Adrenalectomy, dexamethasone or stress alters opioid peptides levels in rat anterior pituitary but not intermediate lobe or brain

Abstract

After boiling and extraction with 4M Guanidine HCl to inactive endogenous peptidases, the anterior and neurointermediate lobes of the rat pituitary were analysed by gel filtration and a beta-endorphin radioimmunoassay which detects proopiocortin, beta-lipotropin and beta-endorphin with equimolar sensitivity. In the anterior lobe, immunoreactive (ir) beta-endorphin was eluted in three peaks: 10% of the total immunoreactivity had an apparent M r of proopiocortin, 57% had the M r of beta-lipotropin and 27% had the M r of beta-endorphin. In the neurointermediate lobe, all beta-endorphin immunoreactivity is eluted in one peak with an apparent M r of synthetic beta-endorphin. Total (ir) Beta-endorphin levels in the anterior lobe were increased by adrenalectomy and decreased after long term administration of dexamethasone (0.2 mg/kg for 16 days) or by stress (1 hour of inescapable footshock). Levels in the neurointermediate lobe were unchanged after these treatments. Neither adrenalectomy or long term administration of dexamethasone at 0.2 mg/kg/day for 16 days had any effects on the levels of (ir) Met 5-enkephalin and (ir) Leu 5-enkephalin in the striatum, hypothalamus and neurointermediate lobe. After larger doses of dexamethasone (1 mg/kg/each 12 hrs for 7 days) (ir) enkephalin levels were increased in the striatum (150% of controls) but not in hypothalamus or neurointermediate lobe. These data further support independent avenues of post-synthetic peptide processing in the brain and pituitary lobes.