Effects of the maturation-inducing steroid on LH secretion and the GnRH system at different stages of the gonadal cycle in Atlantic croaker.
The effects of treatment with the maturation-inducing steroid 17,20beta,21-trihydroxy-4-pregnen-3-one (20beta-S) on luteinizing hormone-releasing hormone analog (LHRHa)-induced LH secretion were examined during several phases of the gonadal cycle in Atlantic croaker, Micropogonias undulatus. 20beta-S (1 and 5 microg/g of body wt) was administered by intraperitoneal (ip) injection, 24 h prior to injection with LHRHa (10-50 ng/g of body wt) and fish were bled 1 h after LHRHa injection. Treatment with both doses of 20beta-S resulted in plasma concentrations of the steroid within the normal physiological range for this species during final oocyte maturation and ovulation. The 20beta-S treatments altered the LH response to LHRHa throughout the reproductive cycle in both sexes, but the direction and magnitude of the response varied. 20beta-S treatment decreased the LH response to LHRHa in fish with recrudescing and fully recrudesced gonads and in females with regressed gonads. On the other hand, 20beta-S treatment significantly increased the LH response to LHRHa in males with regressing or regressed gonads. 20beta-S treatment also altered preoptic anterior hypothalamic (POAH) and pituitary seabream gonadotropin-releasing hormone (sbGnRH) contents, and the patterns of these changes were similar to those observed in LH secretion. The finding that moderate increases in plasma 20beta-S concentrations, similar to those occurring during final oocyte maturation, significantly inhibit the LH response to LHRHa at the end of the reproductive cycle suggests that this action of 20beta-S is of physiological importance during the periovulatory period. Moreover, the fact that concurrent changes occur in POAH and pituitary sbGnRH contents suggests that the actions of 20beta-S on LH secretion are at least partly mediated via the GnRH system.
Mathews
Sonya
S
Marine Science Institute, The University of Texas at Austin, 750 Channel View Drive, Port Aransas, TX 78373, USA.
Khan
Izhar A
IA
Thomas
Peter
P
D000818:Animals; D003350:Cortodoxone / Q000031:analogs & derivatives* / Q000097:blood / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000032:analysis / Q000502:physiology*; D006066:Gonads / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D008297:Male; D010473:Perciformes / Q000502:physiology*; D010902:Pituitary Gland / Q000737:chemistry / Q000187:drug effects; D011301:Preoptic Area / Q000737:chemistry / Q000187:drug effects; D012098:Reproduction / Q000502:physiology
D007987:Gonadotropin-Releasing Hormone; C051954:17,20,21-trihydroxy-4-pregnen-3-one; D007986:Luteinizing Hormone; D003350:Cortodoxone