Elucidating Kisspeptin Physiology by Blocking Kisspeptin Signaling

A. Healthy Subjects All healthy subjects will meet the following criteria: * normal puberty with respect to onset and pace, * no difficulty with blood draws, * no prescription medications for at least 2 months with the exception of asthma medication (albuterol only), hypercholesterolemia medication and psychiatric medication, * no illicit drug use or excessive alcohol consumption (\>10 drinks/week), * no history of a medication reaction requiring emergency medical care, * normal physical exam and laboratory studies within protocol reference ranges. Additional criteria based on subject population: 1. Healthy Men: * between 21 and 40 years old, * normal erectile and ejaculatory function, no history of reproductive disorders, * testicular volume \>15 ml. 2. Healthy women: * between 21 and 40 years old, * not breastfeeding or pregnant, * menstrual cycles between 25 and 35 days in duration with no more than 5 days variability in cycle duration, * no evidence for androgen excess (hirsutism or acne), 3. Healthy postmenopausal women: * between 48 and 60 years old, * no menstrual periods within the last year, * previous history of menstrual cycles between 25 and 35 days in duration, with no more than 5 days variability in cycle duration, * if applicable, able to undergo washout from hormone therapy, * no evidence for androgen excess (hirsutism or acne), * negative screening for Factor V Leiden for those who might receive estradiol treatment as a part of this study. B. Subjects with Reproductive Disorders All subjects with reproductive disorders will meet the following criteria: * all medical conditions stable and well controlled, medications allowed include asthma medication (albuterol only), hypercholesterolemia medication and psychiatric medication, * no medications known to affect reproductive endocrine function for at least 2 months except for medications used to treat the subject's reproductive condition, * no history of a medication reaction requiring emergency medical care, * no illicit drug use or excessive alcohol consumption (\>10 drinks/week), * for women, not breastfeeding or pregnant, * if applicable, able to undergo appropriate washout from hormone therapy, * normal physical exam and laboratory studies within protocol reference ranges, Additional criteria based on subject population: 1. Men and women with hypogonadotropic hypogonadism, * 18 years or older, * Confirmed diagnosis by low sex steroids in the setting of low or inappropriately normal gonadotropins, * If needed, additional labs and imaging tests may be performed. 2. Agonadal men, * Between 18 and 60 years old.