Insulin binding to erythrocytes from pregnant, postpartum, follicular and luteal states.

Specific binding of [125I] insulin to isolate erythrocytes from four groups of women was investigated: (A) pregnant subjects between weeks 38 and 40 of pregnancy (n = 18), (B) postpartum subjects within 6 days after delivery (n = 20), (C) normal women during the follicular phase of the menstrual cycle (n = 12) and (D) normal women during the luteal phase of the menstrual cycle (N = 11). Specific [125I] insulin binding (fraction), fasting plasma glucose concentrations (mmol/l) and the corresponding insulin concentrations (mU/l) were 0.074 +/- 0.012 / 4.00 +/- 0.58 / 29.4 +/- 21.4 for group A, 0.065 +/- 0.016 / 4.40 +/- 0.75 / 41.5 +/- 26.2 for group B, 0.052 +/- 0.008 / 4.58 +/- 0.62 / 6.7 +/- 4.0 for group C and 0.054 +/- 0.011 / 4.49 +/- 0.63 / 8.3 +/- 5.9 for group D. By using a modified Scatchard analysis, statistically significant differences were observed between the receptor affinities of the groups A and D, B and D, A and C. The receptor affinities and concentrations were not significantly different between the follicular and the luteal phases. From the data, no inverse correlation between the plasma insulin concentration and receptor binding was seen, i.e. the phenomenon of downregulation of insulin receptor concentration with hyperinsulinaemia seemed not to apply to erythrocytes.