Short-term profiles of plasma gonadotropin and 17α-hydroxy, 20β-dihydroprogesterone levels in the female rainbow trout at the periovulatory period

Abstract

Individual free-swimming female rainbow trout in which oocytes underwent final stages of germinal vesicle migration, maturation, or ovulation were bled via a dorsal-aortic catheter at frequencies of once every 1, 3, or 4 hr over periods of 9 to 36 hr. Gonadotropin (GtH) and 17 alpha-hydroxy,20 beta-dihydroprogesterone (17 alpha,20 beta-OHP) levels were measured in the plasma samples. GtH levels were elevated and showed wide and progressive daily variations. A high degree of synchronization appeared among the GtH profiles of individual fish. Two distinct daily GtH surges were observed, one at early photophase and the other during the mid-scotophase. The onset of the GtH increases was closely related to the beginning of the photophase and the scotophase, respectively. In females undergoing oocyte maturation or in ovulated females, 17 alpha,20 beta-OHP levels were increasing or high, showing progressive daily fluctuations that were either synchronized with the GtH changes or somewhat phase-shifted in relation to them. These data are discussed in relation to the seasonal changes in the short-term profiles of reproductive hormones in the trout.

Targeted Gene Expression Profiling in the Rainbow Trout (Oncorhynchus mykiss) Ovary During Maturational Competence Acquisition and Oocyte Maturation

“…In contrast, 20␤HSD expression is extremely variable depending on the female. Taken together, these results are consistent with previous observations of strong daily fluctuations in MIS circulating levels in female rainbow trout undergoing oocyte maturation [40]. In addition, it is noteworthy that two closely related rainbow trout 20␤HSD cDNAs, both expressed in vitellogenic ovarian follicles, were previously identified [41].…”

Particularities of reproduction and oogenesis in teleost fish compared to mammals

“…Moreover, if the necessity of some physiological coordination between the acquisition of follicular competence as a whole, and the emission of appropriate stimulating signals from the neuroendocrine system seems obvious, insufficient attention has probably been paid so far to signals from the ovaries, and not only steroids. Finally, the analysis of gonadotropic signals from the pituitary should not be limited to the mean absolute level of FSH and LH, but should also take into account short-term profiles, thus renewing ancient works performed when available assays probably only gave a mean value between both gonadotropins [147].…”

Comparing Sex Steroid Levels During the Annual Cycles of Rainbow Trout (Oncorhynchus mykiss) Diploid Female (XX) and Triploid Female (XXX) Genotypic Sex

“…Increasing GTH levels, required for the oocyte to gain maturational competence (Patino et al. 2001), acts on follicles ready to undergo maturation by modulating the enzymes involved in the synthesis of the maturation‐inducing steroid 17α,20β‐OH‐progesterone (Zohar et al. 1986).…”

“…Low concentrations at the end of vitellogenesis, along with the diminished aromatase activity observed during ovulation (van Bohemen and Lambert 1981), lessen negative feedback on the pituitary and allow the ovulatory gonadotropin surge . Increasing GTH levels, required for the oocyte to gain maturational competence (Patino et al 2001), acts on follicles ready to undergo maturation by modulating the enzymes involved in the synthesis of the maturation-inducing steroid 17a, 20b-OH-progesterone (Zohar et al 1986). The fall in E2 may also be related to the regulation of metabolic clearance (Fostier et al 1986) as well as the progressive switching-off of enzymes just before ovulation .…”