Leptin is an adipocyte-derived cytokine critical to the integration of energy homeostasis and reproduction which putatively acts as a metabolic gate for the onset of puberty. However, it is unknown whether the age of puberty reflects leptin levels or leptin sensitivity. If pubertal age reflects leptin sensitivity, it may also reflect susceptibility to diet-induced obesity.
We hypothesised that age of pubertal onset reflects leptin sensitivity. We assessed leptin sensitivity in female Sprague Dawley rats at three pubertal stages: pre-pubertal, peri-pubertal and one month post pubertal. Rats were administered an intraperitoneal injection of vehicle or leptin (3 mg/kg) at the onset of the dark phase in a cross-over design. Leptin sensitivity was assessed by measuring food intake following leptin versus vehicle at 4 and 24 h post-injection. Rats were retrospectively classified into early (days 3336) or late (days 4144) vaginal opening. Following vaginal opening, rats were switched to a high-fat diet (32% energy from fat) for 4 weeks and body weight monitored daily to determine whether age of pubertal onset predicted susceptibility to diet-induced obesity.
Following 28 days of post-pubertal high-fat feeding, females who had undergone early vaginal opening remained significantly more sensitive to the anorexigenic effects of exogenous leptin than those which had undergone late vaginal opening. There was no significant difference detected in leptin sensitivity between rats which underwent early vaginal opening and those that underwent late vaginal opening in either the pre-pubertal or peri-pubertal period. There was no significant difference in overall body weight or food intake between the early and late groups at the end of the study.
These data suggest that early vaginal opening may be associated with improved leptin sensitivity in later life, but that vaginal opening age does not predict acute leptin sensitivity in the pre-pubertal or post-pubertal period.