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Background & Aims: This study was designed to characterize [D-F 5 Phe 6 D-Ala 11 ]Bn(6-13)OMe (BIM26226) as a gastrin-releasing peptide (GRP)-preferring bombesin receptor antagonist and to determine whether GRP physiologically regulates gastrointestinal motility. Intravenous BIM26226 (5–500 μg · kg −1 · h −1 ) inhibits GRP-induced gallbladder contraction and plasma cholecystokinin (CCK) release in a dose-dependent fashion. Methods: Gastric emptying and small bowel transit of a solid meal were quantified using scintigraphy. Meal-stimulated gallbladder contraction was measured by sonography in a 2-period crossover design. Results: Intravenous BIM26226 potently inhibited gastric lag time (114 ± 7 vs. 41 ± 6 minutes [control]) and gastric emptying rate (0.11 ± 0.02%/min vs. 0.26 ± 0.04%/min [control]), whereas concomitant infusion of BIM26226 accelerated small bowel transit time (153 ± 41 vs. 262 ± 20 minutes [control]). A continuous liquid meal perfusion into the duodenum induced complete gallbladder contraction (t 50% , 35 ± 4 minutes), which BIM26226 inhibited significantly (t 50% , 64 ± 8 minutes). BIM26226 did not alter plasma CCK response, indicating that circulating CCK did not mediate these effects. Conclusions: These data show that BIM26226 is a potent antagonist of exogenous and endogenous GRP and suggest that GRP is a major physiologic regulator of gastric emptying, small bowel transit, and gallbladder contraction. GASTROENTEROLOGY 2001;120:361-368

Although reduced biological activity of the obese gene product, leptin, has been associated with obesity, little information is available concerning leptin alterations during anorexia. Therefore, we measured circulating leptin concentrations and hypothalamic leptin binding in anorectic tumor-bearing and pair-fed control rats. Plasma concentrations of leptin decreased in tumor-bearing rats early in the course of tumor growth, and fell to nearly non-detectable levels during severe anorexia. The pair-fed control rats that ate the same amount of food as did the anorectic tumor-bearing rats exhibited a 50% decrease in plasma leptin concentration. Concentrations of free fatty acids were elevated in both tumor-bearing and pair-fed groups, while circulating levels of triglycerides were increased only in anorectic tumor-bearing rats. Leptin receptor density was doubled in the hypothalamus of tumor bearing rats, while binding affinity was decreased by 50%. These results suggest that peripheral leptin production is down-regulated, perhaps due to increased lipolysis in tumor-bearing rats. It appears that hypothalamic leptin systems up-regulate receptor numbers in response to decreased blood leptin level, however, the decrease in binding affinity may compensate for these alterations. Therefore, the influence of leptin on hypothalamic neuropeptide Y feeding systems may be minimal in anorectic tumor-bearing rats.