Luteal expression of thyroid hormone receptors during gestation and postpartum in the rat

NAVAS P. B.; REDONDO A. L. ; CUELLO CARRION F. D.; VARGAS ROIG L. M.; VALDEZ S. R.; JAHN G. A.; HAPON M. B.

THYROID

MARY ANN LIEBERT INC

Lugar: New York; Año: 2014 vol. 24 p. 1040 - 1050

1050-7256

Background: Progesterone (P4) is the main steroid secreted by the corpora lutea (CL) and is required for successful implantation and maintenance of pregnancy. Although adequate circulating levels of thyroid hormone (TH) are needed to support formation and maintenance of CL during pregnancy, TH signaling has not been described in this gland. We determined luteal thyroid hormone receptor isoforms (TR) expression and regulation throughout pregnancy and under the influence of thyroid status, and in vitro effects of T3 exposure on luteal P4 synthesis. Methods: Female Wistar rats were sacrificed by decapitation on days 5 (G5), 10 (G10), 15 (G15), 19 (G19), and 21 (G21) of pregnancy and 2 (L2) postpartum. Hyperthyroidism and Hypothyroidism were induced by daily administration of T4 (0.25 mg/kg s.c.) or 6-propyl-2-thiouracil (PTU) (0.1 g/L in drinking water), respectively. Luteal TR expression of RNA was determined using real-time RTPCR, and of protein using Western blot and immunohistochemistry. Primary cultures of luteal cells and of luteinized granulose cells from other rats were used to study in vitro effects of T3 on P4 synthesis. Also, the effect of T3 on basal and stimulated (by luteinizing hormone (LH), prolactin (PRL), and prostaglandin E2 (PGE2)) granulosa cell P4 synthesis was evaluated. Results TRá1, TRá2 and TRâ1 mRNA were detected in CL of pregnancy. At the protein level, TRâ1 was abundantly expressed during gestation reaching a peak on G19 and decreasing afterwards. TRá1 was barely expressed during early gestation, peaked on G19 and diminished thereafter. TRâ1 and TRá1 at protein and mRNA level were not influenced by thyroid status. T3 neither modified P4 secretion of the CL of pregnancy nor its synthesis in granulosa-luteinized cell culture. Conclusions This study confirms for the first time the presence of TR isoforms in the CL during pregnancy and postpartum, identifying this gland as a TH target during gestation. TR expression is modulated in this tissue in accordance with the regulation of P4 metabolism, and the abrupt peripartum changes suggest a role of TH during luteolysis. However, TH actions on the CL do not seem to be related to a direct regulation of P4 synthesis.