Preliminary in vivo studies of a new lecithin-based formulation of paclitaxel.

Amorphous paclitaxel dissolves rapidly (1 mg mL(-1)) in an isotonic aqueous dispersion of egg lecithin (5% w/w), a new biocompatible submicron drug carrier consisting of structured aggregates with average size 0.5 microm. The solution is physically stable for at least 24 h and can be administered as an intravenous infusion. After a 5 h infusion in rabbits (0.66 mg kg(-1) h(-1)), changes in blood morphology were comparable to those observed in rabbits that received the commercial product Taxol. No changes in the enzyme profiles (alanine/aspartate aminotransferase or alkaline phosphatase) were observed. However, during infusion of the new formulation plasma concentration of paclitaxel (292 +/- 182 ng mL(-1)) was lower than observed after Cremophor-containing Taxol (540 +/- 262 ng mL(-1)). This result may indicate that the tissue distribution is different for the two drug formulations. Daily intraperitoneal administrations (3 doses/day) in mice demonstrated that the new carrier solution was non-toxic and, relative to Taxol, the new formulation exhibited similar or less toxicity.

Selective inhibition of pinacidil effects by estrogen in guinea pig heart.

BACKGROUND: Recently, gender related differences in heart function have been extensively studied. Some of them, as differences in repolarization between males and females have been explained by direct effect of estrogen on delayed rectifier K+ channels and Ca2+ channels. It seems that estrogen induces overexpression of SUR2A subunits of ATP-sensitive K+ channels. The aim of this paper was to compare heart rate changes in male and female guinea pigs in the presence of different potassium channel openers (PCOs). METHODS: We used spontaneously beating right atria from control and estrogen receptor modulator-treated male and female guinea pigs (17-beta-estradiol as a stimulator and tamoxifen as a blocker of estrogen receptor located in heart muscle). RESULTS: In control females, rilmakalim and diazoxide, but not pinacidil elicited concentration-dependent decrease of heart rate. On the other hand, all three PCOs induced similar negative chronotropic action in hearts obtained from male control group (Emax was between -40 and -70 bpm, respectively). After two weeks of treatment with 17-beta-estradiol, pinacidil failed to significantly decrease heart rate in males however, tamoxifen-pretreated female group responded by decrease in automatism in the presence of rising concentration of pinacidil (Emax=-45+/-6 bpm, not significantly different from Emax in male control=-40+/-5 bpm, n=7). Interestingly, we observed lower blood concentration of the heart form of lactate dehydrogenase (H-LDH) in female than in male control group. Moreover, H-LDH concentration increased in tamoxifen-pretreated female group and decreased in 17-beta-estradiol-treated male group. CONCLUSION: Our results indicate that estrogen downregulates H-LDH production and specifically modulate pinacidil action in guinea pig right atria, probably by changes of binding site for this drug in SUR2A receptor, but not for rilmakalim and diazoxide.

Imidazoline receptors in relaxation of acetylcholine-constricted isolated rat jejunum.

Since 20 years the concept of specific imidazoline receptors has remained controversial. The problem with imidazoline receptors is mostly due to their functional similarity to alpha-adrenoceptors. In this work, a pharmacodynamic model of isolated rat jejunum longitudinal muscle strips constricted with acetylcholine (Ach) was applied to separate functional properties of the two types of receptors. Relaxation of the preparation was measured as a function of concentration of 2-(benzofuranyl)-2-imidazoline (2-BFI), a specific imidazoline I2 receptor ligand, cirazoline, a potent I2 receptor ligand and alpha1-adrenoceptor agonist, phenylephrine, an agonist of alpha1-adrenoceptor, moxonidine, a ligand of I1 receptor, efaroxan, a ligand of I3 receptor and 5-bromo-6-(imidazoline-2-yl-amino)quinoxaline (UK14304), an agonist of alpha2-adrenoceptor. Next, the effects of a series of imidazoline-and/or alpha-adrenoceptor-binding drugs (prazosin, yohimbine, RS79948, RX821002, idazoxan and efaroxan) on the relaxation of the Ach-constricted rat jejunum strips, induced by 2-BFI, cirazoline or phenylephrine, were studied. The obtained results demonstrate the involvement of the postsynaptic imidazoline receptors in rat jejunum motility. These receptors are of I2 subtype and are linked to alpha-adrenoceptors of the predominantly alpha1 subtype. The alpha1 receptors dominate functionally over the I2 in the isolated rat jejnum. The proposed model might be useful in search for more specific new drugs.

