Gall-bladder and sphincter of Oddi response to cholecystokinin in the Australian possum.
The effects of cholecystokinin octapeptide (CCK-OP) on the gall-bladder (GB) and sphincter of Oddi (SO) of the Australian brush tailed possum were examined in 45 anaesthetized animals. CCK-OP (20-640 ng/kg) consistently caused the GB to contract in a dose-dependent manner (Kruskal Wallis P less than 0.05). In 20 animals, the same dose range of CCK-OP produced an excitatory response in the SO, increasing the SO motility index (MI = frequency of contractions x mean peak amplitude) dose-dependently (Kruskal Wallis P less than 0.05). In five animals, an inhibitory response, that is, a decrease in MI, was recorded, with 640 ng/kg of CCK-OP producing a 50% decrease in MI. In the remaining 20 animals, variable responses of both excitation and inhibition were elicited within the same animal. The action of CCK-OP on the SO and GB was not modified by atropine, phentolamine or propranolol. Tetrodotoxin (TTX) reversed the inhibitory responses of the SO to CCK-OP such that responses were excitatory (sign test P less than 0.05). TTX did not alter the response of the GB to CCK-OP. It is concluded that CCK-OP acts directly on smooth muscle receptors of the GB. In the SO, its action is mediated via non-cholinergic, non-noradrenergic inhibitory neurons and also by a direct excitatory action on the smooth muscle of the SO.
Iannos
J
J
Department of Surgery, Flinders Medical Centre, Bedford Park, South Australia.
Saccone
G T
GT
Bushell
M
M
Baker
R A
RA
Toouli
J
J
D000818:Animals; D005704:Gallbladder / Q000187:drug effects / Q000502:physiology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000502:physiology; D009893:Opossums / Q000502:physiology*; D010528:Peristalsis / Q000187:drug effects; D011949:Receptors, Cholecystokinin / Q000502:physiology; D012844:Sincalide / Q000494:pharmacology*; D009803:Sphincter of Oddi / Q000187:drug effects / Q000502:physiology*
D011949:Receptors, Cholecystokinin; D012844:Sincalide