Discordances in the Temporal Pattern of the ACTH/β-Endorphin Releasing Effects of Synthetic CRFs and Partially Purified Bovine CRF in a Superfusion System

Summary

Temporal characteristics of ACTH and β-endorphin secretion induced by bovine hypothalamic CRF-A (void volume) and CRF-B (Kav = 0.583) separated by Sephadex G-100 were compared to those of synthetic ovine or rat CRF, sauvagine and vasopressin. Dispersed cells or minced fragments of rat adenohypophyses perifused in a column were exposed to various secretagogues, and ACTH and/or β-endorphin concentrations of the effluent were measured by radioimmunoassays. CRF-A or CRF-B induced an immediate brisk rise of ACTH and β-endorphin within 1 min after initiation of CRF perifusion. The maximum rate of. ACTH or β-endorphin secretion was reached 1-2 min later. Hormone secretion persisted throughout a 10-min exposure to these secretagogues. More than 80% of the total ACTH or β-endorphin secretion induced by 10-min perifusion with bovine CRF occurred during exposure to CRF. With 10-min perifusion with 300 ng/ml ovine or rat CRF, the onset of the major CRF-stimulated ACTH or β-endorphin secretion was markedly delayed compared to that following bovine CRF. During perifusion with ovine or rat CRF, a modest slow increase in ACTH or β-endorphin secretion was observed. More than 60-70% of the total ACTH or β-endorphin secretion induced by 10-min perifusion with rat or ovine CRF occurred after CRF withdrawal. The ACTH secretory patterns for sauvagine were very similar to those for synthetic rat or ovine CRF. These results suggest some qualitative differences between partially purified bovine CRF and synthetic ovine or rat CRF.

Key-Words

CRF - ACTH - Endorphin - Rat - Sheep - Cattle