The effects of E and F prostaglandins on ovarian cAMP production and follicular contraction in the brook trout (Salvelinus fontinalis).

The effects of PGE1, PGE2, PGF2 alpha (2 micrograms/ml), and forskolin (10 microM) on follicle contraction of brook trout (salvelinus fontinalis) were studied by measuring the weight loss of punctured follicles during in vitro incubation. PGE1, PGE2, and forskolin significantly inhibited spontaneous contraction of follicles. In contrast, PGF2 alpha significantly increased the weight loss of punctured follicles. The results indicate that PGs could influence ovulation through their effects on follicle wall contraction. The effects of PGs and forskolin on cAMP production in follicles were also investigated by incubating intact follicles (without extrafollicular tissue), follicle walls, and denuded oocytes at pregerminal vesicle breakdown (preGVBD) and preovulatory (preOV) stages in vitro with PGE1, PGE2, PGF2 alpha (0.2 and 2 micrograms/ml), or forskolin (10 microM). At the end of incubation, cAMP content in incubation medium and follicular tissue was assayed by a specific protein-binding assay. Intact follicles in control groups contained high amounts of cAMP at both stages, but released significantly more cAMP into the medium at the preGVBD stage (P < 0.05). Forskolin stimulated significantly higher levels of cAMP in incubation medium at either stage. At the preGVBD stage, significantly higher cAMP levels were measured in the medium with higher dose of PGE1 at 1 and 4 hr and with higher dose of PGE2 at 1, 2, and 4 hr. Significantly higher cAMP levels were also measured in incubates with high dose of PGE1 at 2 and 4 hr and with high doses of PGE2 at 2, 4, and 16 hr at the preOV stage. However, follicular cAMP levels were significantly elevated only by forskolin at both stages. Experiments incubating only follicle walls or denuded oocytes demonstrated that most of the medium cAMP measured in preGVBD intact follicle incubates was derived from denuded oocytes, and that the stage difference in cAMP release within intact follicle incubates was due to a stage difference in cAMP release from denuded oocytes. In addition, follicle walls appeared to be more sensitive to forskolin and PG stimulations than denuded oocytes. The stimulation of cAMP accumulation in the medium by PGEs may be significant since both forskolin and PGEs have been shown to inhibit brook trout ovulation in vitro (F. W. Goetz, D. C. Smith, and S. P. Krickle (1982). Gen. Comp. Endocrinol. 48, 154-160) and follicle contraction in the present study.