Hormones of the pituitary-adrenal axis in rats bearing the Walker 256 carcinoma

Male Sprague-Dawley rats (125-150 g) were implanted intramuscularly with the Walker 256 carcinoma. After 3, 5 or 7 days, tumor-bearing rats, along with controls, were killed and plasma levels of adrenocorticotropic hormone (ACTH), beta-endorphin and corticosterone were assessed. Plasma levels of all 3 hormones declined with time following tumor implantation. Plasma levels of ACTH and corticosterone were statistically significantly less than plasma levels of these same hormones in control rats by 7 days post-implantation. Levels of these hormones were reduced by 42% and 33%, respectively, relative to control levels by 7 days. beta-Endorphin levels declined much more rapidly following tumor implantation than did either of the other 2 hormones. beta-Endorphin was significantly decreased by 3 days post-implantation and by 7 days the plasma levels of this factor were 83% lower than in control rats.