[24,25-Dihydroxyvitamin D3 modulates the effect of 1alpha-hydroxyvitamin D3 on B lymphocyte maturation in chickens]

Patterns of calcium metabolism and maturation of lymphocytes in chicken Fabricius bursa were studied in presence of various doses of I alpha-hydroxy vitamin D3 and 24,25-dihydroxy vitamin D3 administered separately and at various combinations. 24,25(OH2)D3 was distinctly less effective in the antirickets activity as compared with I alpha (OH)D3. A decrease in mass of Fabricius bursa and inhibition of lymphocytes maturation within early steps were observed in the birds with rickets. A toxic dose of I alpha (OH)D3 caused pseudohypertrophy of Fabricius bursa. Small doses of these drugs administered simultaneously exhibited higher effect both on rickets and on stimulation of B lymphocytes maturation. 24,25(OH)2D3 attenuated the negative effect of either subtoxic (0.65 nmol/day) or toxic (1.3 nmol/day) doses of I alpha (OH)D3 on an increase in body mass, calcemia, ash content of bones, content of small lymphocytes in Fabricius bursa.