of either 200 mos-mol . l(-1) NaCl or glucose at 0.5 ml . min(-1), with and without prostaglandin inhibition by indomethacin. Birds infu sed with glucose without indomethacin responded to the two low doses o f angiotensin II with dose-dependent reductions in water and sodium ex cretion, whilst the same doses of angiotensin II in saline-loaded bird s caused dose-dependent increases in the renal excretion of salt and f luid. Indomethacin treatment in the animals given glucose had no effec t upon the antidiuretic response to the low doses of angiotensin II bu t did prevent the antinatriuretic effect. In the birds infused with sa line, prostaglandin inhibition reversed the natriuretic/diuretic actio n of angiotensin II, producing renal salt and water conservation. The highest dose of angiotensin II was consistently diuretic/natriuretic a nd independent of prastaglandin investment in each case. The results i ndicate that the antinatriuretic effect of low doses of angiotensin II in glucose-infused birds involves an interaction with prostaglandins, whereas the antidiuretic effect of angiotensin II under this conditio n is independent of prostaglandins. In salt-loaded birds the diuretic/ natriurctic actions of low doses of angiotensin II are mediated by pro staglandins so that inhibition of prostaglandin formation unmasks the ''normal'' salt and fluid-retaining actions of systemic angiotensin II .