Intestinal Absorption of Calcium in Newborn Piglets

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.