Effects of administration of some monoamine-synthesis blockers and precursors on ovariectomy-induced rise in plasma gonadotropin II in the catfish Heteropneustes fossilis.
In the present study, effects of three daily i.p. injections of some monoamine (MA)-synthesis blockers and pre-cursors on plasma gonadotropin (GTH-II) levels were investigated in 3-week ovariectomized catfish, and the effects were correlated with changes in hypothalamic MA contents. Administration of alpha-methylparatyrosine (alpha-MPT; 250 micrograms/g BW, a tyrosine hydroxylase inhibitor) significantly decreased the ovariectomy-induced rise in GTH-II compared to that of the sham control group. Injection of L-dihydroxyphenylalanine (10 micrograms/g BW) in the alpha-MPT-treated fish elevated the GTH-II level significantly over that of the sham control group but not to the level of the ovariectomized fish. Administration of noradrenaline (NA; 5 micrograms/g BW) in combination with alpha-MPT counteracted the effect of the latter and maintained the plasma GTH-II level at that of the ovariectomized fish. Plasma GTH-II level was decreased significantly in the diethyldithiocarbamate (10 micrograms/g BW, a dopamine-beta-hydroxylase inhibitor)-injected fish compared to that of the sham and ovariectomized control groups. Administration of para-chlorophenylalanine (p-CPA; 100 micrograms/g BW, a tryptophan hydroxylase inhibitor) decreased the GTH-II level significantly compared to that of the ovariectomized group. Supplementation of 5-hydroxytryptophan (20 micrograms/g BW) with p-CPA nullified the latter's effect and maintained the GTH-II level at that of the ovariectomized fish. The administration of both p-CPA and alpha-MPT significantly reduced plasma GTH-II to the lowest mark compared to that of the sham, ovariectomized, and all other treatment groups. These results clearly show that the ovariectomy-induced rise in GTH-II was mediated through simultaneous activation of hypothalamic serotonergic and NA-ergic and suppression of dopaminergic mechanisms.
Senthilkumaran
B
B
Centre of Advanced Study in Zoology, Banaras Hindu University, Varanasi, India.
Joy
K P
KP
D000818:Animals; D015306:Biogenic Monoamines / Q000096:biosynthesis*; D002397:Catfishes / Q000378:metabolism*; D004050:Ditiocarb / Q000494:pharmacology; D015259:Dopamine Agents / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000097:blood; D005260:Female; D010134:Fenclonine / Q000494:pharmacology; D006065:Gonadotropins, Pituitary / Q000097:blood*; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism; D007980:Levodopa / Q000494:pharmacology; D008781:Methyltyrosines / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010052:Ovariectomy; D011863:Radioimmunoassay; D018490:Serotonin Agents / Q000494:pharmacology; D013566:Sympathomimetics / Q000494:pharmacology; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors; D019805:alpha-Methyltyrosine
D015306:Biogenic Monoamines; D015259:Dopamine Agents; D004791:Enzyme Inhibitors; D006065:Gonadotropins, Pituitary; D008781:Methyltyrosines; D018490:Serotonin Agents; D013566:Sympathomimetics; D007980:Levodopa; D004958:Estradiol; D019805:alpha-Methyltyrosine; D004050:Ditiocarb; D014446:Tyrosine 3-Monooxygenase; D010134:Fenclonine; D009638:Norepinephrine