The fetal heart insulin receptor responds differently to varying plasma insulin concentrations.
We investigated in vivo the effect of varying plasma concentrations of insulin on the 28- and 30-day-old fetal rabbit heart insulin receptors using plasma membranes. Alloxan induced maternal diabetes (n = 5) associated with fetal hyperglycemia and mild hyperinsulinemia (59.80 +/- 8.10 microU/ml versus a control of 26.25 +/- 3.70, p less than 0.01) increased the insulin receptor number from a control (30 d) of 168 +/- 1.01 to 320 +/- 34 X 10(10)/mg protein (p less than 0.01). Fetal administration of 1.0 U of insulin (n = 4) resulting in normoglycemia and moderately high plasma insulin concentrations (103.3 +/- 34.63 microU/ml versus a control of 13.72 +/- 1.60, p less than 0.05) did not alter the insulin receptor number (28 d). On the other hand fetal administration of 2.0 U of insulin (n = 4) resulting in hypoglycemia and severely high plasma insulin concentrations (288.3 +/- 51 microU/ml versus a control of 13.72 +/- 1.60, p less than 0.01) decreased the insulin receptor number from a control (28 d) of 200 +/- 23 to 82 +/- 23 X 10(10)/mg protein (p less than 0.01). The receptor affinity remained constant. We conclude that the downregulation (decrease) of the fetal heart insulin receptors in vivo is not a physiologic but a pharmacologic effect of insulin.
Devaskar
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Szewczyk
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Devaskar
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D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism; D005260:Female; D005312:Fetal Blood / Q000378:metabolism; D005318:Fetal Heart / Q000378:metabolism*; D007328:Insulin / Q000097:blood*; D008431:Maternal-Fetal Exchange; D011247:Pregnancy; D011254:Pregnancy in Diabetics / Q000378:metabolism; D011817:Rabbits; D011972:Receptor, Insulin / Q000378:metabolism*
D001786:Blood Glucose; D007328:Insulin; D011972:Receptor, Insulin