L-dopa

L-dopa, L-3,4-dihydroxyphenyl alanine, or 3-hydroxy-L-tyrosine, is a pharmaceutically active compound, which is active at the inhibition of symptoms of the Parkinsons disease, particularly at the inhibition of the tremor related to the Parkinsons disease. L-dopa, the metabolic precursor of dopamine, is a commonly administered dopaminergic drug. L-dopa is a compound that is metabolized in the body of mammals by aromatic amino acid decarboxylase to dopamine. Dopamine is a naturally occuring catecholamine considered to be a precursor of norepinephrine. Dopamine plays an important role as a neurotransmitter in the central nervous system and as an inhibitory transmitter in autonomic ganglia. L-dopa is also formed in the body from L-tyrosine. The amino acid tyrosine is the precursor of catecholamine biosynthesis in all nerve cells which produce catecholamines. Tyrosine is converted to L-dopa by the rate-limiting enzyme tyrosine hydroxylase. Tyrosine has been shown to increase or decrease blood pressure depending on the original levels, reduce depression and treat and prevent ventricular fibrillation.

The most widely recognized therapeutic use of L-dopa is in the treatment of Parkinson's disease. Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of the nigrostriatal pathway. The mechanism of L-dopa in the treatment of this disease is attributed to its presumed role in the correction of an imbalance of dopamine and acetylcholine in the basal ganglia, a biochemical defect associated with Parkinsonism. The clinical features of Parkinsonism include tremor, bradykinesia, rigidity and disturbance of posture. There is currently no satisfactory cure for Parkinson's disease. Symptomatic treatment of the disease-associated motor impairments involves oral administration of dihydroxyphenylalanine (L-dopa). L-dopa is transported across the blood-brain barrier and converted to dopamine, partly by residual dopaminergic neurons, leading to a substantial improvement of motor function. It is considered that L-dopa is converted into dopamine in the brain and thereby remedies the deficiency of dopamine in brain. It has recently been known that when L-dopa is used together with a decarboxylase inhibitor which acts on the peripheral system, movement of L-dopa to the central nervous system is enhanced and the therapeutic effect of L-dopa is thereby enhanced.

L-dopa is also known to cause release of growth hormone. Human growth hormone (somatotropin, HGH) is a physiological substance produced in the anterior lobe of the pituitary gland of the human system. It is the most abundant hormone produced by the anterior pituitary lobe. Growth hormone is released from the pituitary. The release is under tight control of a number of hormones and neurotransmitters either directly or indirectly. Growth hormone release can be stimulated by growth hormone releasing hormone (GHRH) and inhibited by somatostatin. There are two ways to approach the problem of increasing circulating levels of growth hormone: increase the level of human growth hormone in the organism directly or increase the organism's natural tendency to produce growth hormone. In addition to the actions of GHRH there are various ways known to release growth hormone. Various HGH releasers such as arginine, L-dopa, glucagon, vasopressin, and insulin-induced hypoglycemia, as well as activities such as sleep and exercise, indirectly cause growth hormone to be released from the pituitary by acting in some fashion on the hypothalamus, perhaps either to decrease somatostatin secretion or to increase the secretion of GHRH.

L-dopa can also be prepared from tyrosine by treatment of the latter with the enzyme tyrosine-hydroxylase obtained from red beets. If one starts with L-tyrosine, the process wil yield a mixture of L-tyrosine and L-dopa. It is known that certain leguminous plants and seeds, such as velvet bean contain L-Dopa and it is known that L-Dopa can be extracted from ground velvet bean by acidified water. L-dopa is also extractible from such L-dopa containing materials as vetch, broad beans, especially Georgia velvet bean, and the African Sommerset bean, as well as the seeds of Mucuna puriens (L) DC Leguminosae.