Seasonal Changes of Serum Leptin, Triiodothyronine, and Thyroxine Levels in Arabian Mares (1)

The objective of study was to determine seasonal changes of leptin, triiodothyronine, and thyroxine and to determine whether an effect of thyroid hormones on leptin levels in Arabian mare. Blood samples were collected via jugular venipuncture from 16 Arabian mares during breeding and non-breeding season. Hormone concentrations were measured by radioimmunoassay. Mean concentrations of leptin were greater in breeding season (2.84±0.19 ng/mL) than non-breeding season (1.91±0.16 ng/mL). Mean concentrations of triiodothyronine were greater in non-breeding season (221±31.61 ng/dL) than breeding season (105±5.91 ng/dL). No differences in thyroxine levels were observed between breeding (30.30±1.83 nmol/L) and nonbreeding season (36.34±4.28 nmol/L). A significant correlation between leptin and triiodothyronine existed for breeding season (r= 0.860, P 0.05). In non-breeding season, there was a significant correlation between triiodothyronine and thyroxine (r= 0.791, P<0.01). These seasonal differences and relationships between leptin, triiodothyronine, and thyroxine suggest that secretion of leptin may be affected by thyroid function in Arabian mares.