A cannabinoid receptor, sensitive to O-1918, is involved in the delayed hypotension induced by anandamide in anaesthetized rats.

BACKGROUND AND PURPOSE: Intravenous injection of the endocannabinoid anandamide induces complex cardiovascular changes via cannabinoid CB(1), CB(2) and vanilloid TRPV1 receptors. Recently, evidence has been accumulating that in vitro, but not in vivo, anandamide relaxes blood vessels, via an as yet unidentified, non-CB(1) vascular cannabinoid receptor, sensitive to O-1918 (1,3-dimethoxy-5-2-[(1R,6R)-3-methyl-6-(1-methylethenyl)-2-cyclohexen-1-yl]-benzene). We here examined whether the anandamide-induced hypotension in urethane-anaesthetized rats was also mediated via a non-CB(1) vascular cannabinoid receptor. EXPERIMENTAL APPROACH: Effects of two antagonists (O-1918 and cannabidiol) of the non-CB(1) vascular cannabinoid receptor on anandamide-induced changes in mean, systolic and diastolic blood pressure (MBP, SBP, DBP), mesenteric (MBF) and renal (RBF) blood flow and heart rate (HR) in urethane-anaesthetized rats was examined. KEY RESULTS: In anaesthetized rats, anandamide (1.5-3 micromol.kg(-1)) and its stable analogue methanandamide (0.5 micromol.kg(-1)) caused a delayed and prolonged decrease in MBP, SBP, DBP, MBF and RBF by about 10-30% of the respective basal values without changing HR. In pithed rats, anandamide (3 micromol.kg(-1)) decreased blood pressure by about 15-20% of the basal value without affecting HR, MBF and RBF. All vascular changes were reduced by about 30-70% by cannabidiol and O-1918 (3 micromol.kg(-1), each). CONCLUSIONS AND IMPLICATIONS: Non-CB(1) cannabinoid vascular receptors, sensitive to O-1918, contribute to the hypotensive effect of anandamide in anaesthetized rats. Activation of these receptors may be therapeutically important as the endocannabinoid system could be activated as a compensatory mechanism in various forms of hypertension.

Positive inotropic and lusitropic effects mediated via the low-affinity state of beta1-adrenoceptors in pithed rats.

1 Activation by CGP 12177 and cyanopindolol of the human and rat low-affinity state of beta(1)-adrenoceptors increases frequency and contractile force and hastens relaxation in isolated cardiac tissues, and probably relaxes isolated vessels. In order to identify the positive inotropic, positive lusitropic and vasodilator effects of both agonists also in vivo, we have determined their effects on the left ventricular systolic pressure (LVSP), the rate of intraventricular pressure rise (+dP dt(-1)(max)) and decline (-dP dt(-1)(max)), the diastolic blood pressure (DBP) and the mesenteric blood flow (MBF) in pithed and vagotomized rats. 2 CGP 12177 (0.1-100 nmol kg(-1)) and cyanopindolol (1-1000 nmol kg(-1)) dose-dependently enhanced all cardiac parameters. The nonselective beta-adrenoceptor antagonist bupranolol 10 micromol kg(-1) diminished the CGP 12177 (100 nmol kg(-1))-stimulated increases in LVSP from 26.3+/-8.2 to 13.1+/-1.8 mmHg (P<0.05), +dP dt(-1)(max) from 5287+/-290 to 2439+/-296 mmHg s(-1) (P<0.001) and -dP dt(-1)(max) from -3836+/-301 to -2187+/-443 mmHg s(-1) (P<0.05), respectively. The beta(1)-adrenoceptor antagonist CGP 20712A 10 micromol kg(-1) (known to block the low-affinity state of beta(1)-adrenoceptors at high doses) inhibited increases in +/-dP dt(-1)(max) elicited by the highest dose of CGP 12177. 3 The highest doses of CGP 12177 and cyanopindolol increased DBP by about 10 mmHg and MBF by 1.4+/-0.3 and 0.6+/-0.3 ml min(-1), respectively. The vascular effects of CGP 12177 were not affected by bupranolol and CGP 20712A. 4 In conclusion, activation of the low-affinity state of beta(1)-adrenoceptors by CGP 12177 and cyanopindolol in pithed rats causes a positive inotropic and lusitropic effect. By contrast, the vascular effects of CGP 12177 and cyanopindolol are not mediated by these receptors and have only marginal influence under in vivo conditions.

[Influence of anandamide, the endogenous agonist of cannabinoid receptors on the circulatory system]. / Wplyw anandamidu, endogennego agonisty receptorów kannabinoidowych na uklad krazenia.

