Antagonism produced by hypertonic nutrient solutions on the depressive effect of carbofuran on isolated guinea pig atria

The action of hyperosmotic nutrient solutions on the depressive effects of carbofuran was studied on spontaneously contracting guinea pig atria. The force and frequency of contraction were recorded using an isotonic lever. Carbofuran 33.0 micrograms ml-1 produced a gradual depressive effect. The time for stabilization of the depressive effect was 6.0 +/- 2.3 min. After the depressive effect of carbofuran was established, NaCl, mannitol, or urea were introduced into the organ bath to increase the osmolarity of the nutrient solution to about 100 mosmol kg-1 of water. This resulted in a reversal of the contraction force and frequency to the initial levels. The addition of the osmotic agents at the same concentrations before the addition of 33.0 micrograms ml-1 carbofuran avoided its depressive effect on guinea pig atria.