Effects of lidocaine and procaine on canine nasal blood vessels

The effects of lidocaine and procaine on contractile responses of isolated canine nasal mucosal blood vessels to field stimulation and methoxamine were investigated. Analysis of cumulative dose-response curves showed that the two local anesthetics antagonized methoxamine and inhibited the field-stimulation response. The latter effect was interpreted as due to the blockade of Na⁺channels. This would inhibit nerve conduction induced by field stimulation. The former effect on methoxamine is probably caused by the effect of these anesthetics on the mobilization of Ca⁺⁺ needed for smooth muscle contraction. Preincubation of the nasal mucosa with low doses of procaine or lidocaine shifts the methoxamine dose-response curve to the right. With higher doses, the maximal response is also reduced. The shift of the dose-response curve showed that procaine or lidocaine can change the α-adrenergic receptor affinity. Commercial 1% lidocaine with 1:100,000 epinephrine also inhibits field stimulation and antagonizes methoxamine contractions. Lidocaine can increase the basal tone of nasal mucosa, while procaine cannot. From these results, we conclude that procaine and lidocaine have common mechanisms in blocking Na⁺ channels but differ in their ability to modify Ca⁺⁺ stores or channels.