Fruit bromelain ameliorates rat constipation induced by loperamide

Unsweetened pineapple juice is beneficial for routine constipation. The objective of this study was to determine the effect of bromelain (EC 3.4.22.33) isolated and purified from pineapple fruit on constipation. A rat constipation model was established by gavage administration of loperamide hydrochloride. The effects of bromelain on constipation in rats were evaluated in vitro and in vivo. In the ex vivo study, the isometric force of jejunal strips and changes in intracellular Ca2+ ([Ca2+]i) were measured simultaneously. The effect of bromelain on myosin light chain kinase (MLCK)-related intestinal contraction was also studied. Bromelain significantly relieved the high visceral sensitivity and infrequent stools in constipated rats. Bromelain also reversed the slow gastric emptying and slow intestinal transit in constipated rats. Bromelain stimulated intestinal contraction, and the stimulatory effect was inhibited by hemicholinium-3 and atropine, which block the synthesis of endogenous acetylcholine (ACh). The amount of ([Ca2+]i) was significantly increased by bromelain. Bromelain significantly reversed the decreased phosphorylation of the 20 kDa regulatory light chain of myosin (p-MLC20) and the expression of MLCK in constipated rats. These results indicated that bromelain triggered the release of endogenous ACh, increased [Ca2+]i, and enhanced p-MLC20 via activation of MLCK expression, resulting in the increase of gut motility. The beneficial effect of pineapple on constipation is partly dependent on fruit bromelain although the fibers and fluid in pineapple juice are also beneficial.