Transmural distribution of biochemical markers of total protein and collagen synthesis, myocardial contraction speed and capillary density in the rat left ventricle in angiotensin II-induced hypertension.

Abstract

The effect of angiotensin II-induced hypertension on selected biochemical parameters was studied in Sprague-Dawley rats. Angiotensin II infusion at rates of 41.7 micrograms h-1 kg-1 and 12.5 micrograms h-1 kg-1 for 2, 5, 10 and 15 days elevated the systolic blood pressure from 143 +/- 7 mmHg to 215-230 mmHg (P less than 0.001) and 185-195 mmHg (P less than 0.001), respectively. The left ventricular weight/body weight ratio increased 10-14% (P less than 0.05) and 23-32% (P less than 0.001) after 2-15 days in rats treated at the lower and higher infusion rates, respectively. Prolyl 4-hydroxylase (PH) activity, a marker of collagen synthesis, was evenly distributed in the left ventricle. PH activity increased by about 100% in both subendocardial and subepicardial layers of the left ventricular wall after angiotensin II infusion for 10 days at 41.7 micrograms h-1 kg-1, but remained unaltered at 12.5 micrograms h-1 kg-1. No change was observed in hydroxyproline concentration. Myosin isoenzymes (V1-V3), which reflect myocardial contractility, were unevenly distributed in the left ventricular wall: the proportion of the fast-turnover isoenzyme (V1) was smaller in the subendocardial layer than in the subepicardial layer. The proportion of V1 decreased after treatment in both layers. Alkaline phosphatase activity, a marker of capillary density, was evenly distributed transmurally in the left ventricular wall. Angiotensin II caused a slight decrease in this activity in both myocardial layers. The results suggest that the elevation of blood pressure leads to transmurally evenly distributed changes in biochemical parameters reflecting collagen synthesis, capillary density and contractile properties of the myocardium.