In vitro zinc stimulation of angiotensin-converting enzyme activities in various tissues of zinc-deficient rats

Angiotensin-converting enzyme (ACE) activities and the effect of the in vitro addition of zinc on ACE activities were studied in various tissues obtained from weanling Sprague-Dawley male rats fed diets containing either 7.7 (zinc-deficient) or 770 μmol of zinc/kg of diet (control) ad libitum for 21 days. Tissue zinc concentrations were measured by atomic-absorption-spectrophotometric method and ACE activities by radioassay using [³H]hippuryl-glycyl-glycine as the substrate. The stimulation of ACE by the in vitro addition of zinc was measured using zinc at a concentration of 17 μmol/L. Plasma ACE activities in zinc-deficient rats were significantly lower than in controls, while ACE activities in lung were two times higher in zinc-deficient rats than in controls. ACE activities in testis were similar in zinc-deficient and control rats. The in vitro addition of zinc increased plasma ACE activities by 70% in zinc-deficient rats, while it had no effect in controls. In lung, testis and aorta, ACE activities were increased significantly by the in vitro addition of zinc in both zinc-deficient and control rats. Plasma ACE stimulation by the in vitro addition of zinc, a measure of apoenzyme production, may be used to evaluate zinc nutriture.