The effects of parenteral injections of adenosine and its analogs on blood pressure and heart rate in the rat

Detection of interactions between genetic marker sets and environment in a genome-wide study of hypertension

As human complex diseases are influenced by the interplay of genes and environment, detecting gene-environment interactions ( G × E ) can shed light on biological mechanisms of diseases and play an important role in disease risk prediction. Development of powerful quantitative tools to incorporate G × E in complex diseases has potential to facilitate the accurate curation and analysis of large genetic epidemiological studies. However, most of existing methods that interrogate G × E focus on the interaction effects of an environmental factor and genetic variants, exclusively for common or rare variants. In this study, we proposed two tests, MAGEIT_RAN and MAGEIT_FIX, to detect interaction effects of an environmental factor and a set of genetic markers containing both rare and common variants, based on the MinQue for Summary statistics. The genetic main effects in MAGEIT_RAN and MAGEIT_FIX are modeled as random or fixed, respectively. Through simulation studies, we illustrated that both tests had type I error under control and MAGEIT_RAN was overall the most powerful test. We applied MAGEIT to a genome-wide analysis of gene-alcohol interactions on hypertension in the Multi-Ethnic Study of Atherosclerosis. We detected two genes, CCNDBP1 and EPB42, that interact with alcohol usage to influence blood pressure. Pathway analysis identified sixteen significant pathways related to signal transduction and development that were associated with hypertension, and several of them were reported to have an interactive effect with alcohol intake. Our results demonstrated that MAGEIT can detect biologically relevant genes that interact with environmental factors to influence complex traits.

Genus Tinospora: Ethnopharmacology, Phytochemistry, and Pharmacology

The genus Tinospora includes 34 species, in which several herbs were used as traditional medicines by indigenous groups throughout the tropical and subtropical parts of Asia, Africa, and Australia. The extensive literature survey revealed Tinospora species to be a group of important medicinal plants used for the ethnomedical treatment of colds, headaches, pharyngitis, fever, diarrhea, oral ulcer, diabetes, digestive disorder, and rheumatoid arthritis. Indian ethnopharmacological data points to the therapeutic potential of the T. cordifolia for the treatment of diabetic conditions. While Tinospora species are confusing in individual ingredients and their mechanisms of action, the ethnopharmacological history of those plants indicated that they exhibit antidiabetic, antioxidation, antitumor, anti-inflammation, antimicrobial, antiosteoporosis, and immunostimulation activities. While the clinical applications in modern medicine are lacking convincing evidence and support, this review is aimed at summarizing the current knowledge of the traditional uses, phytochemistry, biological activities, and toxicities of the genus Tinospora to reveal its therapeutic potentials and gaps, offering opportunities for future researches.

Hypotensive and cardio-chronotropic constituents of Tinospora crispa and mechanisms of action on the cardiovascular system in anesthetized rats

ETHNOPHARMACOLOGICAL RELEVANCE

Tinospora crispa has been used in folkloric medicine for the control of blood pressure. We previously found that an extract of Tinospora crispa stems decreased the mean arterial blood pressure (MAP) with a transient decrease, followed by an increase in the heart rate (HR) in rats.

AIM OF THE STUDY

To identify the active components of the Tinospora crispa extract and investigate the mechanisms of action on blood pressure and heart rate in anesthetized rats.

MATERIALS AND METHODS

The active components of Tinospora crispa extract were separated by column chromatography and a preparative HPLC. The effects and mechanisms of the active compounds on blood pressure and heart rate were studied in anesthetized, normal and reserpinized rats in vivo.

RESULTS

5 active compounds: adenosine, uridine, salsolinol, higenamine and tyramine were isolated. Adenosine decreased MAP and HR and this effect was inhibited by DMPX (A(2A) adenosine receptor antagonist). Uridine increased MAP and decreased HR and this was inhibited by suramin but not by DMPX. Salsolinol decreased the MAP and HR and this was inhibited by phentolamine but not by ICI-118,551 (β(2)-adrenoceptor antagonist) or atropine. In reserpinized rats, salsolinol had a hypertensive effect that was inhibited by prazosin and phentolamine, but not by atenolol, and caused an increase in HR that was inhibited by atenolol, but not by prazosin or phentolamine. Higenamine decreased the MAP with an increase in HR. The hypotensive effect was inhibited by ICI-118,551 or atenolol, whereas the increase in HR was not inhibited by ICI-118,551. Atenolol inhibited the increase in HR at a small dosage of higenamine but potentiated it at a higher dosage. In reserpinized rats, a small dosage of higenamine tended to potentiate the effect but at a higher dosage it caused inhibition. ICI-118,551 significantly inhibited this hypotensive effect. Tyramine caused an increase in MAP and HR and these effects almost disappeared in reserpinized rats.

