Importance of the vasoactive intestinal peptide receptor in the stimulation of cyclic adenosine 3',5'-monophosphate in gallbladder epithelial cells of man. Comparison with the guinea pig

A new neuroregulator: the vasoactive intestinal peptide or VIP

VIP is a neuroregulator occurring in the central and peripheral nervous system which exhibits the function of neurotransmitter in the brain, neuroendocrine substance at the pituitary level, and neuroparacrine substance in peripheral organs. The structure and the specificity of the molecule as studied by antibody and receptor, and its location in brain and peripheral organs are summarized as well as its numerous biological effects. The method used to demonstrate the involvement of VIP in a physiological regulation is described and illustrated by two examples: the effect of VIP on gut epithelium and the neuroendocrine action of VIP in inducing prolactin release from pituitary cells. The consequence of this recent progress in the knowledge of VIP release and action in human physiology and disease is indicated.

Characterization of the VIP- and secretin-stimulated adenylate cyclase system from human lung

The response of a crude particulate adenylate cyclase preparation from surgically removed human lung to guanine nucleotides, sodium fluoride, beta-adrenergic agonists, prostaglandins, vasoactive intestinal peptide (VIP), secretin, and [Val5]secretin was investigated. The enzyme activity increased 5, 10, and 9-fold, respectively, with GTP, Gpp(NH)p, and sodium fluoride. This activity was stimulated (in the presence as well as in the absence of added GTP) by D,L-isoproterenol, L-epinephrine and L-norepinephrine, the relative potency of these agonists being compatible with the existence of beta-adrenoceptors of the beta2 subtype. Prostaglandins E1 and E2, but not PGF1alpha and PGF2alpha, stimulated the enzyme, PGE1 being at least 10 times more potent than PGE2. The biphasic pattern of stimulation of the same adenylate cyclase activity by VIP suggested the presence of high- and low-affinity VIP receptors coupled to the enzyme. This stimulation by VIP was not inhibited by secretin-(7-27). The stimulation of adenylate cyclase by secretin and [Val5]secretin was also biphasic, suggesting the coexistence of high- and low-affinity secretin receptors. Secretin-(7-27) was able to inhibit completely the secretin stimulation acting through high-affinity secretin receptors but exerted no effect on the stimulation operating through low-affinity secretin receptors, which might indicate that the latter receptors were in fact "VIP-preferring receptors". [Val5]secretin was also used to differentiate these peptide receptors, since its properties were more VIP-like than those of secretin.

Secretin binding sites coupled with adenylate cyclase in rat fundic membranes

Specific binding sites for secretin have been identified in rat fundic membranes, using 125I-secretin. The binding was saturable, reversible, time and temperature dependent. Optimal pH for binding was around 7-7.5. Scatchard plots were compatible with the existence of 2 classes of receptors; the first class with a high affinity for secretin (apparent Kd of 4 x 10(-10) M) and a low binding capacity (150 fmol per mg membrane protein, i.e., 4,500 high affinity sites/cell) and a class of receptors with a lower affinity (Kd of 3 x 10(-9) M) and a higher binding capacity (580 fmol per mg membrane protein i.e., 17,400 sites/cell). Glucagon, gastric inhibitory polypeptide and somatostatin had no-effect on secretin binding. In contrast, VIP inhibited 125I-secretin binding and stimulated adenylate cyclase activity, in both cases at a 200-times lower potency than secretin (ID50 and Ka = 2 x 10(-7) M VIP). The properties of these secretin receptors strongly support the concept that secretin acts as a regulatory peptide on the rat gastric epithelium.