Pituitary and thyroid function in male cynomolgus monkeys

In four male cynomolgus monkeys, serum thyrosine was 6.2±0.9 μg/dl, and triiodothyronine was 207±12 ng/dl (mean ±SE). Kinetic studies using ¹³¹I-thyroxine and ¹²⁵I-triiodothyronine showed that the disappearance of both hormones was non-linear and best fit a biexponential equation. The metabolic clearance rates and production rates for thyroxine were 21.5±0.6 ml/kg/day and 1.34±0.23 μg/kg/day, respectively, and T1/2(β)=29.6±2.0 hours. For triiodothyronine, the metabolic clearance rate was 156.6±12.0 ml/kg/day, the production rate was 0.33±0.04 μg/kg/day, and T1/2(β) was 13.3±1.3 hours. Basal serum thyrotropin levels in five euthyroid animals were 1.4±0.6 μU/ml and increased after thyrotropin-releasing hormone to 6.7±2.2 μU/ml. Serum prolactin was 5.8±0.7 ng/ml, and it increased to 26.6±4.5 ng/ml after thyrotropin-releasing hormone. Four animals received chronic dexamethasone therapy (1 mg twice daily for 5.5. months). While baseline and thyrotropin-releasing hormone stimulated thyrotropin values were lower (0.8±0.2 μU/ml and 3.2±0.5 μU/ml, respectively), these reductions were not significant.