Clinical signs and studies of the site of action of purified larkspur alkaloid, methyllycaconitine, administered parenterally to calves.

The purified diterpenoid alkaloid, methyllycaconitine was isolated from Delphinium brownii and injected intravenously into beef calves in order to observe the clinical signs. Following injection and depending upon dosage, calves showed a variety of signs; agitation, respiratory difficulty and loss of muscle control. Collapse occurred at higher doses of methyllycaconitine. Onset of clinical signs after injection occurred within two to three minutes, and recovery was rapid, clinical signs disappearing within five to ten minutes postinjection.The clinical signs observed are consistent with a skeletal neuromuscular site of action. Methyllycaconitine may have a curare-like action of postsynaptic blockage of nicotinic cholinergic receptors in cattle as has been demonstrated by in vitro experiments in other species. Physostigmine appears to be an effective antidote to methyllycaconitine.