CONCLUSIONS

The results demonstrate that these 5 compounds from Tinospora crispa acted in concert on the cardiovascular system of anesthetized rats. Salsolinol, tyramine and higenamine acted via the adrenoreceptors, whereas uridine and adenosine acted via the purinergic adenosine A(2) and P(2) receptors to decrease blood pressure with a transient decrease of HR followed by an increase.

Hypotensive activity of an n-butanol extract and their purified compounds from leaves of Phyllanthus acidus (L.) Skeels in rats

We aimed to investigate the effects, identify the active substances and establish the mechanisms involved in the hypotensive activity of an n-butanol extract from leaves of Phyllanthus acidus (PA extract). PA extract caused a decrease in blood pressure of anesthetized rats that was not modified by atropine or propranolol. PA extract caused a persistent dilatation of thoracic aortic rings preconstricted with either phenylephrine or KCl, and these effects were not modified by LNA or removal of the vascular endothelium. For phenylephrine-preconstricted aortic rings, the dilatory activity of the PA extract was not modified by atropine, propranolol or indomethacin. TEA, glybenclamide or ODQ significantly inhibited the dilatory activity of the PA extract on endothelium-denuded aortic rings. Nifedipine or a Ca(2+)-free medium depressed the aortic rings constrictor response to phenylephrine, and that was further augmented by the PA extract. Adenosine, 4-hydroxybenzoic acid, caffeic acid, hypogallic acid, and kaempferol were isolated from the PA extract. Each caused a decrease in blood pressure and dilatation of the aortic rings. LNA or removal of the endothelium reduced this activity. ODQ and TEA attenuated the vasodilatory activity of adenosine whereas glybenclamide and ODQ attenuated the effect of hypogallic acid. These results suggest that the hypotensive activities of the PA extract is likely the result of the direct action of these five compounds on the blood vessels by stimulating release of nitric oxide from the vascular endothelium, in part through stimulation of soluble guanylate cyclase, and opening of K(ATP) and K(Ca) channels in the vascular smooth muscle.

Antinociceptive effects of NCX-701 (nitro-paracetamol) in neuropathic rats: enhancement of antinociception by co-administration with gabapentin

BACKGROUND AND PURPOSE

Neuropathic pain is characterized by a poor response to classic analgesics. In the present study, we have assessed the antinociceptive activity of NCX-701 (nitro-paracetamol) in neuropathic rats, after systemic and intrathecal (i.t.) administration. In addition, we analysed the possible benefit of the combination of NCX-701 and gabapentin, a well-known potent analgesic, in the treatment of neuropathic pain.

EXPERIMENTAL APPROACH

The antinociceptive effects of i.v. and i.t. NCX-701 and paracetamol were studied in spinal cord neuronal responses from neuropathic adult male Wistar rats, using the recording of single motor units technique. The effect of i.v. and i.t. NCX-701 in combination with i.v. gabapentin was studied by isobolographic analysis.

KEY RESULTS

The experiments showed that NCX-701, but not paracetamol, dose-dependently reduced the nociceptive responses evoked by noxious mechanical and electrical stimulation, after i.v. (ID(50) 542 +/- 5 micromol kg(-1) for noxious mechanical stimulation) or i.t. (ID(50) 932 +/- 16 nmol kg(-1)) administration. The combined administration of i.v. or i.t. NCX-701 and i.v. gabapentin induced a more intense antinociceptive effect than any of the two drugs given alone. The isobolographic analysis showed a synergistic effect.

CONCLUSIONS AND IMPLICATIONS

NCX-701 is an effective antinociceptive compound in situations of neuropathy-induced sensitization, with an action mainly located in the spinal cord. The combination of NCX-701 and gabapentin induces a synergistic enhancement of the depression of nociceptive responses evoked by natural noxious stimulation. The use of NCX-701 alone or in combination with gabapentin might open up new and promising perspectives in the treatment of neuropathic pain.

