"In vitro" duodenal muscle in the pharmacological study on natural compounds

In vitro duodenal muscle was found to be a useful tool in the study of natural compounds. In the field of polypeptides rat duodenum was found to be of definite importance to differentiate the bradykinins (which induce relaxation) from the tachykinins (which evoke contractions). Human duodenum both "in vitro" and "in vivo" is relaxed by peptides of the gastrin and cholecystokinin family (like caerulein), whereas it is contracted by bombesin. Dog and cat duodenum is contracted by all the different types of peptides though in various degrees. Guinea pig duodenum is contracted by many peptides and also by histamine and related substances. In this case another differentiation seems to be possible as contraction induced by stimulation of H1 receptors concerns essentially the longitudinal muscle layer whereas stimulation of H2 receptors seems to inhibit the longitudinal contraction because of a contraction of the circular muscle or because of true relaxation of the longitudinal muscle. All the above considerations suggest that a comparative study performed on duodenal muscle of different animals might give useful information in the screening of new natural active compounds of synthetic analogues.