ZINC-DEFICIENCY INHIBITS THE DIRECT GROWTH EFFECT OF GROWTH-HORMONE ON THE TIBIA OF HYPOPHYSECTOMIZED RATS

The effect of zinc deficiency on the direct-growth effect of growth ho rmone (GH) on tibia growth in hypophysectomized rats was studied. Ther e were three dietary groups. Zinc deficient (ZD) group (0.9 mg/kg diet ), control (C) group (66 mg/kg diet) and zinc adequate pair fed (PF) g roup (66 mg zinc/kg diet). All rats in each group received local infus ion of recombinant human-growth hormone (hGH) (1 mu g/d), except for h alf of the animals in the control group, which were sham-treated, rece iving vehicle infusion only. The substances were infused continuously for 13 d by osmotic minipumps through a catheter implanted into the ri ght femoral artery. Food intake was lower and body weight loss was gre ater in ZD, and PF animals compared with C animals (p < 0.001). Tissue -zinc concentration and plasma alkaline-phosphatase activity were decr eased (p < 0.05) by dietary-zinc deficiency. GH infusion increased the tibial-epiphyseal width of the treated right limb, but not of the non infused left limb in C and PF animals. However, in ZD rats, no differe nce was found between the infused and the noninfused limbs. These resu lts demonstrate that zinc deficiency inhibits the direct-growth effect of GH on long-bone growth.