THE EFFECT OF ATRIAL NATRIURETIC PEPTIDES ON ION-TRANSPORT BY MUSCLE-STRIPPED AND FULL-THICKNESS PREPARATIONS OF RAT COLON

The effects of three atrial natriuretic peptides (ANPs) have been tested for their ability to increase ion transport in muscle-stripped and intact preparations of rat colon. Anaritide (fragment 4-28 of human ANP), human ANP and rat atriopeptin III had no effect on short-circuit current in muscle-stripped preparations. Such insensitivity could not be explained by desensitisation, enzymic destruction or non-specific absorption. Short-circuit current was increased by 8-Br-cGMP and NaNP. The pharmacological activity of anaritide was demonstrated by abolition of phenylephrine-induced tone in rat aortic smooth muscle. In contrast to muscle-stripped colon, intact preparations responded with a tetrodotoxin-sensitive increase in short-circuit current to anaritide even though such preparations were less sensitive to acetylcholine and substance P. These results imply that selective neural damage or the lack of certain nerve pathways, caused by complete muscle stripping, will prevent the pro-secretory effects of anaritide in rat colon.