The Effect of Adrenaline and Noradrenaline on the Activity of Isolated Preparations of the Gut From the Foetal Guinea‐pig

Abstract

A motor response to adrenaline which occurs in the terminal part of the guinea-pig ileum and is stronger in small than in large animals has previously been described (Munro, 1951a). In view of this apparent relation between the adrenaline response and the size of the animal, it was considered worth while making some observations on the response of the foetal gut to adrenaline. The first few observations suggested that the terminal part of the isolated foetal ileum was relaxed by adrenaline. Further work, however, showed that considerable differences in the nature and the degree of response to adrenaline occurred in different terminal segments. The response was often purely motor, as in the adult; but in those segments whose response was a relaxation continued washing, associated with a reduction of the prevailing tone, usually changed it to a contraction.The present paper describes the distribution of the motor response to adrenaline in the foetal gut, and compares the characteristics of the intestinal response to adrenaline and noradrenaline. It has been shown by West and Shepherd (1951) that the foetal suprarenal glands contain a higher concentration of noradrenaline than of adrenaline. It was therefore of interest to determine the relative effects of these two substances on the foetal intestine. METHODS Mature guinea-pig foetuses were used whose weights varied from 50-70 g.; the appearance of the foetuses was very similar to that of the animal after birth. Ten pregnant animals each provided from two to four foetuses. Those which could not be used immediately were destroyed by cutting the carotid arteries and were placed in the refrigerator, to be used when convenient, which was always within four or five hours from death. Preparations made from foetuses which had been frozen for this length of time responded similarly to fresh preparations.The foetal small intestine varied in length between 16 and 20 in. Segments about 2 in. in length were removed from the required levels of the intestine and suspended in a bath of capacity 100 ml. contain-, ing Krebs's physiological salt solution. Four segments taken from different levels of the same intestine were suspended in one bath at the same time, so that simultaneous records were obtained under identical conditions.; Drugs were added to the bath in a concentration of 1: 2 X 104 from a 2-ml. pipette. The concentration of dl-noradrenaline in the bath was twice that of I-adrenaline when responses to the two drugs were to be compared. Fig. 1 A shows the responses to adrenaline (1: 1 X 106) of segments taken from different levels of the foetal intestine. The terminal ileum contracted; immediately higher segments gave progressively smaller contractions, and at still higher levels the response changed to relaxation. In the region of the duodenum there was a biphasic response with initial relaxation followed by a gradual contraction above the original tonus level. However, some preparations from the foetal duodenum only contracted and others only relaxed. When relaxation occ...

Mode of Action of Partial Agonists on the Taenia Caecum of the Guinea Pig and Drug-Receptor Theory

“…Ephedrine contracts the smooth muscle in the concentrations necessary to cause the maximal relaxation in the presence of the cY and Q-adrenergic blockers. The fact that catecholamines contracted the some intestinal smooth muscle from the guinea pig was already reported (15). Since the inhibitory action of ephedrine on the adrenergic receptor was antagonized by its own excitatory action, the intrinsic activity of ephedrine was smaller than that of norepinephrine.…”

ANTIBIOTIC‐ASSOCIATED COLITIS: AN in vitro INVESTIGATION OF THE EFFECTS OF ANTIBIOTICS ON INTESTINAL MOTILITY

“…The ileum was removed and the 10 cm nearest the ileo-caecal junction discarded, owing to its differing pharmacological properties (Munro, 1953). Luminal contents were removed by gentle flushing with Krebs solution at ) Macmillan Publishers Ltd 1981 37°C.…”

Developmental disappearance of excitatory α1 adrenoceptor function in the oesophagus of chick embryo

“…adrenoceptors (McMurphy & Boreus, 1968) or by both a-and #-receptors (Hart & Mir, 1971). On the other hand, in the lower part of colon (Ohkawa, 1978) and the duodenum (Munro, 1953) of guineapig foetus, an excitatory a-adrenoceptor, which does not function in mature animals, was also reported to be present. These findings suggest the possibility that adrenoceptors change during embryonic development.…”