Response of serum 1,25(OH)2D3 to variation of ionized calcium during chronic acidosis.
Chronic ammonium chloride (NH4Cl) administration causes metabolic acidosis and prevents the normal rise of serum 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] during a low-calcium diet (LCD, 0.002% calcium). The suppression of serum 1,25(OH)2D3 was not due to reduced parathyroid hormone concentration, elevated serum phosphorus, or total calcium concentration. Acidosis increased blood ionized Ca [Ca2+] and proton [H+] concentrations. Serum 1,25(OH)2D3 levels were inversely correlated with both [Ca2+] and [H+]. To determine the independent effects of [Ca2+] on serum 1,25(OH)2D3 we varied [Ca2+] at a constant [H+] by infusing either EGTA or saline for 24 h after 11 days of LCD and NH4Cl. EGTA, preequilibrated with three concentrations of Ca, lowered [Ca2+] and raised 1,25(OH)2D3 but did not alter [H+] or serum phosphorus concentration. The log of serum 1,25(OH)2D3 varied linearly and inversely with arterial blood [Ca2+] during saline (r = -0.884, n = 8, P less than 0.001) and EGTA infusions (r = -0.798, n = 22, P less than 0.001). At all levels of [Ca2+], rats infused with EGTA had a higher serum 1,25(OH)2D3 than those infused with saline. Log serum 1,25(OH)2D3 was correlated neither with [H+] nor pH. Elevated [Ca2+] and not [H+] appears to suppress the serum 1,25(OH)2D3 response to LCD during NH4Cl acidosis in the rat.
D000138:Acidosis / Q000097:blood* / Q000139:chemically induced; D000643:Ammonium Chloride; D000818:Animals; D001784:Blood Gas Analysis; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000494:pharmacology*; D002908:Chronic Disease; D003404:Creatinine / Q000652:urine; D000242:Cyclic AMP / Q000652:urine; D004533:Egtazic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000652:urine; D010758:Phosphorus / Q000652:urine; D051381:Rats; D011919:Rats, Inbred Strains
D000643:Ammonium Chloride; D010758:Phosphorus; D004533:Egtazic Acid; D003404:Creatinine; D000242:Cyclic AMP; D002117:Calcitriol; D008274:Magnesium; D002118:Calcium