Effect of 3,3',5-triiodothyronine and 3,5-diiodothyronine on progesterone production, cAMP synthesis, and mRNA expression of STAR, CYP11A1, and HSD3B genes in granulosa layer of chicken preovulatory follicles

In vitro studies were performed to assess whether stimulatory effects of triiodothyronine (T₃) on progesterone (P₄) production in a granulosa layer (GL) of chicken preovulatory follicles are associated with 3′,5′-cyclic adenosine monophosphate (cAMP) synthesis and mRNA expression of STAR protein, CYP11A1, and HSD3B. Effects of 3,5-diiodothyronine (3,5-T₂) on steroidogenic function in these follicles were also investigated. The GL of F3 to F1 follicles was incubated in medium supplemented with T₃ or 3,5-T₂, LH, or forskolin (F), and a combination of each iodothyronine with LH or F. Levels of P₄ and cAMP in culture media were determined by RIA. Expression of genes involved in P₄ synthesis (ie, STAR protein, CYP11A1, and HSD3B) in the GL of F3 to F1 follicles incubated in medium with T₃ or 3,5-T₂ and their combination with LH was performed by real-time PCR. Triiodothyronine increased basal and LH- and F-stimulated P₄ secretion by preovulatory follicles. The 3,5-T₂ elevated P₄ synthesis by F3, had no effect on F2 follicles, and diminished P₄ production by the GL of F1 follicles. It had no effect on LH-stimulated P₄ production; however, it augmented F-stimulated P₄ production by F2 and F1 follicles. Although T₃ did not affect basal and F-stimulated cAMP synthesis by the GL of preovulatory follicles, it increased LH-stimulated synthesis of this nucleotide. However, 3,5-T₂ elevated F-stimulated cAMP synthesis in F3 and F2 follicles; it did not change basal and LH-stimulated cAMP production. Triiodothyronine decreased basal STAR and CYP11A1 mRNAs in F3 follicles, increased them in F1 follicles, and elevated HSD3B mRNA levels in F1 follicles. Triiodothyronine augmented LH-stimulated STAR, CYP11A1, and HSD3B mRNA levels in F2 and CYP11A1 in F1 follicles. However, T₃ decreased LH-stimulated STAR and HSD3B mRNA levels in F1 follicles. The 3,5-T₂ did not affect basal STAR and CYP11A1 mRNA expression in all investigated follicles; however, it decreased LH-stimulated STAR expression in F2 and F1 ones. The effects of 3,5-T₂ caused elevated basal but diminished LH-stimulated HSD3B mRNA levels. In conclusion, data indicate that both iodothyronines are involved in P₄ production in the GL of chicken preovulatory follicles acting alone and additively with LH. Effects of iodothyronines depend on follicle maturation and are associated with modulation of cAMP synthesis and STAR, CYP11A1, and HSD3B mRNA expression. We suggest that iodothyronines participate in maturation and ovulation of chicken follicles.