Antidiuretic hormone and angiotensin II plasma concentrations in febrile Pekin ducks.

1. The objective of this study was to determine the changes in plasma concentrations of the hormones arginine vasotocin (AVT) and angiotensin II (AII) associated with lipopolysaccharide (LPS)-induced fever in Pekin ducks. 2. LPS, intravenously administered into conscious birds at doses of 1, 10 and 100 microgram kg-1, caused dose-dependent and monophasic increases in body temperature, with fever index values of 3.5, 7.0 and 10.6, respectively. 3. Plasma AVT concentrations also increased with the progression of the fever, with the largest elevation (from 8.4 +/- 1. 6 to 25.2 +/- 3.2 pg ml-1; means +/- s.e.m., n = 7) being caused by the highest dose of LPS. 4. Plasma AII concentrations did not significantly change from basal values (mean of 45.5 +/- 6.3 pg ml-1 for all groups) during the acute phase of the fever response. 5. The osmotic status of the birds, as indicated by plasma osmolality and electrolyte values, did not significantly change in any of the experimental animals. 6. The elevation of AVT in avian fever leads to speculation about a possible antipyretic action of this hormone, which would have particular relevance to understanding the evolution of fever.