Growth Hormone Directly Stimulates Testosterone and Oestradiol Secretion by Rat Leydig Cells in vitro and Modulates The Effects of LH and T3.

Abstract

Abstract.The modulatory effect of GH on basal, LH and T3 mediated secretion of testosterone and oestradiol by purified rat (60 day old) Leydig cells was studied in vitro. Percoll gradient purified Leydig cells (1 x 103) were cultured for 48 hours at 34°C in a medium containing different concentrations of rat GH (5-400 ng/mL), after an initial culture for 24 hours at 37°C. GH increased testosterone and oestradiol secretions in a dose dependent manner. While testosterone secretion reached the saturation point with 50 ng GH, oestradiol secretion reached the saturation point with 150 ng GH, followed by diminished secretions. Co-administration of minimum (10 ng) effective does of GH with minimum (25 ng) or maximum (100 ng) effective doses of oLH significantly decreased the testosterone secretion.However, an increased secretion of testosterone was observed when maximum effective doses of rGH (50 ng) and oLH (100 ng) were co-administered. Minimum effective (25 ng) or maximum effective (50 ng) doses of T3 inhibited GH mediated secretion of testosterone in vitro. Oestradiol concentration in the culture medium increased when either dose of rGH was co-administered with the minimum or maximum effective doses of oLH. T3 50 ng augmented the secretion of oestradiol by Leydig cells in the presence of GH. These results indicate that GH acts as a gonadotrophin to stimulate testosterone and oestradiol secretions by Leydig cells, and that it modulates LH or T3 induced secretion of these steroids, depending on the intensity of their stimulation.

Increased testicular insulin-like growth factor 1 is associated with gonadal activation by recombinant growth hormone in immature rats

“…In HSD3B(+) PLCs isolated on PND 21 rats, rhGH treatment increased the steroidogenic pathway gene mRNA and testosterone secretion. These suggest that rhGH treatment directly activates steroidogenesis in PLCs, which is consistent with the previous studies [ 35 ]. The increase in circulating testosterone found in rhGH rats on PNDs 24 and 31 might be attributable to the potentiation of steroidogenic differentiation of PLCs to testosterone-producing LCs, leading to activation of the spermatogenesis.…”

Thyroid Hormones: Their Role in Testicular Steroidogenesis

“…They later found that T3 stimulates the synthesis of a 52-kDa protein in crude Leydig cell preparation, thus suggesting Leydig cell steroidogenesis is stimulated by T3 through this protein [43]. Valenti et al [97] reported that neither T3 nor T4 has influence on basal or LH-mediated T production by Leydig cells, whereas our studies indicated that T3 directly stimulates basal T and E2 secretion from purified adult rat Leydig cells and it modulates LH, GH, and PRL-induced T and E2 secretion in a dosedependent manner [64,65,71]. Recent studies further demonstrated that T3 stimulates mouse Leydig cell=mLTC-1 mouse Leydig tumor cell steroidogenesis (progesterone, T), increases hCG receptor numbers, and increases LHR and StAR mRNA expression through the mediation of steroidogenic factor-1 (SF-1) [57,59].…”

Somatotropic‐Testicular Axis: A crosstalk between GH/IGF‐I and gonadal hormones during development, transition, and adult age

“…24 IGF-I also stimulates proliferation of LC progenitors and their differentiation. 25 Similarly, GH enhances steroidogenic acute regulatory protein (StAR) and increases 3β-HSD gene expression [26][27][28] in LCs.…”