Involvement of central beta2-adrenergic, NMDA and thromboxane A2 receptors in the pressor effect of anandamide in rats.

Intravenous (i.v.) injection of the endocannabinoid anandamide induces triphasic cardiovascular responses, including a pressor effect mediated via unknown central and peripheral mechanism(s). The aim of the present study was to determine the central mechanism(s) responsible for the pressor response to anandamide. For this purpose, the influence of antagonists at thromboxane A(2) TP (sulotroban, daltroban, SQ 29548), NMDA (MK-801) and beta(2)-adrenergic receptors (ICI 118551) on the pressor effect induced by i.v. and intracerebroventricularly (i.c.v.) administered anandamide was examined in urethane-anaesthetized rats. Anandamide (1.5-3 micromol/kg, i.v.) or its stable analogue methanandamide (0.75 micromol/kg, i.v.) increased blood pressure by 25%. Anandamide (0.03 mumol per animal i.c.v.) caused a pure pressor effect (by 20%) but only in the presence of antagonists of CB(1) and TRPV1 receptors. The effects of cannabinoids (i.v. or i.c.v.) were diminished by i.v. daltroban, sulotroban (10 mumol/kg each), and/or SQ 29548 (1 mumol/kg). The effect of anandamide i.v. was reduced by SQ 29548 (0.02 mumol per animal i.c.v.) and by the thromboxane A(2) synthesis inhibitor furegrelate i.c.v. (1.8 micromol per animal). ICI 118551, MK-801 (1 micromol/kg i.v. each), and bilateral adrenalectomy diminished the effect of anandamide i.c.v. Sulotroban (i.v.) failed to affect the response to anandamide (i.v.) in pithed rats, and anandamide and methanandamide did not bind to TP receptors in rat platelets. The present study suggests that central beta(2)-adrenergic, NMDA and thromboxane A(2) receptors are involved in the anandamide-induced adrenal secretion of catecholamines and their pressor effect in urethane-anaesthetized rats.

Three new derivatives of 3-amino-1,2-propanediol; their spectral properties and biological evaluation.

Three new derivatives of 3-amino-1,2-propanediol have been synthesized. Full assignments of signals in their 1H- and 13C-NMR spectra are given. The influence of these compounds on the cardiovascular system in the anaesthetized rat was examined. In contrast to CGP 12177 which induced a strong increase in heart rate and a slight increase in blood pressure, compounds 1, 2 and 3 x HCl at doses up to 1 micromol/kg and compound 3 at doses of 0.01 and 0.1 micromol/kg did not change the cardiovascular parameters. The highest dose of compound 3-1 micromol/kg caused a very short-lasting decrease in heart rate (by 14%) and in blood pressure (by 25%).

Novel histaprodifen analogues as potent histamine H1-receptor agonists in the pithed and in the anaesthetized rat.

We have shown previously that histaprodifen and its Nalpha-substituted analogues methylhistaprodifen and dimethylhistaprodifen are highly potent H1-receptor agonists in vivo. The aim of the present study was to examine the influence of four newly synthesized histaprodifen analogues, 3-fluoro-methylhistaprodifen (1), Nalpha-imidazolylethylhistaprodifen (2), bis-histaprodifen (3) and Nalpha-methyl-bis-histaprodifen (4), on the cardiovascular system in the pithed and in the anaesthetized rat. In pithed and vagotomized rats, diastolic blood pressure (which was increased to 80-85 mmHg by vasopressin infusion) was decreased dose dependently by methylhistaprodifen (the reference compound) and by compounds 1-4. The maximum decrease was about 47-50 mmHg for methylhistaprodifen and compounds 1, 2 and 3. Their potencies, expressed as pED50 (the negative logarithm of the dose in mole per kilogram body weight that decreased diastolic blood pressure by 25 mmHg), were 8.31, 8.23, 8.26 and 7.84, respectively. With compound 4 the maximal effect was not achieved at doses up to 1 micromol/kg (the latter dose decreased blood pressure by about 30 mmHg; pED50 approximately 6.5). The vasodepressor effect of the five compounds was attenuated by the H1-receptor antagonist dimetindene (1 micromol/kg) but was not changed by combined administration of the H2- and H3-receptor antagonists ranitidine and thioperamide (1 micromol/kg each), by combined administration of the alpha1- and alpha2-adrenoceptor antagonists prazosin and rauwolscine (1 micromol/kg each) or by the beta-adrenoceptor antagonist propranolol (3 micromol/kg). In anaesthetized rats methylhistaprodifen and compounds 1-4 induced almost the same fall in blood pressure as in pithed and vagotomized animals; the effects were sensitive to blockade by dimetindene (1 micromol/kg). Higher doses of compounds 1 and 2 (1 micromol/kg) increased heart rate in pithed and vagotomized rats in a manner sensitive to propranolol (3 micromol/kg) but insensitive to dimetindene (3 micromol/kg). The same dose of methylhistaprodifen and of compounds 3 and 4 failed to affect heart rate. We conclude that the agonistic potency of compounds 1 and 2 at H1-receptors in the cardiovascular system of the rat equals that of methylhistaprodifen, the most potent histamine H1-receptor agonist available until recently. Compounds 1 and 2 exhibit sympathomimetic activity at high doses.

Anandamide and methanandamide induce both vanilloid VR1- and cannabinoid CB1 receptor-mediated changes in heart rate and blood pressure in anaesthetized rats.

In anaesthetized rats activation of vanilloid receptors on sensory vagal nerves elicits rapid bradycardia and hypotension (Bezold-Jarisch reflex). Recent in vitro experiments revealed that the endogenous cannabinoid ligand anandamide acts as an agonist at the vanilloid VRI receptors. The present study was aimed at examining whether vanilloid VR1 receptors are involved in the cardiovascular effects of anandamide in the anaesthetized rat. Intravenous injection of anandamide, its stable analogue methanandamide and the vanilloid receptor agonist capsaicin produced a dose-dependent immediate and short-lasting decrease in heart rate and blood pressure with the following rank order of potencies: capsaicin > methanandamide > anandamide. This bradycardia was dose-dependently diminished by the selective vanilloid receptor antagonist capsazepine (0.3-3 micromol/kg) and the nonselective inhibitor of these receptors, ruthenium red (1-10 micromol/kg). Both antagonists reduced or tended to reduce the hypotension stimulated by the agonists. Following this bradycardia and hypotension (presumably evoked by the Bezold-Jarisch reflex; phase I), capsaicin, anandamide and methanandamide led to a brief vasopressor effect (phase II). Subsequently both anandamides, but not capsaicin, induced a more prolonged decrease in blood pressure (phase III). Capsazepine and ruthenium red (at doses up to 3 tmol/kg and 10 micromol/kg, respectively) failed to affect these changes in blood pressure. The cannabinoid CB1 receptor antagonist SR 141716 at 3 micromol/kg abolished the prolonged decrease in blood pressure (phase III) induced by anandamide and methanandamide, but had no effect on the reflex bradycardia and hypotension (phase I) and on the subsequent vasopressor effect (phase II) evoked by capsaicin, anandamide and methanandamide. In conclusion, the endogenous cannabinoid receptor agonist anandamide and its stable analogue methanandamide induce reflex bradycardia and hypotension (phase I) by activating the vanilloid VRI receptor. Whereas the mechanism underlying the brief vasopressor effect (phase II) is unknown, the prolonged hypotension (phase III) results from stimulation of the cannabinoid CB1 receptor.