The effects of aging on the calcemic action of parathyroid hormone were evaluated. In the first and second studies, 1-, 8-, 12-, and 22-month-old male Wistar rats were parathyroidectomized (PTX) or thyroparathyroidectomized (TPTX), injected with parathyroid hormone and bled at 0, 3, 6, 9, and 12 h and plasma calcium determined. In the third study, 2-and 15-month-old TPTX rats were injected with parathyroid hormone and bled at 0, 1, 2, 5, 15, 30 and 120 minutes and plasma immunoreactive parathyroid hormone measured. Since the rats were prestarved, subsequent rise in plasma calcium is due primarily to the effect of parathyroid hormone on bone. The greatest increase in plasma calcium in PTX rats occurred 12 h after the initial injection of parathyroid hormone and was (mean ± S.E.) 2.98±0.48, 1.90±0.24, 0.45±0.19 and 0.2±0.20 mg/100 ml for 1-, 8-, 12-and 22-month-old rats respectively. The peak levels of plasma immunoreactive parathyroid hormone in young and mature rats injected with the hormone were not statistically different. The kidneys of the oldest rats (22-month-old) showed no histological evidence of overt renal disease, and the plasma creatinine and urea of the rats did not increase progressively with age. In TPTX rats, the oldest animals were again much less responsive to the calcemic action of parathyroid hormone than the younger animals. However, the inhibitory effect of aging on the calcemic action of the hormone was more marked in PTX than in TPTX rats.
ASJC Scopus subject areas
- Geriatrics and Gerontology