Manganese deficiency effects circulating growth hormone (GH). IGF-I. and igfbps in the male rat

Mn plays an important role in mammalian glucose homeostasis. Our group has shown that Mn deficient animals display abnormal glucose tolerance, which is related to a diminished capacity to both release and synthesize insulin. These observations coupled with the observation that Mn deficient male rats consistently weigh less than controls led us to hypothesize that Mn deficiency may alter insulin-like growth factor metabolism. In this study. male rats were led either 1(-Mn)or 45(+Mn)ug Mn/g diet. After 3 months, animals were killed and the parameters below ascertained. Data are expressed as mean±SE. Superscript indicates significantly different (p<0.05) from controls. Serum GH and IGF-I were measured by radioimmunoassay. Dietary Bodywt. cumulative GH IFG-I 150kDa 40-25Da 8kDa Group (g) Intake (g) (ng/ml) (ng/ml) (Relative Area) + Mn 538±12 2127+17 25±3 213±21 10±0.4 5.5±0.1 9.1±0.4 - Mn 432±13 1950±40^b 35±3^b 141±15^b 12±0.5^b 4.8±0.1^b 8.2±0.3^b Serum was labeled for 4h at 4°C with ¹²⁵I-IGF-1 and column fractionated under native conditions to characterize IGFBPS. Relative tracer area under each peak at the indicated molecular weight range is shown. IGF-I concentrations in the -Mn group were decreased relative to the +Mn group which is consistent with the differences in body weight between the two groups. -Mn animals had elevated GH relative to +Mn animals, which is congruous with their increased BP3(150kDa) and decreased BP2,1(40-25kDa) relative area. -Mn animals display altered IGF metabolism, with an apparent uncoupling of scrum GH and IGF-I concentrations.