Changes in heart rate and blood pressure upon injection of algesic agents into skeletal muscle.

In cats anaesthetized with chloralose and urethane algesic substances were injected intra-arterially into muscles of the left hindlimb and the resulting changes in heart rate and blood pressure recorded. The vagus nerves and both carotid sinus nerves were cut. Injection of KCl regularly induces acceleration of the heart rate and an increase in blood pressure. With bradykinin both accelerations and decelerations were observed (with or without accompanying pressor or depressor responses respectively). Injection of serotonin was rather ineffective in producing heart rate or blood pressure changes but subsequent injections of either KCl or bradykinin gave rise to enhanced acceleration and pressor responses. In the discussion it will be proposed that the diverse responses are due to differences in the composition of the afferent volleys elicited, probably because besides stimulating nociceptors these algesic substances activate to a varying extent non-nociceptive muscular fine afferent units of different modality and various central actions.