Cerivastatin and hypercholesterolemia reduce apoptosis of cardiomyocytes in guinea pig papillary muscle subjected to hypoxia/reoxygenation.

The aim of this study was to assess how cerivastatin influences contractility and degree of myocardial damage in papillary muscle subjected to hypoxia-reoxygenation in hypercholesterolemic guinea pigs. Study group consisted of guinea pigs, fed standard, hypercholesterolemic or hypercholesterolemic diets with low dose of cerivastatin. During experimental hypoxia-reoxygenation, the contractility was measured. Apoptosis of cardiomioctes was assessed with the use of TUNEL technique. Total cholesterol in standard, hypercholesterolemic and cerivastatin-treated group was 35 +/- 8 mg/dl, 131.6 +/- 30.4 mg/dl and 121.2 +/- 26.2 mg/dl, respectively, and was significantly higher in rats fed hypercholesterolemic and hypercholesterolemic + cerivastatin diets than in control group (p < 0.01). There were no significant differences between all analyzed groups in the post-ischemic cardiac function. Percentage of apoptotic cells after hypoxia-reoxygenation injury in groups fed standard, hypercholesterolemic and hypercholesterolemic + cerivastatin diets was 30 +/- 8%, 20 +/- 4% and 5 +/- 7%, respectively, and was significantly lower in groups that received hypercholesterolmic (p < 0.01) and hypercholesterolemic + cerivastatin (p < 0.001) diets in comparison with standard diet-fed group. In the group treated with cerivastatin, the percentage of apoptotic cells was additionally lower in comparison with hypercholesterolemic group (p < 0.01). Negative correlation between percentage of apoptotic cells and HDL level was found when all groups were considered jointly (r = -0.41, p < 0.05). Our study clearly shows that cerivastatin in hypercholesterolemic animals and hypercholesterolemia itself limit cardiomiocyte damage after hypoxia-reoxygenation.

Synthesis and structure of novel 2,3, 5,6-tetrahydro-1H-imidazo[2,1-b][1,3,5]benzotriazepines with vasocontractile activity in rabbit aortic rings.

A series of novel 2,3,5,6-tetrahydro-1H-imidazo[2,1-b][1,3,5]benzotriazepines (3a-n) and hydrochlorides (4a-b) were prepared and their structure was determined by IR and NMR spectroscopic data as well as by X-ray analysis of the hydrochloride 4a. The newly synthesized benzotriazepine 4b exhibited concentration-dependent vasocontractile activity in isolated rabbit aortic rings. Rimalkalim was found to induce a relaxation in rabbit aortic rings precontracted by 4b (3x10(-5) mol). Present results indicate that K(ATP)-dependant channels may contribute in the contractile activity of benzotriazepine 4b.

Pretreatment of male guinea pigs by 17-beta-estradiol induces hypersensitivity of beta-adrenoceptors in electrically driven left atria.

BACKGROUND: It is well known that estrogen can modulate distribution and function of adrenergic receptors in the heart of different species. We reported here gender differences in adrenergic responsiveness of electrically driven guinea pig left atria. METHODS: Experiments were performed on the guinea pigs divided in four groups: males control (MC), males treated by 17-beta-estradiol (MTE), females control (FC) and females treated by tamoxifen (FTT). After two weeks of treatment, the animals were sacrificed, the left atria were isolated and force of contraction (Fc), velocity of contraction (+dF/dt), velocity of relaxation (-dF/dt) and time to peak contraction (ttp) and relaxation time at 10% of amplitude (tt(10) ) were measured. RESULTS: Apart from significantly lower Fc and longer tt10 in FC (0.97+/-0.12 mN, 233+/-7 ms, respectively) vs. MC (1.66+/-0.3, 176.3+/-18 ms, respectively, n=6, P<0.05), isoprenaline (ISO) and noradrenaline (NOR) (in the presence of prazosine) concentration-response curves were strongly shifted leftward in comparison with male group. Additionally, the maximal effects of. NOR was significantly lower in FC (about 40%) than in MC. Application of 17-beta-estradiol to males and tamoxifen to females guinea pigs confirmed crucial role of estrogen in observed phenomenon. CONCLUSION: Our results indicate that estrogen not only downregulates beta1-adrenoceptors, but induces its hypersensitivity to catecholamines, at least in guinea pig left atria.

