筋緊張性ジストロフィー症における副甲状腺ホルモン調節機構の異常に関する研究
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Although the presence of bone abnormalities has been well known in myotonic dystrophy (MyD), details about calcium metabolism in this condition remain unclear. We already reported that the intestinal calcium absorption is increased in MyD patients due to the elevation of plasma 1, 25 (OH) <SUB>2</SUB> D level. We also reported that serum immunoreactive parathyroid hormone (iPTH) levels and Nephrogenous cyclic AMP (NcAMP) levels are increased in MyD patients. This study was designed to elucidate the mechanism of hyperparathyroid state in MyD patients. <BR>Intravenous calcium tolerance test was performed in 7 patients with MyD and 7 control subjects, 3 patients with other neuromuscular disorder and 4 healthy subjects. Calcium was stepwisely infused at the concentration of 0,104.7,194.9 and 235.5mg every hour. <BR>The basal plasma calcium levels were significantly higher in MyD (9.79 ± 0.27mg/dl, Mean ± SD) as compared with control subjects (9.50±0.19; p<0.05). Basal serum iPTH levels were also significantly higher in MyD (514.0±188.9pg/ml) than those in control subjects (333.7±113.5; p<0.05). <BR>After calcium infusion, serum calcium levels were increased in both groups, but the levels of serum calcium remained significantly higher in MyD than those in control subjects. On the other hand, urinary calcium excretion levels were not different between the two groups. At the same time, %TRP and calcium clearance were significantly lower in MyD than control subjects. <BR>In spite of larger increments of serum calcium level after 235.5mg/h of calcium infusion in MyD (MyD 2.32±0.63mg/dl, control 1.84±0.59), the levels of serum iPTH in MyD remained significantly higher than control subjects (MyD 367.14±134.10pg/ml, control 175.43±67.57; p<0.01). Suppressibility of serum iPTH and NcAMP were decreased in MyD (27.1±13.9% and 58.8± 25.2, respectively) as compared with control subjects (41.1 ±7.1% and 69.6 ± 24.2, respectively). <BR>Therefore, the regulation of iPTH level by serum calcium seems to be less sensitive in MyD. This might be the reason why urinary calcium excretion levels were not different between the two groups while serum calcium levels were higher in MyD. <BR>It may be concluded that MyD patients are in a state of hyperparathyroidism, and this might be due to the insensitivity of the control mechanism of parathyroid hormone secretion by serum calcium level.
- 一般社団法人 日本内分泌学会の論文