We want to find out what happens to reproductive hormone levels; Luteinising Hormone (LH), Follicle Stimulating Hormone (FSH), testosterone and oestradiol when kisspeptin is administered to people for a period of 8 days each month, using either placebo (saline) or kisspeptin in doses of 0.1, 0.3 or 1.0 nmol/kg/hour.

Participants will be invited to have an initial baseline study to look at the hormone levels at regular intervals over the course of a day (8hours). Following this, on a different day, volunteers will have an infusion of kisspeptin, which will be administered by a small pump to deliver the hormone into subcutaneous tissue (fatty tissue just below the skin surface). On day 1 of the pump infusion there will be another day of regular blood sampling for 8 hours. After this the kisspeptin pump will continue and the participants will return to the research unit on day 3 for a review and a single blood test. On day 5 the participants will have a review, a blood test and the kisspeptin pump will be changed. Kisspeptin infusion will continue and on Day 8 the participant will return for another 8 hour study. At the end of this the kisspeptin pump will be removed. The above will be repeated using either placebo (saline) or kisspeptin in doses of 0.1, 0.3 or 1.0 nmol/kg/hour during the early follicular phase of 4 separate menstrual cycles.