Effects of Luteinizing and Thyroid Hormones on the Aged Leydig Cells in Brown Norway Rats

Tae, Hun Jin; Park, Young Jae; Choi, Eun Young; Yang, Hong Hyun; Hong, Chul Un; Ahn, Dong Choon; Kim, In Shik

Abstract

ABSTRACT: The present study was designed to investigate the possibility of restoring the testicular steroidogenic ability of the aged Brown Norway rats by administering luteinizing hormone (LH) and thyroxine (Thy). Rats of 3, 6, 12 months (M) of age (n = 8 per group) and four groups of 18 month old rats (n = 8 per group) were used. Eighteen month old rats were implanted subdermally with Alzet mini osmotic pumps containing saline (control), luteinizing hormone (LH, 24 microgram/day), thyroxine (Thy, 5 microgram/day) and LH and Thy (LH +Thy, 24 microgramday and 5 microgram/day), respectively for four weeks (i.e testing was done at 19 months). The results showed that the testis volume was unchanged among all treatment groups. The number of Leydig cell per testis was not significantly different among all treatment groups. The average volume of a Leydig cell was significantly decreased at 12 months, and a further reduction was observed at 19 months (saline-treated); values for 19 month LH-and-LH +Thy-treated rats were not significantly lower than those at 3 and 6 months of age. Testosterone secretory capacity per testis and per Leydig cell in vitro were significantly reduced concomitantly with age advancement from 6 to 19 months (saline-treated) of age. These values of LH-and Thy-treated 19 month old rats were similar to those at 12 months. LH +Thy-treated rats were equally capable to 3 and 6 month old rats in producing testicular testosterone in vitro in response to LH. Serum testosterone was unchanged from 3 M to 12 M rats but was reduced in 19M control rats. Both LH and Thy significantly raised these values above the 19M control levels, but they were still lower than the 3 M through 12 M levels. Additionally, LH +Thy significantly raised the serum testosterone levels to those of 12M rats, but these values were significantly lower than those of 3 M and 6 M rats. In summary, the present study demonstrated that the exogenous supplementation of LH and Thy was effective in restoring the steroidogenic potential of the aged Leydig cells; the most effective treatment was LH +Thy, which upgraded the capacity of aged testes to those of 3 and 6 months.