Dual concentration-dependent effects of phorbol 12, 13-dibutyrate on spontaneous and acetylcholine-induced electrical responses recorded from isolated circular smooth muscle of the guinea-pig stomach antrum

Pharmacological Studies Pertaining to Smooth Muscle Relaxant, Platelet Aggregation Inhibitory and Hypotensive Effects of Ailanthus altissima

OBJECTIVE

This in vitro and in vivo study was conducted to rationalize some of traditional medicinal uses of Ailanthus altissima in gastrointestinal, respiratory, and cardiovascular systems.

MATERIALS

Crude extract of Ailanthus altissima (Aa.Cr) and its fractions were prepared and utilized in in vitro and in vivo studies. For in vitro studies, Aa.Cr was investigated on isolated rabbit jejunum, isolated tracheal strip, and isolated aorta of rat suspended in tissue organ bath. Platelet rich and platelet poor plasma were used to study platelet aggregation inhibitory activity. In vivo antidiarrheal effect of Aa.Cr was investigated on balb/c mice pretreated with castor oil to induce diarrhea and SD rats were used to study hypotensive activity.

RESULTS

Concentration dependent spasmolytic effects of Aa.Cr and its DCM fraction (Aa.DCM) were observed on spontaneous and spasmogen induced contractions in jejunum isolated from rabbit, but effect against high potassium (high-K+) induced contractions was more potent. Moreover Aa.Cr showed parallel shifting of calcium response curve to the right side. While its aqueous fraction (Aa.aq) caused spasmogenesis of isolated rabbit jejunum, this effect was blocked partially with prior administration of atropine (1μM). Concentration dependent protection against castor oil induced diarrhea was also observed. Relaxant effect was observed by the application of Aa.Cr and Aa.DCM against high-K+ and carbachol (CCh) induced contractions in tracheal strips isolated from SD rats, while Aa.Aq caused partial relaxation of high-K+ induced contractions, but no effect was observed against CCh induced contractions. Relaxation of rat aorta by the application of Aa.Cr and its fractions was also observed. Inhibition of force of contraction in rabbit atrium was also observed. Inhibition of platelet aggregation was observed against epinephrine and ADP induced aggregation.

CONCLUSION

Keeping in view the observed results, it is concluded that smooth muscle relaxant, platelet aggregation inhibitory and hypotensive effect may be due to the blockage of calcium channels.

Pharmacological evaluation of smooth muscle relaxant and cardiac-modulation potential of Phyla nodiflora in ex-vivo and in-vivo experiments

OBJECTIVE

To investigate the pharmacological basis of its uses of Phyla nodiflora (P. nodiflora) for the treatment of anomalies predominantly by smooth muscle containing tissues such as gastrointestinal/vascular/broncho spasm and cardiovascular modulation.

METHODS

The crude hydroalcoholic extract of P. nodiflora (Pn.Cr) and its fractions were evaluated on isolated rabbit jejunum, rat trachea, aorta and atrium. To access the contractile or relaxant effects of testing materials, the tissues were mounted in isolated organ bath and responses were recorded with transducers coupled with data acquisition system. BALB/c mice were challenged with castor oil for the assessment of in-vivo antidiarrheal activity. Normotensive rats were used for in-vivo hypotensive study.

RESULTS

Hydroalcoholic extract of Pn.Cr at variable concentrations inhibited the natural spontaneous rhythm and 80 mmol/L K⁺ mediated contractions in isolated segment of jejunum with EC₅₀ values of 3.18 and 1.91 mg/mL respectively. Verapamil, a Ca²⁺ channel blocker, demonstrated akin pattern in jejunum and therefore possibly suggesting calcium blocking activity. On isolated rat tracheal tissue, Pn.Cr showed relaxation of high-K⁺ and carbachol mediated contractions (EC₅₀ values: 1.24 and 2.42 mg/mL). Pn.Cr treatment relaxed the rat aortic ring in a cumulative doses with high-K⁺ and phenylephrine-induced contractions (EC₅₀ values 0.25 and 0.92 mg/mL). Activity based fractionation of Pn.Cr showed that dichloromethane fraction was more potent for relaxing the tissues spasm compared to aqueous fraction. In-vivo experiments, significant protection by Pn.Cr (P < 0.05) was observed in castor oil-induced diarrhea (50-500 mg/kg) whereas hypotensive effect in anesthetized rats was seen at the dose range of 1-10 mg/kg of Pn.Cr (P < 0.05).

CONCLUSION

This study suggests the blockage of calcium channel in the smooth muscles as a pharmacological application to make usage of P. nodiflora in the management of diarrhea, asthma and hypotensive effect.

Effects of the aqueous extract of Pittosporum mannii Hook. f. (Pittosporaceae) stem barks on spontaneous and spasmogen-induced contractile activity of isolated rat duodenum

ETHNOPHARMACOLOGICAL RELEVANCE

Pittosporum mannii Hook. f. (Pittosporaceae) is a plant widely used in traditional medicine in Cameroon for the treatment of many gastrointestinal disorders including diarrhea. To date, no pharmacological study on the antidiarrheal and the antispasmodic properties of this plant has been reported. The aim of the present study was to evaluate in vitro the relaxant activity of the aqueous extract of stem barks of P. mannii (PMAE) on rat duodenum.

