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

Thymic peptide thymosin α1 (10−9 to 3 x 1010−7 M) is shown to inhibit the specific binding of [125I]VIP to rat blood mononuclear cells and liver plasma membranes. Thymosin α1 was 160 and 6250 times less potent that VIP at inhibiting [125I]VIP binding to blood mononuclear cells and liver plasma membranes, respectively. Thymosin α1 (10−10 to 1010−7 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 α1 may behave as a partial VIP agonist in rat.