Cardiorespiratory and Neuromuscular Effects of Freshwater Cyanophyte Anabena flosaquae in Rats

Abstract

Anatoxin-a, recognised as a potent toxin warfare agent, is considered as a weapon of mass destruction due to its lethal anticholinesterase activity. The intravenous administration of cell-free extract of Anabena flosaquae UTEX-2383(anatoxin-a) produced a transient vasodepressor response followed by a sustained rise in blood pressure. The vasodepressor effect was potentiated by physostigmine and antagonised by atropine and bilateral vagotomy, suggesting the involvement of cholinergic system. On the contrary, the vasopressor response was antagonised by hexamethonium prazosin and hemicholinium-3, indicating that the toxin stimulates the sympathetic system through the release of catecholamines from nerve endings. Prolonged apnoea with attendant bronchoconstriction was observed corresponding to bradycardia and vasppressor response which remained unaltered by atropine while antagonised by bilateral vagotomy. The extract when administered intra-arterially did not modify the apnoea induced by veratridine; but phenyldiguanide potentiated the bronchoconstriction, indicating the involvement of pulmonary vagal afferents. The extract produced a dose- and time-dependent blockade of indirect muscle twitch recorded from gastrocnemius muscle. The neuromuscular blockade was potentiated by neostigmine but unaltered by DTC.