The effect of pentagastrin, cholecystokinin and their analogues on rat arterial blood pressure and isolated heart.

The influence of pentagastrin (PG) and its analogues: 3-leupentagastrin (3-leu-PG), 4-AspOBzl-pentagastrin (4-AspOBzl-PG), and of the cholecystokinin -terminal tetrapeptide (CCK-4) and its analogue CCK-4(Phet) on rat arterial blood pressure and isolated heart were studied. 4-AspOBzl-PG and CCK-4 (Phet) had no effect on the arterial blood pressure or the isolated heart. PG (1.0 microgram/kg iv), slightly raised the systolic and diastolic arterial blood pressure, whereas 3-leu-PG (1.0 microgram/kg iv) slightly lowered the systolic arterial blood pressure. 3-leu-PG (0.1 microgram/0.1 ml), like PG (0.1 microgram/ 0.1 ml) increased the contraction amplitude of the isolated heart and had no effect on the heart rate, but unlike PG, it had no effect on coronary outflow. CCK-4 (1.0 microgram/kg iv) slightly raised the systolic arterial blood pressure but, unlike cholecystokinin had no effect on the isolated heart. We conclude that shortening of the CCK chain to a C-terminal tetrapeptide reduces the positive inotropic effect. Blocking of one of the aspartic acid carboxyl groups by a benzyl radical in the 4 PG position eliminates the PG effect on the circulatory system. Substitution of metionine for leucine at the 3-PG position reduces the PG action on the circulatory system.