British Journal of Nutrition

Interaction involving Inorganic Nutrients

Role of insulin-like growth factor-1 and growth hormone in growth inhibition induced by magnesium and zinc deficiencies

Inge Dørupa1, Allan Flyvbjerga1, Maria E. Evertsa1 and Torben Clausena1

a1 Institute of Physiology, University of Aarhus and Medical Department M (Diabetes and Endocrinology), Aarhus Kommunehospital, DK-8000 Aarhus C, Denmark

Abstract

Nutritional deficiencies of magnesium or zinc lead to a progressive and often marked growth retardation. We have evaluated the effect of Mg and Zn deficiency on growth, serum insulin-like growth factor-1 (s-IGF-1), growth hormone (s-GH) and insulin (s-insulin) in young rats. In 3-week-old rats maintained on Mg-deficient fodder for 12 d the weight gain was reduced by about 34%, compared with pair-fed controls. This was accompanied by a 44% reduction in s-IGF-1, while s-insulin showed no decrease. After 3 weeks on Mg-deficient fodder, growth had ceased while serum Mg (s-Mg) and s-IGF-1 were reduced by 76 and 60% respectively. Following repletion with Mg, s-Mg was completely normalized in 1 week, and s-IGF-1 reached control level after 2 weeks. Growth rate increased, but the rats had failed to catch up fully in weight after 3.5 weeks. Absolute and relative pair-feeding were compared during a Mg repletion experiment. Absolute pair-fed animals were given the same absolute amount of fodder as the Mg-deficient rats had consumed the day before. Relative pair-fed animals were given the same amount of fodder, on a body-weight basis, consumed in the Mg-deficient group the day before. In a repletion experiment the two methods did not differ significantly from each other with respect to body-weight, muscle weight, tibia length and s-IGF-1, although there was a tendency towards higher levels in the relative pair-fed group. The peak in s-GH after growth hormone-releasing factor 40 (GRF 40) was 336 (se 63) μg/l in 5-week-old rats that had been Mg depleted for 14 d, whereas age-matched control animals showed a peak of 363 (se 54) μg/l (not significant).

In 3-week-old rats maintained on Zn-deficient fodder for 14 d weight gain was reduced by 83% compared with pair-fed controls. Serum Zn (s-Zn) and s-IGF-1 were reduced by 80 and 69% respectively, while s-insulin was reduced by 66%. The Zn-deficient animals showed a more pronounced growth inhibition than that seen during Mg deficiency and after 17 d on Zn-deficient fodder s-IGF-1 was reduced by 83%. Following repletion with Zn, s-Zn was normalized and s-IGF-1 had increased by 194% (P <0.05) after 3 d. s-IGF-1, however, was not normalized until after 2.5 weeks of repletion. Growth rate increased but the catch-up in weight was not complete during 6 weeks. The maximum increase in s-GH after GRF 40 was 774 (se 61) μg/l in control animals ν. 657 (se 90) μg/l in 6-week-old rats that had been Zn-depleted for 12 d (not significant). In conclusion, both Mg and Zn deficiency lead to growth inhibition that is accompanied by reduced circulating s-IGF-1, but unchanged s-GH response. Zn deficiency, but not Mg deficiency, caused a reduction in s-insulin. The reduction in s-IGF-1 could not be attributed to reduced energy intake, but seems to be a specific effect of nutritional deficiency of Mg or Zn. It is suggested that the growth retardation seen during these deficiency states may be mediated through reduced s-IGF-1 production.

(Received September 10 1990)

(Accepted February 25 1991)

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