Effect of Drugs Upon Tonus Waves in Excised Auricle and Coronary Vessels of Terrapin.

Abstract

Excised terrapin auricles show continuous tonus waves 20 to 42 hours after excision, when kept in oxygenated Ringer's solution pH 7.8 to 8.0, at room temperature 20.5 to 27° C. Immediately after excision, decreasing the pH from 7.4 to 7.0 causes a disappearance of the tonus waves. 1 These waves reappear when the auricles are replaced in a solution of pH 7.4. Eighteen to 42 hours after excision these same auricles fail to respond by disappearance of tonus waves until a pH of about 6.2 to 6.0 is reached. In one case the tonus waves disappeared only after the pH was reduced to 5.8 and showed optimum tonus waves at pH 6.8. Phosphate buffered solutions tend to stimulate tonus waves. In some auricles, in which carbonate-HCl buffered Ringer's solution pH 6.6 caused the tonus waves to disappear, phosphate buffered Ringer's solution 6.2 caused an increase in tonus waves, and when this solution was replaced by Ringer's pH 7.4 temporary disappearance of the tonus waves occurred.

Small doses of adrenalin (alkaloid) 1:1,000,000,000 solution cause increased tonus in the fresh preparation 2 (stimulation of the positive tono-trophic fibres) but not in the 24-hour strip. The addition of adrenalin to the bath does not initiate these tonus waves in auricles in which they are not present. Larger doses of adrenalin (alkaloid) 1:100,000,000, cause a disappearance of the tonus waves (stimulation of the negative tono-trophic fibres). 2 , 3 This decrease in tonus is independent of changes in pH of the bath. Tyramine acid phosphate influences tonus waves in the same manner as does adrenalin, but a higher concentration is required to stimulate the negative tono-trophic fibres.