CHARACTERISTICS OF THE PROOPIOMELANOCORTIN SYSTEM IN THE OUTDOOR-BREDDOMESTIC GANDER - II - SEASONAL AND CIRCADIAN RHYTHMICITY - EFFECT OFETHER STRESS AND LIPOPOLYSACCHARIDE ADMINISTRATION

The responsiveness of the POMC system to exogenous stimuli and the diu rnal and seasonal rhythmicity of ACTH and beta-endorphin (beta E) in p lasma were studied in outdoor-reared domestic ganders. Plasma levels o f ACTH- and beta E-like immunoreactivities were determined by direct a nd specific radioimmunoassays. In the first series of experiments immu noreactive (ir) ACTH and beta E were measured in the plasma of male do mestic geese after 5 min of ether stress and after administration of 2 mu g/kg lipopolysaccharide (LPS). Both ir-ACTH and ir-beta E levels i ncreased 5 and 10 min after ether inhalation, but the increase in the ir-beta E concentration was only half that of the ir-ACTH. The plasma ir-ACTH levels were elevated after 60 and 120 min but not after 90 min of LPS administration; ir-beta E levels were unchanged at all time po ints. In a second series of experiments blood samples were taken on 30 March, 16 June, 4 August, and 27 October. On these days diurnal sampl ings were performed at 02:00, 06:00, 10:00, 14:00, 18:00, and 22:00 h. A two-way analysis of variance showed significant diurnal and seasona l changes for both hormones and significant interaction between the di urnal and seasonal levels. The highest daily mean values of the plasma ir-ACTH and ir-beta E concentrations were measured in June. The maxim um of the ir-ACTH level was at 10:00 h in March and August, but at 22: 00 h in June and October. The changes in ir-beta E concentrations para lleled those of ir-ACTH, but the changes did not reach statistical sig nificance in every case. (C) 1998 Academic Press.