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The Effects of Biosynthetic Insulin-Like Growth Factor-1 Supplementation on Somatic Growth, Maturation, and Erythropoiesis on the Neonatal Rat

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The Effects of Biosynthetic Insulin-Like Growth Factor-1 Supplementation on Somatic Growth, Maturation, and Erythropoiesis on the Neonatal Rat 0031-3998/88/2303-0298$02.00/0 PEDIATRIC RESEARCH Vol. 23, No.3, 1988 Copyright © 1988 International Pediatric Research Foundation, Inc. Prilued in U. SA. The Effects of Biosynthetic Insulin-Like Growth Factor-1 Supplementation on Somatic Growth, Maturation, and Erythropoiesis on the Neonatal Rat ANTHONY F. PHILIPPS, BENGT PERSSON, KERSTIN HALL, MATS LAKE, ANNA SKOTTNER, TRULS SANENGEN, AND VICKI R. SARA Department of Pediatrics {A.F.P.}, University ofConnecticut Health Center, Farmington, Connecticut 06032; Kabi Gen [M.L.j and Kabi Vitrum [A.S.j, Stockholm, Sweden; Departments ofPediatrics and Pathology [T.S.j, Ulleval Hospital, Oslo, Norway; and Departments ofPediatri cs [B.P.], Endocrinology [K.H.j, and Psychiatry [V.R.S.j, Karolinska Institute, St. Goran's Hospital, Stockholm, Sweden ABSTRACT. Somatomedins are anabolic hormones that ties in a variety of mammalian cell types in vitro ( 1, 2). Although may stimulate growth during the perinatal period. To test they share some structural homology with insulin (1, 2) and do this hypothesis, neonatal rats were injected with a biosyn­ stimulate such insulin-like effects as increased cellular glucose thetic somatomedin, insulin-like growth factor 1 (IGF-1) and amino acid uptake (3), somatomedins also possess potent twice daily for the first 2 wk of life. Two biosynthetic IGF- mitogenic properties in cell types as diverse as fibroblasts, myo­ 1 preparations of different potency were tested as well as cytes, chondrocytes, and erythropoietic stem cells (1-3). Of the a preparation of human growth hormone in five litters of somatomedins, IGF-1 has been studied most extensively. Its rats. When compared to saline-injected rats, IGF-1 injected synthesis in the adult appears to be regulated by circulating GH rats had increased body weight and tail length as well as concentration (2, 4). Somatomedins, including IGF-1, and their specific increases in weights of liver, brain, heart, and receptors have recently been identified in a wide variety of fetal testes. In addition, significant increases in bone marrow and neonatal tissues in several species including man (5-8), erythropoietic cell precursors were apparent after IGF-1 raising the possibility that the rapidity of growth observed in the injection. IGF-1-treated neonatal rats also exhibited pre­ perinatal period may be at least partially regulated by changes in cocious eye opening as a sign of epithelial cell differentia­ somatomedin production. However, although significant IGF-1 tion. Five additional litters of rats received similar injec­ synthesis has been observed in the fetus and neonate (6), the tions but were exposed to postnatal nutritional deprivation mechanisms involved in regulation of IGF-1 production are via artificially increasing litter size. Although I GF-1 caused unclear (9). stimulation of bone marrow erythropoiesis and precocious Unfortunately, hypotheses regarding the effects of somatome­ eye opening, no effects ofiGF-1 on somatic or organ growth dins on growth rate or erythropoiesis have been difficult to test could be documented. This represents the first demonstra­ in other than in vitro systems because of the scarcity of purified tion in vivo of the anabolic effects of IGF-1 in rapidly hormone. Although somatomedins are synthesized by many cell growing neonatal rats but suggests that nutritional suffi­ types, no storage site has been identified and, thus, hormone ciency may also be necessary for the full expression of purification schemes have required time-consuming concentra­ somatomedin effects. (Pediatr Res 23: 298-305, 1988) tion and separation of somatomedins from large amounts of human sera ( 10). Recently, genetic engineering techniques have Abbreviations been applied to the synthesis of somatomedins in order to provide enough purified hormone for use in in vivo animal experiments. CFU-E, erythroid colony-forming cell We report the first use of two biosynthetic preparations of IGF- Ep, erythropoietin 1 in the prewean1ing rat in order to observe whether or not GH, growth hormone exogenous IGF-1 causes any alterations in growth or erythro­ IGF, insulin-like growth factor poiesis during the perinatal period. HSA, human serum albumin PCV, packed r,ed cell volume ANOVA, analysis of variance MATERIALS AND METHODS Hormone preparation. Biosynthetic IGF-1. Two preparations of recombinant human IGF-1 were used. IGF-1 A, produced in Somatomedins, or IGF, comprise a family of relatively low yeast, and IGF-1 B, produced in Escherichia coli, were kindly molecular weight peptides possessing growth promoting proper- provided by Kabi Vitrum and Kabi Gen (Stockholm, Sweden), respectively. The purity of these preparations was confirmed by Received June 25 , 1987; accepted November 16, 1987 . amino acid composition and NH4-terminal sequence. These