Interaction of thymic peptide thymosin alpha 1 with vasoactive intestinal peptide (VIP) receptors

Thymic peptide thymosin alpha 1 (10(-9) to 3 X 10(-7) M) is shown to inhibit the specific binding of [125I]VIP to rat blood mononuclear cells and liver plasma membranes. Thymosin alpha 1 was 160 and 6250 times less potent that VIP at inhibiting [125I]VIP binding to blood mononuclear cells and liver plasma membranes, respectively. Thymosin alpha 1 (10(-10) to 10(-7) M) was weak in stimulating adenylate cyclase activity. Its efficacy is about 25% and 27% that of native VIP in blood mononuclear cells and liver plasma membranes, respectively. Thymosin alpha 1 may behave as a partial VIP agonist in rat.