Abstract
To obtain further information on the negative calcium balance caused by Cd, the factors associated with serum calcium and phosphorus homeostasis other than inhibition of intestinal calcium absorption were studied by using urinary cyclic 3',4'-adenosine monophosphate (cAMP). In rats exposed to Cd for 30 d, the levels of urinary excretion of cAMP after treatment with parathyroid hormone (PTH), parathyroidectomy (PTX), or 1 alpha-hydroxycholecalciferol (1 alpha-OH-D3) showed almost the same patterns as those of control rats: the response of urinary cAMP to treatment with PTH was not influenced by continuous oral administration of Cd. On the other hand, in rats exposed to Cd for 90 d without the other three treatments, the amount of urinary excretion of cAMP was markedly higher than in control rats. In PTX rats exposed to 90 d of Cd, urinary cAMP was unchanged, but it was markedly increased when the parathyroid was intact, with or without treatment with PTX. This phenomenon indicated hyperparathyroidemia in response to continuous oral administration of Cd for 90 d. The negative calcium balance with hyperparathyroidemia occurred after continuous oral administration of Cd and developed via increased urinary excretion of calcium. Urinary excretion of cAMP in Cd-exposed rats was unaffected by the administration of 1 alpha-OH-D3.
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