Effects of bombesin on the canine gallbladder motility: in vivo and in vitro experiments.

The effects of bombesin (BM) on the canine gallbladder motility was studied under two different experimental conditions: (i) in conscious dogs with a balloon chronically implanted into the gallbladder lumen where intragallbladder pressure was recorded in mm Hg by means of a pressure transducer, and (ii) in smooth muscle preparations isolated from different regions of the gallbladder where the contractions were recorded isometrically by means of mechanoelectrical transducers. Similar to CCK8 bolus injection of. BM i.v. increased the gallbladder pressure in a dose-dependent manner. The response was characterized by a slow increase of the tone and a gradual restoration (in 4 to 8 min) of the background activity. The threshold dose and the maximum dose were 30 ng/kg and 100 ng/kg for BM and 1 ng/kg and 10 ng/kg for CCK8, respectively. Both atropin (10 to 50 micrograms/kg) and hexamethonium (0.5 to 3 mg/kg) injected i.v. 5 to 10 min before BM strongly reduced or even abolished the gallbladder response to BM. Somatostatin (1 to 2 micrograms/kg) and VIP (0.5 to 1 microgram/kg) injected 3 to 5 min before BM also exerted a strong inhibitory effect on the canine gallbladder response to BM. However BM (up to 10(-6) M) had no effect on the spontaneous or electrically-induced contractions of the canine gallbladder smooth muscle preparations. The results suggest the involvement of prejunctional cholinergic-, somatostatinergic- and VIP-ergic pathways in the bombesin-induced increase of the gallbladder pressure of conscious dogs.