Effect of insulin-like growth factor I and/or growth hormone on diaphragm of malnourished adolescent rats

Lewis, Michael I., Thomas J. LoRusso, and Mario Fournier.Effect of insulin-like growth factor I and/or growthhormone on diaphragm of malnourished adolescent rats.J. Appl. Physiol. 82(4):1064-1070, 1997.Young growing animals appear to havesignificantly reduced "nutritional reserve" to short periods ofunstressed starvation compared with adults, with resultant growtharrest and/or atrophy of diaphragm (Dia) muscle fibers. The aimof this study was to assess in an adolescent rat model of acutenutritional deprivation (ND; 72 h) the impact of insulin-like growthfactor I (IGF-I), with or without added growth hormone (GH), on thecross-sectional areas (CSA) of individual Dia muscle fibers. Fivegroups were studied: 1) control(Ctr); 2) ND;3) ND given IGF-I (ND/IGF-I); 4) ND given GH (ND/GH); and5) ND given a combination of IGF-I and GH (ND/IGF-I/GH). IGF-I was given by a subcutaneously implanted osmotic minipump (200 µg/day), whereas GH was administered twice daily by a subcutaneous injection (250 µg every 12 h). Isometric contractile and fatigue properties of the Dia were determined in vitro.Forces were normalized for muscle CSA (i.e., specific force). Dia fibertype proportions were determined histochemically, and fiber CSA wasquantified by using a computer-based image-processing system. Totalserum IGF-I concentrations were significantly reduced in ND and ND/GHanimals, compared with Ctr, and elevated in the groups receiving IGF-I.The provision of growth factors did not alter the contractile orfatigue properties of ND animals. Dia fiber type proportions weresimilar among the groups. In ND animals, there was a significantreduction in the CSA of types I, IIa, IIx, and IIc Dia fibers comparedwith Ctr. The administration of IGF-I alone or in combination with GHto ND animals significantly diminished the reduction in Dia fiber size.GH alone had no effect on Dia fiber size in ND animals. We concludethat with acute ND the peripheral resistance to the action of GHappears to be bypassed by the administration of IGF-I alone or incombination with GH.