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.

Amitraz changes NE, DA and 5-HT biosynthesis and metabolism mediated by alterations in estradiol content in CNS of male rats

“…Particularly, activity and expression of enzymes that synthesize and metabolize DA, NE and 5-HT are altered by E2 (Babu and Vijayan, 1984;Chaube and Joy, 2011;Donner and Handa, 2009;Luine and Rhodes, 1983;Luine et al, 1973;Rahman and Thomas, 2013;Scardapane and Cardinali, 1977;Schendzielorz et al, 2011;Serova et al, 2002). In addition, E 2 increases mRNA levels and activity of TH and TRH, the major rate limiting enzymes in catecholamines and indoleamines biosynthesis, respectively (Babu and Vijayan, 1984;Chaube and Joy, 2011;Rahman and Thomas, 2013;Serova et al, 2002;Donner and Handa, 2009;Aggarwal et al, 2012;Hiroi et al, 2006).…”

“…Such enzymes include aldehyde dehydrogenase (AD), catechol-O-metyltransferase (COMT), dopamineb-hydroxylase (DBH), MAO, tyrosine hydroxylase (TH), and tryptophan hydroxylase (TRH), all important for neurotransmitters synthesis and metabolism (Babu and Vijayan, 1984;Chaube and Joy, 2011;Donner and Handa, 2009;De Souza Silva et al, 2009;Handa et al, 1997;Lubbers et al, 2010;Luine and Rhodes, 1983;PurvesTyson et al, 2012;Rahman and Thomas, 2013;Scardapane and Cardinali, 1977;Schendzielorz et al, 2011;Thiblin et al, 1999). This hypothesis is reasonable considering that amitraz alters hepatic metabolism of 17b-estradiol (E2) and testosterone (T) in rats, and increases serum T in male rats at doses of 25 and 50 mg/ kg bw (Chou et al, 2008).…”