CHOLINERGIC ACTIVITY OF SELECTED METHANESULFONATE INSECTICIDES - A PHARMACOLOGICAL PROFILE

Three previously reported methanesulfonate insecticides, 6-isobutylthi o-2-pyridyl methanesulfonate (I) and its sulfoxide (II) and sulfone (I II) analogues were examined in two insect species Lucilia cuprina and Blattella germanica and in tissues from vertebrates. The results of B. germanica tests and cholinesterase assays confirmed the insecticidal activity of the compounds, with cholinesterase inhibition being the mo st likely mode of insecticidal action. The inactivity of the sulfide I and sulfoxide II in vertebrate in-vitro studies may indicate that con version, in vivo, of the sulfide and sulfoxide methanesulfonates to th e sulfone (III) is a requirement for activity. In mouse toxicity tests , matching high toxicity was observed for the alkylthio-, alkylsulfoxy - and alkylsulfone analogues indicating fast metabolic oxidation of th e injected alkylthio- and alkylsulfoxy-compounds. However, in in-vitro tissue tests, the sulfone, although active, did not exhibit the chara cteristic pharmacological profile of the standard acetylcholinesterase inhibitor, physostigmine. The sulfone demonstrated a mixed action, wi th indications that it acts as an inhibitor of specific cholinesterase isozymes, or that it may modify responses at cholinoceptors.