L-METHIONINE AS A MODULATOR OF ATRIAL RHYTHMICITY IN RABBIT AND GUINEA-PIG

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Abstract
L-methionine 10-4 to 10-3 stimulated isolated rabbit and guinea-pig atria and augmented the actions of nicotine, epinephrine and norepinephrine on atrial contraction. L-methionine combined with adrenaline or noradrenaline appeared to act synergistically in stimulating atrail contraction. Reser-pine diminished the marked stimulant action of nicotine, epinephrine or norepinephrine in the presence of L-methionine on atrial contraction, but not that of epinephrine or norepinephrine alone. L-methionine and reserpine appeared to act antagonistically relative to atrail contraction. L-methionine 10-3 to 2 x 10-3 could resume atrial contraction arrested by reserpine 3 x 10-5. This effect was also seen in presence of hexa-methonium or atropine. If the contraction of atria isolated from reser-pinized animals had been arrested by reserpine 10-5, the addition of L-methionine 10-3 to 3 x 10-3 could not restore them. L-methionine 3 x 10-3 could resume atrial contraction arrested by quinidine 3 x 10-5. This may have been due to its atrial sensitization to the action of endogenous epinephrine. The action of L-methionine was discussed regarding its stimulation of the atria and its antagonism to reserpine, which characteristics may be due to its influence on the formation of metan-ephrine, which substance may be a sensitizer of the epinephrine receptor.