The antinociceptive effects of the systemic adenosine A1 receptor agonist CPA in the absence and in the presence of spinal cord sensitization

Adenosine A1 receptor agonists are effective antinociceptive agents in neuropathic and inflammatory pain, though they appear to be weak analgesics in acute nociception. Important discrepancies are observed on the effectiveness and potency of adenosine analogues when comparing different studies, probably due to the use of different ligands, models of antinociception, routes of administration and types of sensitization. We studied the systemic antinociceptive effects of the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) in spinal cord neuronal responses from adult male rats in acute nociception and in sensitization due to arthritis and neuropathy. The experiments showed that CPA was effective in the three experimental conditions, with a similar potency in reducing responses to noxious mechanical stimulation (ID50s: 20 +/- 1.2 microg/kg in acute nociception, 18 +/- 1.1 microg/kg in arthritis, 17.4 +/- 2 microg/kg in neuropathy). The phenomenon of wind-up was also dose-dependently reduced by CPA in the three experimental situations although the main action was seen in arthritis. Depression of blood pressure by CPA was not dose-dependent. We conclude that systemic CPA is a potent and effective analgesic in sensitization due to arthritis and neuropathy but also in acute nociception. The effect is independent of the cardiovascular activity and is centrally mediated since wind-up was inhibited.

Role of central and peripheral adenosine receptors in the cardiovascular responses to intraperitoneal injections of adenosine A1 and A2A subtype receptor agonists

1. The cardiovascular effects of the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) and the adenosine A2A receptor agonist 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680) were investigated in rats implanted with telemetry transmitters for the measurement of blood pressure and heart rate. 2. Intraperitoneal (i.p.) injections of the adenosine A1 receptor agonist CPA led to dose-dependent decreases in both blood pressure and heart rate. These effects of 0.3 mg kg(-1) CPA were antagonized by i.p. injections of the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dimethyl-xanthine (CPT), but not by i.p. injections of the adenosine A2A receptor antagonist 3-(3-hydroxypropyl)-8-(m-methoxystyryl)-7-methyl-1-propargylxanthine phosphate disodium salt (MSX-3). Injections (i.p.) of the peripherally acting nonselective adenosine antagonist 8-sulfophenyltheophylline (8-SPT) and the purported nonselective adenosine antagonist caffeine also antagonized the cardiovascular effects of CPA. 3. The adenosine A2A agonist CGS 21680 given i.p. produced a dose-dependent decrease in blood pressure and an increase in heart rate. These effects of 0.5 mg kg(-1) CGS 21680 were antagonized by i.p. injections of the adenosine A2A receptor antagonist MSX-3, but not by i.p. injections of the antagonists CPT, 8-SPT or caffeine. 4. Central administration (intracerebral ventricular) of CGS 21680 produced an increase in heart rate, but no change in blood pressure. MSX-3 given i.p. antagonized the effects of the central injection of CGS 21680. 5. These results suggest that adenosine A1 receptor agonists produce decreases in blood pressure and heart rate that are mediated by A1 receptors in the periphery, with little or no contribution of central adenosine A1 receptors to those effects. 6. The heart rate increasing effect of adenosine A2A agonists appears to be mediated by adenosine A2A receptors in the central nervous system. The blood pressure decreasing effect of adenosine A2A agonists is most probably mediated in the periphery.

Effects of MaxEPA on salt-induced hypertension: relationship to [3H]nitrobenzylthioinosine binding sites

We investigated the effects of dietary MaxEPA (a major source of eicosapentaenoic acid in fish oil) supplementation on blood pressure (BP) responses and heart rate (HR) of Dahl salt-sensitive (SS) rats fed low (0.4% NaCl) and high (8.0% NaCl) sodium diets. During a four week treatment period, BP remained normotensive in rats on low salt diet but was significantly elevated in those on high salt diet, causing 50% mortality. MaxEPA diminished the BP elevation and prevented the high salt-induced mortality. HR was not affected by either salt diet alone but was reduced in the presence of MaxEPA. At the end of the treatment period, the distribution of [3H]nitrobenzylthioinosine ([3H]NBMPR) binding, a putative marker of adenosine transport and metabolism, was estimated in selected rat tissues in order to evaluate the role of the purinergic system in the BP lowering effect of MaxEPA. Maximal [3H]NBMPR binding capacity (Bmax) in the kidney and platelets were 39% and 82% lower, respectively, in rats on high salt diet than in those on low salt diet. MaxEPA significantly blunted the decrease in Bmax in the kidney but not in platelets and increased Bmax in heart (48%) of low salt group. There were no changes in dissociation constants (Kd). The results suggest that MaxEPA can attenuate salt-induced hypertension, reduce salt-induced mortality and protect the integrity of kidney NBMPR binding sites in salt-induced hypertension.

