Calcium entry blocking activities of MPC-1304 and of its enantiomers and metabolites

Anti-cholinergic and Ca2+-antagonist mechanisms explain the pharmacological basis for folkloric use of Sisymbrium irio Linn. in gastrointestinal, airways and vascular system ailments

ETHNOPHARMACOLOGICAL RELEVANCE

Seeds of Sisymbrium irio Linn has been used traditionally in different regions of Pakistan for the treatment of gastrointestinal, airways and vascular system ailments. To insight the pharmacological basis, in vitro study was conducted in order to validate its folkloric uses.

MATERIAL AND METHODS

70% aqueous-methanolic extract of seeds from S. irio (Si.MEs) was tested on isolated rabbit aorta, jejunum and trachea strip hanged in tissue bath having physiological solutions aerated with carbogen and their responses were measured and recorded via Power Lab.

RESULTS

The Si.MEs exhibited the transient spasmogenic effect (0.01-1.0mg/mL) on spontaneous jejunum contractions, followed by the spasmolytic effect. The addition of atropine resulted in blocking in spasmogenic effect while the spasmolytic effect was originated, suggesting the presence of an antimuscarinic effect. Likewise verapamil, Si.MEs (0.03-5mg/mL) repressed the high concentration K⁺(80mM)-induced contraction and also drifted the Ca²⁺ concentration-response curves toward right (0.3-3.0mg/mL), possibly signifying the Ca²⁺ channel blockade. Furthermore, Si.MEs exhibited nonspecific relaxant effect on carbachol (1µM)- and high concentration K⁺(80mM)-induced tracheal contractions in a way comparable to dicyclomine, suggesting the coexistence of Ca²⁺-antagonistic and/or antimuscarinic properties. Additionally, Si.MEs also relaxed the phenylephrine(1µM)- and high concentration K⁺(80mM)-induced aortic contraction (0.01-3mg/mL), suggesting blockade of Ca²⁺ channel. Moreover, oral administration of Si.MEs, as high as 6g per kg, did not produce lethality among the treated groups of mice.

CONCLUSIONS

Aqueous-methanolic extract of seeds from S. irio (Si.MEs) exhibited the bronchodilator and gut modulator (spasmogenic and spasmolytic) activities, probably through dual blockade of muscarinic receptors and Ca²⁺ channels, whereas, vasodilator effect may be due to Ca²⁺ channels blockade.

Gut modulatory effects of Daphne oleoides are mediated through cholinergic and Ca++ antagonist mechanisms

CONTEXT

The present study describes the spasmogenic and spasmolytic activities of Daphne oleoides Schreb. (Thymelaeaceae), exploring the possible underlying pharmacological mechanisms.

AIM

Pharmacological investigation of Daphne oleoides to provide evidence for its therapeutic application in gastrointestinal motility disorders.

MATERIALS AND METHODS

Methanol crude extract of Daphne oleoides (Do.Cr) was studied in gastrointestinal isolated tissues.

RESULTS

In spontaneously contracting rabbit jejunum preparations, Do.Cr at 0.3-3.0 mg/mL caused moderate stimulation, followed by relaxant effect at the next higher concentrations (5.0-10 mg/mL). In presence of atropine, spasmogenic effect was blocked and the relaxation was emerged, suggesting that the spasmogenic effect of Daphne oleoides is mediated through activation of muscarinic receptors. When tested against the high K+ (80 mM)-induced contractions, Do.Cr (0.3-5.0 mg/mL), like verapamil, inhibited the induced contractions, suggesting Ca++ channel blockade (CCB) effect. The CCB effect was further confirmed when pre-treatment of the tissue with Do.Cr shifted the Ca++ concentration-response curves to the right, similar to that caused by verapamil.

DISCUSSION AND CONCLUSION

These results indicate that Daphne oleoides exhibits gut excitatory and inhibitory effects, occurred via cholinergic and Ca++ antagonistic pathways, respectively.

Antihypertensive activity of substituted 2,3,8,8a-tetrahydro-7H-oxazolo[3,2-a]pyridinedicarboxylate enantiomers

The synthesis and antihypertensive activity of racemates and enantiomers of substituted 2,3,8,8a-tetrahydro-7H-oxazolo[3,2-a]pyridinedicarboxylates have been reported.

