Correlation between mammary prolactin receptors of lactating mice and litter weight

Correlations between numbers and dissociation constants of mammary prolactin receptors of lactating mice and litter weight were examined. The apparent numbers and dissociation constants of mammary prolactin receptors were obtained from Scatchard plots with inhibition of iodine-125 prolactin binding by various concentrations of unlabeled prolactin. Litter weight measured 5 h after separation from the mother showed a nearly quadruple, almost linear increase during the first 15 d after birth. The dissociation constant for prolactin binding was fairly constant through lactation and did not correlate with either number of prolactin receptors or litter weight. The number of prolactin receptors in mammary cells increased rapidly in early lactation, reached a maximum at mid-lactation, began to decrease thereafter, and was correlated closely with litter weights on d 5 (.70) and 10 (.64) postpartum, suggesting that number of prolactin receptors represents the lactational potential of the lactating mouse.