Relationship between hCG receptors disappearance and steroid accumulation during long term hCG stimulation in porcine Leydig cell cultures

'Spare' Luteinizing Hormone Receptors: Facts and Fiction

It is common opinion that maximal activation of luteinizing hormone (LH)-dependent steroidogenic signal occurs at <1% of human LH/choriogonadotropin (hCG) receptor (LHCGR) occupancy. This effect would be a consequence of an excess of receptors expressed on the surface of theca cells, resulting in a pool of LHCGRs remaining unbound (spare). This concept was borrowed from historical pharmacological studies, when discrepancies between ligand-receptor binding and dose-response curves of cAMP were evaluated by treating mouse or rat Leydig cells with hCG in vitro. Recent findings demonstrated the specificity of LH- and hCG-dependent effects, receptor heterodimerization, and differing behaviors of rodent versus human gonadotropin-responsive cells, which may help to revise the 'spare' LHCGRs concept applied to human ovarian physiology and assisted reproduction.

Pig Leydig cell culture: a useful in vitro test for evaluating the testicular toxicity of compounds

In vivo studies have shown that the testis is a target organ for drugs and chemicals. In order to evaluate the testicular toxicity of compounds and to identify the mechanisms of their toxicity, we have developed a miniaturized primary culture of immature pig Leydig cells. Five well-known drugs with differing mechanisms of toxicity on testicular functions were tested to validate the model. Testosterone and progesterone secretion were measured to evaluate testicular function. Cell viability was assessed quantitatively using a colorimetric assay based on the reduction of a tetrazolium salt (3-(4,5-dimethylthiazol)-2,5-diphenyltetrazolium bromide) which stains viable cells only, thus allowing discrimination between specific inhibitors of Leydig cell function and nonspecific cytotoxic drugs. Ketoconazole and aminoglutethimide inhibited both testosterone and progesterone secretion, but without modifying cell viability. Spironolactone specifically blocked testosterone secretion and increased progesterone concentration without inducing cell mortality. Cycloheximide altered testicular steroid secretion by another mechanism of action. Chlorpromazine, which interferes with the secretion of gonadotropins in vivo, produced a significant inhibition of progesterone and testosterone secretion as a result of the cytotoxic effects of the drug. In conclusion, this in vitro test enables one to discriminate accurately between specific and nonspecific inhibitors of steroidogenesis and could reduce the number of false positives when screening for potential testicular toxins.