Renal effects of the calcium channel blocker aranidipine and its active metabolite in anesthetized dogs and conscious spontaneously hypertensive rats

The purpose of this study was to investigate the renal effects of aranidipine, a novel calcium channel blocker of the dihydropyridine type, and its active metabolite in anesthetized dogs and conscious spontaneously hypertensive rats (SHRs). When infused into the renal artery in anesthetized dogs, aranidipine (0.03 microg/kg/min) induced sustained increases in urine volume and urinary excretion of sodium and of potassium. This effect was greater than that elicited by nifedipine (0.1 microg/kg/min). The aranidipine metabolite, M-1 (0.1 microg/kg/min), also caused diuresis and natriuresis almost equal to those of nifedipine. The stop-flow experiment using the anesthetized dog showed that intrarenal infusion of aranidipine (0.03 microg/kg/min), as well as nifedipine (0.1 microg/kg/min), produced natriuresis at the distal tubular site rather than at the proximal site. Aranidipine (0.3, 1, and 3 mg/kg), when administered orally, dose-dependently increased urine volume and urinary excretion of electrolytes in conscious saline-loaded SHRs. M-1 (10 mg/kg, p.o.) also showed diuretic and natriuretic effects comparable to those of nifedipine (10 mg/kg) in SHRs. In addition, after repeated oral administration of aranidipine for 7 days, short-term tolerance was not found for its diuretic and natriuretic effects in SHRs. These results suggest that, apart from antihypertensive efficiency, aranidipine may offer a therapeutic advantage by producing diuresis and natriuresis in hypertensive patients. The metabolite of aranidipine may contribute, in part, to the diuretic, natriuretic, and antihypertensive effects of aranidipine.

Effects of aranidipine, a novel calcium channel blocker, on mechanical responses of the isolated rat portal vein: comparison with typical calcium channel blockers and potassium channel openers

We investigated the effects of aranidipine, a dihydropyridine-type Ca2+ channel blocker, on contractile responses to KCl and spontaneous contractions in isolated rat portal veins in comparison with those of the Ca2+ channel blockers, nifedipine, nicardipine, nitrendipine, diltiazem, and verapamil, and of the K+ channel openers, cromakalim and nicorandil. All the Ca2+ channel blockers concentration-dependently inhibited contractions induced by KCl. Interestingly, aranidipine was more potent against the low K+ (20 mM)-induced contraction than the high K+ (80 mM)-induced contraction, whereas the other Ca2+ channel blockers were equally potent against contractions induced by either concentration of KCl. Cromakalim and nicorandil were effective only on the low K(+)-induced contraction. In addition, all the Ca2+ channel blockers and the K+ channel openers tested inhibited the amplitude of spontaneous contractions of isolated rat portal vein. Tetraethylammonium (TEA), a classic K+ channel blocker, significantly attenuated the effect of aranidipine but not of other Ca2+ channel blockers on the spontaneous contractions. The cromakalim-induced inhibition of spontaneous contractions was antagonized by TEA. Thus aranidipine was found to be different from the typical Ca2+ channel blockers and in part similar to the K+ channel openers in inhibiting mechanical responses of isolated rat portal vein, suggesting that activation of K+ channels may in part in part be involved in the aranidipine-induced vasodilation.

Receptor occupation and pharmacokinetics of MPC-1304, a new Ca2+ channel antagonist, in spontaneously hypertensive rats

MPC-1304, (+/-)-methyl 2-oxopropyl 1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinedicarbonate , is a novel 1,4-dihydropyridine Ca2+ channel antagonist with potent and long-lasting antihypertensive effects. We characterized the ex vivo and in vivo binding properties of MPC-1304 to Ca2+ channel antagonist receptors in myocardial, aortic and brain tissues of spontaneously hypertensive rats (SHR) by radioreceptor assay using [3H](+)-PN 200-110 ([5-methyl-3H](+)-PN 200-110 (4-(2,1,3-benzoxadiazol-4-yl)-1,4,-dihydro-5-methoxycarbonyl-2,6-d imethyl-1,4-dihydro-3-isopropylcarbonylpyridine-5-carboxylic acid methyl ester)). At 1 and 6 h after oral administration of MPC-1304 (10 mg/kg) in SHR, there was significant decrease (48%) in the number of [3H](+)-PN 200-110 binding sites (Bmax) in myocardial membranes compared to control values. The plasma concentration of MPC-1304 in SHR correlated significantly with the occupation by this drug of myocardial Ca2+ channel antagonist receptors. The in vivo specific binding of [3H](+)-PN 200-110 in particulate fractions of aorta of SHR was significantly reduced (74.8 and 37.9%, respectively) at 1 and 6 after oral administration of MPC-1304 (3 mg/kg), while the myocardial [3H](+)-PN 200-110 binding was decreased only at 1 h later. In these rats, there was little change in cerebral cortical [3H](+)-PN 200-110 binding. In conclusion, MPC-1304 exerted more selective and sustained occupation in vivo of Ca2+ channel antagonist receptors in vascular tissues of SHR than in those of myocardial and brain tissues.