Heparin lowers the blood pressure in hypertensive rats

This study describes the effect of heparin on blood pressure, cardiac output, and total peripheral resistance in spontaneously hypertensive and one-kidney, one clip Goldblatt hypertensive rats. Administration of heparin (200 units/day/rat) for 8 weeks to young (6-week-old) spontaneously hypertensive rats (SHR) resulted in an attenuated rise in blood pressure; mean blood pressure in heparin-treated SHR (180 +/- mm Hg) was significantly lower (p less than 0.05) than that in control SHR (205 +/- 7 mm Hg). Similar heparin treatment started immediately after the induction of one-kidney, one clip (Goldblatt) hypertension reduced the rise in blood pressure. After 4 weeks of treatment, heparin-treated Goldblatt hypertensive rats had much lower blood pressure (150 +/- 4 mm Hg) than did control rats (7178 +/- 8 mm Hg). The difference was highly significant (p less than 0.01). Similarly, heparin treatment also lowered the blood pressure in rats with developed Goldblatt hypertension. After the cessation of heparin treatment, the blood pressure returned to pretreatment level in these rats. When compared to vehicle-treated rats, heparin-treated animals with either spontaneous or Goldblatt hypertension concomitantly exhibited a significant increase in cardiac output, and significant decreases in total peripheral resistance and packed cell volume. Further, the left ventricular weight to body weight ratio was significantly lower (p less than 0.05) in heparin-treated than control animals. Since a relationship seems to exist between an increase in packed cell volume and blood viscosity and the rise in arterial pressure, this blood-pressure-lowering effect of heparin may be attributed to a decrease in packed cell volume.