Intestinal absorption of calcium in newborn piglets. Role of vitamin D.

The role of vitamin D for intestinal absorption of Ca was studied in neonatal piglets. Piglets of normal phenotype (heterozygotes) and piglets which suffered from pseudo-vitamin D deficiency rickets, type I, which were devoid of renal 25-cholecalciferol-1-hydroxylase were used for the experiments. Intestinal absorption of Ca was measured after an oral dose of 3-7 MBq 45CaCl2. Intestinal absorption of Ca was the same in heterozygotes and homozygotic rachitic piglets during the first 3-4 weeks of life. Ca absorption began to decline in rachitic piglets at the age of 4 weeks. In 8-week-old rachitic piglets intestinal Ca absorption was 50% of control piglets. Body weights of heterozygotes and rachitic piglets were the same at birth and no different weight gains were seen between the two groups during the first 4-5 weeks of life. No differences were observed during the first weeks of life in the concentrations of plasma Ca, inorganic-phosphate and alkaline-phosphatase activity between the groups. Hypocalcemia and hypophosphatemia developed in rachitic piglets between the 3rd and 5th weeks of life. Concentrations of 1,25-(OH)2D3 in plasma declined in heterozygote piglets from 130 +/- 26 to 88 +/- 19 pg/ml and in rachitic piglets from 67 +/- 37 to 23 +/- 11 pg/ml during the first 6 weeks. An intestinal nuclear 1,25-(OH)2D3 receptor was absent in neonatal piglets of both experimental groups. It is concluded that intestinal absorption of Ca in piglets during the first 2-4 weeks of life is independent of vitamin D.