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Low-Dose Human Chorionic Gonadotropin Maintains Intratesticular Testosterone in Norma

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by , 04-09-2012 at 08:47 PM (1935 Views)
j***.endojournals.org/content/90/5/2595.full

Low-Dose Human Chorionic Gonadotropin Maintains Intratesticular Testosterone in Normal Men with Testosterone-Induced Gonadotropin Suppression

Abstract

In previous studies of testicular biopsy tissue from healthy men, intratesticular testosterone (ITT) has been shown to be much higher than serum testosterone (T), suggesting that high ITT is needed relative to serum T for normal spermatogenesis in men. However, the quantitative relationship between ITT and spermatogenesis is not known. To begin to address this issue experimentally, we determined the dose-response relationship between human chorionic gonadotropin (hCG) and ITT to ascertain the minimum dose needed to maintain ITT in the normal range. Twenty-nine men with normal reproductive physiology were randomized to receive 200 mg T enanthate weekly in combination with either saline placebo or 125, 250, or 500 IU hCG every other day for 3 wk. ITT was assessed in testicular fluid obtained by percutaneous fine needle aspiration at baseline and at the end of treatment. Baseline serum T (14.1 nmol/liter) was 1.2% of ITT (1174 nmol/liter). LH and FSH were profoundly suppressed to 5% and 3% of baseline, respectively, and ITT was suppressed by 94% (1234 to 72 nmol/liter) in the T enanthate/placebo group. ITT increased linearly with increasing hCG dose (P < 0.001). Posttreatment ITT was 25% less than baseline in the 125 IU hCG group, 7% less than baseline in the 250 IU hCG group, and 26% greater than baseline in the 500 IU hCG group. These results demonstrate that relatively low dose hCG maintains ITT within the normal range in healthy men with gonadotropin suppression. Extensions of this study will allow determination of the ITT concentration threshold required to maintain spermatogenesis in man.


Discussion

A significant intratesticular fluid to serum T gradient was observed in this group of young normal men at baseline. In this study, serum T was 1.2% of ITT, an 84-fold gradient. A similar testicular to serum gradient has been reported in studies of testicular biopsy tissue in the 1970s (19) as well as more recently (9, 13). However, the absolute ITT levels reported in testicular homogenates are higher than the ITT levels found in the testicular fluid aspirates in this study. This difference is probably the result of the release of cellular T stores in testicular homogenates compared with secreted T in fluid aspirates obtained with minimal cellular disruption. Normal intratesticular fluid T concentrations were maintained by low doses of hCG (125, 250, and 500 IU every other day for 3 wk) in men with gonadotropin suppression from exogenous T. Presumably, normal ITT levels within the testis should support normal spermatogenesis.

A similar intratesticular to serum T gradient is seen in the rat (17). Rat models of spermatogenesis have shown a testis to serum T gradient with 100-fold higher T levels within the testis (17). The high ITT levels are in excess of the ITT concentration needed to support normal spermatogenesis; ITT can be reduced to 20% of normal levels without impacting normal spermatogenesis in the rat (16). However, below this threshold there is a direct quantitative relationship between ITT and sperm production. High doses of exogenous T can restore spermatogenesis in the rat (20, 21, 22, 23). Additionally, replacing ITT by injecting microspheres containing T directly into the rat testis restored ITT levels as well as spermatogenesis to normal (24). In the rat, the high ITT levels have been shown to exceed the ITT level necessary for normal spermatogenesis. The threshold ITT concentration necessary for normal spermatogenesis in the rat is more than twice the normal serum T concentration (16). Similar studies in man have been limited by the inability to reliably assess the intratesticular microenvironment repeatedly. Studies relying on testicular biopsy have been cross-sectional in design, with the comparison of ITT levels across individuals who have undergone various hormonal manipulations. This study design is biased by the high variability in ITT between individuals. Percutaneous aspiration of testicular fluid has allowed us to perform a longitudinal study, with repeated assessment of the intratesticular hormonal environment in men, which allows for the serial assessment of ITT in response to hormonal manipulation.