Adenosine receptor subtypes in the brainstem mediate distinct cardiovascular response patterns

A limited occipital craniotomy was conducted on urethane-chloralose anesthetized, spontaneously breathing rats to expose the caudal medulla in the region of the obex. Microinjections of highly selective agonists for adenosine receptor subtypes were made into the medial region of the caudal nucleus tractus solitarius (NTS) at the level of the posterior portion of the area postrema. Cardiorespiratory parameters were subsequently recorded for a 60-min test period following microinjection of drug or vehicle solutions. The following selective adenosine receptor agonists were used: the A1 agonist, N6-cyclopentyladenosine (CPA), which is 480-fold selective for A1 receptors in rat brain binding assays, and the A2 agonist, 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680), which is 170-fold selective for A2 receptors in rat brain binding studies and over 1500-fold selective in functional assays. The results showed that distinct and converse cardiovascular response patterns were elicited by these selective agonists for adenosine receptor subtypes following microinjections into the caudal NTS. Specifically, CGS 21680 selectively elicited potent dose-related decreases in mean arterial blood pressure (ED50 = 0.064 nmol/kg) and dose-related decreases in pulse pressure (ED50= 0.058 nmol/kg). Conversely, CPA selectively elicited potent dose-related increases in mean arterial blood pressure (ED50 = 0.62 nmol/kg) and dose-related increases in pulse pressure (ED50 = 0.70 nmol/kg). Additionally, the overall agonist-mediated response patterns were dramatically different wherein the CGS agonist exhibited a considerably more rapid time course in eliciting its hypotensive responses whereas CPA exhibited a more delayed and substantially longer time course to exert its hypertensive responses. Additionally, these distinct and converse cardiovascular response patterns were further shown to be receptor-selective since the depressor responses elicited by the A2 receptor agonist, CGS 21680, and the pressor responses elicited by the A1 receptor agonist, CPA, were completely and selectively blocked, respectively, by the selective A2 receptor antagonist, CGS 15943A, and the selective A1 receptor antagonist, DPCPX. Taken together, these findings provide persuasive in vivo evidence showing that pharmacologic activation of adenosine receptor subtypes in the caudal NTS of rats elicits specific response patterns with selective and opposite actions on cardiorespiratory behavior. These data also indicate that separate physiologic responses are specifically mediated by A2 receptors in the intact nervous system and thereby lend additional support to the case for using in vivo models to assess the functional role of adenosine A2 receptors in brain function.

Cardiorespiratory function is altered by picomole injections of 5'-N-ethylcarboxamidoadenosine into the nucleus tractus solitarius of rats

A limited occipital craniotomy was conducted on urethane-anesthetized, spontaneously breathing rats to expose the caudal medulla in the region of the obex. Microinjections of 5'-N-ethylcarboxamidoadenosine (NECA), an adenosine analog, were made into the medial region of the caudal nucleus tractus solitarius (NTS) at the level of the caudal tip of the area postrema, an area of the NTS in which there is known to be a functional co-existence of cardiovascular and respiratory-related neuronal elements. Cardiorespiratory responses were subsequently recorded for a 60 min test period. Microinjections of NECA, in the dose range of 0.35-350 pmol per rat, produced significant dose-related reductions in respiratory rate which were accompanied by dose-dependent increases in tidal volume and these pronounced effects on respiration persisted throughout the test period. In contrast, the effects of NECA microinjections on cardiovascular parameters in this region of the NTS were bidirectional and elicited considerably more complex responses during the test period. During the initial period (2-5 min) following injection, NECA elicited significant hypotension (at lower doses) and pressor responses (at higher doses) in addition to significant bradycardia (at lower doses) whereas by the end of the 60 min test period, almost all doses of NECA had resulted in hypertension and tachycardia. Multivariate analysis of variance (MANOVA) and correlation statistics indicated that the effects of NECA on blood pressure during the initial 2-5 min were dose-dependent and unlikely related to depression of respiratory frequency. A further examination of the data by MANOVA indicated that the pharmacological effects of NECA during the 60 min test period exhibited a highly significant and specific dose-dependent and time-related response pattern for the respiratory, but not the cardiovascular, parameters. Taken together, these manifold response patterns suggest that the respiratory effects of NECA may be mediated by different intrinsic mechanisms in the NTS than are the cardiovascular effects of NECA. At the end of the 60 min test period following the administration of NECA, the respiratory rate remained profoundly depressed. In view of previous studies showing that microinjections of cyclic AMP analogs, forskolin, isoproterenol and adenosine into the same NTS sites elicit a similar depression of respiration, the results with NECA in the present study further support the notion that cyclic AMP may serve as a second messenger in NTS respiratory control regions and these respiratory depressant effects may be mediated by a single adenosine receptor subtype.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine deaminase and porcine meat quality. II. Effects of adenosine analogues on plasma free fatty acids, glucose and lactate in pigs representing high and low adenosine deaminase red cell activity