Experimental hyperlipidaemia does not prevent preconditioning and it reduces ischemia-induced apoptosis.

BACKGROUND: Although ischemic preconditioning (PC) is known to confer cardioprotection in healthy subjects, it is unclear whether this phenomenon exists in the presence of hyperlipidaemia. The goal of this study was to determine whether the cardioprotective effect of PC is affected by hyperlipidaemia in a guinea pig model. METHODS: We investigated the influence of preconditioning in normo- and hyperlipidaemic animals on papillary muscle contractility and myocardial damage as expressed by the percentage of apoptotic cells. Guinea pigs were fed a normal diet or a hyperlipidaemic diet for 5 weeks. Experiments were performed on papillary muscles subjected to experimental ischemia-reperfusion with or without prior PC. RESULTS: The dietary treatment resulted in significant changes in lipid parameters, which had not affected the functionality of the right ventricle papillary muscle, both at basal conditions and in response to ischemia-reperfusion injury. However, it was found that the hyperlipidaemic diet had an effect on ischemia-induced apoptosis. Papillary muscles of hyperlipidaemic animals with higher HDL plasma concentrations were less susceptible to ischemia-reperfusion injury. CONCLUSIONS: This study demonstrates that hyperlipidaemia does not alter the benefits of ischemic preconditioning such as a reduction of apoptosis and preservation of myocardial contractility. Additionally, it has been shown that plasma HDL may protect cardiomyocytes against ischemia-induced apoptosis.

Hypotonic stress enhances slope conductivity of ATP-sensitive K+ channels activated pharmacologically.

The aim of this paper was to find out the effects of hypotonic stress on the slope conductivity of ATP-sensitive K(+) channels. Using patch clamp technique, rilmakalim and pinacidil as the activators and glibenclamide as an inhibitor of mentioned channels, we have demonstrated that short hypotonic challenge doubled slope conductivity of exploring channels by augmentation of their open probability.

Gender differences in effects of pinacidil but not diazoxide on heart automatism in the isolated guinea pig right atria.

UNLABELLED: The aim of this paper was to investigate the effects of pinacidil and diazoxide, the activators of sarcolemmal and mitochondrial ATP-sensitive K(+) channels (K(ATP)), respectively, on heart rate and force of contraction in female and male guinea pigs. Experiments were performed on the isolated, spontaneously beating, right atria obtained from guinea pigs of both genders. First series of experiments were performed in the spring and repeated in the fall. It was found that diazoxide induced similar negative chronotropic effects in females (-logIC(50) = 4.34 +/- 0.05, E(max) = -90 +/- 6 beats min(-1)) and males (-logIC(50) = 4.42 +/- 0.1, E(max) = -91 +/- 6 beats min(-1)). Additionally, significant positive inotropic effect sensitive to 5-hydroxydecanoate was noted only in males (about 30% above control level at 300 microM). No differences in effects of diazoxide in the spring and in the fall were noted. On the other hand, pinacidil induced significant decrease in heart rate in female guinea pigs only in the fall (-logIC(50) = 4.79 +/- 0.15, E(max) = -77 +/- 9 beats min(-1)), but in males similar negative chronotropic action in the spring (-logIC(50) = 4.53 +/- 0.12, E(50) = -63 +/- 5 beats min(-1)) and in the fall (-logIC(50) = 4.75 +/- 0.2, E(max) = -59 +/- 8 beats min(-1)) was observed. Glibenclamide (10 microM), but not 5-hydroxydecanoate (300 microM) reversed negative chronotropic action of both, pinacidil and diazoxide. No significant inotropic action of pinacidil was observed. CONCLUSIONS: Although negative chronotropic effects of pinacidil and diazoxide are related to activation of sarcolemmal K(ATP) channels, only pinacidil affects heart rate of female and male guinea pigs in a different way. This difference is probably hormone-dependent as it appeared only in the spring.

