Laxative Effects of a Standardized Extract of Dendropanax morbiferus H. Léveille Leaves on Experimental Constipation in Rats

Background and Objectives: This study aimed at investigating the laxative effects of a standardized aqueous extract of Dendropanax morbiferus H. Lév. on two different constipation rat models. Materials and Methods: Animal studies were conducted with low-fiber diet-induced and loperamide-induced constipation animal models, and isolated colons were used in ex vivo analysis to determine the changes in colonic motility caused by D. morbiferus H. Lév. leaf extract (DPL). Results: The results showed that DPL administration significantly improved certain reduced fecal parameters (number, weight, and water content of the stools) in a both low-fiber diet and loperamide-induced constipation models without adverse effects of diarrhea. The laxative effect of DPL was confirmed to improve the charcoal excretion time upon DPL treatment in a low-fiber diet or loperamide-induced constipation model through gastrointestinal (GI) motility evaluation using the charcoal meal test. In addition, when DPL was administered to RAW264.7 cells and loperamide-induced constipation model rats, the production of prostaglandin E2 (PGE2) increased significantly in cells and tissue. Furthermore, DPL dose-dependently stimulated the spontaneous contractile amplitude and frequency of the isolated rat colon. Conclusion: Although our study did not provide information on the acute or chronic toxicity of DPL, our results demonstrated that DPL can effectively promote defecation frequency and rat colon contraction, providing scientific evidence to support the use of DPL as a therapeutic application. However, further toxicity studies of DPL are needed prior to the initiation of clinical trials and clinical applications.

Ascending Excitatory and Inhibitory Motor Activity of Colonic Longitudinal and Circular Muscles in Rat Model

Summary In this experiment we studied the role of excitatory and inhibitory neurotransmissions in the ascending reflex pathways in isolated rat colon. Partitioned organ bath, electrical field stimulation (EFS), drugs and isolated preparations were used to evaluate motor activity of (LM) and circular muscles (CM). Ascending motor responses of LM and CM were frequency-dependent contraction, significantly more expressed in LM. Atropine (0.3 µM) decreased ascending contractions of LM. During atropine treatment spantide (0.1 µM) further suppressed ascending contractile motor responses. In the presence of atropine, L-NNA (0.5 mM) restored ascending contractions of LM, while contractions were strongly depressed after addition of L-arginine (0.5 mM). Ascending response in CM, caused by atropine, consisted of an initial relaxation followed by contraction. Spantide decreased the contraction. L-NNA reduced the relaxation and significantly restored the atropine-influenced contraction, while L-arginine induced a deep relaxation of CM. The presence of ChAT, SP-containing nerve cell bodies and fibers and NADPH-diaphorase-reactive cell bodies and processes in myenteric ganglia were detected. The results indicated that nitric oxide is an important modulator of ascending cholinergic and tachykininergic excitation in colonic region of the large intestine of rats.

Effects of dopamine in isolated rat colon strips

The aim of the present work is to investigate the effects of dopamine on isolated rat colon strips, and whether dopamine receptors are involved in these effects. Experiments on spontaneous motility and under potassium contraction were performed with dopamine and isoprenaline, both in the absence and presence of antagonists (distal colon strips, isotonic recording, Tyrode solution, 31 °C, 1 g of resting tension). At higher concentration (10–4mol/L), dopamine abolished spontaneous motility of the rat colon and this effect was not modified by antagonists. In isolated rat colon strips that were depolarized with potassium, dopamine produced concentration-dependent relaxation, without significant differences in reserpinized rats. Preincubation with sulpiride or Sch 23390, dopamine antagonists, did not modify the effects of dopamine. Propranolol shifted the concentration-response curve to the right, though in a noncompetitive manner. Prazosin and yohimbine (α-antagonists) did not modify the response to dopamine. Isoprenaline produced a concentration-dependent relaxant response to the KCl-induced contraction antagonized by propranolol, but not by prazosin, in a noncompetitive manner. In conclusion, dopamine exhibits a relaxant effect on the isolated rat colon, which is not mediated by specific dopamine receptors or α-adrenoceptors but it may be mediated by atypical β-adrenoceptors. Key words: dopamine, isolated rat colon, dopamine receptors.