Peptides. Vol. 7, pp. 603-607. 1986. ©Ankho InternationalInc. Printed in the U.S.A. 01%-9781/86 $3.00 + .00 The Preferential Release of Beta-Endorphin From the Anterior Pituitary Lobe by Corticotropin Releasing Factor (CRF) ELIZABETH A. YOUNG, JAMES LEWIS* AND HUDA AKIL Mental Health Research Institute, The University of Michigan, Ann Arbor, MI 48109 and *Department of Psychology, University of California-Los Angeles, Los Angeles, CA 90024 Received 10 January 1986 YOUNG, E. A., J. LEWIS AND H. AKIL. The preferential release of beta-endorphinfrom the anteriorpituitary lobe by Cortieotropin Releasing Factor (CRF). PEPTIDES 7(4) 603-607, 1986.--Although a number of investigators have shown that release of ACTH is accompanied by the release of Beta-endorphin (B-End) and Beta-lipotropin (fl-LPH), the propor- tion of the latter two peptides released with stress or by CRF is unclear. To evaluate directly the release of B-End versus B-LPH from the anterior lobe, we used molecular sieving of plasma and subsequent radioimmunoassay to measure release of both B-End and B-LPH into plasma after thirty minutes of inescapable intermittent footshock. We found a substantial increase in circulating B-End which appears to be of anterior lobe origin. The B-End does not appear to represent peripheral conversion of B-LPH to B-End since the ratio of B-LPH:fl-End released remained constant between five and thirty minutes of stress, and the rate of disappearance of B-LPH is slower than the rate of disappearance of fl-End following the termination of stress. Further confirmation of these findings was obtained by examining the POMC derived peptides released by pituitary cell suspensions in the presence and absence of oCRF. While unstimulated release consisted of equal proportions of B-End and B-LPH, stimulation of the anterior lobe cell suspensions with oCRF resulted in the release of two-fold more B-End than B-LPH. Beta-endorphin Anterior pituitary lobe Corticotropin releasing factor Radioimmunoassay Beta-lipotropin THE post-translational processing of proopiomelanocortin (POMC) to Beta-endorphin (/3-End) and Beta-lipotropin (fl- LPH) differs in the anterior and intermediate lobes of rat pituitary. In the anterior lobe (AL), the molar ratio of/3-End to fl-LPH is approximately 1:2, while in the intermediate lobe (IL), virtually all of the precursor is processed to/3-End sized or smaller material [2, 5, 12]. One might expect, there- fore, that the products released during stimulation of each lobe would reflect these molar ratios; the anterior lobe should release primarily/3-LPH, while the IL would release /3-End 1-31 or modified forms of fl-End (e.g., alpha N-acetylated fl-End 1-27). Consequently, the circulating levels in plasma should reflect both anterior and intermediate lobe contributions. At rest, the majority of B-End immunoreactivity circulat- ing in rat plasma is fl-End 1-31 size [1]. The source of this plasma fl-End is presumed to be intermediate lobe, since a sizeable proportion is alpha N-acetylated fl-End (NAc fl-End 1-31) [1]. In contrast, stress activates primarily the anterior lobe of the pituitary to release ACTH accompanied by both fl-LPH or fl-End [6]. Thus, if the released material truly reflects the molar ratios of stored/3-LPH and/3-End in the anterior lobe, after stress, approximately 2/3 of the newly released/3-End like immunoreactivity in plasma should be /3-LPH size. However, the existence of subpopulations of releasable pools has been shown for POMC derived peptides in the IL of the frog [8]. Similarly, we have recently shown that after repeated phasic stress the IL releases primarily NAc fl-End 1-31. In the IL, however, this peptide is not the most abun- dantly stored [I], suggesting the existence of specifically re- leasable pools. Whether such pools exist for anterior lobe POMC derived peptides is not known. Using mouse anterior lobe primary cell cultures and a double labelling technique, Allen et al. [3] showed that the contents of older ACTH containing granules were preferentially released over newly synthesized material, when the culture was stimulated by partially purified rabbit corticotropin releasing factor. As expected, these mature granules contained both fl-LPH and fl-End. However, this study did not address the issue of differential release of fl-LPH versus fl-End. Consequently, it is not clear if the release of ACTH from the anterior lobe is accompanied primarily by the release of fl-LPH, as would be expected from the molar ratio, or, if significant amounts of fl-End can be released. Since older granules would have more time to continue processing, even the slowest process- ing reactions may have time to proceed to completion. Thus the preferential release of the more mature ACTH granules suggests that these granules could contain the most proc- essed form, that is, B-End. 603