Pharmacological Effects of Dopamine, March 11, 1990

Pharmacological Effects of Dopamine, March 11, 1990

Dopamine is a neurotransmitter secreted by sympathetic nerve endings, similar to norepinephrine, directly stimulating α and β receptors. Among similar drugs, such as epinephrine and norepinephrine, epinephrine directly acts on α receptors, while isoproterenol directly acts on β receptors; metaraminol indirectly stimulates both α and β receptors. As a central nervous system anticholinergic drug, dopamine excites the sympathetic nervous system, thereby increasing myocardial contractility, boosting cardiac output, and raising blood pressure. At the same time, this drug also dilates visceral blood vessels, increasing blood flow to the heart, kidneys, intestines, and other organs. As a neurotransmitter in brain tissue, in certain diseases, there is a noticeable decrease in its levels, while toxic pseudo-neurotransmitters participate in the metabolic products of these diseases—for example, in Parkinson’s disease and hepatic coma, the reduction of dopamine in brain tissue leads to the binding of pseudo-neurotransmitters, causing a series of symptoms. Therefore, using dopamine in such cases is often effective. Clinically, levodopa is commonly used; this drug is a precursor to dopamine, because dopamine itself cannot directly cross the blood-brain barrier, whereas levodopa can. Thus, levodopa is frequently used clinically to achieve the effects of dopamine, with most of it being converted to dopamine in the liver and a small portion in the heart, kidneys, and brain. The essence of this process is dehydroxylation. Levodopa tablets: 0.5g, taken orally three to four times daily, or 0.5g intravenously once daily. When treating Parkinson’s disease, the initial dose should be small. In treating hepatic coma, levodopa not only repels pseudo-neurotransmitters but also prevents the formation of potentially toxic methylamines and blocks the intestinal absorption of aromatic amino acids such as phenylalanine, tyrosine, methionine, and tryptophan.