CHARACTERISTICS OF THE PROOPIOMELANOCORTIN SYSTEM IN THE OUTDOOR-BREDDOMESTIC GANDER - I - ACTH AND BETA-ENDORPHIN LEVELS IN THE BRAIN, PITUITARY, AND PLASMA

Immunoreactive (ir-) adrenocorticotropic hormone (ACTH) and beta-endor phin (beta E) levels were determined in seven brain regions, in the th ree pituitary lobes, and in the plasma of the domestic gander by speci fic radioimmunoassays. In the brain regions studied the relative conce ntrations of ir-ACTH and ir-beta E were the highest in the mediobasal hypothalamus and in the paraventricular nucleus. There were lower leve ls of these peptides in the supraoptic nucleus, in the septum, and in the dorsal thalamus. Very low ir-ACTH and -beta E contents were found in the archistriatum and in the lobus parolfactorius. In the pars dist alis of the pituitary gland the cephalic lobe contained about 10 times more ir-ACTH (3596 pmol/lobe) and 4 times more ir-beta E (867 pmol/lo be) than the caudal lobe (383 pmol/lobe and 189 pmol/lobe, respectivel y). Sephadex G-50 chromatography of pooled cephalic and caudal lobe ex tracts resulted in two distinct ir-beta E peaks, with elution volumes corresponding to the mammalian beta-lipotropin and beta E, and three i r-ACTH peaks, the second one coeluting with mammalian ACTH. In the neu ral lobe the ir-ACTH/-beta E concentrations were similar to those in t he hypothalamus. Resting plasma ir-ACTH (12.8 +/- 1.47 pmol/ml) but no t ir-beta E (31.4 +/- 1.22 pmol/ml) levels were significantly increase d following castration (to 41.4 +/- 1.11 pmol/ml). Serial blood sampli ng indicated pulsatile ir-beta E secretion (mean, coefficients of vari ation, and minimum-maximum range: 17.5, 62.78, and 2.9-49.7, respectiv ely, for gander 1 and 23.3, 62.85, and 5.00-61.5, respectively, for ga nder 2). (C) 1998 Academic Press.