Background and purpose:
A putative novel cannabinoid receptor mediates vasorelaxation to anandamide and abnormal‐cannabidiol and is blocked by O‐1918 and by high concentrations of rimonabant. This ...study investigates VSN16, a novel water‐soluble agonist, as a vasorelaxant potentially acting at non‐CB1, non‐CB2 cannabinoid receptors in the vasculature.
Experimental approach:
VSN16 and some analogues were synthesized and assayed for vasodilator activity in the rat third generation mesenteric artery using wire myography. Also carried out with VSN16 were haemodynamic studies in conscious rats and binding studies to CB1 receptors of rat cerebellum.
Key results:
VSN16 relaxed mesenteric arteries in an endothelium‐dependent manner. The vasorelaxation was antagonized by high concentrations of the classical cannabinoid antagonists, rimonabant and AM 251, as well as by O‐1918, an antagonist at the abnormal‐cannabidiol receptor but not at CB1 or CB2 receptors. It did not affect 3HCP55,940 binding to CB1 receptors in rat cerebellum. The vasorelaxation was not pertussis toxin‐sensitive but was reduced by inhibition of nitric oxide synthesis, Ca2+‐sensitive K+ channels (KCa) and TRPV1 receptors. In conscious rats VSN16 transiently increased blood pressure and caused a longer‐lasting increase in mesenteric vascular conductance. Structure‐activity studies on vasorelaxation showed a stringent interaction with the target receptor.
Conclusions and implications:
VSN16 is an agonist at a novel cannabinoid receptor of the vasculature. It acts on the endothelium to release nitric oxide and activate KCa and TRPV1. As it is water‐soluble it might be useful in bringing about peripheral cannabinoid‐like effects without accompanying central or severe cardiovascular responses.
British Journal of Pharmacology (2007) 152, 751–764; doi:10.1038/sj.bjp.0707470; published online 24 September 2007
Background and Purpose
Lysophosphatidylinositol (
LPI
), a lipid signalling molecule, activates
GPR
55 and elevates intracellular
Ca
2+
. Here, we examine the actions of
LPI
in the rat resistance ...mesenteric artery and
Ca
2+
responses in endothelial cells isolated from the artery.
Experimental Approach
Vascular responses were studied using wire myographs. Single‐cell fluorescence imaging was performed using a MetaFluor system. Hypotensive effects of
LPI
were assessed using a Biopac system.
Key Results
In isolated arteries,
LPI
‐induced vasorelaxation was concentration‐ and endothelium‐dependent and inhibited by
CID
16020046, a
GPR
55 antagonist. The
CB
1
receptor antagonist
AM
251 had no effect, whereas rimonabant and
O
‐1918 significantly potentiated
LPI
responses. Vasorelaxation was reduced by charybdotoxin and iberiotoxin, alone or combined.
LPI
decreased systemic arterial pressure.
GPR
55 is expressed in rat mesenteric artery.
LPI
caused biphasic elevations of endothelial cell intracellular
Ca
2+
. Pretreatment with thapsigargin or 2‐aminoethoxydiphenyl borate abolished both phases. The
PLC
inhibitor
U
73122 attenuated the initial phase and enhanced the second phase, whereas the Rho‐associated kinase inhibitor
Y
‐27632 abolished the late phase but not the early phase .
Conclusions and Implications
LPI
is an endothelium‐dependent vasodilator in the rat small mesenteric artery and a hypotensive agent. The vascular response involves activation of
Ca
2+
‐sensitive
K
+
channels and is not mediated by
CB
1
receptors, but unexpectedly enhanced by antagonists of the ‘endothelial anandamide’ receptor. In endothelial cells,
LPI
utilizes
PLC
‐
IP
3 and perhaps
ROCK
‐
RhoA
pathways to elevate intracellular
Ca
2+
. Overall, these findings support an endothelial site of action for
LPI
and suggest a possible role for
GPR
55 in vasculature.
Putative receptors for endothelin were localised autoradiographically in frozen sections of rat and human brain using 125Iendothelin as a ligand. In the rat brain the highest densities were in the ...granular layer of the cerebellum, choroid plexus, hippocampus, and habenular nucleus. Similar brain high densities were found in the human cerebellum and hippocampus. The non-vascular pattern of distribution suggests that endothelin may have a function as a modulator of neuronal function in addition to its possible involvement in the regulation of vascular tone.
The effect of beta-adrenoceptor activation on levcromakalim-induced relaxation was investigated in myograph-mounted rat mesenteric arteries. The nonselective beta-adrenoceptor agonist isoproterenol ...(at a concentration causing approximately 30% relaxation of methoxamine-induced tone) potentiated relaxation to levcromakalim; higher concentrations exerted no additional effect. The modulatory and relaxant effects of isoproterenol were inhibited by the beta(1)-adrenoceptor antagonist atenolol, but the ATP-sensitive K(+) (K(ATP)) channel inhibitor glibenclamide did not inhibit relaxations to isoproterenol. The protein kinase A inhibitor Rp-adenosine 3',5'-cyclic monophosphothioate triethylamine (Rp-cAMPS) inhibited the ability of isoproterenol to modulate levcromakalim relaxation. However, neither Rp-cAMPS nor N-2-(p-bromocinnamylamino)ethyl-6-isoquinolinesulfonamide (H-89) (another protein kinase A inhibitor) markedly reduced isoproterenol-induced relaxation, although Rp-cAMPS inhibited relaxations induced by forskolin (an adenylyl cyclase activator). Iberiotoxin (50 nM), an inhibitor of large conductance Ca(2+)-activated K(+) channels (BK(Ca)), attenuated isoproterenol relaxation. Moreover, both Rp-cAMPS and H-89 caused inhibition of the effects of isoproterenol in the presence of iberiotoxin, whereas glibenclamide did not. We conclude that isoproterenol modulates the actions of levcromakalim through beta(1)-adrenoceptors and protein kinase A, even though K(ATP) channels do not contribute to its relaxant effects. However, the major relaxant mechanism for isoproterenol appears to be protein kinase A-independent activation of BK(Ca), with cyclic AMP-dependent mechanisms only being unmasked when the BK(Ca) mechanism is inhibited. Although direct G protein-mediated activation of BK(Ca) has been demonstrated previously in electrophysiological studies of single smooth muscle cells, this is the first time that such a mechanism has been shown to be functionally important in an intact blood vessel preparation.
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