Effect of pithing on the postjunctional sympatho-inhibitory action of captopril in cats.

Pithing of anaesthetized normotensive cats significantly lowered the arterial blood pressure and augmented plasma renin activity (PRA). Captopril dose-dependently diminished mean arterial blood pressure in both pithed and intact anaesthetized normotensive cats. The hypotensive effectiveness of captopril was most pronounced in pithed cats. Captopril inhibited the hypertensive response to intravenously administered noradrenaline in pithed cats, but did not attenuate the hypertensive response to noradrenaline in intact cats. The results do not exclude that the hypotensive activity of captopril in intact cats may be causally independent of the attenuating effect of converting enzyme inhibition on the postjunctional alpha-adrenoceptor mediated vasoconstriction as observed in pithed animals.