Central cardiovascular effects of L-DOPA and clonidine in the lizard, Agama caudospinosa.
The effects of L-DOPA alone and in combination with two inhibitors of 1-aromatic-amino acid decarboxylase (DC), carbidopa and benserazid on the blood pressure (BP) and catecholamine (CA) content in the heart and brain has been investigated in the lizard Agama caudospinosa. The effect of clonidine on BP has also been examined in intact lizards and after spinal cord transection. It is concluded that dopamine (DA) is formed from L-DOPA in brain and heart and that carbidopa reduces the DA formation in the heart but penetrates the blood brain barrier (BBB) poorly, allowing a central decarboxylation of L-DOPA. Benserazid, on the other hand, penetrates the BBB and inhibits the central as well as the peripheral synthesis of DA from L-DOPA. L-DOPA in combination with carbidopa lowers the BP significantly in lizards tilted 45 degrees (head upwards) whereas the supine BP is unaffected. Benserazid pretreatment abolishes the decrease in BP after L-DOPA. L-DOPA alone does not produce any consistent changes in BP. Clonidine lowers BP in intact, tilted animals, while the BP is increased in spinal animals. The results indicate a central mode of action of L-DOPA as well as clonidine in the lizard studied.
D000818:Animals; D001545:Benserazide / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D001812:Blood-Brain Barrier / Q000187:drug effects; D001921:Brain / Q000378:metabolism; D002230:Carbidopa / Q000494:pharmacology; D002395:Catecholamines / Q000378:metabolism; D003000:Clonidine / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D007980:Levodopa / Q000494:pharmacology*; D008116:Lizards / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism
D002395:Catecholamines; D007980:Levodopa; D001545:Benserazide; D003000:Clonidine; D002230:Carbidopa