Effects of aging on the in vivo release of thyrotropin (TSH), triiodothyronine, and thyroxine induced by TSH-releasing hormone in the cynomolgus monkey (Macaca fascicularis).

We demonstrated the usefulness of the human TSH immunoradiometric assay for the measurement of cynomolgus monkey serum samples, and investigated the age-related changes in serum levels of TSH, T3, and T4, in laboratory-bred cynomolgus monkeys. In the females, age-related decrease in the serum TSH concentration was not observed, but decreases in serum T3 (2.1-1.4 ng/ml) and T4 (59-48 ng/ml) were observed. However, the serum T4 level of the oldest group (19 yr old) significantly increased as compared with the 11-yr-old group (56 ng/ml). In the males, age-related decreases in the serum TSH, T3, and T4 were observed. Furthermore, significant increases in serum TSH concentrations after injection of TRH were detected. The oldest group (16 yr old) showed the highest response among the five different age groups tested. However, the highest responses of T3 and T4 release from the thyroid gland after TRH injection were obtained by the 10-yr-old group. The results suggest that the sensitivity of the thyroid gland to TSH and/or the productive or releasing capacities of T3 and T4 in the thyroid gland decreased with increasing age in this primate species.