Changes in basal secretion rates of thyroxine and 3,3',5-triiodothyronine from the thyroid gland during aging of the rat.
The present experiments were carried out to examine age-related changes in the basal secretion rates of both thyroxine (T4) and 3,3',5-triiodothyronine (T3) from the thyroid gland. The experiments were performed on male Wistar rats of three different ages, i.e., (1) adult rats of 6-8 months old, (2) middle-aged rats of 25-26 months old, and (3) aged rats of 28-30 months old. The rats were anesthetized with 1.0% halothane. The thyroid venous blood as well as systemic arterial blood was collected and secretion rates of both immunoreactive T4 (iT4) and T3 (iT3) from the thyroid gland were calculated from the differences in concentrations of iT4 and iT3 in these two blood plasmas, and from the flow rate of thyroid venous blood plasma. The secretion rates of thyroid iT4 in the three different age groups were as follows: 483 +/- 68 pg/min (mean +/- S.E.) in the adult rats, 598 +/- 104 pg/min in the middle-aged rats, and 491 +/- 150 pg/min in the aged rats. There were no significant differences among the secretion rates of thyroid iT4 in these rats. The secretion rates of thyroid iT3 in the groups were as follows: 36.2 +/- 7.5 pg/min in the adult rats, 58.9 +/- 13.9 pg/min in the middle-aged rats, and 61.3 +/- 7.6 pg/min in the aged rats. The secretion rates of thyroid iT3 in both middle-aged and aged rats were approximately 1.6-1.7 times as high as the value in adult rats (p less than 0.05). These results indicate that the thyroid secretion of iT4 is well maintained, while that of iT3 increases during aging.
Hotta
H
H
Department of Autonomic Nervous System, Tokyo Metropolitan Institute of Gerontology, Japan.
Ooka
H
H
Sato
A
A
D000375:Aging / Q000502:physiology*; D000818:Animals; D001158:Arteries; D001783:Blood Flow Velocity; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013961:Thyroid Gland / Q000098:blood supply / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood / Q000378:metabolism*; D014284:Triiodothyronine / Q000097:blood / Q000378:metabolism*; D014680:Veins
D014284:Triiodothyronine; D013974:Thyroxine