Mucosal gastrin receptor. VIII. Sex-related differences in binding

The purpose of the current study was to determine whether gastrin binding differed between the sexes and, if so, to ascertain the factors responsible. Male and female rats were killed at various times from 15 to 60 days after birth. Binding capacities in male and female rats were equal until puberty. By day 40 there were significantly more receptors present in males than females. Females had 2.4 fmol receptor/mg prot by day 40, and this value remained constant into adulthood. In male rats the number of receptors continued to increase to 4.0 fmol/mg prot at day 60. Castration did not significantly decrease the number of receptors in male rats. Ovariectomy, however, increased the number of receptors in female rats to a value not significantly different from male controls. Ovariectomized females consumed more food and had higher serum gastrin levels. If ovariectomized rats were pair fed to the level of intact females, the number of receptors and serum gastrin levels decreased over those present in ovariectomized rats fed ad libitum but still remained significantly higher than those in intact females. Adrenalectomy of ovariectomized females caused a further increase in receptor number.