Changes of urinary cyclic AMP excretion and plasma parathyroid hormone levels before and after parathyroidectomy in patients with primary hyperparathyroidism

Late increase in serum 1,25-dihydroxyvitamin D one month after surgery for adenomatous hyperparathyroidism

This study was designed to follow the evolution of serum 1,25(OH)2D after surgery for primary hyperparathyroidism. Ten patients were studied before and for up to 85 d after removal of a single parathyroid adenoma. Blood and 24 h urine were obtained at various time points, for the measurement of serum or urinary phosphate and calcium indices. Before surgery, serum calcium (2.91 +/- 0.06 mmol/l; mean +/- SEM), parathyroid hormone (354 +/- 47 pg/ml) and 1,25(OH)2D (61.2 +/- 7.8 pg/ml) were elevated while serum phosphate (1.01 +/- 0.07 mmol/l) tended to be low. Relative hypoparathyroidism was evident for up to 5 d after surgery with the lowest value for serum parathyroid hormone (41 +/- 16 pg/ml) on day 1, serum calcium (2.12 +/- 0.06 mmol/l) on day 3 and highest value for serum phosphate (1.41 +/- 0.13 mmol/l) on day 5. As expected, serum 1,25(OH)2D levels decreased to 35.9 +/- 4.2 pg/ml 24 h after surgery. Stabilization of serum and urinary parameters to normal values was seen between day 5 and day 27; the only exception was serum 1,25(OH)2D, which increased again at day 27 to 57.6 +/- 5.0 pg/ml, a value as high as that before surgery. It was still elevated at day 50 (58.3 +/- 4.3 pg/ml), but returned towards normal values in three out of four patients (44 +/- 3.9 pg/ml) by day 80. No variation in 25(OH)D or 24,25(OH)2D was seen throughout the study. 1,25(OH)2D values could be related to serum parathyroid hormone values before surgery (r = 0.659, P less than 0.05) but not after. The secondary increase in serum 1,25(OH)2D could not be related to variations in serum calcium, phosphate, parathyroid hormone or diet. Further studies will be required to explain this phenomenon.

Effect of renal function on renal responsiveness to parathyroid hormone in primary hyperparathyroidism and chronic renal failure

The effect of renal function on the cyclic AMP (cAMP) response to exogenous parathyroid hormone (PTH) was examined in patients with chronic renal failure (n = 22) and primary hyperparathyroidism (n = 19). In the patients with chronic renal failure there was marked resistance to the effect of exogenous PTH. In primary hyperparathyroidism the cAMP responses were variable; most of the patients with an abnormally small response having impaired renal function. After parathyroidectomy, responsiveness improved to varying degrees. In three patients repeatedly tested up to several months after parathyroidectomy, the recovery of responsiveness was a gradual process which began within days but did not, however, return to normal. Thus, there was an irreversible component to the resistance to PTH in these patients. A strong negative correlation between plasma creatinine and the cAMP response to PTH (P less than 0.001) was found in a group of patients, some with treated primary hyperparathyroidism and some with chronic renal failure. Thus, renal impairment is an important, but probably not the sole, contributory factor involved in the irreversible resistance to the action of PTH in hyperparathyroidism.

Acute effects of removal of parathyroid adenoma on plasma and urinary hydroxyproline levels

This study was carried out to investigate early effects of parathyroidectomy (PTx) on bone matrix collagen metabolism. Eleven patients suffering from primary hyperparathyroidism were studied by measuring urinary excretion of hydroxyproline (OHPr) and cAMP in samples collected before PTx and, on the day of surgery, at intervals of 1-3 h for the first 10 h and then at longer intervals. In six patients nondialyzable urinary OHPr and free plasma aminoacid levels were also assayed. We found that the average period required for OHPr/Cr ratio and plasma OHPr to reach normal values was longer than the mean time required for cAMP/Cr ratio to reach normal limits. In all patients the total amount of nondialyzable OHPr decreased in the first 24 h after PTx but thereafter a daily increase in the urinary excretion of nondialyzable component was seen, so that the fractional amount of nondialyzable OHPr in the fourth postoperative day (26.8 +/- 5.2 SE) was significantly higher than that of preoperative one (6.1 +/- 1.0; p less than 0.02). Our results confirm that PTx induces a reduction in the rate of bone collagen resorption and indicate that changes of OHPr/Cr ratio and free plasma OHPr values may be considered useful indices of successful parathyroid surgery, even though they lag behind those of cAMP. The different behavior of total and nondialyzable OHPr after surgery indicates that acute deficiency of parathyroid hormone induces a positive uncoupling of the two processes of bone remodeling, thus supporting the view that the acute direct effect of the hormone on bone formation is an inhibition of this process.

The 24-h urinary cyclic adenosine 3', 5' monophosphate/creatinine ratio: an useful approach to the diagnosis of parathyroid disorders and function

24-h urinary cyclic adenosine 3', 5'-monophosphate/creatinine (cAMP/Cr) ratio was assessed in 10 patients with hypoparathyroidism, 6 with primary hyperparathyroidism, 7 with normocalcemic hypercalciuria and recurrent nephrolithiasis, 14 with osteomalacia, 25 with Paget's disease and 53 with symptomatic postmenopausal osteoporosis. In hypoparathyroid subjects the mean values of 24 h cAMP/Cr ratio were significantly lower than the control values, whereas in patients with parathyroid adenoma the mean values were higher and fell after parathyroid surgery. Patients with nephrolithiasis due to absorptive hypercalciuria showed low or normal cAMP/Cr ratio, whereas in those with osteomalacia and mean values of cAMP/Cr ratio were significantly higher than the control values and decreased after vitamin D treatment. The mean value of the 24 h urine cAMP/Cr ratio was normal in patients with Paget's disease or postmenopausal osteoporosis and increased significantly after long term treatment with calcitonin or diphosphonate. This increase paralleled a significant decrease of calcium plasma level. A significant improvement of fractional calcium absorption was observed in women with postmenopausal osteoporosis at the end of treatment with calcitonin or diphosphonate.