The adenosine analogues 5'-(N-ethyl) carboxamidoadenosine (NECA) and N6-(phenylisopropyl) adenosine (R-PIA) were shown to differ in their effect on the plasma level of free fatty acids (FFA), glucose and lactate in pigs representing low (Ada 0) and high (Ada A) red cell adenosine deaminase activity. At the same dosage range (0.001-0.005 mg/kg) R-PIA produced a much stronger suppression of the FFA level than NECA, indicating that A1 adenosine receptors predominate in porcine adipose tissue. Pretreatment with 8-phenyltheophylline completely abolished the antilipolytic effect of both adenosine analogues. NECA in contrast to R-PIA elevated the blood glucose concentration, suggesting that A2 adenosine receptors are involved in the stimulation of glycogenolysis. This effect of NECA was not altered by a beta-adrenoceptor blockade providing evidence for a direct effect of adenosine on glycogenolysis. Whereas the changes in plasma FFA following NECA administration were of similar magnitude in Ada A and Ada 0 pigs, the changes in the blood glucose concentration were different in these two groups of pigs.

A central role for adenosine in the hypotension elicited by hypoxia in anesthetized rats

Brief inhalation of an oxygen-deficient (5%) gas mixture evoked a rapidly developing, profound hypotension in anesthetized rats. Recovery upon reoxygenation was also rapid. A potential involvement of adenosine in the genesis of this hypotension was evaluated with various peripherally administered adenosine antagonists. Caffeine (10 mg/kg), which readily crosses the blood-brain barrier, significantly attenuated the hypoxia-evoked hypotension. 8-p-Sulphophenyltheophylline and xanthine amine congener, which do not readily penetrate the blood-brain barrier, had little effect on the magnitude of the hypotension. The data suggests that hypoxia-elicited hypotension in anesthetized rats results from the activation of central adenosine receptors.

Quinolinic acid neurotoxicity: protection by intracerebral phenylisopropyladenosine (PIA) and potentiation by hypotension

In the present study we have used the purine agonist R-phenylisopropyladenosine (PIA) which suppresses excitatory amino acid release to assess its effect on quinolinate toxicity. Quinolinic acid was injected into the rat hippocampus alone or with PIA and the animals allowed to recover. After 4 days the brain was removed for histological examination. The extent of neuronal degeneration was assessed blind by an independent observer on a scale of 0 (no damage) to 10 (complete degeneration). Co-administration of PIA protected against the toxicity, and this protective action of PIA was blocked by a xanthine adenosine receptor antagonist. However, systemic injections of PIA or the non-purine ganglion blocking drug trimetaphan, both of which caused significant depression of blood pressure, potentiated quinolinate toxicity. The results may indicate an interaction between endogenous excitotoxins and episodes of hypotension which may be critical in determining cell death in the CNS.

Cardiovascular effects of microinjection of adenosine into the nucleus tractus solitarius

Rats were anesthetized with urethane and limited occipital craniotomy was conducted to expose the caudal medulla in the region of the obex. Microinjections of adenosine were made into the nucleus tractus solitarius and heart rate and blood pressure responses recorded. Adenosine produced dose-related decreases in blood pressure and heart rate. The data indicate that adenosine may play a neuromodulatory role in central cardiovascular control areas.

Cardiovascular effects of microinjections of adenosine analogs into the fourth ventricle of rats

Rats were implanted with chronic indwelling cannulae into the posterior region of the fourth ventricle. After recovery from surgery, acute experiments on blood pressure were conducted under urethane anesthesia. The blood pressure and heart rate responses following administration of two adenosine analogs, NECA and L-PIA were examined. Microinjections of both analogs produced dose-dependent reductions in blood pressure and heart rate. NECA was approximately 20-fold more potent than L-PIA in reducing blood pressure and depressing heart rate. The cardiovascular effects of both analogs were antagonized by parenteral injections of caffeine. These findings show that microinjections of analogs of adenosine into the fourth ventricle can influence areas of the central nervous system involved in cardiovascular control.