EFFECTS OF IN-VIVO ADMINISTRATION OF 1,25-DIHYDROXYVITAMIN D-3 ON IN-VITRO PROLIFERATION OF BOVINE LYMPHOCYTES

Continuous infusion of 1,25-dihydroxyvitamin D-3 in the bovine elevate d 1,25-dihydroxyvitamin D-3 in plasma. Plasma 1,25-dihydroxyvitamin D- 3 remained elevated until infusions were discontinued. Increased 1,25- dihydroxyvitamin D-3 was associated with hypercalcemia (11 to 12 mg/dl ) that continued for several days postinfusion. Elevated 1,25-dihydrox yvitamin Dg also was associated with a significant 70% enhancement of lymphocyte proliferation in cells treated with concanavalin A. Cessati on of infusion of 1,25-dihydroxyvitamin D-3 resulted in the return of 1,25-dihydroxyvitamin D-3 in plasma and lymphocyte proliferative respo nse to preinfusion amounts. Proliferation in response to pokeweed mito gen was significantly inhibited on d 3 of infusions of 1,25-dihydroxyv itamin D-3. Administration of parathyroid hormone for 4 d resulted in a sustained hypercalcemia (approximate to 13 mg/dl) and a transient 1- d increase in 1,25-dihydroxyvitamin D-3 in plasma. Parathyroid hormone treatment generally did not affect the response of bovine lymphocytes to mitogen. In vivo elevation of 1,25-dihydroxyvitamin D-3 is either moderately immunostimulating or exerts no effect on mitogen-stimulated proliferation of lymphocytes. These results contrast with the in vitr o results suggesting that 1,25-dihydroxyvitamin D-3 is only immunosupp ressive.