levodopa bradycardia

We have investigated the mediation of the hypotensive action of L-DOPA after peripheral DOPA decarboxylase (DC) inhibition in the sea-gull, Larus argentatus. Vagotomy prevented the bradycardia and hypotension occurring after L-DOPA in birds pretreated with an inhibitor of peripheral DC. L-DOPA alone, given to intact birds, resulted in a slight increase in blood pressure (BP), accompanied by a tendency to bradycardia. Spinal transection in combination with vagotomy reversed the bradycardia and reinforced the increase in BP seen in intact birds after L-DOPA...

The effects of clonidine (1.5 mcg/kg of body weight), L-DOPA (4 mg/kg) and propranolol (0.1 mg/kg) on the reflex bradycardia caused by stimulation of the arterial baroreceptors were studied in 46 waking cats in encephale isole preparations. The drugs were administered into the vertebral artery. They increased the gain of the cardiovagal reflex from the arterial baroreceptors by 162%, 162.5%, 150% respectively with regard to the control values. A similar effect of clonidine and propranolol was manifested also in cats with spinal cord destroyed between the segments C1 to Th12...

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In monoamine oxidase-inhibited dogs whose peripheral dopa decarboxylase was inhibited with MK-486, L-dopa (K mg/kg i.v.) caused significant hypotension and bradycardia. In addition, reflex bradycardia but not pressor responses to norepinephrine were markedly enhanced by the drug. Similar results were obtained after intracerebroventricular administration of L-dopa (0.5 mg/kg) in monoamine oxidase-inhibited dogs not receiving MK-486. Proparnolol prevented the bradycardia caused by L-dopa but was without effect on the reflex facilitation...

The alpha-adrenergic blocking drugs, phentolamine and Hydergine, both act centrally at different sites to depress and enhance the pressor and sympathetic nerve response to decreased baroreceptor afferent input in anesthetized cats. Depression of the rise in blood pressure and sympathetic nerve discharge during bilateral carotid occlusion (BCO) followed injection of the agents into the 4th cerebral ventricle when the brain was intact but not when connections were interrupted at the midcollicular level by transection or lesion...

L-Dopa (5 mg/kg i.v.) decreased blood pressure and heart rate after extracerebral decarboxylase inhibition with MK-486 (25 mg/kg i.v.) in anesthetize MAO-inhibited dogs. In addition, reflex bradycardia caused by injected norepinephrine was significantly enhanced by L-dopa, DL-Threo-dihydroxyphenylserine had no effect on blood pressure, heart rate or reflex responses to norepinephrine. FLA-63, a dopamine-beta-oxidase inhibitor, did not have any effect on the hypotension, bradycardia or reflex-enhancing effect of L-dopa...