Diabetes and renal calcium binding protein in the rat.
Renal calcium binding protein (CaBP), a vitamin D-dependent protein of 28,000 Mr, may be involved in calcium transport by cells of the renal tubule. The streptozotocin-diabetic rat is hypercalciuric and shows markedly decreased concentration of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] in serum and of CaBP in small intestine. To examine the relationship of renal CaBP in diabetes to 1,25-(OH)2D3 and urinary calcium excretion, renal CaBP, serum 1,25-(OH)2D3, and urinary calcium were measured in control, diabetic, and insulin-treated diabetic rats. Treatment of the diabetic rat with insulin decreased urinary calcium excretion and elevated 1,25-(OH)2D3 toward normal. Renal CaBP was found to be the same in controls and diabetics despite a tenfold difference in concentration of 1,25-(OH)2D3 in serum, and to be unaffected by insulin treatment, which elevated 1,25-(OH)2D3 by a factor of 7 above untreated diabetics. It is concluded that in the diabetic rat either (1) the threshold concentration of 1,25-(OH)2D3 for inducing synthesis of renal CaBP is set at a much lower level than that for intestinal CaBP, or (2) since both 1,25-(OH)2D3 and renal CaBP are produced in the kidney, 1,25-(OH)2D3 exerts a paracrine effect on renal CaBP production because of its high local concentration. The increased urinary calcium excretion in the untreated streptozotocin-diabetic rat is not secondary to an alteration in renal CaBP.
D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D001835:Body Weight; D002112:Calcifediol / Q000097:blood; D002117:Calcitriol / Q000097:blood; D002118:Calcium / Q000652:urine; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000188:drug therapy / Q000378:metabolism*; D007328:Insulin / Q000627:therapeutic use; D007668:Kidney / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains
D001786:Blood Glucose; D002135:Calcium-Binding Proteins; D007328:Insulin; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium