AN ANALYSIS OF THE PERIPHERAL EFFECTS OF l‐DOPA ON AUTONOMIC NERVE FUNCTION

Abstract

1 The ability of intravenous L-DOPA to block sympathetic and parsympathetic nerves has been studied in cats and dogs pretreated with a monoamine oxidase inhibitor. 2 L-DOPA inhibited positive chronotropic and pressor responses to dimethylphenylpiperazinium (DMPP) and McN-A-343 in dogs, and contractions of the nictitating membrane produced by these ganglion stimulants in cats. 3 Responses of the cat nictitating membrane to preganglionic stimulation were inhibited by L-DOPA to a greater extent than those to postganglionic stimulation of the cervical sympathetic chain. 4 In dogs, L-DOPA had no vagolytic action, but depressed vasoconstrictor responses elicited in the perfused hind-limb by electrical stimulation of the lumbar sympathetic chain. 5 The degree of lumbar sympathetic chain inhibition correlated with the pressor response following L-DOPA, and both effects were prevented by prior decarboxylase inhibition. 6 These results suggest that the decarboxylation products of L-DOPA do not impair parasympathetic nerve activity but depress sympathetic nerve function predominantly by inhibiting both muscarinic and nicotinic sites of sympathetic ganglia.

Headache in Parkinson's Disease

“…Different authors report conflicting evidence concerning this problem and describe opposite effects of 1-Dopa and DA-agonist drugs on pain sensations. 2,[13][14][15][16][17] However, our study did not reveal any significant differences between the two groups on this point.…”

Effect of a single dose of standard levodopa on cardiac autonomic function in Parkinson′s disease

“…[22] Reports on the effect of levodopa on the parasympathetic system have been few and conflicting. Antonaccio and Robsin [23] reported that levodopa had no effect on the vagal activity. However, another study demonstrates the possible beneficial effect of levodopa on parasympathetic dysfunction in de-novo PD patients as observed by an improvement in the deep breathing test.…”

Central and Peripheral Catecholamine Mechanisms in Circulatory Control

“…However, the baroreflex impairment induced by levodopa appears to be peripheral in origin as reflex impairment is reversed by concurrent administration of the extracerebral decarboxylase inhibitor carbidopa (1 «-methyldopa hydra zine: MK 486) [40], As this decarboxylase inhibitor does not penetrate the brain in significant amounts [35], it limits the effects of amines formed from levodopa to the central nervous system and prevents the drug's action in the periphery. The mechanism of the peripheral impairment of baroreflex func tion is not clear but may be due to an effect on ganglionic transmission [1] or post-ganglionic neuronal blockade [48].…”