Tyrosine hydroxylase and choline acetyltransferase activities in ischemic canine heart.

After coronary artery occlusion, enzymes involved in the synthesis of sympathetic and parasympathetic neurotransmitters may change disparately. We investigated this in the canine heart by measuring the activity of tyrosine hydroxylase (TH) and choline acetyltransferase (CAT) in normal and ischemic tissue. Myocardial blood flow in selected regions was measured by the microsphere technique. Dogs had either ligation of the anterior descending coronary artery (LAD) or sham ligation (S). In the ischemic zone 5 h after LAD ligation, TH activity was lower than in corresponding anterior apical zones of S dogs (5.1 +/- 1.7 vs. 13.5 +/- 2.3 nmol.g-1.h-1) (P less than 0.05) with a tendency for greater decreases in endocardium than in epicardium. In contrast, there were insignificant changes in CAT activity 2.5 and 5 h after LAD ligation. Thereafter, progressive and significant (P less than 0.05) decreases occurred in CAT activity at 25 and 170 h after LAD ligation. Thus there are early heterogeneous decreases in TH activity that correlate directly with heterogeneous deficits in blood flow. Although decreases in CAT are also heterogeneous and correlate with deficits in perfusion, these changes occur later. These results indicate differences in the effects of infarction on these biochemical indices of sympathetic and parasympathetic innervation in canine heart.