Angiotensin II-mediated vasodilation is reduced in adult spontaneously hypertensive rats despite enhanced expression of AT2 receptors.

1. The vasodilator action of angiotensin (Ang) II has not yet been demonstrated in spontaneously hypertensive rats (SHR), nor have any possible changes in this response during the development of hypertension. 2. In the present study, the vasodilator effect of AngII was evaluated in the rat isolated, preconstricted mesenteric arterial bed (MAB) from 6- (young) and 24-week-old (adult) SHR and compared with effects on MAB from age-matched normotensive rats (control). 3. Angiotensin II (10-300 nmol) induced vasodilation in noradrenaline (NA)-preconstricted MAB that was greater in vessels from young compared with adult rats in both the control and SHR groups. Angiotensin II-induced vasodilation was reduced by the angiotensin AT(2) receptor antagonist PD 123319 (10 micromol/L), the angiotensin-(1-7) receptor antagonist A779 (1 micromol/L) and the bradykinin B(2) receptor antagonist HOE-140 (0.01 micromol/L), but not by the AT(1) receptor antagonist losartan (30 micromol/L). Expression of AT(2) receptors was weak in vessels from adult control rats compared with that in young control rats, whereas in young SHR AT(2) receptor expression was increased compared with that in young control rats. This increased expression of AT(2) receptors was maintained in adult SHR and there was no significant difference in AT(2) receptor expression between young and old SHR. 4. The findings of the present suggest that AngII induces an AT(2) receptor-mediated vasodilator effect in the MAB via activation of angiotensin-(1-7) and bradykinin receptors, an action that is reduced in adult control rats and adult SHR. In adult control rats, the attenuated response of AngII is probably due to endothelial dysfunction and reduced expression of AT(2) receptors, whereas in adult SHR it is associated with endothelial dysfunction alone. Increased expression of AT(2) receptors in SHR may represent a counteracting response for modulating blood pressure.

Mitochondrial injury in pancreatitis.

Pancreatitis is an increasingly common disease that carries a significant mortality and which lacks specific therapy. Pathological calcium signalling is an important contributor to the initiating cell injury, caused by or acting through mitochondrial inhibition. A principal effect of disordered cell signalling and impaired mitochondrial function is cell death, either by apoptosis that is primarily protective, or by necrosis that is deleterious, both locally and systemically. Mitochondrial calcium overload is particularly important in necrotic injury, which may include damage mediated by the mitochondrial permeability transition pore. The role of reactive oxygen species remains controversial. Present understanding of the part played by disordered pancreatic acinar calcium signalling and mitochondrial inhibition offers several new potential therapeutic targets.

Calcium signalling and pancreatic cell death: apoptosis or necrosis?

Secretagogues, such as cholecystokinin and acetylcholine, utilise a variety of second messengers (inositol trisphosphate, cADPR and nicotinic acid adenine dinucleotide phosphate) to induce specific oscillatory patterns of calcium (Ca(2+)) signals in pancreatic acinar cells. These are tightly controlled in a spatiotemporal manner, and are coupled to mitochondrial metabolism necessary to fuel secretion. When Ca(2+) homeostasis is disrupted by known precipitants of acute pancreatitis, for example, hyperstimulation or non-oxidative ethanol metabolites, Ca(2+) stores (endoplasmic reticulum and acidic pool) become depleted and sustained cytosolic [Ca(2+)] elevations replace transient signals, leading to severe consequences. Sustained mitochondrial depolarisation, possibly via opening of the mitochondrial permeability transition pore (MPTP), elicits cellular ATP depletion that paralyses energy-dependent Ca(2+) pumps causing cytosolic Ca(2+) overload, while digestive enzymes are activated prematurely within the cell; Ca(2+)-dependent cellular necrosis ensues. However, when stress to the acinar cell is milder, for example, by application of the oxidant menadione, release of Ca(2+) from stores leads to oscillatory global waves, associated with partial mitochondrial depolarisation and transient MPTP opening; apoptotic cell death is promoted via the intrinsic pathway, when associated with generation of reactive oxygen species. Apoptosis, induced by menadione or bile acids, is potentiated by inhibition of an endogenous detoxifying enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1), suggesting its importance as a defence mechanism that may influence cell fate.