Previous studies have shown that weekly administration of either 200 or 300 mg T, im, maximally suppresses gonadotropin secretion (6); moreover, these doses of T inhibit gonadotropin secretion within 23 d of administration (25). As expected, we observed that serum gonadotropin levels were significantly reduced by exogenous T in this study. Gonadotropin suppression without hCG administration caused dramatic reductions in ITT (94%) from baseline in the TE and placebo hCG group. Exogenous TE (200 mg weekly) has also been shown to reduce sperm production to azoospermic levels in approximately 70% of Caucasian men (7, 8). Spermatogenesis was not assessed in this 3-wk study, but in a previous study of normal men (n = 7) with gonadotropin suppression induced with 6 months of T and a progestin, levonorgestrel (LNG), intratesticular fluid T was suppressed 98% from baseline (15). Intratesticular fluid T levels in these men after 6 months of TE plus LNG treatment were similar to their baseline serum T levels. In this group of seven men, ITT levels suppressed to levels approximating their baseline serum T levels were coincident with suppressed spermatogenesis. The addition of progestins to exogenous T has been shown to enhance gonadotropin suppression and azoospermia in a greater proportion of men (26, 27, 28) than T alone. The ITT levels (13 nmol/liter) in this small study were lower than the ITT levels in the TE/placebo hCG group in the current study (72 nmol/liter). The lower ITT levels may relate to the longer treatment phase (6 months vs. 3 wk), the additive effect of LNG to LH suppression, or other inhibitory effects of progestins within the testis. Although this low ITT level (13 nmol/liter) appeared to be insufficient to maintain spermatogenesis, the minimum ITT concentration required for normal spermatogenesis in men is unknown.

The quantitative use of hCG to selectively replace LH activity within the testis would allow for manipulation of the intratesticular androgenic environment, thereby enabling a study of the quantitative relationship between ITT and spermatogenesis. In this study, hCG increased the ITT concentration, presumably through stimulation of Leydig cell steroidogenesis. The dose of hCG required to maintain baseline ITT concentrations in men with maximal gonadotropin suppression is significantly lower than that historically used in the treatment of infertility due to hypogonadotropic hypogonadism.

...

Studies of the intratesticular hormonal environment can be undertaken if we can develop a model in which we can reliably control the ITT concentration. Clamping the pituitary with exogenous hormones and/or GnRH receptor analogs (39, 40, 41) allows for the selective repla***ent of gonadotropins to determine the relative contributions of intratesticular androgens and FSH in normal spermatogenesis. Clearly, low-dose hCG can restore ITT to normal levels in men with gonadotropin suppression from exogenous T administration. Although there was no statistically significant difference in ITT among the 125-, 250-, and 500-IU hCG dose groups in pairwise comparisons, there was a linear increase in ITT with increasing hCG dose, which was statistically significant by simple linear regression (P < 0.001). The 250-IU dose group had posttreatment ITT levels closest to their baseline levels of all the groups, with a posttreatment ITT 7% lower than their baseline ITT. However, the two higher hCG groups (250 and 500 IU) had higher serum T during TE/hCG treatment than the TE/placebo group or the TE/125-IU hCG group. The ITT concentration achieved with TE/125-IU hCG (group 2) was also not statistically different from baseline, and this group had lower serum T than the two higher hCG dose groups. The contribution of serum T to ITT levels is not clear, and these results must be interpreted with caution, given that different immunoassays were used to measure T in serum and intratesticular fluid.

In summary, assessment of the testicular hormonal environment through percutaneous fluid aspiration has shown a similar testis to serum T gradient as previous testicular biopsy studies in men and rats. Additionally, low doses of hCG maintain baseline levels of ITT in men with gonadotropin withdrawal from exogenous T administration. Lower doses of hCG may be as effective in treating male infertility due to hypogonadotropism as the higher doses used historically. Selective repla***ent of LH activity with low-dose hCG, as demonstrated in this study, will allow the design of future studies investigating the relative roles of intratesticular androgens and FSH in the control of human spermatogenesis. Such work will be applicable to the goal of developing uniformly effective male contraception.
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