Regulation of 1,25-dihydroxyvitamin d3 by calcium in the parathyroidectomized, parathyroid hormone-replete rat

Oxford University Press (OUP) - Tập 4 Số 6 - Trang 929-935 - 1989
Eduardo Slatopolsky1, Murray J. Favus2, Craig B. Langman3, David A. Bushinsky2
1Universidad Central de Venezuela, Caracas, Venezuela
2The Pritzker School of Medicine, University of Chicago, Chicago, IL 60637
3Children's Hospital, Northwestern University, Chicago, IL

Tóm tắt

AbstractParathyroid hormone (PTH) is a major stimulus for the renal production of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Elevated arterial blood ionized calcium ([Ca2+]) depresses serum 1,25-(OH)2D3 in nonparathyroidectomized rats even when serum PTH is maintained at high levels by infusion. However, suppression by [Ca2+] of endogenous PTH, causing the fall in 1,25-(OH)2D3, cannot be excluded. To determine whether [Ca2+] regulates 1,25-(OH)2D3 in the absence of a variation in PTH, we parathyroidectomized (PTX) rats (post-PTX calcium levels <7.0 mg/dl), inserted arterial and venous catheters, and then replaced PTH using an osmotic pump. We varied [Ca2+] by infusing either 75 mM sodium chloride (control), 0.61 μmol/min of EGTA (EGTA), or calcium chloride at 0.61 μmol/min (low calcium) or 1.22 μmol/min (high calcium) for 24 h 5 days after surgery. Blood was then drawn from the rat through the arterial catheter. Compared with the control, [Ca2+] fell with EGTA, remained constant with the low-calcium infusion, and rose with the high-calcium infusion. 1,25-(OH)2D3 was correlated inversely with [Ca2+] in all four groups together (r = −0.635, n = 34, p < 0.001), within the control group alone (r = −0.769, n = 11, p < 0.002), and within the EGTA group alone (r = −0.774, n = 10, p < 0.003). Serum phosphorus, PTH, and arterial blood pH were not different in any group, and none correlated with serum 1,25-(OH)2D3. We conclude that 1,25-(OH)2D3 levels are regulated by [Ca2+] independently of serum PTH, phosphorus, and acid-base status, all of which support the hypothesis that [Ca2+] is a principal regulator of serum 1,25-(OH)2D3 in the rat.

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Tài liệu tham khảo

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Oxford University Press (OUP)

Tập 4 Số 6

929-935

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