The effects of novel vasodilator long chain acyl carnitine esters in the isolated perfused heart of the rat.

1. The effects of palmitoyl carnitine (PC) and novel derivatives were examined on the isolated Langendorff perfused heart of the rat. 2. Bolus injections of PC (1-300 nmol) produced coronary constriction accompanied by a cumulative irreversible depression of contractility. 3. Prior storage of PC in chloroform containing 2% ethanol in heat-sealed ampoules resulted in production of the ethyl ester of the compound (PCE). This compound was isolated and also synthesized (P1E). In contrast to PC, both PCE and P1E exhibited potent vasodilator activity. 4. Increasing the fatty acid chain length from palmitoyl to stearoyl resulted in a significant reduction in coronary dilator activity of the ester compound, whereas different ester groups did not affect the vasodilator action appreciably. Complete removal of the fatty acid chain abolished all vascular effects at the doses used. 5. The vasodilatation produced by these acyl carnitine esters was comparable to that produced by several known vasodilator drugs including verapamil, cromakalim, amyl nitrate and iloprost; however, the duration of the vasodilator response was more prolonged with the carnitate derivatives.

Effect of niflumic acid on noradrenaline-induced contractions of the rat aorta.

1. The effects of niflumic acid, an inhibitor of calcium-activated chloride channels, were compared with the actions of the calcium channel antagonist nifedipine on noradrenaline-evoked contractions in isolated preparations of the rat aorta. 2. The cumulative concentration-effect curve to noradrenaline (NA) was depressed by both nifedipine and niflumic acid in a reversible and concentration-dependent manner. The degree of inhibition of the maximal contractile response to NA (1 microM) produced by 10 microM niflumic acid (38%) was similar to the effect of 1 microM nifedipine (39%). 3. Contractions to brief applications (30 s) of 1 microM NA were inhibited by 55% and 62% respectively by 10 microM niflumic acid and 1 microM nifedipine. 4. In the presence of 0.1 microM nifedipine, niflumic acid (10 microM) produced no further inhibition of the NA-evoked contractions. Thus, the actions of niflumic acid and nifedipine were not additive. 5. In Ca-free conditions the transient contraction induced by 1 microM NA was not inhibited by niflumic acid (10 microM) and therefore this agent does not reduce the amount of calcium released from the intracellular store or reduce the sensitivity of the contractile apparatus to calcium. 6. Niflumic acid 10 microM did not inhibit the contractions produced by KCl (up to 120 mM) which were totally blocked by nifedipine. Contractions induced by 25 mM KCl were completely inhibited by 1 microM levcromakalim but were unaffected by niflumic acid. 7. It was concluded that niflumic acid produces selective inhibition of a component of NA-evoked contraction which is probably mediated by voltage-gated calcium channels. These data are consistent with a model in which NA stimulates a calcium-activated chloride conductance which leads to the opening of voltage-gated calcium channels to produce contraction.

Selective inhibitory effects of niflumic acid on 5-HT-induced contraction of the rat isolated stomach fundus.

The effects of niflumic acid (NFA), an inhibitor of calcium-activated chloride currents I(Cl(Ca)), were compared with the actions of the voltage-dependent calcium channel (VDCC) blocker nifedipine on 5-hydroxtryptamine (5-HT)- and acetylcholine (ACh)-induced contractions of the rat isolated fundus. NFA (1 - 30 microM) elicited a concentration-dependent inhibition of contractions induced by 5-HT (10 microM) with a reduction to 15. 5+/-6.0% of the control value at 30 microM. 1 microM nifedipine reduced 5-HT-induced contraction to 15.2+/-4.9% of the control, an effect not greater in the additional presence of 30 microM NFA. In contrast, the contractile response to ACh (10 microM) was not inhibited by NFA in concentrations /=10 microM. Our results show that NFA can exert selective inhibitory effects on the chloride-dependent 5-HT-induced contractions of the rat fundus. The data support the hypothesis that activation of Cl((Ca)) channels leading to calcium entry via VDCCs is a mechanism utilized by 5-HT, but not by ACh, to elicit contraction of the rat fundus.

