Catecholamine

About: Catecholamine is a research topic. Over the lifetime, 10753 publications have been published within this topic receiving 379056 citations. The topic is also known as: catecholamines.

Blockade of endogenous norepinephrine synthesis by alpha-methyl-tyrosine, an inhibitor of tyrosine hydroxylase.

Abstract: Repeated administration of the tyrosine hydroxylase inhibitor, α-methyl-tyrosine to guinea pigs decreased catecholamine levels in brain stem, caudate nucleus, heart and spleen to undetectable levels. Serotonin was unaffected. That the catecholamine decrease was a consequence of inhibition of tyrosine hydroxylase was shown by the following: tissue concentrations of norepinephrine failed to rise following monoamine oxidase inhibition and decarboxylase inhibitors failed to block the α-methyl-tyrosine effect; the conversion of tyrosine-C14 to norepinephrine was inhibited whereas that from dopa-H3 was not; and there was a normal uptake of exogenous norepinephrine by heart and spleen in animals pretreated with α-methyl-tyrosine. Preliminary studies of the pharmacologic consequences of blockade of norepinephrine synthesis indicate impairment of motor activity and mild sedation in cats and guinea pigs and a reduction of the tyramine and norepinephrine pressor responses in guinea pigs and rats.

Dopamine: a prolactin-inhibiting hormone.

Abstract: A. Introduction DOPAMINE (DA) is an interesting and versatile compound. In the central nervous system (CNS) it is involved with the control of fine movements and mental processes. Its association with disorders such as Parkinsonism and schizophrenia is well recognized. In the hypothalamo-hypophysial axis, DA is the primary physiological inhibitor of PRL secretion. Currently, this catecholamine represents the only nonpeptidergic hypothalamic agent with a well defined hypophysiotropic function. By virtue of its dual role as a neurotransmitter and a hormone, DA provides perhaps the best example of neuroendocrine interactions. It also possesses a more universal property. In all hormonal systems studied thus far, whether at the hypothalamic, posterior pituitary, or anterior pituitary level, DA functions as an inhibitor. Perhaps the common denominator to these diverse cells is the presence of D2 DA receptors, which are negatively linked to the adenylate cyclase system.

Application of steady state kinetics to the estimation of synthesis rate and turnover time of tissue catecholamines

Abstract: A method of measuring the rate of synthesis of catecholamines in various tissues takes advantage of the steady state relationship in which the rate of catecholamine formation is equal to the rate of efflux. After tyrosine hydroxylase is blocked with α-methyltyrosine, the brain levels of norepinephrine (NE) and dopamine and the NE levels in various peripheral tissues of rats and rabbits decline exponentially. The rate of synthesis of the catecholamines is calculated from the product of the rate constant of amine decline and the normal catecholamine level. The value for heart NE yielded by this method is almost identical with that obtained from the decline in radioactivity after labeling with dl -H3-NE. The application of this method to studies in the rat shows that the turnover time for NE in heart, salivary gland and iris is about 12 hr, compared to 6 hr for brain NE, 3 hr for brain dopamine and 2 hr for NE in the cervical sympathetic ganglia. In the rabbit hypothalamus, NE is formed five times more rapidly than in the midbrain, though the turnover times are almost identical. This suggests that the rate of synthesis might be similar in each adrenergic unit and that variations in rates of synthesis in different brain areas are a function of the number of neurons per gram of tissue.