Effects of soman on vascular contractility of rabbit arteries

The effects of soman (pinacolyl methylphosphonofluoridate), an organophosphorus cholinesterase inhibitor, on vascular contractility were examined on helically cut central ear arteries (CEA) or superior mesenteric arteries (M) from New Zealand White rabbits. Concentrations of soman up to 20 microM added cumulatively to arterial strips did not alter their resting tension. Concentrations of soman up to 10 microM also did not alter the tension responses to cumulatively added norepinephrine (NE), histamine, potassium (KCl), or serotonin (5-HT). Concentration-response curves obtained to each agonist initially, or 2 h later, did not differ in artery strips from control rabbits and those from rabbits given soman at 5 micrograms/kg sc daily for 7 d. Changes in responses to NE between the two time periods did differ in arteries from soman-treated and control rabbits in both the CEA and M, and to histamine in the M. Soman at 10 microM potentiated contractions to single concentrations of agonists in most cases. Soman at 10 microM also further increased the tension of strips already contracted by the agonists. Thus, although soman did not alter the concentration-response curves of the agonists at contracting rabbit arteries, it potentiated contractions to single concentrations of agonists both when added before the agonist and when added at the peak of the agonist-induced contraction. It also altered the rate of change with time of both M and CEA in responses to NE of artery strips from rabbits given soman at 5 micrograms/kg daily for 7 d.