Physiologic Concentrations of Bile Salts Inhibit Rat Hepatic Alkaline Phosphatase but Not the Intestinal Isoenzyme

Objective: The effect of bile salts on alkaline phosphatase (EC 3.1.3.1) activity from Wistar rat liver, duodenum, jejunum, and serum was investigated. Design and results: For concentrations higher than 1 mM conjugated bile salts (glycocholate, glycochenodeoxycholate, taurocholate, taurodeoxycholate, and taurochenodeoxycholate) inhibited hepatic ALP but, up to concentrations of 10 mM, had no effect on intestinal ALP. Also cholate, deoxycholate, and chenodeoxycholate, within the same concentration range, did not have any effect on intestinal ALP. ALP inhibition induced by conjugated bile salts was significantly higher in serum of starved rats than in serum of fed animals, what is in good agreement with the known higher proportion of hepatic ALP and lower proportion of intestinal ALP in serum of starved rats. Conclusions: Bile salts can, thus, be used to help discriminating between tissue-nonspecific and intestinal ALP isoenzymes and identifying pathologic conditions where the relative quantities of these isoenzymes are altered in serum. Inhibition of hepatic ALP by physiologic concentrations of bile salts may bear some relation to the bile salts effects on their own enterohepatic circulation and/or biosynthesis.