SEX-DIFFERENCES IN SERUM LH AND FSH PATTERNS IN HAMSTERS EXPOSED TO SHORT PHOTOPERIOD

When hamsters are exposed to a short photoperiod (10L:14D) suppression of gonadal function is observed in both sexes, and this is accompanied by alterations in the pattern of pituitary gonadotropin (GTH) secretion. Short photoperiod exposure leads to decreased serum concentrations of both LH and FSH in males. In females daily surges of LH and FSH were observed during the midafternoon in short photoperiod. The daily cycle in GTH release continued after ovariectomy in short photoperiod females. Daily surges of GTH were not observed in short photoperiod males. Females treated with androgen shortly after birth failed to show estrous cyclicity in adulthood and also failed to display daily GTH surges when exposed to short photoperiod. These data suggest (1) that the capacity to release GTH cyclically in both long and short photoperiods is a sexually differentiated trait in the hamster, (2) that the development of this trait depends on the presence or absence of sex steroids during perinatal life, and (3) that the daily surges of GTH in short photoperiod females are probably regulated by the same neural mechanism which is responsible for triggering the preovulatory surge of GTH in the ovulating female. © 1979.