Sodium orthovanadate induces in vitro ovulation and ovarian prostaglandin synthesis in brook trout (Salvelinus fontinalis)
✍ Scribed by Hsu, Sheau-Yu ;Goetz, Frederick William
- Publisher
- John Wiley and Sons
- Year
- 1991
- Tongue
- English
- Weight
- 640 KB
- Volume
- 260
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Abstract
The in vitro effects of sodium orthovanadate (Na~3~VO~4~), a G‐protein activator, on ovulation and prostaglandin (PG) synthesis were investigated in the brook trout (Salvelinus fontinalis) ovary. PGE and PGF levels in incubation medium of either extrafollicular (EF) tissue or follicles were measured by specific radioimmunoassays (RIA). PGE levels in follicle incubates were increased by Na~3~VO~4~ at both pre‐germinal vesicle breakdown (preGVBD) and preovulatory (preOV) stages. However, an increase of PGF levels in follicle incubates was observed only in preGVBD follicles in the presence of Na~3~VO~4~. The preOV follicles spontaneously released more PGF than preGVBD follicles and the level was not affected by Na~3~VO~4~ treatment. In contrast, in incubates of EF tissue, Na~3~VO~4~ induced dosage‐dependent increases in PGE and PGF at either stage. The Na~3~VO~4~‐stimulated increase of PGE in preOV follicle incubates was significantly reduced by the translational inhibitor, cycloheximide (5 μM), but not by the transcriptional inhibitor, actinomycin (5 μM). PGF levels in preOV follicle incubates were also significantly reduced by cycloheximide and actinomycin in controls, but not in the presence of 0.1 mM Na~3~VO~4~. The results suggest that protein synthesis was required for Na~3~VO~4~ to increase accumulation of PGE, and in maintaining control PGF levels in preOV follicles. In addition, since PGF levels in preOV follicles were not reduced by either inhibitor in the presence of Na~3~VO~4~, a Na~3~VO~4~‐stimulated increase of PGF levels was unmasked that apparently acts through a non‐translational pathway. In vitro ovulation was also significantly increased by 0.1 mM Na~3~VO~4~. However, the Na~3~VO~4~‐induced ovulation was not inhibited by either actinomycin or cycloheximide. The data imply that the mechanism(s) by which Na~3~VO~4~ induces ovulation are distinct from that for stimulating PG accumulation. When preOV follicles were incubated with 10 μM forskolin, no stimulatory effect on ovulation, or on PGE and PGF levels was observed. The data strongly indicate that the effects of Na~3~VO~4~ on ovulation and ovarian PG levels were not mediated by an increase in cAMP.