AN EVALUATION OF THE ACTION OF SUBSTANCE P ON THE JEJUNUM OF THE RABBIT

¹ Department of Pharmacology, Tufts University School of Medicine, Boston , Mass.

The contractile responses of the longitudinal muscle of rabbit jejunum induced by substance P and barium were not affected by concentration of hexamethonium, tetraethylammonium and cocaine, which readily depressed the response to nicotine. Substance P, therefore, does not stimulate the intrinsic ganglia of isolated rabbit jejunum.

The resistance of substance P to atropine blockade is slightly greater than that of nicotine and barium. Acetyicholine and physostigmine are most susceptible to atropine blockade.

Oxygen-deprivation at 1° and 3° C. for 19 to 24 hours rendered the intestine unresponsive to substance P. A much longer time was required to make the tissue unresponsive to other agents.

In segments deprived of oxygen at 37° C. and in other segments deprived of glucose at 37° C. the responses to substance P, barium and physostigmine were depressed, while the response to nicotine was not markedly altered.

Reducing the temperature of the tissue to 30° C. resulted in (a) a marked depression of the responses to substance P, barium and physostigmine; (b) a slight depression of the response to nicotine; (c) no change in the response to histamine and choline; and (d) an increase in the response to acetylcholine. These changes were readily reversed by raising the temperature to 37° C.

The importance of these results in relation to the site of action of substance P is discussed.