Spontaneous hypertension in the fawn-hooded rat: a cardiovascular disease model.

The fawn-hooded (FH) rat develops hypertension spontaneously. Systolic blood pressure is already elevated at 5 weeks of age, increases with age, and the final range is 180-240 mmHg at the age of 1 year. Concomitantly with the rise in blood pressure proteinuria occurs and increases with age. Fawn-hooded rats reaching the accelerated phase of the hypertension are characterized by blood pressure values exceeding 220 mmHg, heavy proteinuria and increased heart, kidney, liver, adrenal and spleen weights. Those prone to malignant hypertensive disease show a period of increased water turnover for several weeks after weaning; during this period, they do not show the pronounced decrease in water intake upon fasting for 24 h as observed in FH rats of the same age prone to a milder form of hypertension, i.e. diuresis and drinking continue even when no food is consumed. The major cause of death for FH rats is malignant nephrosclerosis with the nephrotic syndrome and/or cardiac failure with chronic pulmonary congestion. Some animals die of bleeding from mesenteric vessels with periarteritis nodosa. In FH rats with malignant hypertension, heart, kidney, liver and spleen weights are significantly increased compared with FH rats of the same age with mild hypertension. Histopathology shows myocardial fibrosis and myocardial infarctions. Generalized arteriolosclerosis is common, sometimes accompanied with local fibrinoid degeneration and (peri)arteritis. Some major arteries show intimal proliferation. It is concluded that the FH rat provides an interesting model for the study of hypertension and its consequences.