Bile-stimulated secretin release in cats

Duodenal perfusion with sodium taurocholate (TC), pH 10.5 (60 mM, made isotonic with NaCl, 30 ml/h for 90 min), increased the plasma immunoreactive secretin level (IRS) from 2.1 +/- 1.0 to 19.1 +/- 6.0 pM (p less than 0.025; n = 6) in anaesthetized cats. Dose-response studies with TC, pH 7.2 (0-60 mM, made isotonic with NaCl, 45 ml/h for 20 min), demonstrated a threshold concentration of TC for IRS release between 10 and 15 mM (p = 0.05; n = 6). Instillation of gallbladder bile from the same animal (1.5 +/- 0.1 ml, pH 7.0 +/- 0.1, over 12 min) increased the IRS concentration from 1.5 +/- 0.4 to 8.1 +/- 3.4 pM (p less than 0.025; n = 6). IRS concentrations also increased when gallbladder bile was mixed with either saline (from 3.4 +/- 1.7 to 11.6 +/- 2.5 pM; p less than 0.05; n = 5) or feline pure pancreatic juice (PPJ) (from 3.1 +/- 0.7 to 5.7 +/- 1.1 pM; p less than 0.025; n = 6). The peak value was significantly lower when bile was mixed with PPJ than with saline (p less than 0.05). We conclude that TC, the dominating bile salt in feline bile, can release IRS also above pH 7, that physiological concentrations of TC can elicit this response, that the response is also produced by gallbladder bile from the same animal, and that PPJ inhibits the bile-induced IRS release. Thus secretin release by bile is likely to be a physiological principle in the regulation of the pancreatic secretion.