Interactions between vagus nerve stimulation and pentagastrin or secretin on the guinea pig gallbladder

In guinea pigs, anaesthetised with urethane, stimulation of the peripheral cut end of the cervical vagus activates cholinergic excitatory and non-adrenergic inhibitory fibres to the gallbladder. Central vagal stimulation reflexly contracts the gallbladder by an efferent pathway in the vagus and also activates an adrenergic, non-vagal inhibitory pathway to the gallbladder. Injections of pentagastrin (12-33 mug kg-1 s.c.) or secretin (0.1-0.2 U kg-1 i.a.), doses which produce no effect on gallbladder tone when administered alone, significantly increase the contractions evoked by vagal stimulation.