Inhibitory action of niflumic acid on noradrenaline- and 5-hydroxytryptamine-induced pressor responses in the isolated mesenteric vascular bed of the rat.

1. The effects of niflumic acid, an inhibitor of calcium-activated chloride currents, were compared with the actions of the calcium channel blocker nifedipine on noradrenaline- and 5-hydroxytryptamine (5-HT)-induced pressor responses of the rat perfused isolated mesenteric vascular bed. 2. Bolus injections of noradrenaline (1 and 10 nmol) increased the perfusion pressure in a dose-dependent manner. Nifedipine (1 microM) inhibited the increase in pressure produced by 1 nmol noradrenaline by 31 +/- 5%. Niflumic acid (10 and 30 microM) also inhibited the noradrenaline-induced increase in perfusion pressure and 30 microM niflumic acid reduced the pressor response to 1 nmol noradrenaline by 34 +/- 6%. 3. The increases in perfusion elicited by 5-HT (0.3 and 3 nmol) were reduced by niflumic acid (10 and 30 microM) in a concentration-dependent manner and 30 microM niflumic acid inhibited responses to 0.3 and 3 nmol 5-HT by, respectively, 49 +/- 8% and 50 +/- 7%. Nifedipine (1 microM) decreased the pressor response to 3 nmol 5-HT by 44 +/- 9%. 4. In the presence of a combination of 30 microM niflumic acid and 1 microM nifedipine the inhibition of the pressor effects of noradrenaline (10 nmol) and 5-HT (3 nmol) was not significantly greater than with niflumic acid (30 microM) alone. Thus the effects of niflumic acid and nifedipine were not additive. 5. In Ca-free conditions the transient contractions induced by 5-HT (3 nmol) were not reduced by 30 microM niflumic acid, suggesting that this agent does not inhibit calcium release from the intracellular store or the binding of 5-HT to its receptor. 6. Niflumic acid 30 microM did not inhibit the pressor responses induced by KCl (20 and 60 mumol) which were markedly reduced by 1 microM nifedipine. In addition, 1 microM levcromakalim decreased pressor responses produced by 20 mumol KCl. These data suggest that niflumic acid does not block directly calcium channels or activate potassium channels. 7. It is concluded that niflumic acid selectively reduces a component of noradrenaline- and 5-HT-induced pressor responses by inhibiting a mechanism which leads to the opening of voltage-gated calcium channels. Our data suggest that the Ca(2+)-activated chloride conductance may play a pivotal role in the activation of voltage-gated calcium channels in agonist-induced constriction of resistance blood vessels.

Inhibitory effects of Rb+ on the responses to levcromakalim and P1060 in the isolated human myometrium.

The mechanoinhibitory effects of two structurally dissimilar K+ channel openers, levcromakalim and P1060, and verapamil were compared in strips of human myometrium bathed in either K-PSS (normal Krebs solution) or Rb-PSS (K+ salts replaced by Rb+ equivalents). In Rb-PSS the effects of levcromakalim and P1060 on amplitude and frequency of spontaneous contractions were inhibited by more than 20- and 138-fold, respectively, whereas those of verapamil were unaltered. These results indicate that K+ channel openers possess Rb-sensitive and Rb-insensitive mechanoinhibitory actions on the human uterus, the former being more important in the effects of P1060 than levcromakalim.

Differential vasorelaxant effects of levcromakalim and P1060 in the isolated KCl- and RbCl-precontracted human saphenous vein: possible involvement of intracellular Ca2+ stores.

