THE EFFECT OF GROWTH-HORMONE TREATMENT ON GROWTH IN ZINC-DEFICIENT RATS

The ability of human growth hormone (hGH) to alleviate the effects of zinc deficiency on growth was investigated in the rat. The 18-day experiment was a completely randomized block design with a 3x2 factorial combination of 3 dietary groups (< 1 ppm zinc, 100 ppm zinc, and pair fed) and 2 hGH treatments (hGH in saline and saline alone). The hGH treatment began on Day 8 and continued for 10 days. Human GH treatment had no significant effect on food consumption, growth parameters or plasma IGF-1. Food consumption, tail length, liver weight, and tibia weight were significantly lower in the zinc deficient group. Body weight was significantly reduced in the zinc deficient and pair fed groups compared to the control. A significant interaction between zinc and hGH was found for tibial epiphyseal cartilage width but there were no significant differences between the groups receiving hGH and the respective shams. Plasma IGF-I was numerically lower in the zinc deficient rats compared to the pair fed rats but this difference did not reach statistical significance. Tissue zinc content and plasma alkaline phosphatase were significantly decreased by the dietary zinc deficiency. Plasma zinc was higher in the groups receiving hGH. Significant interactions between zinc and hGH was found for liver iron, tibial zinc, and tibial copper. Copper and iron showed a competitive interaction with zinc and were lower in the rats receiving the control diet. Both lowered zinc and food intake contributed to the effects of the zinc deficiency; however, these effects were not equally distributed. Food intake had the greater effect on growth and plasma IGF-I while tissue mineral content showed a greater effect for zinc intake.