The hepatobiliary transport of two cholephilic anions, bilirubin and bromosulfophthalein, is compared in the rat following the administration of clofibrate. In the treated rats, the bilirubin transport maximum (on a whole liver basis) increased by 84%. This increase is related to a higher excretion rate of conjugated bilirubin in bile. Hepatic unconjugated bilirubin is not modified. On the contrary, bromosulfophthalein transport decreased slightly but significantly. These results suggest that clofibrate acts primarily on bilirubin hepatic transport by stimulating the conjugating enzyme activity.
The duodenal mucosa has long been shown to be the source of hormones which participate in the control of exocrine pancreatic secretion. However, little is known of the stimulation of these hormones by food substrates. In order to study this regulation, the following experiment has been carried out: an oral glucose load or a lactalbumin-hydrolysate load was given to a first series of rats: the duodenal mucosa was removed at various times after the oral load: 5, 15, 30, 45 and 60 min. Aqueous extracts of the mucosae were injected into the coeliac trunk of a second series of rats while collecting pancreatic juice for amylase and trypsin activity measurements. The extracts of mucosae removed from the first series of rats 30 min after an oral glucose load and injected into the second series induced an amylase stimulation which was significantly different from that of control rats, whereas trypsin activity remained low. Conversely, extracts of mucosae removed 5 and 45 min after an oral load of lactalbumin-hydrolysate elicited a marked stimulation of trypsin, whereas amylase activity did not differ from that of control rats.
The release of hydrolases from rat pancreas was stimulated in vivo and in vitro by somatostatin. In vitro this hypersecretion was accompanied by a moderate but significant rise in intracellular cyclic AMP. In addition, the tetradecapeptide inhibited rises of cyclic AMP provoked by secretin. The existence of the same sequence of four amino acid residues in the two peptides suggests that somatostatin's activation of the exocrine pancreas depends on its interaction with secretin receptors.
