Endocrine Abstracts

Leptin is best known as an appetite and metabolic rate modulator secreted from fat, but it also has a range of other functions including modulation in reproductive physiology. To date, most studies examining the role of leptin in male reproduction have focussed on individual tissues, often in vitro. In the current report, a bolus physiological dose of iodinated leptin was administered intravenously to male mice to and samples collected over a one hour time course to determine potential targets for leptin action in the male reproductive tract. The testis and the epididymis accumulated approximately 0.3% of the administered dose, remaining relatively stable over the time course. In the seminal vesicles, the dose recovered increased from 0.35±0.1% to 1.37±0.3% of the dose from 5 to 45 min after administration. In terms of dose recovered per gram of tissue, recovery from testis and epididymis remained relatively stable at approximately 0.9% dose/g, 2.5% dose/g, respectively. Recovery from the seminal vesicles 5 min after administration was 1.14±0.1%dose/g, increasing to 4.15±0.4%dose/g 45 min after administration, before a decline to 3.10±0.2% dose/g observed 60 min post-injection. Major targets for leptin binding have been characterised in previous studies including work from out lab. These studies showed that leptin was rapidly cleared from these tissues. In the male reproductive tract leptin appears to accumulate, with the seminal vesicles being a preferential target, although the testis and epididymis also accumulate leptin for a period of time. Leptin receptors are expressed in each of these tissues, and leptin signalling has been shown to attenuate testosterone secretion in the testis, while in the epididymis leptin increases spermatozoa differentiation. However, it is still unclear why leptin would accumulate in the seminal vesicles. Leptin and the soluble leptin receptor (LepRe) have been recovered from ejaculate and, leptin is known to facilitate in vitro fertilisation and implantation, and LepRe increases the half-life of leptin. Thus, leptin in the male reproductive tract may play a role in the normal fertilisation and implantation processes.