Insulin-like growth factor-I stimulates erythropoiesis when administered enterally.
BACKGROUND
Insulin-like growth factors I and II (IGF-I and IGF-II) are potent growth factors involved in development. IGF-I stimulates proliferation of erythropoietic progenitors and parenteral IGF-I administration stimulates in vivo erythropoiesis in animals. IGF-I and IGF-II are both present in mammalian milks and when milk-borne, are resistant to neonatal gastrointestinal degradation. Whether milk-borne IGF-I or IGF-II regulates neonatal erythropoiesis in not known. We hypothesized that physiological doses of enteral IGFs stimulate erythropoiesis in suckling rats.


METHODS
Eight day-old Sprague Dawley rats were artificially fed for 4 days with rat milk substitute (RMS) or RMS supplemented with physiological levels of IGF-I or IGF-II. Rats fed IGF-I and IGF-II were compared to control RMS. Blood and marrow were collected; measures of red cell mass, measures of erythropoietic stimulus, and indices of iron status were measured.


RESULTS
Rats fed IGF-I had higher hemoglobin (Hb) levels (100 +/- 10 g/l), compared to those fed RMS (94 +/- 9) or IGF-II (91 +/- 6), p < 0.001. After IGF-I supplementation, red blood cell counts (RBC) (p < 0.04) and hematocrits (p < 0.002) were also higher. Plasma erythropoietin (Epo) levels, reticulocytes, plasma iron and erythrocyte iron incorporation were similar.


CONCLUSIONS
Intact enteral IGF-I reaches distal erythropoietic tissue resulting in greater red cell mass, but not by increasing plasma Epo levels or by altering cellular iron transport.
Kling
Pamela J
PJ
Department of Pediatrics, Steele Memorial, Children's Research Center, The University of Arizona Health Sciences Center, Tucson, AZ 85724, USA. pkling@wisc.edu
Taing
K Muy
KM
Dvorak
Bohuslav
B
Woodward
Suann S
SS
Philipps
Anthony F
AF
D000818:Animals; D000831:Animals, Newborn; D004750:Enteral Nutrition; D004920:Erythropoiesis / Q000502:physiology*; D004921:Erythropoietin / Q000502:physiology; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000502:physiology*; D007335:Insulin-Like Growth Factor II / Q000008:administration & dosage / Q000502:physiology*; D007501:Iron / Q000502:physiology; D051381:Rats; D011994:Recombinant Proteins
D011994:Recombinant Proteins; D004921:Erythropoietin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D007501:Iron