AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 4 1003-R1009, Copyright © 1991 by American Physiological Society
Albumin enhances negative feedback effect of cortisol on ACTH release from sheep pituitary cells
R. J. Kemppainen, C. A. Zerbe and J. L. Sartin
Department of Physiology and Pharmacology, Auburn University College of Veterinary Medicine, Alabama 36849.
Albumin binds circulating glucocorticoids such as cortisol and consequently
may modify the biological activity of these steroids by altering access to
target cells. Because albumin is likely present in pituitary interstitial
fluid, this study was designed to compare the negative feedback effect of
cortisol on pituitary adrenocorticotropic hormone (ACTH) secretion from
isolated sheep pituitary cells perifused with media containing 0.25% or 2%
bovine serum albumin (BSA). Pituitary cells released less (P less than
0.05) immunoreactive ACTH in response to a 10-min treatment with 10 nM
ovine corticotropin-releasing hormone (oCRH) after 45 min pretreatment with
0.5 microM cortisol when media contained 2% BSA vs. 0.25% BSA. A similar
enhancement in negative feedback potency was observed when cells were
treated with cortisol followed by 1 nM oCRH for 60 min, with an additional
10 min co-addition of arginine vasopressin. This potentiation was not
observed when a noncortisol binding protein, ovalbumin, was substituted for
BSA. However, the potentiating effect of albumin was present in perifused
rat pituitary cells, indicating that the effect was not species specific.
We conclude that albumin enhances the negative feedback potency of cortisol
in anterior pituitary corticotrophs and that the process may operate under
physiological conditions to enhance cell specific delivery of this steroid
to appropriate targets.
