Bradykinin-induced water intake and brain fos-like immunoreactivity in rats.

We have previously shown that peripheral injection of bradykinin in combination with the kininase II inhibitor, captopril, to rats produces a robust water intake. We now extend this observation to another kininase II inhibitor, enalapril. Water intake increases with dose of dose of bradykinin, but has an inverted U-shaped relationship with dose of kininase II inhibitor. The induced water intake is completely blocked by peripheral administration of the bradykinin antagonist, Hoe 140, and is partly attenuated by peripheral injection of an angiotensin (Ang) II receptor antagonist, losartan. Relative to captopril alone, the combination of captopril and bradykinin greatly elevated plasma renin activity, but did not reduce blood pressure. We further show that, while either bradykinin or enalapril alone induce little or no Fos-like immunoreactivity in areas of the brain related to fluid balance, their combination induces staining in many cells in the supraoptic and paraventricular magnocellular nuclei, as well as along the lamina terminalis. These data suggest that bradykinin may have a role in regulation of fluid balance, partly mediated through Ang II.