Luteinizing hormone differentially regulates the secretion of testicular oxytocin and testosterone by purified adult rat Leydig cells in vitro.

The aims of the present study were to determine whether Leydig cells in vitro synthesize oxytocin, and whether LH modulates the secretion of oxytocin by Leydig cells. Highly purified adult Leydig cells were prepared from adult rats and cultured for 3 days in the presence or absence of 0.1 ng/ml ovine LH, and media were changed daily. The total amount of oxytocin present in the culture was estimated by RIA of cell extracts before culture (day 0) and at the end of day 3 of culture and in media on days 1-3. The content of immunoreactive oxytocin in cell extracts on day 0 (3.4 +/- 1.2 pg/10(6) cells) was significantly lower than the total amount that had been released into the medium and was present in the cell extracts at the end of day 3 (+LH, 27.8 +/- 3.3; -LH, 16.5 +/- 2.7 pg/10(6) cells), suggesting that Leydig cells are able to synthesize and secrete oxytocin. This hypothesis was supported by the observation that oxytocin release into the medium was significantly reduced during a 3-h treatment of Leydig cells with the protein synthesis inhibitor cycloheximide (5 micrograms/ml for 3 h). The role of LH in regulating testosterone production by Leydig cells is well defined, but whether LH also regulates oxytocin is unknown. Therefore, the effects of LH on oxytocin and testosterone production by Leydig cells were compared. The production of both hormones was stimulated by increasing doses of LH (0.001-100 ng/ml), but no further rise in oxytocin release could be elicited with amounts of LH greater than 0.1 ng/ml. Testosterone production, however, continued to increase with doses of LH up to 100 ng/ml. Furthermore, the two hormones differed in the rate of their responses to both 3- and 12-h exposures to LH; testosterone secretion increased more rapidly than that of oxytocin. These data provide direct evidence that adult Leydig cells produce immunoreactive oxytocin, and that their production of this peptide is regulated by LH.