Correspondence and reprints Anthony F. Philipps, M.D., Department of Pedi­ atrics, The University of Connecticut Health Center, Farmington, CT 06032. preparations differed in specific activity, assessed by placenta Supported by grants from the University of Connecticut Research Foundation, radioreceptor activity (II) as follows: IGF-1 A (5000 U/mg) and the National Institutes of Health (R-0 l-DK26067), the Expressen Prenatal Fund, IGF-1 B (10,000 U/mg). the Swedish Diabetes Association, The Bergvalls Foundation, the Norwegian So­ Biosynthetic IGF-1 was dissolved in 35 % CH CN. Aliquots ciety for Fighting Cancer, and the Swedish Medical Research Council. A.F.P. was 3 also supported by a research fellowship from the Fogarty International Center, were removed, placed in albumin-coated tubes, freeze dried, and National Institutes of Health (I F06 TWO l 050). before administration, dissolved in sterile saline with 0.1% HSA. 298 BIOSYNTHETIC INSULIN-LIKE GROWTH FACTOR-! 299 This method gave IOO% recovery of activity after syringe injec­ Growth and Maturation Parameters. Measurements of weight, tion. Saline controls received identically treated aliquots of 35% length, and tail length were obtained daily from study animals CH3CN, freeze dried and reconstituted in sterile saline with 0.1% from day 3 through 16. Length was measured as the distance HSA. between posterior occiput (a dot was placed between the ears Human GH. Crescormon was kindly provided by Kabi Vitrum using indelible pen ink) and anus. Tail length was measured as and aliquotted into 2-nmol portions. the distance between anus and tail tip. Estimates of maturation Experimental protocol. Animals. Twelve litters of Sprague­ were performed twice daily using the following parameters. Eye Dawley rats were studied in the first 2 wk of postnatal life. Opening. Time (closest 12 h) when both eyes fully open. Tooth Animals were supplied by a commercial breeder and birth dates eruption. Time (Closest 12 h) when both mandibular incisors were accurate to within 12 h. visibly erupted. Hair growth. Estimated on a scale of 0-3 where Kinetic Studies. Two litters of rats were studied on the 3rd or 0 = no visible hair, 1 = sparse white hair on. torso, 2 = thick hair 15th postnatal day, in order to assess the efficiency of absorption with scattered bare areas, 3 = pelt fully covers torso. ofbiosynthetic IGF-1 when injected subcutaneously. In the first On day 16, approximately 16 h after the last injection, blood study, six 3-day old rats were injected subcutaneously over the samples were obtained from each study subject via tail section lumbar spine with purified IGF-lA using plastic tuberculin sy­ for analysis of PCV, reticulocyte count, plasma glucose, and ringes and 27-guage needles. Aliquots of 15 JLg of lyophilized insulin concentrations. All animals were then exsanguinated via hormone preparation (see below) were dissolved in delivery cardiac puncture while under ether anesthesia. Blood samples volumes of 50 JL1 of normal saline immediately before injection. were allowed to clot at room temperature and the sera then Blood samples were then obtained for IGF-1 assay by exsangui­ stored at -20° C for later analysis of rat growth hormone and nation via cardiac puncture under ether anesthesia. Samples IGF-1 activity. were drawn at 0.25, 0.5, 1.0, 2.0, and 24 h after injection. Thus, After exsanguination, cerebrum and liver were removed from because of the small blood volume available per animal and the each animal, weighed, and stored for later analysis of protein limited amount of pure hormone available, each point in time and DNA content. Rat livers were removed in toto and cere­ was represented by blood IGF concentrations from a single brums were removed after cleavage of the medulla at the level animal (two animals were used to study blood levels at 24 h). of the posterior occipital horns. Other organs, including heart, Two litter mates also served as noninjected controls. In addition, lungs, kidneys, spleen, testes, thymus, pituitary, and adrenals 10-JLI blood samples were obtained by tail section before anes­ were also removed and weighed. Both femurs were removed thesia for estimation of plasma glucose concentration. When aseptically from ·each animal in two of the normal sized litters possible, urine was obtained from the rats by gentle abdominal and three of the large litters. The femurs were kept on a-medium pressure before cardiac puncture and urine concentrations of at 18° C until the bone marrow was expressed. The bone marrow IGF-1 were studied. cells were then cultured in order to detertnine the number of In the second study, a similar IGF-1 dose ( 15 JLg) was given to CFU-E in the respective treatment groups, and to test the in vitro three 15-day-old rats. Because of their relatively larger blood sensitivity of these cells to exogenous Ep. volumes, serial blood sampling for glucose and IGF-1 concentra­ Analytical methods. Plasma glucose concentration was meas­ tion could both be performed by tail vein section. Thus, all three ured using the glucose oxidase technique (Beckman Instruments, rats were studied serially at 0, 0.5, 1.0, 5.0, and 24 h.
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