The influence of rubidium-substituted physiological salt solution (Rb-PSS) on the relaxant effects of K+ channel openers was investigated in the human saphenous vein. In tissues precontracted with 20 mM KCl (in K-PSS) levcromakalim and P1060 produced complete, sustained relaxations. However, in Rb-PSS (containing 20 mM RbCl) these effects were inhibited and, although complete relaxations still occurred, were transient. When caffeine was applied at the beginning of this fade of levcromakalim-induced relaxation in Rb-PSS its contractile effect was potentiated. Similarly, the contraction to noradrenaline was potentiated when applied at the beginning of this fade of levcromakalim-induced relaxation, whereas this response was attenuated in control tissues bathed in 20 mM KCl (in K-PSS). Our results show that the relaxant effects of K+ channel openers in human saphenous vein are inhibited in Rb-PSS, in agreement with previous studies in animal tissue, and suggest that an increased Ca2+ uptake into intracellular stores may be contributory to vasorelaxation.

Vasodilator action of the isopropyl ester of palmitoyl carnitine in the rat coronary circulation and mesenteric vascular bed.

The vasodilator action of the isopropyl ester of palmitoyl carnitine (P1Pi) has been examined in perfused rat hearts and mesenteric vessels. The coronary vasodilator effect P1Pi was not significantly inhibited by flurbiprofen (10 microM), BW755C (10 microM), glibenclamide (10 microM) or the bradykinin B2 receptor antagonist D-Arg0[Hyp3,Thi5,8,D-Phe7]bradykinin (1 microM), indicating that the action of P1Pi is not mediated via arachidonic acid metabolites, ATP-dependent K+ channels or bradykinin B2 receptors. L-NG-Nitro arginine (100 microM) did not inhibit the vasodilator action of P1Pi whilst superoxide dismutase (20 and 50 U.ml-1) attenuated its vasodilator action. Methylene blue (10 microM) caused inhibition in three out of four hearts, while haemoglobin (1 microM) caused an irreversible inhibition of the action of P1Pi which was associated with a depression of myocardial contractility. In air-damaged mesenteric vascular beds the vasodilator action of P1Pi was not attenuated, whilst that of acetylcholine was abolished. In K(+)-depolarised mesenteric vascular beds the constrictor action of Ca2+ was attenuated by P1Pi. Therefore the vasodilator effect of P1Pi appears to be the result of a direct effect on smooth muscle.

Comparative effects of niflumic acid and nifedipine on 5-hydroxytryptamine- and acetylcholine-induced contraction of the rat trachea.

The effects of niflumic acid, an inhibitor of Ca(2+)-activated Cl(-) (Cl((Ca))) channels, were compared with those of the voltage-dependent Ca(2+) channel (VDCC) blocker nifedipine on 5-hydroxytryptamine (5-HT)- and acetylcholine-induced contractions of the rat isolated trachea. Niflumic acid (3-100 microM) induced a concentration-dependent inhibition of 5-HT (10 microM)-induced contractions, with a reduction to 37.0+/-9.5% of the control at the highest concentration. One micromolar nifedipine, which completely blocked 60 mM KCl-induced contractions, reduced the response to 5-HT similarly to 39.2+/-11.5% of the control. The inhibition of the 5-HT response was not significantly different from that produced by the combined presence of nifedipine (1 microM) and niflumic acid (100 microM), suggesting that their effects were not additive. In contrast, neither niflumic acid (3-100 microM) nor nifedipine (1 microM) inhibited acetylcholine-induced contractions. The contraction to 5-HT (10 microM) in Cl(-)-free solution was decreased by more than approximately 85% of the control, whilst that of acetylcholine was reduced only by approximately 36%. Our data show that niflumic acid exerts selective inhibitory effects on 5-HT-induced contraction, and suggest that activation of Cl((Ca)) channels may be a mechanism whereby 5-HT (but not acetylcholine) induces Ca(2+) entry via VDCCs to elicit contraction.

Levcromakalim-induced modulation of membrane potassium currents, intracellular calcium and mechanical activity in rat mesenteric artery.

