Cholecystokinin octapeptide, caerulein, substance P, neurotensin, and angiotensin II: species-typical effects on the isolated portal vein of guinea pig and rat.

The isolated, spontaneously active portal vein of guinea pig was stimulated by the following compounds (the pD2 is given in parentheses): caerulein (CER, 8.02), cholecystokinin octapeptide (CCK-8, 7.59), substance P (SP, 4.68), and carbachol (5.37), whereas neurotensin (NT) was ineffective and angiotensin II (AII) produced inhibition. On the portal vein of the rat, CER and CCK-8 were ineffective, whereas stimulation occurred with SP (5.72), NT (6.79), AII (7.89), and carbachol (5.50). Tetrodotoxin did not modify these effects in both types of preparation. Cyclic dibutyryl guanosine monophosphate reduced the effect of CCK-8 and CER but not that of carbachol. It is concluded that the peptides stimulate the portal vein in a way independent from intramural neurons. It may be speculated that receptors for CCK-8 and CER are absent in the portal vein of rat and those for NT in the guinea pig vein.