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Insulin Binding is a Specific Marker of Fetal Erythrocytes in Ruminants^1,2,3,

University of Florida⁴, Gainesville 32610

Abstract

The ability of erythrocytes (RBC) from sheep and cattle of various gestational and postnatal ages to bind insulin specifically was studied. Insulin binding to RBC decreased as gestational and postnatal age advanced and was absent in blood obtained from adult animals. Maximal percentage ¹²⁵I-Insulin bound to RBC (3.6 x 10⁹ /ml) was highest in the fetuses of sheep and cattle (7.3 ± .6 and 7.8 ± .9, respectively) compared to postnatal animals (2.3 ± .2 and 2.2 ± .3, respectively), or adults (no binding) of the same species. The decrease in binding began antenatally, and binding was projected to be insignificant by the end of the second postnatal month. Most of the observed decrease was due to a progressive decrease in the number of receptors on the cell surface. The time course of this phenomenon, as well as the total absence of insulin receptors on the RBC of adult-ruminants, provides independent evidence that two distinct populations of RBC in ruminants exist. The gradual appearance of the adult RBC with no insulin binding results in a decrease in observed binding to RBC in a given blood specimen as fetures and postnatal animals age.

¹ I would like to acknowledge the technical support of Muriel Turlington, Ann Wiley, Carol Underwood and Dallas Foster, and the technical and statistical help of Dr. Andrea Moffa-White. Dr. Leslie Plotnick was an integral part of the earlier work at the Johns Hopkins Hospital, which forms part of the present study. I would like to acknowledge the outstanding secretarial assistance of Ms. Mary Beall and Oonagh Kater.

² This study was partially supported by Research Grant #HD06284 and Traineeship Grant AM-07116 of the National Institutes of Health, USPHS at the Johns Hopkins Hospital; Biomedical Research Support Grant RR05362-19; Division of Sponsored Research Support #DSR-D-18 at the Univ. of Florida College of Medicine; and by a contract for the Univ. of Florida Diabetes Research Education and Treatment Center from the Dept. of Health and Rehabilitative Services of the State of Florida.

³ Blood specimens were kindly provided by Drs. J. R. Willey, M. Simmons, M. D. Jones, A. Rosenberg and R. Molteni, Eudowood Neonatal Division, Dept. of Pediatrics, The Johns Hopkins Hospital (National Foundation March of Dimes), Dr. D. Caton, Dept. of Obstetrics and Gynecol. (Grant #R01-HD05659, NIH, USPHS), Dr. W. Drummond, Dept. of Pediatrics (Grant #R01-HD12987, NIH, USPHS), Univ. of Florida. College of Medicine and Drs. Wm. Thatcher and H. Head, Dept. of Dairy Sci., Univ. of Florida.

⁴ Dept. of Pediatrics and Biochem./Mol. Biol., College of Med.