A neuroendocrine predisposition for homosexuality in men

Area of Science:

• Neuroendocrinology
• Sexual Differentiation
• Human Behavior

Background:

• Androgen deficiency in male rats during development leads to a female-differentiated brain and homosexual behavior.
• A positive estrogen feedback effect on luteinizing hormone (LH) secretion is observed in these rats.

Purpose of the Study:

• To investigate the estrogen feedback effect in homosexual men compared to heterosexual and bisexual men.
• To explore the potential link between brain differentiation and sexual orientation in humans.

Main Methods:

• Intravenous administration of 20 mg Presomen (estrogen) to 21 homosexual men and 20 heterosexual/5 bisexual men.
• Measurement of serum LH levels before and after estrogen administration.
• Radioimmunoassay to determine plasma testosterone and urinary unconjugated testosterone levels.

Main Results:

• Homosexual men showed a significant decrease in LH followed by an increase above initial levels after estrogen administration.
• Heterosexual and bisexual men exhibited a significant LH decrease but no subsequent increase above initial levels.
• Adult homosexual men had normal plasma testosterone and urinary testosterone levels, comparable to heterosexual men.

Conclusions:

• Homosexual men display a positive estrogen feedback effect, suggesting a predominantly female-differentiated brain.
• This brain differentiation may be activated by normal adult androgen levels to manifest homosexual behavior.
• Findings support a neurobiological basis for sexual orientation involving early organizational effects of hormones.