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Drinking rates were measured in the euryhaline fish Fundulus heteroclitus in the presence and absence of angiotensin II or its competitive inhibitor P-113 and converting enzyme inhibitor (SQ20881). Angiotensin stimulated drinking in Fundalus adapted to salt- or freshwater. More significant, P-113 decreased drinking rates in saltwater-adapted fish and to ones acutely exposed to saltwater. SQ20881 was also effective in inhibiting drinking. These data are interpreted to support the hypothesis that endogenously produced angiotensin is a physiological stimulus for drinking in fish.

Arterial blood pressure, urine flow rate, and plasma and urine electrolytes were measured in the aglomerular goosefish (L. americanus) before, during, and after the intravenous infusion of angiotensin II (from 5 to 280 ng/min.kg body wt). Increases in arterial blood pressure were directly related to the logarithm of the angiotensin infusion rate (r = 0.62, P less than 0.005). Angiotensin also increased urine flow from 0.676 +/- 0.065 to 0.755 +/- 0.068 ml/h.kg body wt (P less than 0.005) and Na excretion from 41.0 +/- 5.5 to 54.4 +/- 7.0 mumol/h.kg body wt (P less than 0.001). In 17 of the 19 fish infused with angiotensin the diuretic and natriuretic effects were directly related to the logarithm of the infusion rate (r = 0.44, P less than 0.04 and r = 0.51, P less than 0.02, respectively). There was no relationship between the pressor and the diuretic or natriuretic effects of angiotensin II. These results are consistent with inhibitory effects of angiotensin on solute transport by aglomerular tubules.

Drinking rates in both marine and freshwater stenohaline fish were studied by measuring the ingestion of polyethylene glycol that had been added to the aquarium water. Two marine species, the long-horned sculpin and the flounder, and three freshwater species, the common goldfish, the mottled sculpin, and the common shiner, were used. Control drinking rates in freshwater fish averaged 0.03-0.1% body wt/h and in marine fish varied between 0.06 and 0.24% body wt/h. Intramuscular injections of angiotensin II (ANG II) stimulated drinking two- to threefold in the two marine species but had no effect on the drinking rate of the freshwater species. Hemorrhage (1-2% of body wt) also stimulated drinking in the two marine species (6- to 10-fold) but did not affect the drinking rate of two freshwater species. Thus exogenous ANG II and hemorrhage stimulate drinking in two marine stenohaline fish as they do in mammals. These responses were absent in the three freshwater fishes studied. However, injection of converting enzyme inhibitor (SQ 20881) or saralasin in order to block endogenous ANG II did not attenuate either basal or hemorrhage-stimulated drinking in the marine fish.