Benzodiazepine analogues L365,260 and L364,718 as gastrin and pancreatic CCK receptor antagonists

Abstract

We examined the ability of the recently described 3-(benzoylamino)benzodiazepine analogue L365,260 and the 3-(acylamino)benzodiazepine analogue L364,718 to distinguish gastrin from pancreatic cholecystokinin (CCK) receptors. Neither L365,260 nor L364,718 when present alone (1 microM) caused stimulation of amylase release from guinea pig pancreatic acini or caused contraction of smooth muscle cells from guinea pig stomach. Each analogue inhibited CCK-stimulated amylase release, gastrin-17-I-stimulated smooth muscle contraction, binding of 125I-Bolton-Hunter-cholecystokinin octapeptide (125I-BH-CCK-8) to pancreatic CCK receptors, and binding of 125I-gastrin-17-I to gastrin receptors on pancreatic acini. L365,260, (Ki, 7.3 +/- 0.8 nM) was 50-70 times more potent than L364,718 at inhibiting binding of 125I-gastrin to pancreatic acini or gastrin-stimulated smooth muscle contraction. In contrast, L364,718 (Ki, 4 +/- 1 nM) was 145-200 times more potent than L365,260 at inhibiting binding of 125I-BH-CCK-8 to pancreatic acini or CCK-stimulated amylase release. Neither L364,718 nor L365,260 distinguished between high- and low-affinity CCK binding sites. L365,260 and L364,718 did not inhibit binding of radiolabeled vasoactive intestinal peptide, secretin, bombesin, substance P, or N-methylscopolamine to pancreatic acini. These results demonstrate that, in contrast to other gastrin-CCK receptor antagonists described, L365,260 is a selective gastrin receptor antagonist having an 80-fold higher affinity for gastrin than pancreatic CCK receptor, whereas L364,718 has a 125-fold higher affinity for pancreatic CCK receptors. Because of the selectivity of these two antagonists the involvement of CCK and gastrin in various physiological processes can be differentiated even when both receptors occur on the same cell.

Characterization of CCK receptors in a novel smooth muscle preparation from the guinea‐pig stomach by use of the selective antagonists CI‐988, L‐365,260 and devazepide

“…The data obtained in this study disagree with the observations made in isolated cell preparations wherein the CCKA selective antagonist, devazepide, was more powerful than L-365,260 at inhibiting the contractile responses to gastrin (Grider & Makhlouf, 1990). However, the data are in agreement with those obtained in a similar isolated cell preparation in which L-365,260 was more powerful than devazepide at blocking the contractile effects of CCKB-selective agonists (Huang et al, 1989).…”

Functional comparisons of gastrin/cholecystokinin receptors in isolated preparations of gastric mucosa and ileum

“…This non-selective action may account for the increasing antagonist activity and maximal depression seen with lorglumide as an antagonist of CCK-8 ( (Makovec et al, 1986;Bock et al, 1989;Hughes et al, 1990). However, different estimates of receptor binding affinity for these antagonists have been observed in other studies (Hill & Woodruff, 1989;Huang et al, 1989). In the present studies we have attempted to characterize gastrin/ CCK receptors by determining the apparent affinities of gastrin/CCK receptor antagonists in functional studies using isolated preparations of rat gastric mucosa (RGM) and guinea-pig ileum longitudinal muscle myenteric plexus (GPI).…”

The use of receptor desensitization to analyse CCKA and CCKB/gastrin receptors coupled to contraction in guinea‐pig stomach muscle

“…Previous reports have been inconsistent with respect of the involvement of specific CCKA-or CCKB/gastrin receptors in the contractile effects of CCK-8 and PG in guinea-pig stomach muscle (Bitar & Makhlouf, 1982;Huang et al, 1989;Menozzi et al, 1989;Grider & Makhlouf, 1990;Boyle et al, 1992;1993). Boyle et al (1993) have suggested that both were coupled to muscle contraction.…”

“…Previously, the guinea-pig gastric muscle has been shown to contract in response to stimulation by both CCK and gastrin and the effects of the selective antagonists, devazepide and L-365260, have been examined (Bitar & Makhlouf, 1982;Huang et al, 1989;Menozzi et al, 1989;Grider & Makhlouf, 1990;Boyle et al, 1992Boyle et al, , 1993. The results of these studies are in conflict with respect to the involvement of specific CCKA-or CCKB/gastrin receptors in gastric smooth muscle contraction, in contrast to in vitro results in gastric acid secretory assays where CCK and gastrin only stimulate secretion by an action at CCKB/gastrin receptors (Spraggs & Patel, 1989).…”

“…The results of these studies are in conflict with respect to the involvement of specific CCKA-or CCKB/gastrin receptors in gastric smooth muscle contraction, in contrast to in vitro results in gastric acid secretory assays where CCK and gastrin only stimulate secretion by an action at CCKB/gastrin receptors (Spraggs & Patel, 1989). For example, L-365260 was reported to be 50-fold more potent than devazepide as an inhibitor of gastrininduced, guinea-pig gastric muscle contraction suggesting that the contraction was mediated by CCKB/gastrin receptors (Huang et al, 1989). In contrast, Grider & Makhlouf (1990) reported that devazepide (10 nM) abolished the contractile Brkish Joumal of Phannmlogy (1995) 1K 339-348 3L.A.…”