In freshly-dispersed cells from rat mesenteric artery, levcromakalim (1 and 10 microM) induced a non-inactivating potassium current (IKCO), an event which was associated with increased current noise. IKCO was fully inhibited in the presence of 10 microM glibenclamide. Stationary fluctuation analysis of the current noise associated with IKCO induced by levcromakalim at a holding potential of -10 mV indicated that the unitary conductance of the underlying K-channels was 10.2 pS at 0 mV under the quasi-physiological conditions of the experiment. In isolated arterioles both levcromakalim (10 nM-10 microM) and nifedipine (10 nM-10 microM) each elicited full, concentration-dependent, parallel reductions of the increases in [Ca2+]i (assessed using fura-2) and tension induced by 10 microM noradrenaline. However, the effects of both drugs on KCl-induced increases in tension and in [Ca2+]i, did not follow a simple relationship. Levcromakalim relaxed KCl- and noradrenaline-induced sustained contractions with a similar potency. This was in contrast to nifedipine which was approximately 20 times more potent against KCl-induced contractions. It is concluded that levcromakalim relaxes rat mesenteric arterioles primarily by the opening of a small conductance, glibenclamide-sensitive K-channel. An additional action of levcromakalim is suggested by its relative inability to suppress the increase in [Ca2+]i produced by 30 mM K(+)-PSS.

The synthesis, and structure-activity relationships of some long chain acyl carnitine esters on the coronary circulation of the rat isolated heart.

The synthesis of the isopropyl ester of carnitine and a series of fatty acid derivatives with fatty acid lengths C8-C30 is described. Bolus doses of these compounds (0.03-300 nmol) showed coronary vasodilator activity in the rat isolated heart. Increasing fatty acid chain length from C8 to C16 resulted in an increased vasodilator potency. Longer lasting vasodilation was observed with the C20 compound. Increasing fatty acid chain length to C30 was associated with a small dilator response preceded by vasoconstriction.

Bronchodilator activity of Mikania glomerata Sprengel on human bronchi and guinea-pig trachea.

The effects of aqueous extracts and hydro-alcoholic extract (HAE), and of a dichloromethane fraction (MG1) obtained from the HAE of Mikania glomerata leaves on isolated respiratory and vascular smooth muscle have been investigated. Aqueousextracts and HAE induced a significant inhibition on the histamine contractions on the isolated guinea-pig trachea. HAE extract induced a concentration-dependent relaxation on guinea-pig trachea pre-contracted with histamine (IC50 0.34 (0.29-0.39) mg mL(-1)), acetylcholine (IC50 0.72 (0.67-0.77) mg mL(-1)) or K+ (IC50 1.41 (1.18-1.64) mg mL(-1)) and on isolated human bronchi precontracted with K+ (IC50 0.34 (0.26-0.42) mg mL(-1)). The dichloromethane fraction induced a concentration dependent relaxation in guinea-pig trachea precontracted with K+ (IC50 0.017 (0.012-0.022) mg mL(-1)). The dichloromethane fraction had also a small vasodilator effect on the isolated mesenteric vascular bed and on the isolated rat aorta, and a significant reduction of the oedema induced by subplantar injections of Bothropsjararaca venom in mice. When tested on plasmid DNA, MG1 did not damage the DNA. Chromatographic analysis showed the presence of 11.4% w/w coumarin in MG1. The results supported the indication of M. glomerata products for the treatment of respiratory diseases where bronchoconstriction is present.

Vasorelaxant effects of the potassium channel opener SR 47063 on the isolated human saphenous vein and rat aorta.

