Mechanism of action of the anti-shock effect of CCK-8: influence of CCK antagonists and of sympatholytic drugs

In an experimental model of haemorrhagic shock that causes 100% mortality in rats within 30 min, the intravenous bolus injection (20 micrograms/kg) of sulfated cholecystokinin octapeptide (CCK-8) induces a prompt and sustained rise in blood pressure and pulse amplitude, all treated animals still surviving at the end of the experiment (2 h). This effect of CCK-8 is completely blocked by reserpine (5 mg/kg i.p.), significantly antagonized by prazosin (0.1 mg/kg i.v.) and yohimbine (1 mg/kg i.v.), and unaffected by practolol (15 mg/kg i.v.) and proglumide (0.2 mg/kg i.v.); it is completely antagonized by the intravenous (0.01-0.05 mg/kg), but not by the intracerebroventricular (0.002 mg/kg) injection of the 'peripheral' CCK antagonist, L-364,718. The present data indicate that the cardiovascular effects of CCK-8 in haemorrhagic shock involve peripheral CCK receptors, and require the functional integrity of the sympathetic nervous system.