Comparison of behavioral and cardiovascular effects of L-DOPA and 5-HTP in conscious dogs

Moderate doses of l-DOPA (30–40 mg/kg) alone produced depressant effects, emesis and a mild hypertensive response in dogs. These depressant effects included decreased alertness, reduced response to overt stimuli such as whistling or sharp noises, reduced response to handling and a degree of flaccidity. Haloperidol completely blocked the behavioral and emetic effects of l-DOPA and, in most cases, significantly reduced the hypertensive response. Methysergide prevented the depressive effects and significantly attenuated emesis but had variable effect on the hypertensive response of l-DOPA. HMD and Ro 4-4062, in doses which selectively inhibit peripheral decarboxylase, completely blocked most of the behavioral effects, markedly attenuated emesis and prevented or reduced the hypertensive response, of l-DOPA. HMD, in addition, converted the hypertensive response of l-DOPA to a hypotensive response. dl-Parachlorophenylalanine completely blocked the behavioral effects and significantly reduced the cardiovascular effect of l-DOPA but had no effect on emesis induced by l-DOPA.