The vasorelaxant effects of SR 47063 (4-(2-cyanimino-1, 2-dihydropyrid-1-yl)-2,2-dimethyl-6-nitr ochromene), a new K(+)-channel opener structurally related to levcromakalim, were examined in isolated human saphenous vein (HSV) and rat aorta (RA). HSV or RA rings were precontracted with either KCl or noradrenaline and cumulative relaxant concentration-response curves were obtained for SR 47063 (0.1 nM to 1 microM) in the presence or absence of 3 microM glibenclamide. SR 47063 potently relaxed HSV and RA precontracted with 20 mM (but not 60 mM) KCl or 10 microM noradrenaline in a concentration-dependent manner, showing slightly greater activity in the aorta. The potency of the effect of SR 47063 on HSV and RA was 12- and 58-fold greater, respectively, than that reported for the structurally related K(+)-channel opener levcromakalim. The vasorelaxant action of SR 47063 in both blood vessels was strongly inhibited by 3 microM glibenclamide, consistent with a mechanism of action involving ATP-dependent K(+)-channels.

Antinociceptive properties of the essential oil of Ocimum gratissimum L. (Labiatae) in mice.

We have investigated the antinociceptive effects of the essential oil of Ocimum gratissimum L. (Labiatae) (EOOG) in two classical models of pain in male Swiss mice (25-35 g), the writhing test and the formalin test. At doses of 30, 100 and 300 mg/kg (po), EOOG produced a dose-dependent inhibition (from 58.3 4.4 to 40.7 6.3, 36.4 3.6 and 24.6 3.6, respectively; N = 8-10, P<0.05) of acetic acid-induced writhing, causing up to a ~60% inhibition at the highest dose used, comparable to that obtained with indomethacin (10 mg/kg, po). At the same doses, EOOG predominantly inhibited the late (inflammatory) phase of the formalin-induced pain response (from 59.3 8.3 to 40.4 4.8, 23.2 2.8 and 25.3 5.5, respectively; N = 6, P<0.05), with a maximal reduction of ~60% of the control, although a significant reduction of the initial (neurogenic) phase was also observed at 300 mg/kg (from 62.5 6.07 to 37 5.9; P<0.05). On the basis of these data, we conclude that EOOG possesses interesting antinociceptive properties in the writhing and formalin tests. Due to the relatively low toxicity of EOOG, further detailed examination is strongly indicated for a better characterization of its pharmacological properties and its potential therapeutic value.

Oxidative stress in acute pancreatitis: lost in translation?

Oxidative stress has been implicated in the pathogenesis of acute pancreatitis, a severe and debilitating inflammation of the pancreas that carries a significant mortality, and which imposes a considerable financial burden on the health system due to patient care. Although extensive efforts have been directed towards the elucidation of critical underlying mechanisms and the identification of novel therapeutic targets, the disease remains without a specific therapy. In experimental animal models of acute pancreatitis, increased oxidative stress and decreased antioxidant defences have been observed, changes also detected in patients clinically. However, despite the promise of studies evaluating the effects of antioxidants in these model systems, translation to the clinic has thus far been disappointing. This may reflect many factors involved in the design of both preclinical and clinical evaluations of antioxidant therapy, not least the fact that most experimental studies have focussed on pre-treatment rather than post-injury assessment. This review has examined evidence relating to the involvement of oxidative stress in the pathophysiology of acute pancreatitis, focussing on experimental models and the clinical experience, including the experimental techniques employed and potential of antioxidant therapy.

Fatty acids, alcohol and fatty acid ethyl esters: toxic Ca2+ signal generation and pancreatitis.

Pancreatitis, a potentially fatal disease in which the pancreas digests itself as well as its surroundings, is a well recognized complication of hyperlipidemia. Fatty acids have toxic effects on pancreatic acinar cells and these are mediated by large sustained elevations of the cytosolic Ca(2+) concentration. An important component of the effect of fatty acids is due to inhibition of mitochondrial function and subsequent ATP depletion, which reduces the operation of Ca(2+)-activated ATPases in both the endoplasmic reticulum and the plasma membrane. One of the main causes of pancreatitis is alcohol abuse. Whereas the effects of even high alcohol concentrations on isolated pancreatic acinar cells are variable and often small, fatty acid ethyl esters--synthesized by combination of alcohol and fatty acids--consistently evoke major Ca(2+) release from intracellular stores, subsequently opening Ca(2+) entry channels in the plasma membrane. The crucial trigger for pancreatic autodigestion is intracellular trypsin activation. Although there is still uncertainty about the exact molecular mechanism by which this Ca(2+)-dependent process occurs, progress has been made in identifying a subcellular compartment--namely acid post-exocytotic endocytic vacuoles--in which this activation takes place.

