title: Effects of larkspur (Delphinium barbeyi) on heart rate and electrically evoked electromyographic response of the external anal sphincter in cattle.
abstract: OBJECTIVE-To determine whether larkspur-derived N-(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids alter heart rate and electrically evoked electromyographic (eEMG) response of the external anal sphincter (EAS) in cattle and whether these effects can be reversed by acetylcholinesterase inhibitors. ANIMALS-12 beef heifers and 4 cows. PROCEDURES-3 or 4 heifers were used in 1 or 2 of 7 dose-response experiments; heart rate and EAS eEMG response were assessed before and 24 hours after oral treatment with larkspur (doses equivalent to 0.5 to 15 mg of MSAL-type alkaloids/kg). In 3 subsequent experiments, 3 heifers (1 of which was replaced with another heifer in the control experiment) each received 10 mg of MSAL-type alkaloids/kg and were injected IV with physostigmine (0.04 mg/kg), neostigmine (0.04 mg/kg), or saline (0.9% NaCl) solution 24 hours later, prior to assessment. Additionally, EAS eEMG response was measured in 4 cows before and after epidural administration of 2% lidocaine hydrochloride. RESULTS-Larkspur-treated heifers developed dose-related increases in heart rate and decreases in EAS eEMG response. Twenty-four hours after administration of MSAL-type alkaloids, neostigmine decreased heart rate but did not affect eEMG response, whereas physostigmine did not affect heart rate but caused a 2-fold increase in eEMG response. In cows, epidural anesthesia did not alter eEMG response, suggesting that transdermal stimulation of the EAS pudendal innervation did not occur. CONCLUSIONS AND CLINICAL RELEVANCE-In cattle, cardiac effects and muscle weakness or loss of EAS eEMG response induced by larkspur-derived MSAL-type alkaloids were reversed by neostigmine or physostigmine, respectively. Treatment with anticholinesterase inhibitors may alter the clinical effects of larkspur poisoning in cattle.
authors.affiliation: USDA Agricultural Research Service, Poisonous Plant Research Laboratory, 1150 E 1400 N, Logan, UT 84321, USA.
authors.forename: Benedict T
authors.initials: BT
authors.lastname: Green
authors.forename: James A
authors.initials: JA
authors.lastname: Pfister
authors.forename: Daniel
authors.initials: D
authors.lastname: Cook
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Welch
authors.forename: Bryan L
authors.initials: BL
authors.lastname: Stegelmeier
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Lee
authors.forename: Dale R
authors.initials: DR
authors.lastname: Gardner
authors.forename: Edward L
authors.initials: EL
authors.lastname: Knoppel
authors.forename: Kip E
authors.initials: KE
authors.lastname: Panter