No abstract

We compared in humans simultaneous motor responses of the jejunum, ileum, proximal colon, and gallbladder (GB) to intravenous cholecystokinin octapeptide (CCK-OP). To gauge the physiological relevance of the doses of CCK-OP, intestinal motility and GB contraction were also quantified after a fatty meal. Eight healthy volunteers participated in both experiments. Six graded, 30-min intravenous infusions had a mean range of 2.2 to 73.2 pmol X kg-1 X h-1 of CCK-OP; these spanned from subphysiological (negligible contraction of GB) to pharmacological (producing intestinal symptoms and a 70-99% contraction of GB) levels. CCK-OP inhibited interdigestive cycles of motility, though in some persons fasting patterns persisted with doses of CCK-OP, which produced up to 50% reduction in GB volume. Motility indices of the ileum and proximal colon responded to CCK-OP by decreasing initially but then increasing with larger doses; motility of the jejunum increased gradually at all doses. Judged by the gallbladder's response to food (reduction in volume down from 74 to 29% of original volume), the physiological range of infused CCK-OP was approximately 5-16 pmol X kg-1 X h-1. Within this range of doses of CCK-OP, motility of the jejunum increased, whereas motility of the proximal colon was reduced. These data are consistent with CCK being a "physiological" mediator of intestinal motility in humans; responses of the intestine to the peptide appear to vary regionally.

SUMMARY Patients with chronic renal failure have an abnormal immunoreactive gastrointestinal hormone profile, which is characterised by raised fasting serum concentrations of hormones that have antagonistic effects on exocrine pancreatic function. In addition, in this present study we have found that in renal insufficiency cholecystokinin disappears slowly from the plasma after a constant intravenous infusion of the hormone (p=O0O5 compared with healthy subjects). To evaluate whether the stimulatory or inhibitory hormones have a predominant effect, pancreatic exocrine function under conditions of mannitol perfusion of the duodenum and continuous intravenous cholecystokinin stimulation was studied in eight patients who had severe chronic renal failure and eight age-matched and sex-matched control subjects. Compared with healthy subjects, patients with renal insufficiency had hypersecretion of trypsin in response both to mannitol perfusion of the duodenum and to cholecystokinin stimulation (p<0-05). No significant differences in lipase secretion were noted between the patients with renal insufficiency and control subjects. These findings are consistent with the hypothesis that, of the abnormally raised fasting serum concentrations of gastrointestinal hormones found in renal insufficiency, hormones that stimulate rather than inhibit pancreatic exocrine function predominate. Secondly, the dissociation between trypsin and lipase outputs in chronic renal failure may suggest a differential trophic influence of stimulatory hormones -that is, hypercholecystokininaemia -on pancreatic exocrine enzyme secretion. capacity (CCK-stimulated) in a group of patients with severe chronic renal failure and in age-matched and sex-matched normal subjects and then measured the disappearance of CCK after terminating a continuous CCK intravenous infusion. Methods SUBJECTSEight patients (men, aged 25 to 62 years) with severe chronic renal failure (serum creatinine concentrations 12.0 to 16-9 mg/dl, mean 14.3) and eight age-matched and sex-matched controls were studied after giving written informed consent. The patients with renal failure were on chronic haemodialysis programmes for at least 18 months before the study and had their care in medicinal programme supervised by one of us (JCM). The patients were studied on non-dialysis days, when serum ionised calcium concentrations were normal and non-fluctuating. All

Although hepatic uptake of cholecystokinin (CCK) has been demonstrated, the liver cell involved and the mechanism of uptake remain unclear. We have used dispersed rat hepatocytes, Kupffer cells, and hepatic endothelial cells to characterize uptake and metabolism of radiolabeled CCK peptides. Only rat hepatocytes showed significant uptake of 125I-labeled cholecystokinin octapeptide (125I-CCK-8). Peptide specificity of uptake by hepatocytes was similar to that seen in the isolated perfused rat liver, with extraction of 125I-CCK-8 being sevenfold greater than that of 125I-CCK-33. Uptake was saturable, as 10(-4) M CCK-4 inhibited uptake of 125I-CCK-8 by 85%. Uptake was rapid, temperature dependent, and extensive and was decreased by metabolic inhibition, a proteolytic enzyme (trypsin), organic anions (sulfobromophthalein and taurocholic acid), and an inhibitor of anion transport 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. In addition, uptake was dependent on extracellular anions but not on extracellular sodium, calcium, or magnesium. After uptake, hepatocytes released radiolabel in a time- and temperature-dependent manner, predominantly in metabolized forms. Thus the hepatocyte is the liver cell that extracts CCK by an active, anion-dependent process. The characteristics of the uptake process resemble those described for organic anions and small, cyclic peptides and suggest that small, linear peptides may undergo hepatocyte extraction by a similar mechanism.

We have shown that radiolabeled cholecystokinin octapeptide (CCK-8), CCK-8-desulfate, and CCK-4 are extracted by the liver in a structurally specific manner. Thus, we studied the fate of the extracted radiolabeled peptides by quantitating biliary excretion and determining the nature of the metabolites in bile. There was rapid biliary excretion of labeled CCK-8, CCK-8-desulfate, and CCK-4 by the isolated, perfused rat liver; greater than 75% of the extracted dose and greater than 20% of the injected dose appeared in bile within 20 min after a single pass across the liver. By means of high-performance liquid chromatography and immunoprecipitation, we showed that CCK-8-desulfate and CCK-4 appeared in bile in completely metabolized forms. In contrast, for CCK-8, approximately 20% of the major forms of the label in bile was intact labeled octapeptide. To gain insight into the subcellular sites of metabolism and transhepatic transport of CCK-8, we also determined the effects of taurocholate, lysosomotropic agents, and microtubule binding agents on biliary excretion. Taurocholate had no effect on the percentage of the extracted label excreted into bile. Neither the percentage of the extracted label excreted into bile. Neither lysosmotropic agent, leupeptin, nor chloroquine affected the percentage of the extracted label or the nature of the metabolites appearing in bile. Two microtubule binding agents, vinblastine and colchicine, also did not affect the percentage of the extracted label appearing in bile.(ABSTRACT TRUNCATED AT 250 WORDS)