Prolactin Causes the Dissociation of Prolactin from Membrane Receptor in Lactating Mouse Mammary Action of High Prolactin Concentration Plasma Cell:

In order to characterize the dissociation of receptor-bound prolactin (PRL) by mammary cells, cells were prepared from lactating mice by collagenase digestion and loaded with PRL. The dissociation reaction was performed in the presence of PRL. In the concentration range 1 ng/ml-1 μg/ml examined, PRL at higher than 10 ng/ml accelerated the dissociation of PRL in a concentration-dependent manner. The action of PRL on dissociation was completed within a short period. At the end of the 1 h-incubation period, the dissociation rate constant (k_,) was about 2 times larger in the presence of 1 μg/ml of PRL than in its absence. The action of PRL occurred predominantly at the level of the plasma membrane receptor. Mammary cells with greater PRL-binding capacities had larger k_1 in response to PRL. The present data showed that the dissociation of PRL from the receptor was influenced by the concentration of PRL and by the PRL-binding capacity of the cell. The rate of PRL-receptor interaction is expressed by the equation of k_1(PRL-bound receptors). It is probable that at exceedingly high levels of PRL, the PRLreceptor interaction occurs more frequently in the presence of PRL-dependent dissociation than in its absence.