Does prolactin affect steroid secretion by isolated rainbow trout ovarian cells?

Area of Science:

• Endocrinology
• Reproductive Biology
• Fish Physiology

Background:

• The annual reproductive cycle in female fish involves complex hormonal regulation of ovarian steroidogenesis.
• Understanding the role of pituitary hormones like prolactin (PRL) in modulating ovarian function is crucial for fish aquaculture and conservation.

Purpose of the Study:

• To investigate the in vitro secretion of progesterone (P(4)), androgen (A), and estradiol (E(2)) by rainbow trout ovarian follicular cells throughout the annual cycle.
• To determine the effect of prolactin (PRL) on the secretion of these steroids.

Main Methods:

• Ovarian follicular cells were isolated monthly from rainbow trout over a full annual cycle.
• Cells were cultured as monolayers in media with or without prolactin (PRL) supplementation.
• Steroid concentrations (P(4), A, E(2)) in culture media were measured using established assays.

Main Results:

• Estradiol (E(2)) secretion peaked in September and January, coinciding with vitellogenesis and pre-spawning periods.
• Prolactin (PRL) significantly suppressed E(2) secretion during peak periods (16% at end of vitellogenesis, 32% before ovulation).
• Progesterone (P(4)) levels increased in February-March, potentially for 17alpha20betaOH-P synthesis, and PRL also suppressed P(4) secretion during this time.

Conclusions:

• Prolactin (PRL) exhibits a suppressive effect on estradiol (E(2)) and progesterone (P(4)) secretion in rainbow trout ovarian follicular cells.
• These findings highlight a significant role for PRL in regulating steroidogenesis and reproductive timing in fish.