Effects of soman on vascular contractility of rabbit arteries

Acetylcholinesterase-independent action of diisopropyl-flurophosphate in the rat aorta

Recent studies have shown that many organophosphates can bind competitively and noncompetitively to membrane muscarinic receptors. The present study investigated the responses of the rat aortic rings to diisopropyl-flurophosphate (DFP), an organophsophorus cholinesterase inhibitor, and the possible involvement of muscarinic receptors. DFP caused a concentration-dependent contraction when added cumulatively from 10(-8) to 10(-4) M. This contraction was inhibited in a noncompetitive manner by high concentrations of atropine (1.5 x 10(-6) and 1.8 x 10(-6) M) but was unaffected by similar concentrations of selective muscarinic receptor subtype antagonists, pirenzepine, 11-2[2-[(diethylamino)methyl]-1-piperidinyl]acetyl-5, 11-dihydro-6H-rido[2,3-b][1,4]benzodiazepin-6-one (AF-DX116) and 4-Diphenylacetoxy-N-methyl piperidine methiodide (4-DAMP). Phentolamine, an alpha-adrenoceptor antagonist, was able to inhibit the DFP-induced contraction in a noncompetitive manner at a concentration of 10(-7) M. These findings suggested that the DFP-induced contraction in the rat aortic rings was mediated by norepinephrine that was released from sympathetic nerve terminals present in the aortic rings.

Effects of soman on calcium uptake in microsomes and mitochondria from rabbit aorta

Daily administration of soman for several days results in several alterations in the vascular neuroeffector system. To determine whether or not soman alters intracellular Ca2+ uptake, the effects of acute exposure to soman or 7-day administration of 5 micrograms kg-1 of soman on the capacity of microsomes and mitochondria from rabbit aortic vascular smooth muscle to take up 45Ca2+ were determined. Acute exposure to soman concentrations of 1-100 microM did not alter significantly (P greater than 0.05) 45Ca2+ uptake by either microsomes or mitochondria. On the other hand, 7-day soman administration markedly reduced (P less than 0.05) 45Ca2+ uptake by both microsomes and mitochondria. Thus, calcium uptake and intracellular calcium uptake-dependent responses will be affected by repeated soman administration.

Effects of soman on calcium influx into rabbit aorta

The acute addition of 10 microM soman to rabbit aorta rings did not increase resting 45Ca2+ influx significantly in the absence or presence of 10 microM norepinephrine or 80 mM potassium (P greater than 0.05). However, agonist-induced 45Ca2+ influx into aorta rings from rabbits that received soman daily for 7 days was significantly reduced (P less than 0.05) compared to agonist-induced influx into rings from control rabbits. The resting influx of 45Ca2+ into aorta rings from 7 day soman-treated and control rabbits was not different (P greater than 0.05). The depression by soman of norepinephrine- and K(+)-induced 45Ca2+ influx may be due to adaptive changes resulting from the 7-day administration of soman.

The effects of soman on norepinephrine uptake, release, and metabolism

The effects of 7-day administration of 5 micrograms/kg/day of soman sc on norepinephrine (NE) content, and catechol-O-methyl-transferase (COMT) and monoamine oxidase (MAO) activities of three rabbit tissues were examined. Effects on NE uptake by, and electrically stimulated release from, rabbit aorta were also determined, both in the 7-day study and with acutely applied soman. Tissues examined were the thoracic aorta, mesenteric artery, and brain stem. Significant (p less than 0.05) increases following 7 days of soman were observed in NE content: thoracic aorta, 20%; mesenteric artery, 48%; and brain stem, 121%. MAO activity decreased by 29% in the thoracic aorta, 20% in the mesenteric artery, and 48% in the brain stem. COMT activity also significantly decreased in two tissues, the thoracic aorta by 18% and brain stem by 23%. Acutely applied soman reduced electrically released NE from the thoracic aorta, but 7-day soman administration increased it. Seven-day soman administration, but not acutely applied soman increased NE uptake by the thoracic aorta. Thus, 7-day soman administration increased sympathetic capability by increasing NE content, nerve stimulation evoked NE release, and NE uptake, and by decreasing MAO and COMT activity. Therefore, repeated low-dose exposure to soman might exaggerate the response to any given level of sympathetic nerve stimulation and to NE-releasing agents.