Distinct receptors for IGF-I, IGF-II, and insulin are present on bovine capillary endothelial cells and large vessel endothelial cells.

Endothelial cells were cultured from bovine fat capillaries, aortae and pulmonary arteries and their interactions with 125I-IGF-I, 125I-MSA (an IGF-II), 125I-insulin and the corresponding unlabeled hormones were evaluated. Each endothelial culture showed similar binding parameters. With 125I-insulin, unlabeled insulin competed with high affinity while IGF-I and MSA were approximately 1% as potent. With 125I-MSA, MSA was greater than or equal to IGF-I in potency and insulin did not compete for binding. Using 125I-IGF-I, IGF-I was greater than or equal to MSA whereas insulin decreased 125I-IGF-I binding by up to 72%. Exposing cells to anti-insulin receptor antibodies inhibited 125I-insulin binding by greater than 90%, did not change 125I-MSA binding, while 125I-IGF-I binding was decreased by 30-44%, suggesting overlapping antigenic determinants between IGF-I and insulin receptors that were not present on MSA receptors. We conclude that cultured capillary and large vessel endothelial cells have distinct receptors for insulin, IGF-I and MSA (IGF-II).