title: Vasotocin induces final oocyte maturation and ovulation through the production of a maturation-inducing steroid in the catfish Heteropneustes fossilis.
abstract: The study reports for the first time vasotocin (VT) induction of final oocyte maturation and ovulation through the production of the maturation-inducing steroid 17, 20β-dihydroxy-4-pregnen-3-one (MIS, 17, 20β-DP). Post-vitellogenic follicles of the catfish Heteropneustes fossilis were incubated with different concentrations of VT (1, 10, 100 and 1000 nM) for different time periods. Germinal vesicle breakdown [GVBD, as a marker of final oocyte maturation (FOM)] and ovulation were scored. In another series of experiments, the follicles were incubated with VT alone or in combination with VT receptor (V(1) and V(2)) antagonists, and GVBD and ovulation were increased with progesterone, 17-hydroxy-4-pregnene-3, 20-dione (17-P) and 17, 20β-DP levels. VT stimulated both GVBD and ovulation in a concentration and time-dependent manner, and the responses were inhibited to varying degrees in groups incubated with the VT receptor antagonists. The V(1) antagonist inhibited the responses by 2- to 3-fold and more than the V(2) antagonist, and the combination was more potent than the separate incubation. Progestins increased time-dependently in the VT groups and the fold increase was greater for the MIS. The VT-induced steroid stimulation was significantly inhibited to near the control levels in co-incubations with both V(1) and V(2) receptor antagonists, in the order 17, 20β-DP > 17-P > P(4). The inhibition by the V(1) receptor antagonist was greater than that with the V(2) blocker, and followed the same order of inhibition described above. The results suggest that VT induces FOM and ovulation mainly through the V(1) receptors.
authors.affiliation: Department of Zoology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India.
authors.forename: V
authors.initials: V
authors.lastname: Singh
authors.forename: K P
authors.initials: KP
authors.lastname: Joy
mesh_terms: D000818:Animals; D065092:Antidiuretic Hormone Receptor Antagonists; D002397:Catfishes; D005260:Female; D006908:Hydroxyprogesterones / Q000378:metabolism*; D009865:Oocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D006080:Ovarian Follicle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010060:Ovulation / Q000187:drug effects*; D011374:Progesterone / Q000494:pharmacology; D011372:Progestins / Q000494:pharmacology; D017483:Receptors, Vasopressin / Q000819:agonists / Q000378:metabolism; D014668:Vasotocin / Q000494:pharmacology*
chemical_list: D065092:Antidiuretic Hormone Receptor Antagonists; D006908:Hydroxyprogesterones; D011372:Progestins; D017483:Receptors, Vasopressin; C034862:vasotocin receptor; C007433:17,20-dihydroxy-4-pregnen-3-one; D011374:Progesterone; D014668:Vasotocin