Differential Response of Enterocytes to Vitamin D during Embryonic Development: Induction of Intestinal Inorganic Phosphate, D-Glucose and Calcium Uptake

Abstract

Chick intestine maintained in organ culture at day 20 of embryonic life responds to appropriate dose levels of 1,25-dihydroxyvitamin D₃ or vitamin D₃ in the culture medium by stimulation of Na⁺-dependent uptake of inorganic phosphate (P_i) and D-glucose as well as by increased calcium absorption. The intensity of each single response to vitamin D varies along the small intestine: Only the jejunum shows high vitamin D increments of all three transport systems under investigation. Inhibition of vitamin D responses by actinomycin D suggests the involvement of gene activation in the sterol's action of raising intestinal transport activities. Determination of the developmental pattern of each vitamin D-dependent transport system showed that only calcium absorption could be induced in undifferentiated cells on day 15, while complete expression of vitamin D action, including elevation of Na⁺-dependent uptake of D-glucose and P_i, required a fairly advanced state of epithelial maturation and was thus not observed before the final day 20 of embryonic development. This indicates a progressive change of hormone sensitivity of absorptive cells during differentiation.