Leptin originally thought to be derived predominantly from adipose tissue is now known to be almost ubiquitously expressed in many tissues. The complete absence of leptin is not developmentally lethal and results in early onset obesity, stunted skeletal and brain growth, extreme insulin resistance, hyperphagia, a compromised immune system and infertility. In this study we examine the effects of passive immunization on seminal vesicle weight, and testosterone in prepubertal mice.
Immature Swiss random bred male mice, aged three weeks, were randomly allocated into four treatments groups (n=12), and were given three subcutaneous (sc) injections (100 µl) every 48 h of the following treatments (A) non-immune Ig (50 µg) as the control group; (B) anti-leptin antibody (JMCK#16, 50 µg); (C) eCG (40 IU) with non-immune Ig (50 µg); (D) anti-leptin antibody (50 µg) with eCG (40 IU). On the morning of day 6 of treatment, animals were euthanized, blood was collected and seminal vesicles dissected out and weighed. Testosterone concentration was measured in the plasma.
No difference in final body weight was observed, however seminal vesicle weight was significantly increased by the treatments (P<0.001) with lowest in the controls (31.7±5.6mg) followed by anti-leptin (47.0±7.1mg), eCG (57.0±8.7mg) and eCG plus anti-leptin (57.8±7.0mg). Plasma testosterone concentrations were significantly (P<0.01) elevated in the eCG group (3.00±0.10ng/ml), the anti-leptin treatment had the lowest testosterone (0.24±0.09ng/ml) although not significantly different from the control (0.82±0.42ng/ml) or eCG plus anti-leptin groups (1.20±0.55ng/ml). These results suggest that while leptin inhibits testosterone production it may also have a direct suppressive effect on seminal vesicle maturation in the immature male that is independent of the effects of androgens. This supports our earlier pharmacokinetic work showing the seminal vesicles are a target for leptin.