The effect of various corticotropin-releasing factor trains on the release of adrenocorticotropin, beta-endorphin, and beta-lipotropin from perifused ovine pituitary cells.

The dynamics of the release of proopiomelanocortin-derived hormones from ovine anterior pituitary cells in response to varying pulse characteristics of ovine corticotropin-releasing factor (CRF) were investigated with an in vitro automated 15-column simultaneous perifusion system. Columns of cells were stimulated continuously or with trains of CRF pulses of varying pulse length (2-16 min), pulse period (20-160 min), and concentration, for 500 min. Ovine ACTH, beta-lipotropin, and beta-endorphin immunoreactivity were measured by unextracted RIA. Each pulse of CRF stimulated clearly defined and highly correlated (r greater than 0.9) pulses of the three pituitary hormones, suggesting similar mechanisms controlling release. In dose-response experiments, the minimum concentration of CRF in a 10-min pulse required to significantly raise the output of ACTH was 200 pM, and initial responses had not attained maximal levels with concentrations of CRF increased to 2 microM. Responses to pulsed CRF stimulation decreased with time with all stimulation patterns selected, although previously unstimulated control columns retained the initial capacity to respond. Multiple linear regression analysis showed that hormone output per pulse of CRF (43 nM) increased with increasing pulse period and pulse length. Output of pituitary hormones per unit of CRF applied decreased with pulse length but increased with pulse period. In summary, the responses of proopiomelanocortin derivatives were shown to be sensitive to abrupt increases in CRF, to reduce output under continued stimulation, and to have an inherent time lag before responding maximally to subsequent pulsed stimulation.