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Objectives: Cleistanthins A and B are the active compounds isolated from Cleistanthus collinus leaves. The hypotensive activity of both cleistanthins A and B and the leaf extract has been previously demonstrated, but the exact mechanism of action is not clear. So, this study was designed to test the vasorelaxant property of cleistanthins A and B and delineate its mechanism of action. Methods: Variable force transducers were used to record the force of contraction from the aortic rings of 24 male guinea pigs. The effect of cleistanthin A, cleistanthin B, prazosin and vehicle on the phenylephrine-induced contractions and potassium chloride-induced contractions was demonstrated and compared. Results: Cleistanthin B inhibited the phenylephrine-induced contractions in a dose-dependent manner and demonstrated potency (pIC50 = 6.8 ± 1.06) comparable to prazosin (pIC50 = 5.7 ± 0.7). Cleistanthin A potency could not be calculated. Both cleistanthin A (4 µg) and cleistanthin B (40 µg) caused a reduction of the maximal response of phenylephrine demonstrating irreversible blockade. They did not affect the potassium chloride-induced contractions. This illustrates that cleistanthins A and B are noncompetitive α1 adrenergic blockers and the potency of cleistanthin B is comparable to prazosin. Conclusion: Both cleistanthins A and B have vasodilatory action on guinea pig aorta. The action is through non-competitive α1 adrenergic receptor inhibition and calcium channel blockade does not contribute to the inhibition. [ABSTRACT FROM AUTHOR]

Objectives: Cleistanthins A and B (CAB), active phytochemicals present in Cleistanthus collinus, have been proven to have alpha 1-adrenoceptor blocking property. However action on alpha 2-adrenoceptor is not studied. We aimed to study the action of CAB on alpha 2-adrenoceptor by measuring platelet aggregation, insulin and blood glucose levels with yohimbine as a standard comparator control and alpha 1-adrenoceptor by measuring the blockade of relaxation induced by phenylephrine in the jejunum of Wistar albino rats. Materials and methods: Forty eight adult male Wistar rats were divided into eight drug groups of six each, namely control (CMC 0.5%), yohimbine 2 mg/kg, 10, 30 and 100 mg/kg doses of cleistanthin A and cleistanthin B. Blood samples were drawn at baseline, after 5 h and after high-epinephrine dose (5 mg/kg) from the retro-orbital sinus and used for estimation of platelet aggregation and plasma insulin levels. Blood glucose levels were estimated at six different time points. Degree of jejunal relaxation was studied by relaxing the acetylcholine pre-contracted jejunum with phenylephrine. Results: All groups, except control and cleistanthin A 10 mg/kg group, significantly inhibited the platelet aggregation when compared to the respective baseline values (p<0.05). No significant difference was observed between different drug groups in plasma insulin and blood glucose levels. With regard to phenylephrine induced jejunal relaxation, the median IC50 for all three doses of cleistanthin A and cleistanthin B 100 mg/kg differ significantly from that of control (CMC 0.5%). Conclusion: CAB block both alpha 1 and 2-adrenoceptorand hence are non-selective alpha-adrenoceptor blockers. [ABSTRACT FROM AUTHOR]

To study the diuretic effects of cleistanthin A and cleistanthin B, phytoconstituents were isolated from the leaves of Cleistanthus collinus in Wistar rats. The in vivo diuretic effects of cleistanthins A and B were determined according to the Lipschitz test. Prior to the experiment, the animals were fasted for 5 h and placed individually in metabolic cages. Cleistanthins A and B (12.5, 25, and 50 mg/kg) and furosemide (5 mg/kg) were suspended in 0.5% w/v carboxymethyl cellulose and administered orally. The urine was collected up to 5 h after administration and subsequently up to 24 h after administration. The acidity and urine volume were measured immediately. The urinary sodium and potassium levels were determined using a flame photometer, and the chloride level was determined by argentometric titration. The diuretic index and diuretic activity were calculated mathematically. While cleistanthins A and B showed a diuretic index of more than one, the diuretic activity of these compounds was less than one, indicating inferior activity compared with furosemide. Both cleistanthin A and B produced a significant increase in the urine volume and alterations in urinary electrolyte levels. However, the effect of the compounds was not dose dependent. Cleistanthin A and cleistanthin B exert diuretic effects in male Wistar rats without affecting the urinary acidity. [ABSTRACT FROM AUTHOR]