[Actions and mechanisms of counterirritants on the muscular circulation]

Studies were conducted on the direct actions of counterirritants on the peripheral circulation and the reflex actions on muscular circulation that would refer to the skin nerve excitation activated with counterirritants . Blood pressure falling tendencies were observed with menthol, thymol, and methyl salicylate (MS) without any effects on respiration, heart rates, and blood flow in femoral artery and gastrochemius muscle. Vasodilatation was caused by the direct application of menthol, camphor, and MS in the isolated ear vessels of rabbits, but none of the counterirritants had effects when they were externally applied on the skin of the ear in plaster form. An increase (circa 40%) in gastrocnemius muscle blood flow was induced by the external application of plasters which contained menthol, camphor, or nonylic vanilyl amide ( NVA ) on the skin of rabbit's hind limb. A slight augmentation was also observed after the application of plasters with MS and without drugs, but these effects disappeared after the hemisection electrical stimulation on the sural nerve of rabbits disappeared almost completely after the pretreatment with propranolol (40 micrograms/kg, i.v.), but atropine (1 mg/kg, i.v.) had no effect. A rise of blood flow in the deep radial muscle elicited by electrical stimulation on the superficial radial nerve remained after the spinal transection at the C 3 level, and at this time, the A beta and A delta components were involved in the superficial radial nerve. These results suggest that when plasters containing counterirritants were externally applied on the skin, direct actions of percutaneously absorbed drugs on peripheral circulation are not expected, but a rise of muscle blood flow is thought to be induced by the spinal somato sympathetic reflex that will cause a suppression on tonic activity in the sympathetic vasoconstrictor nerve or a stimulation on beta-adrenoceptors referred to adrenaline released from the adrenal gland.