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

The in vitro secretion of progesterone (P-4), androgen (A) and estradiol (E-2) by follicular cells, isolated monthly from the rainbow trout ovaries during the whole annual cycle, was studied. Cells were cultured as monolayers in control and prolactin (PRL) supplemented media. E, secretion showed two distinct maxima in September and January: 4959 +/- 220 pg/ml and 3166 +/- 121 pg/ml, respectively, i.e. during vitellogenesis and before the spawning time. PRL had a significant (16%) suppressive effect on E-2 secretion when the level of secreted steroid was at its highest (4167 +/- 193 pg/ml) at the end of vitellogenesis and by 32% (2157 +/- 124 pg/ml), before ovulation. Increased P4 levels observed in February (988 +/- 69 pg/ml) and March (2008 +/- 74 pg/ml) may be connected with the need for a substrate for the synthesis of 17alpha20betaOH-P (MIS). At this time, the secretion of P-4 was also suppressed by PRL and was reduced to 1395 +/- 78 pg/ml. Our results indicate that PRL may play a role in fish reproduction. (C) 2002 Elsevier Science Inc. All rights reserved.