| Summary: | The role of the renin-angiotensin system (RAS) in the control of blood pressure and drinking was investigated in fresh water (FW)- and seawater (SW)-adapted eels, Anguilla anguilla, by comparing the effects of pharmacological manipulation through the use of papaverine (stimulator) and captopril (inhibitor) on the endogenous system. In SW eels basal blood pressure levels were lower (23.3 ± 0.8 mm Hg) with correspondingly higher basal drinking rates (0.51 ± 0.07 ml/kg/hr) and plasma AII concentrations (32.89 ± 4.19 fmol/ml) compared to FW eels (33.8 ± 1.3 mm Hg, 0.06 ± 0.02 ml/kg/hr, 9.72 ± 0.60 fmol/ml, respectively). In FW eels papaverine caused immediate hypotension with full recovery, decrease in plasma osmolality, and increase in drinking rate and plasma AII concentration, but in SW eels, hypotension with full recovery and an increase in plasma osmolality. drinking rate, and plasma AII concentration occurred. In FW eels captopril had no effect on the parameters measured, but in SW eels it caused a sustained decrease in blood pressure and a decline in the basal drinking rate and plasma AII concentration. Papaverine was also administered 15 min after captopril In FW eels this manipulation caused hypotension only after the papaverine injection, followed by a partial recovery. Osmolality was unaffected, the previously observed papaverine-induced dipsogenic response was blocked, and the rise in plasma AII concentrations was smaller than with papaverine only. In SW eels there was an immediate hypotension after captopril administration with full recovery. The dipsogenic papaverine-induced response was blocked 90%, with elevated plasma osmolality and plasma AII concentrations compared to control values, although at a lower level compared to papaverine alone. A physiological role of RAS in the control of basal drinking in the SW eel is suggested. Copyright © 1995 Academic Press. All rights reserved.
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