Behavioral performance effects of nifedipine in normotensive and renovascular hypertensive baboons.

Behavioral performances of normotensive and hypertensive adult male baboons were tested before, during, and following chronic oral dosing with nifedipine. Performances during a five-color simultaneous match-to-sample task were measured during three dosing schedules (0.20, 0.68, and 1.14 mg/kg/day) and vehicle. Each dose was administered for 21 consecutive days preceded and followed by 14-day baseline and recovery periods, respectively. Choice reaction times increased by 191 ms over baseline at the 0.68 mg/kg dose. Choice reaction times above the 95th percentile (i.e., the slowest reaction times) were the most slowed by nifedipine. Accuracy of color matching was decreased at 0.20 and 0.68 mg/kg by an average range of 2-4%. The yellow and white stimuli were the most difficult to discriminate correctly, and were also the most impaired by nifedipine. Nifedipine's behavioral effects were not modulated by blood pressure changes because daily changes in choice reaction time and systolic blood pressure were not correlated, and hypertensive status did not determine the behavioral effects. Potential sources of nifedipine's behavioral performance effects are discussed, with blood pressure changes excluded as a probable mechanism.