Early effects of hypothyroidism on the ovarian function in the rat.

HAPON, M.B.,; BUZZIO, O.L.,; GAMARRA-LUQUES, C.D.,; JAHN, G.A.

Vancouver, Canada

Congreso; XXXVII Annual Meeting of the Society for the Study of Reproduction.; 2004

Society for the Study of Reproduction.

Hypothyroidism (hypoT) in the female is associated with delayed puberty, menstrual abnormalities, PCOS, infertility and spontaneous abortion. We have observed previously that hypoT female rats have irregular estrous cycles, spontaneous pseudopregnancies (Psp) and smaller litters. IGF I and some of its binding proteins (BPs) are produced locally in the ovary, IGF 1 is involved in FSH and GH stimulated preovulatory follicular development and IGFBP 3, 4 and 5 regulate the action of IGFI. The expression of the IGF system is modified in altered thyroid states. To explore the early effects of hypoT on ovarian function we studied the effects of PTU 0.01 % in the drinking water given to 3-4 months old female virgin rats, on cycling, reproductive hormone profiles (T3, T4, TSH, PRL, GH, E2 and P4) measured by RIA, and the abundance of mRNA (measured by semicuantitive RT-PCR and expresssed relative to S16) for IGF I, IGF-BP 3 and 5, and GH (GHR), estrogen (ER) and PRL (PRLR) receptors, during the 2nd cycle after the initiation of PTU treatment. Measurements were taken at 20h on all days of the cycle and also at 08h on proestrus (P) and estrus (E). The PTU rats showed increased TSH and decreased T3 and T4. Ovulation rate and circulating P4, LH and FSH presented no changes between groups, but PRL and E2 increased on E 8 and 20h and GH decreased on P 8h. Expression of IGFI did not change, IGFBP3 fell in the hypoT group on diestrus (D) 1 and 2: and rose at P 08h and IGFBP5 fell on D1. PRLR decreased on D1, GHR increased at P 20hs, ERa decreased at P 20.00h and increased at E 08.00h and ERb increased at P 20.00h and E 20.00h. The increased GHR mRNA on P may have compensated the lower secretion of GH in P8h in the hypoT group. The increases in circulating PRL and E2 may be responsible for the posterior apparition of spontaneous Psps. The changes observed in ovarian gene expression were not sufficient to induce alterations in the studied cycle, but may play a role in the posterior ovarian dysfunctions and establishment of PCOS observed in HypoT rats.