Mechanism of cholecystokinin-A- receptor antagonist on human pancreatic exocrine secretion. Localization of CCK-A receptor in the human duodenum.

Expressions of the cholecystokinin (CCK)-A and -B receptor genes in human duodenum, pancreas and gallbladder were examined by Northern blot analysis and reverse transcriptase polymerase chain reaction (RT-PCR) followed by Southern blot hybridization. The autoradiographic study of CCK-A and -B receptors in the human duodenum and pancreas was examined in vitro. To determine the subtypes to CCK receptors in the pancreas or duodenum, we studied the abilities of CCK-A and -B receptor agonists (CCK-8 and gastrin) and antagonists (loxiglumide, L-364,718 and L-365,260) to inhibit binding of 125I-CCK-8. CCK-A receptor mRNA was not expressed in the human pancreas, but was expressed in the gallbladder and duodenum, although it was expressed in the pancreas by RT-PCR. CCK-B receptor mRNA was expressed in the pancreas, but not in gallbladder and duodenum. Using autoradiography, high concentrations of CCK-A receptors were detected in the duodenal mucosa, although in the pancreas only CCK-B receptors were detected by this method. These results suggest that localization of CCK-A receptor in human duodenum provides a biochemical and morphological basis for some physiological functions of CCK.

Biochemical and pharmacological profiles of loxiglumide, a novel cholecystokinin-A receptor antagonist.

Loxiglumide ((+/-)-4-(3,4-dichlorobenzamido)-N-(3-methoxypropyl)-N- pentylglutaramic acid, CAS 107097-80-3, CR1505) is a new derivative of glutaramic acid. Radioligand displacement assay was performed to characterize the selectivity of loxiglumide to CCK-A (cholecystokinin-A) receptor (rat pancreas and bovine gallbladder) and CCK-B/gastrin receptors (guinea pig cerebral cortex and guinea pig gastric parietal cell). And tissue bioassay was performed to investigate the effect of the compound on contractions of the guinea pig gallbladder and ileum. Loxiglumide inhibited 125I-CCK-8 binding to rat pancreatic and bovine gallbladder membranes with IC50 values of 195 and 77.1 nmol/l, respectively. Loxiglumide also inhibited 125I-CCK-8 binding to guinea pig cerebral cortex membranes and parietal cells with IC50 values of 12363 and 15455 nmol/l, respectively. In addition, loxiglumide inhibited 125I-gastrin binding to guinea pig parietal cells with IC50 values of 6134 nmol/l. These results indicate that the affinity of loxiglumide to CCK-A receptor is at least 63 times greater than that to CCK-B/gastrin receptors. In vitro functional studies utilizing CCK-induced contractions of the isolated guinea pig gallbladder and ileum further demonstrate that loxiglumide acts as a competitive CCK antagonist with a high affinity to these tissues (gallbladder, pA2:6.71).

[Quantitative evaluation of liver function with 99mTc-GSA scintigraphy using extraction index].

Extraction index (EI5) was introduced to evaluate liver function quantitatively with 99mTc-GSA (GSA) scintigraphy, and it was compared with conventional indices; receptor index (LHL15) and clearance index (HH15). EI5 is expressed as following equation: EI5 = (L5 - L3)/(H3 + H5) * PH/PL where L3, L5: counts at 3 or 5 minutes after the injection in the liver ROI, respectively, H3, H5: counts at 3 or 5 minutes in the heart ROI, respectively; PL, PH: numbers of pixels in the liver- and heart-ROI, respectively. We performed GSA scintigraphy in 40 patients with liver dysfunction and calculated values of the indices. Good correlations were observed between EI5 and liver function tests. Correlation coefficients were almost equal to or higher than those between conventional parameters and liver functional tests. EI5 was thought to be a practical index, and it could be calculated in a short time without aid of computer. Evaluation of local liver function may be possible, because EI5 was corrected with numbers of pixels in the liver- and heart-ROI; which was not considered in the conventional parameters.