Failure of captopril to lower blood pressure in spontaneously hypertensive rats offered water and saline to drink.

The hypotensive action of chronic oral captopril treatment (50 mg/kg per day) was examined in two groups of male spontaneously hypertensive rats (SHR) of the Okamoto strain, one group offered a choice of water and 0.9% saline as drinking fluid, the other offered water alone, a third group of SHR, offered a choice of water and 0.9% saline, were treated with vehicle (0.9% saline, 2 ml/kg per day). Captopril treatment, over ten days, significantly lowered blood pressure in the group drinking water only but failed to significantly alter the blood pressure of SHR drinking a choice of water and 0.9% saline. Vehicle treatment did not alter the blood pressure of SHR drinking a choice of saline and water. In an identical experiment using male, genetically hypertensive rats (GHR) of the Smirk strain, captopril lowered blood pressure to the same extent in GHR drinking either a choice of water and 0.9% saline or water alone. In conclusion, the reported exaggerated saline preference of the spontaneously hypertensive rat appears to antagonize the hypotensive action of captopril.