Gonadal influences on the inhibition of monoamine oxidase type B activity

Monoamine oxidase type B (MAO‐B) was similarly active in the hypothalamus of 60‐day‐old male and female Charles River rats. A single, 2 mg/kg IP injection of deprenyl, however, resulted in a significantly greater inhibition of hypothalamic MAO‐B in normal males than in normal females. Repeated administration of estrogen (estradiol valerate) to intact males postnatally, a treatment which disrupts the masculinization process, although not provoking true “feminization,” decreased the inhibition of MAO‐B, thus abolishing the sex‐specific difference. The intensity of deprenyl‐provoked hypothermia and ptosis in males exceeded that of females; neonatal and postnatal estrogenization of males resulted in diminution of these effects. Androgen administration to neonate females did little affect the biochemical and in vivo parameters of MAO inhibition. It is concluded that sex‐specific, biochemical differences in MAO‐B inhibition may have pharmacological correlates, and both facets of MAO inhibition are sensitive to neonatal exposure to estrogen.