Changes in thyroxine, triiodothyronine and metabolic rate in the dik-dik antelope (Rhynchotragus kirkii): effects of temperature and dehydration

Abstract

1. Changes in plasma total thyroxine, triiodothyronine (T3) and metabolic rate were investigated in both hydrated and dehydrated dik-diks after prolonged exposure to ambient temperatures (Ta) of 25°C, 35°C and 15°C. 2. AtTa of 25°C, metabolic rate, T3 and T4 were 2.58 W·kg−1, 56.3 ng ml−1 and 0.93 ng ml−1 for the hydrated group, and 1.95 W·kg−1, 70.0 ng ml−1 and 0.85 ng ml−1 for the dehydrated group, respectively. 3. Exposure to 15°C increased metabolic rate and total hormonal concentrations in both groups. 4. Following dehydration and exposure toTa of 35°C a significant decrease in metabolic rate occurred in the presence of a significant increase in both T3 and T4 concentrations. 5. Levels of total plasma T3 and T4 alone are unlikely to be responsible for the decrease in metabolic rate observed in the dehydrated dik-dik antelopes.