Cannabinoids, the active ingredients of Cannabis sativa, have been used by humans as hallucinogens and therapeutic agents for thousands of years. These agents are now known to act through the cannabinoid CB1 and CB2 receptors. The recent discovery of endogenous cannabinoids and the fact that they are involved in the pathology of hypotension associated with hemorrhage, sepsis, cirrhosis, and myocardial infarction indicate that cannabinoids play a greater role in human and animal pathophysiology than initially anticipated. Anandamide is the first of the endogenous cannabinoid ligands discovered. Its intravenous administration produces a characteristic three-phase response in the circulatory systems of experimental animals: In phase 1--a short-lasting decrease in heart rate and systemic blood pressure is related to activation of vanilloid TRPV1 receptors. In phase 2 an increase in blood pressure involves multiple mechanisms, both central (probably through the rostral ventrolateral medulla) and peripheral (vascular, Ca2+-dependent). In phase 3 there is a prolonged decrease in blood pressure and sometimes bradycardia, related to the activation of cannabinoid CB1 and vanilloid TRPV1 receptors. On the basis of this three-phase mechanism, the present paper intends to describe the participation of anandamide in the circulatory system under physiological and pathophysiological conditions. It also discusses the possibility of applying cannabinoid ligands as new therapeutic agents for the treatment of some pathologies.

A search for presynaptic beta3-adrenoceptors in the rat.

Presynaptically localized adrenoceptors occur on a variety of neurones. In particular, alpha2-adrenoceptors, occurring on neurones of the peripheral and central nervous system, inhibit the release of the respective transmitters whereas beta2-adrenoceptors on some types of postganglionic sympathetic neurones facilitate noradrenaline release. Since only little information is available whether there are also presynaptic beta3-adrenoceptors, we examined the effect of beta3-adrenoceptor agonists on noradrenaline release from the resistance vessels and the hippocampus of the rat and on serotonin and acetylcholine release from the rat hippocampus. In rat hippocampal slices preincubated with (H-noradrenaline, 3H-serotonin and 3H-choline and superfused in the presence of an inhibitor of the neuronal transporter of the respective neurone, the beta3-adrenoceptor agonist CL 316243 did not affect the electrically evoked tritium overflow. The latter was, however, inhibited by at least 50% by agonists of the respective autoreceptors. CL 316243 and another three beta3-adrenoceptor agonists (BRL 37344, ZD 2079 and CGP 12177) failed to affect the electrically evoked tritium overflow also in slices preincubated with 3H-noradrenaline and superfused in the presence of the alpha2-adrenoceptor antagonist rauwolscine whereas prostaglandin E2 caused a marked inhibition. In pithed and vagotomized rats, the increase in diastolic blood pressure induced by electrical stimulation of the sympathetic outflow was also not affected by CL 316243 but markedly inhibited by the cannabinoid receptor agonist WIN 55212-2. CL 316243 and WIN 55212-2 were devoid of an effect on the rise in diastolic blood pressure induced by exogenous noradrenaline. In conclusion, our data suggest that the noradrenergic neurones innervating the resistance vessels of the rat and the noradrenergic, serotoninergic and cholinergic neurones of the rat hippocampus are not endowed with presynaptic beta3-adrenoceptors.

Central and peripheral components of the pressor effect of anandamide in urethane-anaesthetized rats.

1. We wanted to search for the mechanism(s) responsible for the brief pressor response induced by anandamide in urethane-anaesthetized rats. 2. The anandamide-induced pressor effect was not modified by the antagonists of cannabinoid CB(1) and vanilloid TRPV(1) receptors, SR 141716A (3 micromol kg(-1)) and capsazepine (1 micromol kg(-1)), respectively, by bilateral vagotomy and by pithing. Replacement of urethane by pentobarbitone virtually abolished the pressor effect of anandamide, both in pithed and vagotomized and in 'intact' rats (i.e. not treated in this manner). 3. The pressor effect of anandamide was reduced by the nonselective TRPV family inhibitor ruthenium red (3 micromol kg(-1)) and by the blocker of L-type calcium channels nifedipine (1 micromol kg(-1)), both in pithed urethane-anaesthetized rats and in 'intact' urethane-anaesthetized rats. The nonselective beta-adrenoceptor antagonist propranolol (0.1 or 0.3 micromol kg(-1)) and the nonselective NMDA receptor antagonist MK-801 (1 micromol kg(-1)) diminished the anandamide-induced vasopressor response in 'intact' but not in pithed rats. The inhibitory effect of propranolol in 'intact' rats was mimicked by the beta(2)-adrenoceptor antagonist ICI 118551 (1 micromol kg(-1)), but not by the beta(1)-adrenoceptor antagonist CGP 20712 (1 micromol kg(-1)). 4. The present study revealed that two mechanisms may be responsible for the anandamide-induced pressor response in urethane-anaesthetized rats. The first involves the central nervous system (probably the medulla oblongata) and is sensitive to propranolol and MK-801. The second, which is located peripherally (most probably in blood vessels), is sensitive to nifedipine, ruthenium red and pentobarbitone and, hence, probably represents a Ca(2+)-dependent mode of action.

[Beta-adrenergic receptors in the cardiovascular system. The participation of propranolol insensitive beta-adrenoceptors in the regulation of the cardiovascular system]. / Receptory beta-adrenergiczne w ukladzie krazenia. Udzial niewrazliwych na propranolol receptorów beta-adrenergicznych w regulacji ukladu krazenia.

In this paper we described the participation of beta-adrenoceptors in the regulation of the cardiovascular system. We characterized mainly the low-affinty state of beta1-adrenoceptors and beta3-adrenoceptors, which are insensitive to propranolol (the antagonist of beta1-/beta2-adrenoceptors). We also illustrated their function in the healthy and failing heart. In addition the vasodilatory effects of these receptors ligands were described.