Comparison of the effects of substance P and substance K on blood pressure, salivation and urinary bladder motility in urethane-anaesthetized rats.

The effects of substance P and substance K on blood pressure, salivation and urinary bladder motility were investigated in urethane-anaesthetized rats. On intravenous administration, both peptides produced dose-related reductions in blood pressure, substance P being 25-30 times more potent than substance K. Substance P induced a dose-dependent increase of salivation, while substance K was half as active and induced only 40% of the maximum effect of substance P. The two tachykinins induced contractions of the urinary bladder, substance K being about twice as effective as substance P. Substance K was more effective than substance P in activating micturition. These findings provide further evidence that multiple receptor types are involved in mediating the effects of tachykinins in peripheral organs.