Genetic and environmental modification of spontaneous hypertension.

The further selection of stroke-prone spontaneously rats (SHR) by the grade of hypertension resulted in the separation of substrains with more and less severe hypertension, respectively. Their average tail blood pressures at the age of 100 days were 240 and 200 mmHg. The ratios of cerebral hemorrhage to infarction were markedly decreased from 1/2 in the former into less than 1/30 in the latter. Also a similar attempt separated stroke-resistant SHR into substrains with moderate and mild hypertension; blood pressures at the age of 100 days were 200 and 180 mmHg, respectively. On the other hand, development of severe hypertension was attenuated and the incidence of stroke was significantly reduced in stroke-prone SHR when they were fed on a high-fat-cholesterol diet or a high fish protein diet. The selection of substrains with different grades of hypertension in stroke-prone and stroke-resistant SHR indicates the additional involvement of some hypertension genes, and the alteration of the course and the level of hypertension by nutritional factors substantiates the importance of gene-environment interaction in spontaneous hypertension.