Individual lactotropes release prolactin in a temporally divergent and sexually dimorphic pattern

Recent studies reveal that individual lactotropes vary in the amount of prolactin (PRL) released from day to day and that the magnitude of these variations is gender specific. In an attempt to further elucidate the dynamics of hormone secretion by single cells, we have investigated short-term variations in PRL release from male and lactating female rat lactotropes. To this end, hormone release from individual lactotropes was monitored at 12-min intervals for up to 2 h, using a modified version of the reverse hemolytic plaque assay. We found that pituitary cells from both genders could release PRL in either an intermittent or continuous mode, but that the former pattern of secretion predominated for male lactotropes. Interestingly, the mode of hormone secretion was tightly coupled (P < 0.001) to the amount of hormone released (continuous >> intermittent), regardless of the gender of the pituitary donor. The existence of gender-specific differences in secretory modalities indicates that this fluctuating pattern of hormone secretion by individual cells is not random but regulated, perhaps through entrainment in vivo by gonadal steroids.