The inter-relationship between gonadal steroids and POMC peptides, beta-endorphin and alpha-MSH, in the control of sexual behavior in the female rat.

Estradiol benzoate (10 microg EB) given to ovariectomized-adrenalectomized rats induced sexual receptivity in half the animals and increased alpha-MSH in the preoptic area, ventromedial nucleus (VMN) and arcuate nucleus (ARC), in all the animals, although levels were significantly higher in the VMN and ARC of the receptive (R) subgroup. EB also raised levels of beta-endorphin in the VMN and ARC in the R rats only. POMC expression was not altered. EB did not affect alphaMSH in extra-hypothalamic areas, but addition of progesterone, raised levels in the septum, amygdala, hippocampus and caudate putamen. Only in the VMN, ARC and septum were the steroid-induced increases correlated with onset of sexual behavior.