The effects of heparin treatment on hypertension and vascular lesions in stroke-prone spontaneously hypertensive rats.

Stroke-prone spontaneously hypertensive rats (SPSHRs) were used to test the theory that heparin treatment may prevent the development of "malignant" hypertension and fibrinoid vascular lesions in the kidney. Subcutaneous injections of heparin (100 units/100 g body weight) were given every 8 hours over a 5-week period to 12 young (10-week-old) SPSHRs. A control group of 12 SPSHRs was injected with saline. Both heparin-treated and control animals showed an incremental rise in mean systolic pressure, but the pressure was significantly lower (P less than 0.05) in the heparin-treated animals during weeks 1-4 of treatment. There were significantly fewer fibrinoid vascular lesions (P less than 0.03) in the heparin-treated group. In 7 additional heparin-treated and 7 control SPSHRs plasma and blood volumes were determined for assessment of the effects of heparin treatment. There was no significant difference in total blood volume or plasma volume between the two groups, but heparin-treated animals had lower hematocrit levels. In 8 SPSHRs direct arterial pressures were recorded for 1 hour after a single heparin injection, and no acute changes in blood pressure were observed. The results suggest that heparin treatment prevents the development of severe fibrinoid vascular lesions and also attenuates the rate of the rise in systolic blood pressure; moreover, this reduction in blood pressure is not caused by a significant reduction in blood volume or an acute hypotensive effect of heparin.