Leptin treatment restores estrous cyclicity in fasted animals, but not in animals that have also received injections of 2-deoxyglu-cose. This implies that leptin’s effects on reproduction may be due to its influence on metabolic fuel availability, and that leptin acts to provide signals to glucose-sensitive regions of the brain, which then influence GnRH secretion. Cheap Diskus Advair
Does the discovery of leptin revise the way that we think about the ‘‘critical body fat’’ hypothesis of fertility? Should we now refer to a ‘‘critical leptin level’’ hypothesis? A majority of the data supporting the ‘‘critical body fat’’ hypothesis are correlative and do not prove causality (see for review). Leptin has the potential to act as a metabolic signal to the reproductive system to reflect energy reserves; unfortunately, leptin’s multi-faceted influence on metabolism makes it difficult to discern between primary and secondary actions of this hormone. Since reproductive failure can still be observed in fasted animals despite their having adequate leptin levels, there may not be a ‘‘leptin sensor’’ per se that acts as a switch to activate the HPG axis. Leptin may only be a signal insofar as it is able to influence the availability of metabolic fuels, such as glucose or fatty acids. Future experiments will undoubtedly clarify leptin’s role as a regulator of the reproductive system.