MATERIALS AND METHODS

Different concentrations of PMAE were tested separately (10-80 µg/mL) or cumulatively (5-80 µg/mL) on spontaneous and spasmogen (carbachol, histamine and KCl)-induced contractions of isolated rat duodenum strips.

RESULTS

At concentrations ranging from 10 to 80 µg/mL, PMAE significantly decreased the tonus and the amplitude of spontaneous contractions. However, at high concentration (80 µg/mL), the extract elicited a transient relaxation was followed by a slight increase of tonus, while the amplitude remained lower compared to the normal spontaneous activity. The relaxant effect of the extract was not significantly affected in the presence of atropine (0.713 µg/mL) and promethazine (0.5 µg/mL). In addition, PMAE (20, 40, and 80 µg/mL) partially but significantly inhibited in a concentration related manner the contractions induced by carbachol (10(-9)-10(-4)M) and histamine (10(-9)-10(-4)M) on rat duodenum. PMAE (10-80 µg/mL) also significantly induced a concentration-dependent relaxation on KCl (20mM, 50mM, 10(-3)-6.10(-3)M)-induced contraction of rat duodenum.

CONCLUSIONS

These results show that the aqueous extract of P. mannii stem barks possesses antispasmodic and spasmolytic effects at lower concentrations; therefore, supporting the use of the stem barks of this plant in the folk medicine for the treatment of diarrhea. However, caution should be paid while using higher concentrations that instead might produce spasmogenic effect and might worsen the diarrheal condition. The relaxant effect of PMAE appears to be non-specific of muscarinic or histaminic receptors, but may involve at least in part a mechanism of inhibition of the Ca(2+) influx into the smooth muscle cells through voltage-operated Ca(2+) channels.

Factors which determine the duration of follower potentials in longitudinal smooth muscle isolated from the guinea-pig stomach antrum

In isolated longitudinal muscle tissues of the guinea-pig stomach antrum, recording electrical responses from smooth muscle cells revealed a periodical generation of follower potentials with variable durations. The I-D relationship, made by plotting the duration as a function of the interval before generating follower potential, was linear. Experiments were carried out to investigate the effects of chemicals which had been known to modulate the release of Ca(2+) from the internal stores (2-aminoethoxy-diphenyl-borate, cyclopiazonic acid, caffeine), inhibit mitochondrial metabolic activity (m-chlorophenyl hydrazone, 2-deoxy-D-glucose, potassium cyanide, rotenone), inhibit ATP-sensitive K-channels distributed in mitochondria (glibenclamide, 5-hydroxydecanoic acid) and inhibit the activity of proteinkinase C (chelerythrine), on the I-D relationship of follower potentials. The effects of depolarization on follower potentials were assessed by stimulating tissues with high potassium solution. Experiments were carried out mainly in the presence of nifedipine which minimized the movements of muscles with no modulation of follower potentials. Cycropiazonic acid and caffeine reduced the slope of I-D relationship, with associated reduction of the duration and frequency of follower potentials. 2-Aminoethoxydiphenyl borate reduced the duration and amplitude and increased the frequency of follower potentials, with depolarization of the membrane, and the effects were simulated by high potassium solution. m-Chlorophenyl hydrazone, potassium cyanide, 2-deoxy-D-glucose, rotenone, 5-hydroxydecanoic acid and glibenclamide reduced the slope of I-D relationship, with associated reduction of the frequency of follower potentials. Chelerythrine did not modulate the slope of I-D relationship, with reduced frequency of follower potentials. It seemed likely that the amount of Ca(2+) released from the internal stores and also mitochondrial function had causal relationship to the duration of pacemaker potentials, suggesting that internal Ca-stores and mitochondria are taking the central role for determining the duration of the pacemaker activity. Proteinkinase C did not seem to participate to the function of mitochondria and internal Ca(2+) stores.

Factors modifying the frequency of spontaneous activity in gastric muscle

The cellular mechanisms that determine the frequency of spontaneous activity were investigated in gastric smooth muscles isolated from the guinea-pig. Intact antral muscle generated slow waves periodically; the interval between slow waves was decreased exponentially by depolarization of the membrane to reach a steady interval value of about 7 s. Isolated circular muscle bundles produced slow potentials spontaneously or were evoked by depolarizing current stimuli. Evoked slow potentials appeared in an all-or-none fashion, with a refractory period of approximately 2-3 s. Low concentrations of chemicals that modify intracellular signalling revealed that the refractory period was causally related to the activity of protein kinase C (PKC). Activation of PKC increased and inhibition of PKC activity decreased the frequency of slow potentials. Chemicals that inhibit mitochondrial functions reduced the frequency of slow waves. Inhibition of internal Ca(2+)-store activity decreased the amplitude, but not the frequency of slow potentials, suggesting that the amplitude is causally related to Ca(2+) release from the internal store. The results suggest that changes in [Ca(2+)](i) caused by the activity of mitochondria may play a key role in determining the frequency of spontaneous activity in gastric pacemaker cells.