Effects of chronic metabolic alkalosis on Ca2+, PTH and 1,25(OH)2D3 in the rat.
The effect of chronic metabolic alkalosis on arterial blood ionized calcium concentration ([Ca2+]) and the levels of serum parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is difficult to predict. Although a fall in pH directly decreases [Ca2+], chronic alkalosis reduces urine calcium excretion, which could elevate [Ca2+]. [Ca2+] modulates the serum level of PTH and the level of 1,25(OH)2D3 directly and through PTH. To determine the effect of chronic metabolic alkalosis on [Ca2+], PTH, and 1,25(OH)2D3, rats were made alkalemic by feeding a chloride-deficient diet (LCl) or LCl with 75 mM NaHCO3 in the drinking water (LCl + HCO3-) and compared with controls fed a chloride-replete diet (NCl). Compared with NCl, after 8 days of LCl and LCl + HCO3- arterial pH and PTH rose and [Ca2+] fell. Serum 1,25(OH)2D3 tended to rise with LCl and rose with LCl + HCO3-. Serum 1,25(OH)2D3 was correlated inversely with [Ca2+] (r = -0.510, n = 54, P less than 0.001) and with pH (r = -0.291, n = 57, P less than 0.03) but not with PTH or phosphorus. Stepwise regression analysis indicated that [Ca2+] accounted for the majority of the variance of serum 1,25(OH)2D3. Chronic metabolic alkalosis induced by a low-chloride diet and HCO3- appears to increase serum PTH and 1,25(OH)2D3 through a fall in [Ca2+].
Bushinsky
D A
DA
Pritzker School of Medicine, University of Chicago 60637.
Kittaka
M K
MK
Weisinger
J R
JR
Langman
C B
CB
Favus
M J
MJ
D000471:Alkalosis / Q000097:blood* / Q000652:urine; D000818:Animals; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000097:blood* / Q000652:urine; D002712:Chlorides / Q000502:physiology; D004573:Electrolytes / Q000097:blood / Q000652:urine; D006863:Hydrogen-Ion Concentration; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood*; D051381:Rats; D011919:Rats, Inbred Strains
D002712:Chlorides; D004573:Electrolytes; D010281:Parathyroid Hormone; D002117:Calcitriol; D002118:Calcium