Introduction

Said & Mutt (1972) first isolated a vasodilator peptide of 28 amino acids from porcine duodenum and designated it vasoactive intestinal peptide (VIP). Thereafter, VIP was found to be present not only in the duodenum but also in a variety of tissues, including central and peripheral nervous systems, small and large intestines, pancreas, lung and urogenital tract, functioning mainly as a neurotransmitter or neuromodulator (Håkanson et al, 1982; Hökfelt et al, 1982; Marley & Emson, 1982; Fahrenkrug, 1982). Islets of Langerhans are innervated by peptidergic as well as cholinergic and adrenergic nerve fibers: the peptidergic nerve fibers contain VIP immunoreactivity (Miller, 1981) and VIP has been shown to stimulate glucagon and insulin secretion from islets (Schebalin et al, 1976). VIPomas, VIP-producing tumors, often arise in the islets of Langerhans, and many patients with VIPomas associated with the watery diarrhea, hypokalemia and achlorhydria (WDHA) syndrome have been reported (Verner & Morrison, 1958; Bloom et al, 1973; Mekhjian & O'Dorisio, 1987).

In 1983, Itoh et al first characterized the mRNA coding for human VIP precursor (Itoh et al, 1983). The entire amino acid sequence of the precursor, deduced from the nucleotide sequence, indicated that the precursor protein contains not only VIP but also a novel PHI-like peptide of 27 amino acids, PHM-27. This article reviews the current knowledge of the structure and expression of the VIP/PHM-27 gene. In particular, it focusses on the organization of the VIP/PHM-27 gene and on the transcriptional regulation by cAMP and phorbol esters of VIP/PHM-27 gene expression.