Regulation of thyroid hormones on the production of testosterone in rats

Abstract

The effects of a thyroidectomy and thyroxine (T4) replacement on the spontaneous and human chorionic gonadotropin (hCG)-stimulated secretion of testosterone and the production of adenosine 3',5'-cyclic monophosphate (cAMP) in rat testes were studied. Thyroidectomy decreased the basal levels of plasma luteinizing hormone (LH) and testosterone, which delayed the maximal response of testosterone to gonadotropin-releasing hormone (GnRH) and hCG in male rats. T4 replacement in thyroparathyroidectomized (Tx) rats restored the concentrations of plasma LH and testosterone to euthyroid levels. Thyroidectomy decreased the basal release of hypothalamic GnRH, pituitary LH, and testicular testosterone as well as the LH response to GnRH and testosterone response to hCG in vitro. T4 replacement in Tx rats restored the in vitro release of GnRH, GnRH-stimulated LH release as well as hCG-stimulated testosterone release. Administration of T4 in vitro restored the release of testosterone by rat testicular interstitial cells (TICs). The increase of testosterone release in response to forskolin and androstenedione was less in TICs from Tx rats than in that from sham Tx rats. Administration of nifedipine in vitro resulted in a decrease of testosterone release by TICs from sham Tx but not from Tx rats. The basal level of cAMP in TICs was decreased by thyroidectomy. The increased accumulation of cAMP in TICs following administration of forskolin was eliminated in Tx rats. T4 replacement in Tx restored the testosterone response to forskolin. But the testosterone response to androstenedione and the cAMP response to forskolin in TICs was not restored by T4 in Tx rats. These results suggest that the inhibitory effect of a thyroidectomy on the production of testosterone in rat TICs is in part due to: 1) the decreased basal secretion of pituitary LH and its response to GnRH; 2) the decreased response of TICs to gonadotropin; and 3) the diminished production of cAMP, influx of calcium, and activity of 17beta-HSD. T4 may enhance testosterone production by acting directly at the testicular interstitial cells of Tx rats.

Thyroid Hormone and Leptin in the Testis

“…Thyroidectomy in adult rats led to decreased secretion of testosterone and 17 b -hydroxy steroid dehydrogenase (HSD) activity ( 161 ). Leydig cells cultured from adult rats show an increase in testosterone and estrogen secretion after treatment with T 3 , under basal conditions and in response to LH ( 148 ).…”

Stem Leydig cells: From fetal to aged animals

“…One possibility could be the difference in the severity of induced thyroid deficiency. Thus, severe thyroid deficiency, such as that induced by thyroidectomy, may result in changes in the hypothalamic‐pituitary–testicular axis (Chandrasekhar et al, 1986; Antony et al, 1995; Chiao et al, 1999; Maran et al, 2000). Changes in LH undoubtedly would affect Leydig cell regeneration.…”

Effect of thyroidectomy on the histology of rat sublingual gland

“…Previous studies have indicated that total thyroidectomy reduces triiodothyronine (T 3 ), thyroxin (T 4 ), insulin, prolactin, corticosterone levels and acid phosphatase activities, and increases cholesterol and glutamic oxaloacetic transaminase activities in rats (2–4). Hypothyroidism also diminishes hypothalamic gonadotropin‐releasing hormone, pituitary lutinizing hormone, follicle‐stimulating hormone, growth hormone and testicular testosterone secretions (4–6). However, all these hormonal changes have been shown to be normalized by the administration of T 4 to rats with hypothyroidism (2, 5, 6).…”