Binding in vitro of vasoactive intestinal peptide on isolated acini of rat parotid glands.

Binding of 125I-labelled vasoactive intestinal peptide (VIP) to rat parotid acini was saturable, temperature-dependent and reversible, and reflected interaction with a single class of binding sites. Parotid glands possessed approx. 400 fmol binding sites per mg protein and binding of the tracer to these sites could be inhibited by VIP [concentration for half-maximal effect (KD), 24 nM], by the peptide histidine isoleucine (KD, 140 nM), by secretin (KD, 470 nM) and by the human pancreatic growth hormone-releasing factor (hpGRF; KD, 3200 nM). In the same acini preparation, 10 microM VIP also stimulated amylase release 4-fold and increased cyclic AMP 11-fold. Thus, VIP might be a neurotransmitter in the rat parotid gland.