Differential salutary effects of nonselective and selective COX-2 inhibitors in postoperative ileus in rats.

BACKGROUND: Postoperative ileus (PI) is a common surgical complication, the treatment of which consists of supportive measures. AIM: The effects of several cyclooxygenase (COX) inhibitors and their interaction with L-arginine/nitric oxide synthase (NOS) pathway were tested in a rat PI model. METHODS: Intestinal transit was measured as Evans blue migration after skin incision, laparotomy, or laparotomy followed by evisceration and gut handling. RESULTS: In contrast to a selective inducible NOS (iNOS) blocker, L-N(6)-(1-iminoethyl)lysine hydrochloride (L-NIL), N(omega)-nitro-L-arginine methyl ester (L-NAME) reversed the additional inhibitory effects of gut manipulation after laparotomy on the gastrointestinal transit (GI) in a dose-dependent, L-arginine-sensitive manner. Laparotomy and manipulations of small intestine increased blood plasma nitrites and nitrates level (NOx), an effect preventable by L-NAME. Indomethacin, resveratrol (selective COX-1 blocker), and COX-2 antagonists, nimesulide, NS-398, DuP-697, and L-752860, attenuated the additional inhibitory effects of gut manipulation following laparotomy in a dose-dependent manner. In contrast, only nimesulide, NS-398, DuP-697, and L-752860 partly, but significantly, reversed the effects of laparotomy on the intestinal transit. Administration of L-NAME subsequent to COX inhibitors abolished the salutary effects of the latter, implying that at least the synthesis of either NO or prostanoids must remain unaffected to enable a return of GI transit during the postoperative period. CONCLUSION: In addition to NO synthesized by constitutive NOS (cNOS), prostaglandins produced by both COX-1 and COX-2 participate in the pathogenesis of PI, albeit in different pathological mechanisms. Thus laparotomy stimulated COX-2 activity, whereas gut manipulation led to an excessive cNOS activity and prostaglandin synthesis by COX-1.

Mechanism of the contractile effects of galantide and Galanin(1-14) [alpha-aminobutyric acid]scyliorhinin-I in rat isolated fundus strips.

BACKGROUND: The study was undertaken to establish the pharmacological basis of the stimulatory activity of galantide (M15) and galanin(1-14)-(a-aminobutyric acid8-[Abu8])scyliorhinin-I [Scy-I] in gastric smooth muscle. MATERIAL/METHODS: Isotonic contractions of the isolated, longitudinal rat gastric fundus strips were recorded. RESULTS: Galanin, galanin(1-15)-NH2, M15 and galanin(1-14)-[Abu8]Scy-I elicited concentration-dependent contractions. Their EC50s equaled 12.95, 174, 70.06 and 187 nM respectively. Hill's coefficients for galanin and galanin(1-15)-NH2 were not different from unity, indicating an interaction of one peptide molecule with one receptor according to the principles of classical receptor theory. Hill's coefficients were 0.73 and 1.56 for M15 and galanin (1-14)-[Abu8]Scy-I, respectively, a value significantly different from unity. Cold-storage denervation, tetrodotoxin-TTX (1 mM), spantide (100 mM) and NK1-3 receptor antagonists SR140333, 48968, 142801 (up to 10 mM) notably diminished M15, galanin(1-14)-[Abu8]Scy-I, SP(5-11) and [Abu8]-Scy-I evoked contractions without affecting activities of galanin and galanin(1-15)-NH2. Additionally, cross-desensitization experiments attenuated activity of M15 and galanin(1-14)-[Abu8]Scy-I without any noticeable action on galanin or galanin(1-15)-NH2. CONCLUSIONS: The action of chimeric peptides on the smooth muscle of the rat gastrointestinal tract depended not only on the myogenic interaction of those peptides with galanin binding sites, but also on the activation of tachykinin receptors or the release of endogenous mediators from the presynaptic terminals.