Aging and isomyosin pattern of the left ventricle in spontaneously hypertensive and Wistar Kyoto rats.

Changes of the contractile proteins in the left ventricle from spontaneously hypertensive rats (SHR) are extensively documented with the development of the hypertensive state and with ageing. This study was undertaken to determine whether also the left ventricle from normotensive rats exhibits age-related changes of the myosin pattern. The relative distribution of myosin isoforms was investigated in Wistar Kyoto (WKY, n = 50) and SHR (n = 50), both at the 5th, 9th, 24th, 48th and the 72nd week of life. A significant decrease in V1 as well as an increase in V3 percentage values, compared to the data obtained at the 5th week were observed in SHR from the 9th week, concomitantly to the rise in blood pressure values. These changes were more consistent with ageing (5 weeks: V1 99.0 +/- 0.9%, V2 0.6 +/- 0.1%, V3 0.4 +/- 0.3%; 72 weeks: V1 5.3 +/- 3.9%, V2 3.0 +/- 2.7%, V3 91.7 +/- 9.7%). In WKY rats, a significant decrease in V1 percentage values was detected at the 24th week and it was evident till the 72nd week. V3 significantly changed only at the 48th and the 72nd week (5 weeks: V1 100.0 +/- 0.0%; 72 weeks: V1: 41.4 +/- 6.5%, V2 13.3 +/- 2.8%, V3 45.5 +/- 6.9%). The results of this study confirm that alterations in the left ventricle isomyosin pattern occur early in SHR with the rise in blood pressure values and the increase in left ventricular mass. In contrast, modifications in the myosin isoform distribution were found only in WKY with ageing. These findings may be related to the biochemical changes occurring in the myocardial tissue either gradually, during the advanced ages of life, or early due to the hypertensive state.