The renin-angiotensin system and the regulation of plasma cortisol in the flounder, Platichthys flesus.

The changes in arterial blood pressure and plasma cortisol concentration in response to exogenous angiotensin II (AII) and to manipulation of the endogenous renin-angiotensin system (RAS) have been examined in the flounder, Platichthys flesus. Intravenous [Asp1Val5]AII was pressor in a dose-dependent manner over the range of 0.25-250 micrograms/kg. Sequential blood sampling revealed steroidogenic stimulation, measured as change in plasma cortisol concentration, by doses of AII greater than 2.5 micrograms/kg. Enhanced circulating cortisol levels were measured some time after recovery of normal systemic blood pressure, suggesting that the change in plasma steroid concentration was not entirely dependent on the change in systemic blood pressure. Administration of the vasodilator papaverine produced immediate hypotension followed by gradual recovery in blood pressure, which was accompanied by a sustained increment in circulating cortisol. Both blood pressure recovery and the increased plasma steroid concentration were inhibited by prior treatment with the angiotensin converting enzyme inhibitor captopril. These results are consistent with a physiologically important role for the RAS in the control of plasma cortisol levels which complements its demonstrated pressor and dipsogenic actions in the flounder: the RAS may thus afford an integrating influence on the mechanisms of body fluid homeostasis in this euryhaline species.