Interaction between (plus or minus)-amphetamine and atropine on the rat cardiovascular system.

1. The effects of atropine on the pithed rat blood pressure after (+/-)-amphetamine depend on the pattern of the cardiovascular responses to the latter.2. If the pressor response to amphetamine is followed by oscillations of blood pressure and a reduction in pulse pressure or by a fall in blood pressure terminating in circulatory failure, atropine increases blood pressure, but if it is not followed by these patterns, atropine decreases blood pressure.3. The fall in blood pressure produced by atropine after amphetamine might be due to weak alpha-adrenoceptor blockade.