title: Estradiol-17β modulates dose-dependently hypothalamic tyrosine hydroxylase activity inhibited by α-methylparatyrosine in the catfish Heteropneustes fossilis.
abstract: The brain is a target for organizational and activational effects of oestrogens synthesized de novo or transported from the peripheral organs. A neuroprotective role of oestrogens has been documented in a variety of vertebrates. In the present study in the catfish Heteropneustes fossilis, we have demonstrated that estradiol-17β (E(2)), the major circulating oestrogen at low dosages (0.05 and 0.1 μg/g body weight of fish for 3 days) stimulated hypothalamic tyrosine hydroxylase (TH) activity, and countered the negative effects of ovariectomy (3-week) or α-methylparatyrosine (α-MPT: 250 μg/g body weight, a competitive inhibitor of TH). In contrast, high dosages of E(2) (1 and 2 μg/g body weight of fish for 3 days) were inhibitory and further amplified the inhibitory effects of ovariectomy and α-MPT. The inhibiting role of E(2) was higher in gonad-active (prespawning) phase than gonad-inactive (resting phase) phase. The dual roles of E(2) may ensure a tight regulation of catecholaminergic activity, activating and inhibiting the system against wide fluctuations that are characteristic of seasonally breeding animals.
authors: Department of Zoology, Mahila Mahavidyalaya, Banaras Hindu University, Varanasi, 221005, India. chauberadha@rediffmail.com
authors: Radha
authors: R
authors: Chaube
authors: Keerikkattil P
authors: KP
authors: Joy
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002397:Catfishes; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004958:Estradiol / Q000008:administration & dosage / Q000502:physiology*; D005260:Female; D007031:Hypothalamus / Q000187:drug effects / Q000201:enzymology*; D018696:Neuroprotective Agents / Q000008:administration & dosage; D009490:Neurosecretory Systems / Q000502:physiology; D012098:Reproduction / Q000502:physiology; D018709:Statistics, Nonparametric; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*; D019805:alpha-Methyltyrosine / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D018696:Neuroprotective Agents; D004958:Estradiol; D019805:alpha-Methyltyrosine; D014446:Tyrosine 3-Monooxygenase