The Role of Thyroid Hormone as a Biological Amplifier of the Actions of Follicle-Stimulating Hormone in the Functional Differentiation of Cultured Porcine Granulosa Cells*

Abstract

To characterize thyroid hormone action on the ovary, the direct effects of T4 or T3 were investigated in vitro using a monolayer culture system of porcine granulosa cells. Monolayer cultures were maintained for 6 days in 4% serum-supplemented medium in the absence or presence of porcine FSH (20 ng/ml), with or without graded doses of T4 or T3. Combined treatment with FSH and T4 (10(-7) M) induced morphological alternation resembling epithelioid cells, while FSH alone or T4 alone failed to bring about the epithelioid morphology. Concomitant treatment with FSH and T4 (10(-7) M) markedly increased FSH-stimulated induction of [125I]iodo-human CG binding to cultured granulosa cells obtained from small follicles. The combined treatment with FSH and T4 (10(-7) M) also resulted in a significant increase in progesterone and estrogen secretion by the cultured cells relative to treatment with FSH alone. Increases in progesterone, 17 beta-estradiol, and estrone secretion caused by the combined treatment with FSH and T4 (10(-7) M) were further augmented in response to the addition of exogenously provided substrate pregnenolone, testosterone, and androstenedione, respectively. Furthermore, aromatase activity assessed by the release of [3H]water from [1 beta-3H, 4-14C]androstenedione was significantly higher in cells treated concomitantly with FSH and T4 (10(-7) M) than that in cells treated with FSH alone. All the stimulatory effects of T4 (10(-7) M) on the morphological and functional differentiation of cultured granulosa cells were also found in combined treatment with FSH and T3 (10(-9) M). Either treatment with higher or lower concentrations of T4 or T3 gave attenuated effects, and T4 or T3 alone without FSH was incapable of exhibiting these stimulatory effects. These findings suggest that thyroid hormones synergize with FSH to exert direct stimulatory effects on granulosa cell functions, including morphological differentiation, LH/human CG receptor formation and steroidogenic enzyme (3 beta-hydroxysteroid dehydrogenase and aromatase) induction. Hence, decreases in ovarian functions during the states of hypo- or hyperthyroidism may account for diminished responsiveness of the granulosa cells to FSH.

Clinical endocrinology of thyroid gland function in ruminants

“…Furthermore, T 3 and T 4 directly alter ovarian granulosa cell steroidogenesis in pigs and humans. Specifically, Hayashi et al (1985) and Maruo et al (1987) observed that T 4 stimulated follicle stimulating hormone (FSH) induced estradiol (E 2 ) production by porcine granulosa cells. Later Wakim et al (1995a, b) found that T 4 stimulated progesterone (P 4 ) and E 2 production by human granulosa cells.…”

“…In an in vitro system, T 3 caused about a twofold increase of protein synthesis in rat granulosa cells compared to cells without T 3 (Bandyopadhyay et al, 1996). In vitro T 3 assisted FSH and LH to enhance steroid biosynthesis in porcine (Chan and Tan, 1986;Maruo et al, 1987;Gregoraszczuk et al, 1998) and human (Goldman et al, 1993;Wakim et al, 1995a, b) granulosa cells. A recent study has reported that T 3 mediated stimulation of P 4 release from human luteal cells is not direct, but is mediated through a putative protein factor (Datta et al, 1998).…”

Histomorfometria e histoquímica dos ovários, tubas e útero de ratas hipotireóideas em metaestro-diestro

“…Apesar da influência comprovada dos hormônios tireoidianos na foliculogênese e esteroidogênese ovarianas, o mecanismo pelo qual as disfunções da tireóide alteram a função ovariana ainda não foi totalmente elucidado (Maruo et al, 1987;Dijkstra et al, 1996). A definição se a ação desses hormônios sobre o ovário é direta ou indireta ainda não foi obtida.…”

Characteristics of infertility in female hypothyroid (hyt) mice

“…Experimental findings in vitro indicate that presence of an adequate concentration of thyroid hormone is needed for appropriate FSH-mediated granulosa cell differentiation (luteinization). Since the adequate differentiation of granulosa cells is the pivotal event in formation of the normal corpus luteum, hypothyroxinaemia may be assumed to be one condition responsible for deficient corpus luteum formation (Maruo et al, 1987). Consistent with the possible involvement of thyroid hormones in corpus luteum function, thyroid hormone replacement therapy has been found to be very effective for the treatment of LPD associated with subclinical hypothyroxinaemia.…”