Exogenous recombinant human growth hormone effects during suboptimal energy and zinc intake

BACKGROUND: Energy and Zinc (Zn) deficiencies have been associated with nutritional related growth retardation as well as growth hormone (GH) resistance. In this study, the relationship between suboptimal energy and/or Zn intake and growth in rats and their response to immunoreactive exogenous recombinant human GH (GHi), was determined. RESULTS: Rats treated with GHi and fed ad-libitum energy and Zn (100/100) had increased IGFBP-3 (p < 0.05) as compared with NSS (215 +/- 23 vs. 185 +/- 17 ng/ml) along with similar body weight gain. Rats treated with GHi and fed suboptimal energy and full Zn (70/100) had significantly increased weight gain (109.0 +/- 18.2 vs. 73.8 +/- 11.0 g) and serum IGF-I levels (568 +/- 90 vs. 420 +/- 85 ng/ml), along with decreased total body water (TBW; 61.0 +/- 1.6 vs. 65.7 +/- 2.1%) as compared to NSS controls. However, body weight gain was reduced (p < 0.05) as compared with rats fed ad-libitum energy. Growth hormone treated rats fed only suboptimal Zn (100/70), had increased weight gain (217.5 +/- 13.2 vs. 191.6 +/- 17.9 g; p < 0.05) compared to those given NSS. These rats gained weight in similar amounts to those fed full Zn. Rats treated with GHi and fed both suboptimal energy and Zn (70/70) showed similar results to those fed suboptimal energy with appropriate Zn (70/100), along with significant increases in IGFBP-3 levels (322 +/- 28 vs. 93 +/- 28 ng/ml). All restricted rats had reduced 24-h EE (kcal/100 g BW) and physical activity index (oscillations/min/kg BW) and GHi did not overcome these effects. CONCLUSION: These results suggest that GHi enhances weight gain in rats with suboptimal energy and Zn intake but does not modify energy expenditure or physical activity index. Suboptimal Zn intake did not exacerbate the reduced growth or decrease in energy expenditure observed with energy restriction.