Meeting Abstract
15.7 Monday, Jan. 4 Seasonal changes in leptin and ghrelin concentrations associated with intake and body condition of captive Steller sea lions RICHMOND, J.P.*; KEOGH, M.; ATKINSON, S.; ZINN, S.A.; University of Connecticut, Storrs; University of Alaska Fairbanks; University of Alaska Fairbanks; University of Connecticut, Storrs julie.richmond@uconn.edu
Leptin and ghrelin are peripheral endocrine signals that regulate body fat and appetite in mammals, and are involved in photoperiod-mediated, seasonal regulation of food intake. While intake is known to vary seasonally in Steller sea lions (SSL; Eumetopias jubatus), seasonality of hormones that regulate intake is not known. The objectives of this study were to 1) validate assays that accurately and precisely quantify serum concentrations of leptin and ghrelin, 2) determine the seasonal pattern of these hormones, and 3) quantify their relationship to body composition and intake in SSL. Blood samples were collected monthly for 18 mo from captive adult SSL (n=4). Intake was recorded daily. Hormones were quantified using kits for Human ghrelin RIA and Canine leptin ELISA. Sensitivity, recovery of mass, assay precision, parallelism and dilution linearity were determined for each assay. Both ghrelin and leptin immunoassays exhibited validation parameters indicating both assays provide accurate and precise quantification of serum hormone concentrations. Intake and ghrelin were greatest (P=0.02) in the winter (2332±139 pg/ml) and declined in the summer (1048±191 pg/ml). In contrast, leptin followed the opposite pattern with the greatest concentrations (P=0.01) observed in summer (8.5±0.7 ng/ml; winter 4.9±0.9 ng/ml) when animals’ intake was reduced. These results suggest that ghrelin and leptin are strongly influenced by season in SSL. The insensitivity of ghrelin and leptin to intake in the winter may facilitate SSL foraging by stimulating appetite. The contrasting pattern in summer may inhibit appetite during the summer breeding season when SSL typically fast for extended periods of time.
