Endocrine And Immune Profiles Of Immature Pinnipeds

Abstract

There is increasing interest in assessing the health of individuals and populations of pinnipeds found in the North Pacific, primarily due to population declines leading to conservation concerns. This study assessed the "health" of animals by quantifying hormones associated with fat mass (leptin), lipid and water metabolism (cortisol and aldosterone), and growth and metabolism (thyroxine and triiodothyronine) as well as circulating total and differential leukocyte counts and in vitro proliferation of peripheral blood mononuclear cells (PBMC). Body mass and condition are influenced by an individual's disease and nutritional state. Glucocorticoids are known to affect the immune system and may be stimulated by a multitude of factors. I hypothesized that age or body mass would influence leukocyte counts, PBMC proliferation, and hormone concentrations in Steller sea lion (Eumetopias jubatus) pups and that the response of cortisol to an acute stressor would impact immune parameters in juvenile harbor seals (Phoca vitulina ). Further, given the inherent requirements of disturbance and animal handling necessary for sampling pinnipeds, the impact of these activities on endocrine and immune profiles was assessed. Total white blood cell (WBC) counts, neutrophil counts and T cell proliferation decreased with increasing age in Steller sea lion pups. However, no relationship between body condition index and circulating concentration of hormones quantified was detected. Circulating concentrations of cortisol, thyroxine, and triiodothyronine were influenced by the rookery disturbance. However, the variation attributed to the disturbance was low and did not alter total or differential WBC counts or in vitro proliferation of PBMC. In harbor seals, cortisol and aldosterone concentrations increased following an acute stressor which resulted in a stress leukogram. Total WBC decreased driven primarily by the decrease in neutrophil counts with simultaneous increase in lymphocytes leading to an overall decrease in neutrophil to lymphocyte ratio. These findings highlight the endocrine system's influence on the immune system in immature pinnipeds.