Chronic stimulation of anterior pituitary cell cultures with CRF leads to the secretion of lipotropin.

Time course studies have shown that the secretion of beta-endorphin-related peptides from primary cultures of rat anterior pituitary reached a plateau after 1 h of stimulation by 10(-7) M corticotropin-releasing factor (CRF); the major peptide released was beta-endorphin 1-31. Further incubation of the cells with CRF led to a decline in the rate of secretion and to the appearance of a different pattern of peptides in which lipotropin was the principal component; analysis of the peptides remaining in the cells, however, showed that beta-endorphin was still the major peptide. Chronic blockade of the anterior pituitary cells with dexamethasone (10(-6) M) resulted in diminished secretion and the released peptides were found to contain a higher proportion of the intact prohormone, pro-opiomelanocortin (POMC). In all the experiments involving stimulation of the pituitary cells with CRF or blockade with corticosteroids it was observed that the pattern of secreted peptides differed from the intracellular patterns, which suggests that selective release can occur from vesicles or cells that contain different segments of POMC.