Early exercise regimen improves insulin sensitivity in the intrauterine growth-restricted adult female rat offspring

Abstract

We examined the effect of early exercise training (Ex) on glucose kinetics, basal, and insulin-stimulated skeletal muscle (SKM) plasma membrane (PM) GLUT4 in pre- and/or postnatal nutrient-restricted adult rat offspring compared with sedentary (Sed) state. Pregestational control female (Ex CON vs. Sed CON) and offspring exposed to prenatal (Ex IUGR vs. Sed IUGR), postnatal (Ex PNGR vs. Sed PNGR), or pre- and postnatal (Ex IUGR + PNGR vs. Sed IUGR + PNGR) nutrient restriction were studied. The combined effect of exercise and pre/postnatal nutrition in the Ex IUGR demonstrated positive effects on basal and glucose-stimulated plasma insulin response (GSIR) with suppression of endogenous hepatic glucose production (HGP) compared with sedentary state. Ex PNGR was hyperglycemic after glucose challenge with no change in glucose-stimulated insulin production or HGP compared with sedentary state. Ex IUGR + PNGR remained glucose tolerant with unchanged glucose-stimulated insulin production but increased endogenous HGP compared with sedentary state. Basal SKM PM-associated GLUT4 was unchanged by exercise in all four groups. Whereas Ex PNGR and Ex IUGR + PNGR insulin responsiveness was similar to that of Ex CON, Ex IUGR remained nonresponsive to insulin. Early introduction of regular Ex in the pregestational female offspring had a positive effect on hepatic adaptation to GSIR and HGP in IUGR and IUGR + PNGR, with no effect in PNGR. Change in insulin responsiveness of SKM GLUT4 translocation was observed in exercised IUGR + PNGR and PNGR but not in exercised IUGR.

Fig. 1.

A: study design demonstrating the control (CON) group and nutrient restriction achieved by cross-fostering postnatal rat pups. Nutrient-restricted mothers received 50% of daily nutrient intake from mid- to late pregnancy [embryonic days 11 (e11) to 21 (e21)] through lactation [postnatal days 1 (PN1) to 21 (PN21)]. B: experimental protocol for exercise (Ex) in 4 groups is shown. The CON and nutrient-restricted groups of animals either underwent supervised exercise or remained sedentary (Sed) from PN day 21 (d21) to PN day 60 (d60) (2 mo). Ad lib, ad libitum; IUGR, intrauterine growth restricted; PNGR, postnatal growth restricted.

Fig. 2.

A: plasma glucose concentration at 0, 5, 15, 30, 60, and 120 min after intravenous glucose challenge is shown in Ex and Sed states in individual graphs (graph 1, CON; graph 2, PNGR; graph 3, IUGR; graph 4, IUGR + PNGR). *P < 0.006, **P < 0.02, ***P < 0.05, Ex vs. Sed counterpart. B: area under the curve (AUC) for plasma glucose concentration during glucose tolerance test (GTT) is shown for all groups. Two-way ANOVA revealed a significant effect of exercise × pre/postnatal nutrition (F = 4.07, P = 0.013) but no effect of exercise alone (F = 0.491, P = 0.488) or pre/postnatal nutrition (F = 0.653, P = 0.586) alone. Holm-Sidak test showed *P < 0.04, Ex CON vs. Sed CON; **P < 0.03, Ex PNGR vs. Sed PNGR. C: plasma insulin concentration at 0, 5, 15, 30, 60, and 120 min after an intravenous glucose challenge is shown in Ex and Sed states in individual graphs (graph 1, CON; graph 2, PNGR; graph 3, IUGR; graph 4, IUGR + PNGR). The scale for plasma insulin is adjusted from 0 to 50 nmol/l to show the lower values in PNGR (graph 2) and IUGR + PNGR (graph 4). Holm-Sidak test shows a significant decrease at 5, 15, 30, 60, and 120 min in Ex CON and Ex IUGR compared with their respective Sed counterparts (*¹P < 0.017, *²P < 0.005, *³P < 0.004, *⁴P < 0.03). D: AUC for plasma insulin concentration during GTT is shown for all groups. Two-way ANOVA revealed significant effect of exercise (F = 13.926, P = <0.001), pre/postnatal nutrition (F = 14.843, P = <0.001), and exercise × pre/postnatal nutrition (F = 6.94, P = <0.001). Holm-Sidak test revealed significant changes in Ex CON and Ex IUGR groups (*P < 0.0001, **P < 0.001) compared with their respective Sed states; n = 6 for all study groups, except n = 5 each for Sed and Ex PNGR groups alone.

Fig. 3.

