Serum Concentrations Of Immunoreactive Parathyroid Hormone Research Articles

Prostaglandin E production and hypercalcaemia in rats bearing the Walker carcinosarcoma.

The hypothesis that there is prostaglandin-mediated hypercalcaemia associated with the Walker carcinosarcoma in the rat was tested by measuring PGE production during the development of the hypercalcaemia, and determining the effects of inhibition of prostaglandin synthesis on serum calcium concentration. Parathyroid hormone (PTH) activity was estimated by the determination of the serum concentration of immunoreactive PTH. There was a 3-fold increase in the urinary excretion of 7α-hydroxy-5,11-diketotetranor-prostane-1,16-dioic acid (PGE-M), a major urinary metabolite of the E prostaglandins from basal levels. Treatment with indomethacin, a potent inhibitor of prostaglandin synthesis, did not lower serum calcium concentrations with two different doses (1·6 mg/kg/day orally and 5 mg/kg/day i.m.); effective inhibition of prostaglandin synthesis was demonstrated by the suppression of PGE-M excretion rates below basal levels. Serum concentrations of immunoreactive PTH were not significantly altered by either tumour growth or indomethacin. Dexamethasone (0·5 mg/kg/day i.m.) attenuated both the increased urinary excretion of PGE-M and the rise in serum calcium concentration, suggesting that one or several lipoxygenase products might be the actual mediators of the hypercalcaemia. We conclude that the hypercalcaemia in the rat with Walker carcinosarcoma is probably not mediated by E-prostaglandins and probably not by any other product of the cyclo-oxygenase pathway. The increased PGE turnover may be considered as a biochemical marker of tumour load, but not as an indicator of a prostaglandin-mediated hypercalcaemia.

The Acute Effects of 1,25-Dihydroxycholecalciferol on Serum Immunoreactive Parathyroid Hormone in the Dog*

There is considerable evidence which suggests that the parathyroid gland may be a target for vitamin D metabolites. To investigate the effects of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] on parathyroid hormone (PTH) secretion, the serum concentrations of immunoreactive PTH (IPTH), calcium, and phosphate were measured over a 12-h period after the single iv injection of 1 μg (2.4 nmol) 1,25(OH)2D3 in five normal and nine vitamin D-deficient puppies. In the vitamin Ddeficient animals, the mean serum calcium increased significantly by 8 h, and at 12 h was approximately 1 mg/dl above the basal value. Serum phosphate concentrations showed no significant change after 1,25(OH)2D3. An acute, transient increase in serum IPTH concentration followed the injection of 1,25(OH)2D3 in most but not all of the vitamin D-deficient puppies. However, the increase was not statistically significant in the mean serum IPTH concentration for the group. At 12 h, the mean IPTH concenration had decreased significantly from the bas...