Melatonin Effects on Steroid Production by Rainbow Trout Ovarian Follicles In Vitro: Influence of Stage of Follicle Maturation
Titel:
Melatonin Effects on Steroid Production by Rainbow Trout Ovarian Follicles In Vitro: Influence of Stage of Follicle Maturation
Auteur:
Leatherland, John F. Lin, Lucy
Verschenen in:
Biological rhythm research
Paginering:
Jaargang 32 (2001) nr. 5 pagina's 557-568
Jaar:
2001-12
Inhoud:
Rainbow trout ovarian follicles at four different stages of maturation (very early vitellogenesis, early vitellogenesis, peak vitellogenesis, and pre-ovulatory) were incubated either in Cortland's medium alone, or medium containing melatonin at one of five concentrations (1 × 10-10, 1 × 10-8, 1 × 10-6, 1 × 10-4 or 1 × 10-2M) to assess the direct actions of melatonin on basal (non-gonadotrophin stimulated) secretion of 17β-estradiol and testosterone. Testosterone secretion by peak vitellogenic phase follicles was significantly (p < 0.01) reduced by melatonin at 1 × 10-4 or 1 × 10-2 M, but there were no other significant effects of melatonin on T secretion. There were no significant effects of melatonin at concentrations of 1 × 10-10 or 1 × 10-8 M on 17β-estradiol secretion for any stage of follicular maturation, although for follicles at the peak vitellogenesis stage, melatonin at 1 × 10-6 M had a significant (p < 0.05) stimulatory effect compared with the controls. Melatonin also stimulated 17β-estradiol secretion by very early vitellogenic stage follicles (1 × 10-2 M concentration; p < 0.05). At concentrations of 1 × 10-4 and 1 × 10-2 M, melatonin significantly (p < 0.01) inhibited 17β-estradiol secretion of peak vitellogenic and preovulatory stage follicles. The findings suggest a stimulatory action of melatonin on steroidogenesis of early stage ovarian follicles, a shift to an inhibitory action of the higher concentrations of melatonin in later stages of development, but with a bimodal action of melatonin (related to hormone concentration) being present during the time of maximum follicular growth.
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