Ontogeny of Erythrocyte Insulin Binding in the Sheep*

Abstract

The ontogeny of insulin binding in the sheep was studied using the erythrocytes (RBCs) of 31 fetuses, 10 lambs, and 5 adult animals. Six fetuses were studied on three occasions over a 2-week period from 120–135 days of gestation to provide longitudinal data on changes in insulin binding. Maximal percent binding of [¹²⁵I]iodoinsulin and receptor concentration decreased significantly as the age of the animal increased (r = -0.76, P < 0.001 and r = -0.49, P 50 = 0.55% phosphate-buffered saline vs. 0.76% phosphate-buffered saline, respectively; P < 0.001). The data suggest that fetal RBCs of lower osmotic fragility and high insulin binding capacity are progressively replaced during late prenatal and early postnatal life by adult-type RBCs of increased osmotic fragility and lacking binding capacity for insulin. The timing of the disappearance of insulin binding to RBCs coincides with the final transition in the animals from a monogastric to a ruminant metabolic state, and may reflect a change in the need for insulin with age.