The traditional antidiarrheal remedy, Garcinia buchananii stem bark extract, inhibits propulsive motility and fast synaptic potentials in the guinea pig distal colon

Abstract

Background: Garcinia buchananii bark extract is a traditional African remedy for diarrhea, dysentery, abdominal discomfort, and pain. We investigated the mechanisms and efficacy of this extract using the guinea pig distal colon model of gastrointestinal motility.

Methods: Stem bark was collected from G. buchananii trees in their natural habitat of Karagwe, Tanzania. Bark was sun dried and ground into fine powder, and suspended in Krebs to obtain an aqueous extract. Isolated guinea pig distal colon was used to determine the effect of the G. buchananii bark extract on fecal pellet propulsion. Intracellular recording was used to evaluate the extract action on evoked fast excitatory postsynaptic potentials (fEPSPs) in S-neurons of the myenteric plexus.

Key results: Garcinia buchananii bark extract inhibited pellet propulsion in a concentration-dependent manner, with an optimal concentration of ∼10 mg powder per mL Krebs. Interestingly, washout of the extract resulted in an increase in pellet propulsion to a level above basal activity. The extract reversibly reduced the amplitude of evoked fEPSPs in myenteric neurons. The extract's inhibitory action on propulsive motility and fEPSPs was not affected by the opioid receptor antagonist, naloxone, or the alpha- 2 adrenoceptor antagonist, yohimbine. The extract inhibited pellet motility in the presence of gamma-aminobutyric acid (GABA), GABA(A) and GABA(B) receptor antagonists picrotoxin and phaclofen, respectively. However, phaclofen and picrotoxin inhibited recovery rebound of motility during washout.

Conclusions & inferences: Garcinia buchananii extract has the potential to provide an effective, non-opiate antidiarrheal drug. Further studies are required to characterize bioactive components and elucidate the mechanisms of action, efficacy, and safety.

Figure 1

Intraluminal and bath applications of G. buchananii bark extract inhibit pellet propulsion in isolated segments of guinea pig distal colon. A. Bar graph showing the effects of intraluminal vs. bath delivery of the extract (1 g bark powder/100 ml Krebs solution; 5 minute application) on propulsive motility. No difference was detected between intraluminal and bath applications of the vehicle with regard to pellet velocity (bracket with ns). Intraluminal and bath extract applications reduced pellet velocity (bracket with asterisks). 1 g powder in 100 ml Krebs had larger inhibitory effects when applied in the bath vs. an intraluminal delivery (bracket with triangle). B. The concentration-dependent effects of the extract and the effects of washout on pellet propulsion. Lower concentrations (0.01- 0.1 g bark powder/100 ml Krebs) did not alter motility. Higher concentrations (1 - 10 g/100 ml Krebs) inhibited propulsion in a concentration-dependent fashion. At concentrations of 1 g bark powder/100 ml Krebs and below, pellet propulsion was rapidly restored to normal values and an increased rate of propulsive motility (30-100% above baseline) was observed following washout for 10-20 min. Normal pellet propulsion was not restored by 20 min. of washout after treatment with G. buchananii bark powder at a concentration of 10 g/100 ml Krebs.

Figure 2

Demonstration that evoked fEPSPs activity was inhibited by application of G. buchananii extract (0.25 - 0. 5 g bark powder/100 ml Krebs), and these actions were not mediated by opioid or alpha-2 adrenoceptor receptors. A. Representative traces of fEPSPs, demonstrating that G. buchananii extract inhibited fEPSPs in S neurons in the myenteric ganglia of guinea pig distal colon. These actions were not affected by the opioid receptor antagonist, naloxone (10 μM), or by the alpha-2 adrenoceptor antagonist, yohimbine (1 μM). B. Summary data showing that G. buchananii bark extract (0.25 g bark powder/100 ml Krebs) reduced fEPSPs amplitudes in the myenteric neurons after 5 min (bracket with triangle). The inhibitory actions of G. buchananii extract on fEPSPs persisted in the presence of the opioid receptor antagonist, naloxone (10 μM) and the alpha-2 adrenoceptor antagonist, yohimbine (1 μM) (bracket with asterisk). The fEPSPs amplitudes were restored to normal values by washout for 5-10 minutes, and were not affected by naloxone (ns bracket).

Figure 3

Inhibitory actions of G. buchananii extract (2 g bark powder/100 ml Krebs) on pellet motility do not involve opioid or α-2 adrenergic receptor activation. A-B: Summary data showing that neither naloxone (10 μM; A, bracket with triangle) nor yohimbine (1μM; B, bracket with triangle) altered the ability of G. buchananii extract to reduce propulsive motility. The rebound prokinetic effect of G. buchananii extract detected after washout also persisted in the presence of naloxone and yohimbine (3 A-B, brackets with asterisks).

Figure 4

G. buchananii extract contains bioactive components that act as GABA receptor ligands. A-B: Summary data showing that GABA (50 μM, A, triangle), the GABA_B receptor antagonist, phaclofen (PCF, 40 μM; B, star), and the GABA_A receptor antagonist picrotoxin (PTX, 30 μM; B, square), did not alter the effects of G. buchananii extract (2 g bark powder/100 ml Krebs, delivered by bath application) on propulsive motility after 5-10 minutes. Recovery of propulsive motility by post-treatment washout was similar to vehicle results for GABA treatment (increasing propulsive motility by up to 70% above baseline at 15-20 minute washout intervals; (A, bracket with asterisk; P<0.05). A slower recovery was observed during washout after treatment using the extract in combination with picrotoxin (PTX, 30 μM) or phaclofen (PCF, 40 μM). In these cases, motility was still significantly lower than that of vehicle after 20 minutes of washout (bracket with asterisk in B; P<0.05).