tetragastrin and cholecystokinin-9

The ascending excitatory reflex is an important part of the myenteric reflex. In order to study the ascending neural pathways, isolated segments of rat ileum were stimulated by electrical stimulation of the gut wall (20 V, 3 pulses per second, 1 ms) using platinum electrodes. The excitatory contractile response was recorded using perfused manometric side-hole tubing located 2 and 4 cm orally to the stimulation site. The contractile response to electrical stimulation was abolished by atropine (10(-6) M) or hexamethonium (10(-4) M). The excitatory response increased after administration of the cholecystokinin A (CCK(A)) receptor antagonists lorglumide (3x10(-6) M: +44.1%), devazepide (10(-8) M: +19.4%; 10(-7) M: +30.0%) and SR-27897 (10(-10) M: +21.8%, 10(-8) M: +47.0%, P<0.05, n=8). However, the CCK(B) receptor antagonist L-365,260 also caused a significant increase in the oral excitation (10(-6) M: +27.4%). sCCK-8 caused a significant reduction in the ascending response (10(-8) M: -11.5%) and induced spontaneously occurring contractions at doses ranging from 10(-10)-10(-6) M. CCK-9 significantly increased the ascending response (10(-7) M: +10.9%, P<0.05). However, caerulein (10(-10) M: -25.9%, 10(-8) M: -26.8%; P<0.01) and pentagastrin (10(-10) M: -20.2%, P<0.05; 10(-8) M: -23.7%, P<0.01; 10(-6) M: -28.3%, P<0.001) reduced the ascending contractile response significantly. These data, obtained with potent and highly specific CCK receptor antagonists, demonstrate an inhibitory role of endogenously released CCK within the ascending neural pathway. The data further suggest that exogenously applied CCK-related peptides have different effects on the myenteric reflex which might be due to excitation of the different involved neurons (short and long ascending inter- and motorneurons) in an unphysiological order. Thus in experiments investigating more complex neuronal circuits, experiments with antagonists should be regarded as more specific.

Topics: Animals; Atropine; Ceruletide; Cholecystokinin; Depression, Chemical; Electric Stimulation; Gastrointestinal Agents; Hexamethonium; Ileum; In Vitro Techniques; Male; Muscle Contraction; Muscle, Smooth; Myenteric Plexus; Neural Pathways; Pentagastrin; Peptide Fragments; Peristalsis; Rats; Rats, Wistar; Receptor, Cholecystokinin A; Receptor, Cholecystokinin B; Receptors, Cholecystokinin; Sincalide; Tetragastrin

(Thr28,Nle31)CCK(23-33) (CCK-9) and gastrin(1-17)I (gastrin) inhibited adenylate cyclase activity in membranes from the tumoral rat pancreatic acinar cell line AR 4-2J through a Bordetella pertussis toxin-sensitive mechanism. This contrasted with the stimulatory effect exerted by CCK-9 on adenylate cyclase activity in membranes from normal rat pancreas. The relative potency of CCK-9, gastrin, and related peptides in inhibiting adenylate cyclase, when confronted with previous evidence, suggests that 'non-selective CCK-gastrin CCK-B receptors' predominating over 'selective CCK-A receptors' in the AR 4-2J cell line, favored the coupling of the first receptors to adenylate cyclase through Gi, while CCK-A receptors capable of stimulating the enzyme through Gs were detected only after Bordetella pertussis toxin pretreatment.

Topics: Adenylate Cyclase Toxin; Adenylyl Cyclase Inhibitors; Animals; Cell Membrane; Cholecystokinin; Gastrins; Guanosine Triphosphate; Pancreas; Pancreatic Neoplasms; Pentagastrin; Peptide Fragments; Pertussis Toxin; Rats; Secretin; Tetragastrin; Tumor Cells, Cultured; Vasoactive Intestinal Peptide; Virulence Factors, Bordetella