Constriction of human umbilical artery induced by local anesthetics

Effects of lidocaine on rat's isolated tracheal smooth muscle

Lidocaine has been used as an injection or spray solution to protect spasm reaction during tracheal intubation and bronchoscopy. The effect of lidocaine for local anesthesia is well known. However, the effect of the drug to tracheal smooth muscle is not well explored. We used our preparation to test the effectiveness of lidocaine on rat's isolated tracheal smooth muscle. The following assessments of lidocaine were performed: (1) effect on tracheal smooth muscle resting tension; (2) effect on contraction caused by 5 x 10(-6) M methacholine as a parasympathetic mimetic; (3) effect of lidocaine on electrically induced tracheal smooth muscle contractions. The addition of lidocaine induced a relaxation response to methacholine-induced contraction. Low doses of the drug resulted in a slight decrease in contraction and higher doses relaxed the trachea much more quickly. At 10(-3) M of lidocaine, almost 51% of 5 x 10(-6) M methacholine-induced contraction was decreased. Using the same concentration, the drug also could totally inhibit the electrical field stimulation-induced spike contraction. Lidocaine elicited a negligible response to the resting tension of trachea as the concentration increased. The study indicated that lidocaine could cause bronchodilation not only from blocking parasympathetic tone, but also from directly antagonizing the effect of cholinergic receptors.

Impaired cyclic nucleotide-mediated vasorelaxation may contribute to closure of the human umbilical artery after birth

1. The mechanical and biochemical effects of agents that relax vascular smooth muscle either through elevation of guanosine 3':5'-cyclic monophosphate (cyclic GMP) or adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels were compared in isolated ring preparations of human umbilical artery and rat aorta. Tone was established by preconstriction with 5-hydroxytryptamine. 2. The endothelium-dependent vasodilator calcium ionophore (A23187) (which stimulates endothelium-derived relaxing factor [EDRF] release and thus acts through soluble guanylyl cyclase), sodium nitroprusside (which stimulates soluble guanylyl cyclase directly), and atrial natriuretic peptide (which stimulates particulate guanylyl cyclase) relaxed rat aorta but not human umbilical artery. 3. Sodium nitroprusside, 10 microM, increased cyclic GMP levels from 10 to 390 pmol mg-1 protein at 2 min in rat aorta, as compared with a slower, relatively attenuated rise from 5 to 116 pmol mg-1 protein after 15 min in human umbilical artery. The rise in cyclic GMP in the umbilical artery was not significantly augmented by the cyclic GMP phosphodiesterase inhibitor, MB22948. Atrial natriuretic peptide increased cyclic GMP levels in rat aorta but not in human umbilical artery. 4. Forskolin, 10 microM, which stimulates both soluble and particulate adenylyl cyclase, maximally relaxed rat aorta and increased cyclic AMP levels from 15 to 379 pmol mg-1 protein at 15 min, but did not significantly relax or increase cyclic AMP levels in human umbilical artery. After preincubation with the cyclic nucleotide phosphodiesterase inhibitor, IBMX, 10 microM forskolin increased cyclic AMP levels to 1365 pmol mg-1 protein at 30 min in human umbilical arteries, but these high levels were not accompanied by mechanical relaxation.5. 8-Bromo-cyclic GMP and 8-bromo-cyclic AMP which are lipophilic analogues of cyclic GMP and cyclic AMP, both maximally relaxed the rat aorta at a concentration of 10 microM, but did not significantly relax the human umbilical artery.6. The findings indicate that elevated cyclic nucleotide levels are not associated with mechanical relaxation of the post-partum human umbilical artery, as in other vessels such as rat aorta. This impaired response to cyclic nucleotides may contribute to closure of the umbilical artery after birth.

Experimental nerve ischemia and injury produced by cocaine and procaine

The effects of ethanol, glycerol, procaine, and cocaine were tested on rat sciatic nerve blood flow. Blood flow measurements were made using a laser Doppler blood perfusion monitor with a 1 mm diameter probe. The local anesthetics procaine and cocaine produced a dose-dependent and time-dependent decrease in nerve blood flow, but 80% ethanol, 80% glycerol, and 0.9% saline did not significantly alter nerve blood flow either acutely (10 min) or for up to 4 h. For histopathologic studies, the same nerves were removed at 2 days after blood flow tests. Evidence of nerve injury (edema and nerve fiber pathology) was observed for the neurolytic agents ethanol and glycerol and for both local anesthetics. No relationship between nerve blood flow and injury was seen for either ethanol or glycerol; however, both local anesthetics exhibited a highly significant negative correlation (P less than 0.01) between blood flow at 4 h and injury at 2 days. These data provide additional evidence that local anesthetics can decrease nerve blood flow; and these results are consistent with an ischemic mechanism for local anesthetic-induced nerve injury.

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 alpha-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.