Catecholamines endogenous

Fig. 2. Chemical stmcture of the endogenous catecholamines, epinephrine (8), and norepinephrine (7), and several synthetic phenethano1 amines that alter...

Norepinephrine. An endogenous catecholamine that functions as a neurotransmitter. 

Together with dopamine, adrenaline and noradrenaline belong to the endogenous catecholamines that are synthesized from the precursor amino acid tyrosine (Fig. 1). In the first biosynthetic step, tyrosine hydroxylase generates l-DOPA which is further converted to dopamine by the aromatic L-amino acid decarboxylase ( Dopa decarboxylase). Dopamine is transported from the cytosol into synaptic vesicles by a vesicular monoamine transporter. In sympathetic nerves, vesicular dopamine (3-hydroxylase generates the neurotransmitter noradrenaline. In chromaffin cells of the adrenal medulla, approximately 80% of the noradrenaline is further converted into adrenaline by the enzyme phenylethanolamine-A-methyltransferase. 

The turnover rate of a transmitter can be calculated from measurement of either the rate at which it is synthesised or the rate at which it is lost from the endogenous store. Transmitter synthesis can be monitored by administering [ H]- or [ " C]-labelled precursors in vivo these are eventually taken up by neurons and converted into radiolabelled product (the transmitter). The rate of accumulation of the radiolabelled transmitter can be used to estimate its synthesis rate. Obviously, the choice of precursor is determined by the rate-limiting step in the synthetic pathway for instance, when measuring catecholamine turnover, tyrosine must be used instead of /-DOPA which bypasses the rate-limiting enzyme, tyrosine hydroxylase. 

The in vitro data and the results from this clinical trial were synthesized in a so-called dynamic model of receptor kinetics by Liggett [72]. According to this theory, Gly/Gly homozygous individuals are already down-regulated as a result of exposure to endogenous catecholamines. Thus, the recurring exogenous exposure to... 

Beta-1, beta-2, and beta-3 adrenergic receptors are G-protein-coupled receptors. Beta-1 and beta-2 receptors mediate the positive inotropic, chronotropic, and dro-motropic effects of the endogenous catecholamines epinephrine and norepinephrine. The beta-3 subtype seems to play a role in regulating thermogenesis and lipid mobilization in brown and white adipose tissue. Several coding and promoter polymorphisms of these receptors have been identified. Clinical studies in asthma... 

Theophylline and aminophylline may produce bronchodilation by inhibition of phosphodiesterase (thereby increasing cyclic adenosine monophosphate levels), inhibition of calcium ion influx into smooth muscle, prostaglandin antagonism, stimulation of endogenous catecholamines, adenosine receptor antagonism, and inhibition of release of mediators from mast cells and leukocytes. 

Smith, R. C., Boggan, W. O., and Freedman, D. X. (1975) Effects of single and multiple dose LSD on endogenous levels of brain tyrosine and catecholamines. Psychopharmacology, 42 271-276. 

Becker JB, Ramirez VD (1980) Dynamics of endogenous catecholamine release from brain fragments of male and female rats. Neuroendocrinology 31(1) 18-25 Beckett AH, Gorrod JW, et al (1971) The effect of smoking on nicotine metabolism in vivo in man. 1 Pharm Pharmacol 23 62S-67S... 

Endogenic (epinephrine, norepinephrine, and dopamine) and synthetic catecholamines (isoproterenol, dobutamine). 

Epinephrine, and endogenic catecholamine, is better known by its official English name adrenaline. Epinephrine is a powerful agonist of both a- and j8-adrenergic receptors. Its action is very complex and depends not only on the relative distribution of adrenergic receptors in... 

As drugs of mixed action, amphetamines activate adrenergic receptors and simultaneously release endogenic catecholamines (norepinephrine and dopamine) from neurons of the brain and periphery. Sympathomimetic effects on the periphery are very similar to those of ephedrine. Amphetamine elevates systolic and diastolic blood pressure and has weakly expressed, broncholytic action. These effects are more prolonged, yet less expressed, than with epinephrine. The distinctive feature of amphetamines is their psychostimulatory activity. Larger doses can cause hallucinations and mental conditions similar to paranoid schizophrenia. As a sympathomimetic, amphetamine is sometimes used for uterine inertia. Synonyms of amphetamine are phenamine and benzedrine. 

The adrenergic receptors (or adrenoceptors) are a class of G-protein coupled receptors, which are the targets of catecholamines. Adrenergic receptors specifically bind their endogenous ligands, the catecholamines, epinephrine, and norepinephrine (also called adrenaline and noradrenaline), and are activated by these. 

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