絕經後骨質疏鬆腸鈣代謝吸收障礙之研究

The Research of Intestine Calcium Absorption Disturbance of post-menopausal Osteoporosis

林文彬(Wen-Ping Lin)

《中醫藥研究論叢》 10卷1期 (2007/03) Pp. 175-205

https://doi.org/10.6516/TJTCM.200703_10(1).0016

摘要

絕經後骨質疏鬆症乃因雌激素缺乏導致骨吸收增加和腸鈣吸收下降，而引起負鈣平衡所致。然而高鈣攝入不能替代雌激素，並且對骨質疏鬆較嚴重的病人不宜單獨用補鈣治療。
低鈣攝入時，機體會產生一系列適應性反應來保留體鈣，其途徑有二；一是血PTH升高→腎lα羥化酶活性增強→腎1, 25(OH)2D3合成增加→血l, 25(OH)2D3升高→小腸上段鈣主動吸收增加→血鈣正常，同時糞鈣排出減少。
另一途徑是血PTH升高→腎遠端小管鈣重吸收增加→血鈣正常，同時尿鈣排出減少。
這兩條途徑的作用，一是“開源”，即是儘可能通過腸道多吸收鈣；二是“節流”，即儘可能通過腎臟多保留鈣；最終目的是保持血鈣穩定。
鈣結合蛋白和鈣離子的親和力是鈣與小腸上皮刷狀綠親和力的4倍。鈣離子從腸道內進入細胞後，還必須通過一種叫做ATP依賴性漿膜鈣泵(PMCP)系統，將其泵入血循環。PMCP對鈣離子的親和力大約是鈣結合蛋白的2.5倍，其可被活性維生素D3啟動。
在健康成人，低鈣膳食時，新的骨重建單位啟動頻率增加，骨轉換增加；高鈣時，骨轉換下降，因低鈣攝入，血清鈣下降，刺激PTH分泌，加速骨轉換，高鈣攝入時則相反，因此補鈣能矯正缺鈣引起的繼發性副甲狀腺亢進。
影響鈣吸收的因素有：膳食中鈣攝入量、磷的影響、鈣的狀態、胃腸道PH值、飲食中草酸和植酸、膳食中的纖維、蛋白質等。許多消化系統疾病會影響鈣吸收，與骨質疏鬆症有密切的關係，如胃切除術、慢性肝病、炎症性腸病等。
雌激素不足是引起絕經後腸鈣吸收障礙的原因，絕經後腸鈣吸收功能障礙並不能單純從繼發性PTH和維生素D合成下降來解釋。可能是由於雌激素不足導致腸道功能缺陷，小腸對維生素D處於不敏感或抵抗狀態。雌激素治療可以增加小腸對維生素D的敏感性。
雌激素能直接調節維生素DR表達，而不是間接通過PTH和1, 25(OH)2D3節維生素DR。因此，有人推測雌激素能直接作用於小腸的ER而調節鈣吸收。絕經後或卵巢切除後雌激素不足，直接影響雌激素受體而導致腸鈣吸收障礙。

關鍵字

腸鈣 ； 雌激素 ； 骨質疏鬆

並列摘要

The reason of post-menopausal osteoporosis is estrogen deficiency cause the bone absorption increase and the intestines calcium absorption decrease to the negative calcium balance. However the high calcium takes cannot substitute the estrogen, and not suitable alone uses to the osteoporosis serious patient by the calcium treatment.
When the low calcium in diet, the body can produces a series of compatibilities to respond retains the calcium, its always has two way:
one way is to elevate the blood PTH-＞ the renal la hydroxide activeness to strengthen-＞the renal 1, 25(OH)2D3 synthesis to increase-＞ the blood 1, 25(OH)2D3 to be elevated-＞ the upside small intestine calcium initiative absorption to increase-＞the blood calcium to be normal, simultaneously the excrement calcium discharges the reduction.
Another way is blood PTH to elevate-＞the renal distal tubule increase calcium heavy absorption-＞the blood calcium to be normal, the urine calcium discharge to reduce simultaneously.
These two ways function, one is opens the source, is as far as possible through the intestinal tract to absorb calcium; another one is reduces expenses, as far as possible through kidney to retain calcium; The final goal is to maintains the blood calcium to be stable.
The affinity of calbidin with calcium ion is 4 times of calcium with the intestinal epithelium. The calcium ion enters the cell after the intestinal tract, but must be through PMCP system, pumps it into circulation. The affinity of PMPC to the calcium ion probably 2.5 times to the calbidin, it may be activated by vitamin D3.
When healthy adult have low calcium meals, the new bone reconstruction unit had start frequently, the bone transfer increase. When have high calcium, the bone transfer down low. Because the low calcium takes in, the serum calcium drops, and stimulates the PTH secretion, accelerate the bone transfer; the high calcium takes in when then opposite. Therefore supplement the calcium can able to rectify secondary hyper-parathyroid.
The influence factor of calcium absorption that include: the calcium quantity in the meals tack in, the phosphorus influence, the calcium condition, the PH value of Gastro-Intestine tract, the diet acid, the fibers in meals, the protein etc, there are many digesting system disease can affect the calcium absorption that has close relationship with osteoporosis, such as stomach excise, chronic liver disease, inflammatory intestine disease.
The estrogen insufficiency is the reason of postmenopausal intestine calcium absorption disturbance. But, the intestine calcium absorption disturbance of postmenopausal cannot be simply explained by the depress of secondary PTH and vitamin D synthesis. May be the estrogen insufficiency caused the intestinal function flaw, the small intestine at to vitamin D is insensitive or resistance condition. The estrogen treatment can increase the small intestine sensitive to vitamin D
The estrogen can control vitamin DR expression directly, but is not indirectly through PTH and 1, 25(OH)2D3 to adjust vitamin DR. Therefore some people think about that the estrogen can act the small intestine ER directly to adjust the calcium absorption. The postmenopausal or after the ovary excision, that estrogen insufficiency that affect the estrogen receptor to the intestine calcium absorption disturbance.

並列關鍵字

Intestine calcium ； estrogen ； osteoporosis