Synthesis and biological activities of a fluorescent photoaffinity analog of vasopressin.

The present study describes the synthesis and biological activities of a vasopressin (VP) analog which binds covalently to receptors via a photoreactive p-azido group in position 3 and which contains a rhodamine label in position 8 for localization of hormone-receptor complexes by image-intensified fluorescence microscopy. 1-Deamino[3-(p-azidophenylalanine)]-N epsilon-rhodamyllysine-VP (Rhod-N3-dLVP) was obtained in a two-step procedure from the precursor 1-deamino[3(p-aminophenylalanine)]-LVP which was synthesized by a solid phase technique. The rat antidiuretic activity of this compound was 0.34 +/- 0.3 U/mg. Although both Rhod-N3-dLVP and its congener without a rhodamine label, N3-dLVP, did not have any hydroosmotic activity in the isolated toad urinary bladder in the absence of UV light, after UV irradiation they increased both urea and water transport across the bladder wall. Moreover, these permeability effects of Rhod-N3-dLVP persisted during prolonged and repeated periods of washout, suggesting that the photoproducts of this analog had formed covalent complexes with toad bladder receptors. Binding of Rhod-N3-dLVP was inhibited when photolysis was carried out in the presence of 1-deamino-LVP. These studies suggest that Rhod-N3-dLVP has the requisite biological properties to serve as a tool for the localization by fluorescence microscopy of VP receptors in various target tissues.