Cyclic AMP production in isolated colonic epithelial crypts: a highly sensitive model for the evaluation of vasoactive intestinal peptide action in human intestine

Epithelial cells of human colon were isolated in the form of entire epithelial crypts devoid of vasoactive intestinal peptide (VIP) as measured by radioimmunoassay. This preparation allowed the demonstration, in any conditions tested, of the considerable sensitivity of cyclic AMP accumulation in colonic epithelium to VIP. The magnitude of cyclic AMP accumulation in this preparation was dependent on temperature, time of incubation and concentration of phosphodiesterase inhibitor. At 37 C, in the presence 0–2 mM 3‐isobutyl‐l‐methylxanthine, a 4‐fold increase of cyclic AMP above basal was observed 5 min after addition of 10‐10 M VIP and a 16‐fold increase (maximal response) was obtained after 20 min by 10‐8 M VIP. The dose‐response curve was studied in conditions of equilibrium, i.e. a 60 min incubation at 15CC in the presence of 0–2 mM 3‐isobutyl‐l‐methylxanthine, and appeared to be monophasic with a half‐maximal stimulation at l‐2 times 10‐9 M VIP. Synthetic secretin, porcine intestinal histidine isoleucine amide (PIHI) and the other active substances (prostaglandins E and isoproterenol) were 2500, 600, and at least 100 times less potent than VIP, respectively. Adenylate cyclase of membranes prepared from epithelial crypts was stimulated by concentrations of VIP identical to those acting on cyclic AMP level in intact crypts. Plasmas from patients with the watery diarrhoea syndrome were able to induce a significant rise of cyclic AMP production in human colonic epithelial crypts. This effect was suppressed by previous exposure of the plasmas to a specific anti‐VIP immunserum.