Role of the serotonergic pathway in uterotonic activity of Ananas comosus (L.) Merr. - An in vitro and in vivo study.

BACKGROUND: Ananas comosus (L.) Merr. has been used as a traditional medicine in inducing abortion in many countries. Our previous in vitro experiments showed that the aqueous fraction (F4) of A. comosus extract stimulated the rat and human uterine contractions. PURPOSE: The aim of this study was to identify the bioactive compound and further investigate the molecular mechanism of F4 induced contraction and the in vivo uterotonic effect of F4. MATERIALS AND METHODS: Organ bath studies were employed to compare the stimulatory effect of F4 in non and late pregnant uterine tissue followed by isolation of protein from late pregnant uterine tissue for the western blot analysis. The PhysioTel transmitter was implanted in pregnant SD rats to measure the changes in intrauterine pressure (IUP). Analyses of the crude extract and active principle in F4 was performed using LC-HRMS. RESULTS: Ripe F4 in a similar manner as serotonin produced a greater stimulatory response in late pregnant than non-pregnant uterine tissue without significant change in potency; ripe F4 also increased ERK phosphorylation which eventually led to a significant increase of the final product, MMP-13. In pregnant rats (E18), oral ripe F4 (1.5 g.100 g-1 body weight) and ergometrine (1 mg) did not stimulate the uterine contraction probably due to the low level of estradiol and as a consequence low 5-HT receptors at the time of administration. In contrast, in postpartum rats, oral administration of F4 and ergometrine produced a significant increase in maximal IUP to 4.3 and 4.9 folds of basal IUP respectively. Contrary to the folklore use, unripe F4 did not stimulate the uterine activity during pregnancy and postpartum. Bioassay guided fractionation identified serotonin as a major bioactive compound in ripe F4. CONCLUSIONS: Our data clearly indicate that the uterotonic effect of ripe F4 is mediated via the serotonergic pathway and suggest that serotonin rich diet may increase the peripheral serotonin and implicate in diverse physiological functions, including uterine motility.

Potent tocolytic activity of ethyl acetate fraction of Ananas comosus on rat and human uteri.

The aim of this study was to investigate the tocolytic properties of Ananas comosus extract in rat and human uterine tissue in vitro and in the rat in vivo. Organ bath technique was employed to perform functional studies in vitro. The PhysioTel transmitter was implanted in SD rats to measure the changes in intrauterine pressure (IUP) in vivo. Analyses of F2 was performed using LC-HRMS. F2 produced a non-selective inhibitory response on oxytocin, prostaglandin F2α, acetylcholine and KCl. The inhibitory activity of F2 on oxytocin-induced contraction was not attenuated by propranolol, TEA, glibenclamide and indomethacin. Nω-Nitro-L-arginine, a nitric oxide synthase inhibitor, suppressed the maximal tocolytic activity of F2 by 25%. DIDS, an inhibitor of chloride channels, appeared to suppress the relaxant effect of F2. F2 suppressed the oxytocin-induced contraction in Ca2+ free solution. The in vivo tocolytic activity of F2 and ritodrine were observed in non-pregnant rats during the estrous stage by suppressing the frequency and amplitude of IUP peaks following intrauterine administration. Chemical analysis confirmed the involvement of citric acid in the tocolytic activity of F2. However, another less polar fraction is essential to accompany citric acid to produce such potent inhibitory response of F2. It is likely that F2 exerted tocolytic activity by multiple mechanisms, including antagonizing L-type Ca2+ channels, interfering with the intracellular Ca2+ release mechanism and releasing nitric oxide. F2 would be a promising candidate to develop as a tocolytic agent.