In vitro effects of catecholamines and catecholestrogens on brain tyrosine hydroxylase activity and kinetics in the female catfish Heteropneustes fossilis.
Effects of catecholamines and catecholestrogens on tyrosine hydroxylase (TH) activity and kinetics were investigated in the telencephalon and hypothalamus of female Heteropneustes fossilis in gonad quiescent (resting) and recrudescent (preparatory) phases. Dopamine, noradrenaline and adrenaline and the catecholestrogen, 2-hydroxyestradiol-17 beta inhibited TH activity in a concentration-dependent manner in both resting and preparatory phases, with a higher effect in the resting phase. Two- methoxyestradiol-17 beta did not alter TH activity in any season. The catecholamines inhibited TH in a competitive manner increasing apparent K(m) values significantly without altering the apparent V(max). Two-hydroxyestradiol-17 beta inhibited significantly the enzyme in a noncompetitive manner and decreased apparent V(max) without altering apparent K(m) values. The apparent K(i) is higher for dopamine than noradrenaline or adrenaline. The apparent K(i) for 2-hydroxyestradiol-17 beta is not significantly different from that of noradrenaline. The present results suggest an interaction between oestradiol-17beta (E2) and catecholamine metabolism at the level of tyrosine hydroxylation and E2 effects on catecholamines may be mediated through its 2-hydroxylation.
Chaube
R
R
Department of Zoology, Banaras Hindu University, Varanasi, India.
Joy
K P
KP
D000077584:2-Methoxyestradiol; D000818:Animals; D002395:Catecholamines / Q000494:pharmacology*; D002397:Catfishes; D004298:Dopamine / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004837:Epinephrine / Q000494:pharmacology; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D002393:Estrogens, Catechol / Q000494:pharmacology*; D005260:Female; D007031:Hypothalamus / Q000187:drug effects / Q000201:enzymology; D066298:In Vitro Techniques; D007700:Kinetics; D009638:Norepinephrine / Q000494:pharmacology; D013687:Telencephalon / Q000187:drug effects / Q000201:enzymology*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
D002395:Catecholamines; D002393:Estrogens, Catechol; D004958:Estradiol; D000077584:2-Methoxyestradiol; C001390:2-hydroxyestradiol; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine; D009638:Norepinephrine; D004837:Epinephrine