pP₂ of eserine and neostigmine on acetylcholine responses of isolated ileum

Abstract

pP2 values of 7*9 and 8-0 for eserine and neostigmine show that these compounds are respectively about 200 and 300 times more potent in potentiating acetylcholine (ACh) responses on isolated cavy ileum than was previously found on frog rectus muscle. The increased tone and spontaneity usually produced by eserine and neostigmine were not prevented by morphine (10 to 100 ,ug/ml), which itself potentiated both ACh and histamine responses. Edge (1967) Results.- Figure 1 Fig. 1. were obtained in the presence of morphine, 10 jug/ml. However, morphine did not prevent spontaneity, tonal increase or mucus expulsion which occurred in three of the four ileal segments used (Fig. Id).Morphine alone also caused an increase in the response to a constant dose of ACh. This potentiation was slight with 10 Mg/ml but more marked with 100 ,ug/ml. These concentrations sometimes caused graded increases in rhythmic movements. The effects were quickly reversed following washout.The potentiating action of morphine was not ACh-specific. A similar potentiation of histamine responses (Paton, 1957) That anticholinesterases increase spontaneity and tone in various smooth muscle preparations is well known. Burn (1952) showed the effect in rabbit duodenum is glucose dependent. Paton (1957) found that morphine reduced the resting release from cholinergic nerve endings in cavy ileum and "quietened" the preparation. In the present experiments morphine tended to increase spontaneity. Carlyle (1963) attributed increase in tone of cavy trachealis muscle to stimulation of ACh release from nerve endings, an action of