A: %change in plasma glucose concentration from the “0” time point value during insulin tolerance test is shown in Ex and Sed states in individual graphs (graph 1, CON; graph 2, PNGR; graph 3, IUGR; graph 4, IUGR + PNGR). Holm-Sidak test shows significant response in Ex PNGR, Ex IUGR, and Ex IUGR + PNGR groups (†P < 0.01, ††P < 0.03, *P < 0.0001, **P < 0.0004) compared with corresponding Sed group at the same time point. B: AUC for %change in plasma glucose concentration during the insulin tolerance test for all Ex and Sed groups is shown. Two-way ANOVA revealed a significant effect of exercise alone (F = 34.793, P < 0.001) and exercise × pre/postnatal nutrition (F = 3.16, P < 0.03) but not of pre/postnatal nutrition alone (F = 2.763, P = 0.057). Holm-Sidak test demonstrated a difference at *P < 0.0001 between Ex IUGR and Ex IUGR + PNGR vs. their corresponding Sed groups; n = 6 for all study groups, except n = 5 each for Sed and Ex PNGR groups alone.

Fig. 4.

A: AUC for endogenous hepatic glucose production during GTT is shown in all Ex and Sed groups. Two-way ANOVA revealed a significant effect of pre/postnatal nutrition alone (F = 3.338, P = 0.03) and exercise × pre/postnatal nutrition (F = 4.64, P < 0.008) but no effect of exercise alone (F = 1.053, P = 0.311). Holm-Sidak test demonstrated differences between the Ex and Sed counterparts at *P < 0.02, **P < 0.04, and ***P < 0.05. B: total glucose clearance (mg·kg⁻¹·min⁻¹) is shown for all Ex and Sed groups. Two-way ANOVA did not demonstrate an effect of exercise (F =1.497, P = 0.229), pre/postnatal nutrition (F = 0.480, P = 0.698), or exercise × pre/postnatal nutrition (F = 2.298, P = 0.094). C: hepatic glucose recycling or glucose futile cycling is shown for all Ex and Sed groups. Two-way ANOVA revealed a significant effect of exercise × pre/postnatal nutrition (F = 3.714, P = 0.02) but no effect of exercise (F = 0.695, P = 0.410) or pre/postnatal nutrition alone (F = 0.581, P = 0.631). Holm-Sidak test demonstrated a difference between the Ex IUGR + PNGR vs. the corresponding Sed group at #P < 0.015; n = 6 for all study groups, except n = 5 each for Sed and Ex PNGR groups alone.

Fig. 5.

A: skeletal muscle AMPKα1 and -α2 isoform-specific activities measured 15 min after acute Ex (n = 4) or in a Sed state (n = 3) and expressed as a percent of the sedentary CON state are shown in a subgroup of control animals. *P < 0.04, acute Ex vs. Sed CON; **P < 0.01, acute Ex vs. Sed CON. B: skeletal muscle pAMPK and total AMPK protein concentrations measured 48–72 h after last bout of exercise training (n = 3–4 each for all groups) did not significantly change when compared with the Sed counterpart (n = 3–4 each for all groups). Representative Western blots are shown at top, and the densitometric quantification of pAMPK/total AMPK expressed as a percent of Sed CON is shown as a bar graph. C: skeletal muscle AMPK (AMPKα1 and -α2 isoforms) enzyme activity measured 48–72 h after the last bout of exercise training and expressed as a percent of Sed CON did not show any significant difference when compared to the sedentary counterpart (n = 3–4 each for all Ex and Sed groups). D: skeletal muscle total GLUT4 protein concentrations were no different between the Sed and Ex groups (n = 3 each for all groups). Representative Western blots of GLUT4 and vinculin (internal control) are shown at top, and the densitometric quantification of total GLUT4/vinculin expressed as a percent of Sed CON is shown as a bar graph. E: basal and insulin-responsive skeletal muscle GLUT4 distribution in plasma membrane (PM) and low-density microsomes (LDM) of Ex CON, Ex PNGR, Ex IUGR, and Ex IUGR + PNGR is shown; n = 3 each for PM and LDM in all experimental groups. Top: representative Western blots of GLUT4 in PM and LDM subfractions in the presence (+) and absence (−) of insulin administration in the 4 Ex groups (Ex CON, Ex PNGR, Ex IUGR, and Ex IUGR + PNGR). The densitometric quantification is expressed in arbitrary units as a bar graph. PM GLUT4 concentrations increased after insulin administration (+) vs. the corresponding basal state (−) in Ex CON, Ex PNGR, and Ex IUGR + PNGR (*P < 0.05) but not in Ex IUGR. PM GLUT4 concentrations in the Ex IUGR + PNGR were higher than Ex CON (#P < 0.05). Sed state results were reported previously (41) and not shown.