Brain kinins are responsible for the pressor effect of intracerebroventricular captopril in spontaneously hypertensive rats.

The role of the brain kallikrein-kinin system in the regulation of arterial blood pressure of normotensive and spontaneously hypertensive rats was evaluated. Intracerebroventricular administration of the kinin antagonist [DArg0]Hyp3-Thi5,8[DPhe7]bradykinin caused no change in mean blood pressure in Wistar-Kyoto, Sprague-Dawley, or spontaneously hypertensive rats. The antagonist proved to be very potent in blocking the pressor effect of intracerebroventricular bradykinin (32 +/- 3 vs. 3 +/- 1 mm Hg, p less than 0.01). It was specific, as the pressor effect induced by other unrelated peptides was similar during the infusion of either vehicle or kinin antagonist (angiotensin II, 25 +/- 4 vs. 26 +/- 2 mm Hg; prostaglandin E2, 48 +/- 3 vs. 47 +/- 8 mm Hg; norepinephrine, 17 +/- 2 vs. 18 +/- 2 mm Hg; leucine-enkephaline, 15 +/- 2 vs. 16 +/- 1 mm Hg; neurotensin, 18 +/- 2 vs. 19 +/- 1 mm Hg; substance P, 19 +/- 2 vs. 19 +/- 2 mm Hg). Intracerebroventricular administration of 1 mg captopril, an inhibitor of kininase II (one of the enzymes responsible for kinin degradation), caused no change in mean blood pressure in normotensive rats, whereas it increased mean blood pressure by 44 +/- 9 mm Hg (p less than 0.01) in spontaneously hypertensive rats. This increase in mean blood pressure was blocked and then reversed into a hypotensive effect (22 +/- 6 mm Hg, p less than 0.05) during the infusion of kinin antagonist. Our data suggest that the pressor effect induced by intracerebroventricular captopril is due to a transient elevation in endogenous brain kinin levels, supporting the hypothesis that the brain kallikrein-kinin system plays a role in the central regulation of blood pressure in spontaneously hypertensive rats.