The purpose of the research study is to learn more about the regulation of reproductive hormones in adult men. We would like to understand what role testosterone and estradiol play in controlling the release of LH (lutenizing hormone) and FSH (follicle stimulating hormone). Testosterone and estradiol come from the testes, and LH and FSH are released from a gland in the head called the pituitary.

Men involved in the study will have detailed evaluations that involve overnight stays in the hospital and frequent blood sampling. The men in the study will also be receiving medications that affect the levels of various hormones in the body. This will allow the researchers to learn how various hormones influence each other. Men that participate in the study will receive medical evaluations and monetary compensation. Information gathered from this study will help in the development of new treatments for infertility and potentially new hormonal forms of contraception.

In the United States 10-15% couples seek evaluation for infertility, of whom a male factor is identified in approximately 50% of cases. To date, however, most infertility research has focused on the female partner and in the majority of instances the etiology of male infertility remains poorly understood with inconsistent elevation in FSH levels. Given that spermatogenesis is highly dependent on FSH secretion, this project will focus on delineating the feedback control of FSH in the human male. Such studies, although difficult to perform in the human, are critical to understanding not only the pathophysiology of male infertility, but also to determining the feasibility of hormonal approaches to male contraception. In this protocol, studies of normal, GnRH-deficient and agonadal men employing reversible sex steroid ablation, physiologic sex steroid replacement and manipulation of the GnRH input to the pituitary will permit the non-steroidal, sex steroid, and GnRH-dependent components of FSH regulation to be selectively elucidated.

Inclusion Criteria:

• Men aged 18 to 50 years
• In good health
• On no medications

Exclusion Criteria:

Subjects will not be enrolled in this study if there is a history of:

• Liver disease or if screening blood tests demonstrate abnormal liver function tests
• Excessive alcohol consumption
• Illicit drug use
• Severe drug allergy
• Use of any concomitant medications
• Peptic ulcer disease or gastritis