Inhibitory effects of the essential oil of Mentha pulegium on the isolated rat myometrium.

The effects of the essential oil of Mentha pulegium L. (EOMP), a plant commonly known as "pennyroyal" or "poejo" that is used in folk medicine as an abortifaceant, were assessed on the isolated rat myometrium. Myometrial strips were stimulated with 10 nM oxytocin or 10 microM PGF (2alpha). EOMP (10 - 300 microg/mL) concentration-dependently and reversibly inhibited the amplitude of oscillatory contractions, being approximately 3-fold more active against contractions stimulated by oxytocin than those by PGF (2alpha) (IC (50) values of 45.7 +/- 5.6 microg/mL and 160.9 +/- 5.9 microg/mL , respectively), although the maximal inhibitory effect occurred at the same concentration (300 microg/mL ) in both cases. This action was shared by pulegone (30 - 300 microM), the principal component of the essential oil (IC (50) values of 21.8 +/- 2.1 microg/mL and 12.7 +/- 4.6 microg/mL , respectively). Nifedipine (30 nM - 30 microM) also abolished agonist-stimulated contractions, and was approximately twice and 12 times as potent as EOMP in inhibiting oxytocin- and prostaglandin F (2alpha) (PGF (2alpha))-stimulated contractions, respectively. In conclusion, our results show that the essential oil of the abortifaceant plant Mentha pulegium exerts an inhibitory effect on the contractile activity of the isolated rat myometrium. This oil shares a common effect with the voltage-dependent calcium channel (VDCC) blocker nifedipine, although ostensibly acting via a different mechanism. It thus appears that EOMP and pulegone do not exert direct toxic effects on the myometrium per se that would cause abortion, and other possibilities such as systemic metabolism of plant constituents may rather underlie the abusive use of Mentha pulegium in popular medicine.

Temporal variation of chemical composition and relaxant action of the essential oil of Ocimum gratissimum L. (Labiatae) on guinea-pig ileum.

The medicinal plant Ocimum gratissimum L. (Labiatae) is widely encountered in the Northeast of Brasil where it is used to treat digestive problems. Its leaves have an essential oil (EOOG) content whose chemical composition varies according to the time of plant collection. We have compared the effects of the EOOG, collected at 08:00 a.m. (EOOG8) and at 12:00 a.m. (EOOG12), on the relaxation of guinea-pig isolated ileum. Both EOOG8 and EOOG12 (30-300 microg/ml) reversibly relaxed the spontaneous tonus of the guinea-pig ileum in a concentration-dependent manner, with similar IC50 values (49.3 and 23.8 microg/ml, respectively). The magnitude of the decrease in resting tonus was similar to that of the recognised smooth muscle relaxant papaverine. EOOG8 and EOOG12 relaxed 60 mM KCl-precontracted preparations similarly (38.33 +/- 9.91 microg/ml and 35.53 +/- 6.70), whereas a significantly more potent relaxant effect of EOOG12 compared to EOOG8 was observed when tissues were contracted using 10 microM acetylcholine (IC50 values of 69.55 +/- 4.93 and 128.16 +/- 15.70 microg/ml, respectively; p < 0.05). The principal constituents of the essential oil, eugenol and cineole, also relaxed KCl-precontracted preparations, although they were less potent than EOOG, suggesting that they alone were not responsible for EOOG-induced relaxations. Our results show that the essential oil extracted from the leaves of O. gratissimum L., collected at different time periods, exerts significant relaxant effects on isolated guinea-pig ileum which may underlie the therapeutic action of the plant.