title: Sumatriptan elicits both constriction and dilation in human and bovine brain intracortical arterioles.
abstract: 1. Little is known about serotonin (5-HT) receptors present on brain microvessels that are innervated by brainstem serotonergic neurons. Using 5-HT, sumatriptan and subtype selective 5-HT(1) receptor agonists and/or the 5-HT(1) receptor antagonist GR127935, we characterized the 5-HT receptors involved in regulating microvascular tone of pressurized intracortical arterioles (approximately 40--50 microm) isolated from human and bovine cerebral cortex. The role of nitric oxide (NO) on these responses was assessed with the N(omega)-nitro-L-arginine (L-NNA, 10(-5) M), an inhibitor of NO synthesis. Bovine pial arteries were studied for comparative purposes. 2. At spontaneous tone, 5-HT induced a dose-dependent constriction of human and bovine microarteries (respective pD(2) values of 7.3+/-0.2 and 6.9+/-0.1); a response potently inhibited by GR127935 (pIC(50) value of 8.5+/-0.1) in bovine microvessels. 3. In both species, the 5-HT(1) receptor agonist sumatriptan induced a biphasic response consisting of a small but significant dilation at low concentrations (1 and/or 10 nM) followed by a constriction at higher doses (pD(2) for contraction of 6.9+/-0.1 and 6.6+/-0.2 in human and bovine vessels, respectively). Pre-incubation with L-NNA abolished the sumatriptan-induced dilation and significantly shifted the dose-response of the constriction curve to the left. In contrast, the selective 5-HT(1D) (PNU-109291) and 5-HT(1F) (LY344864) receptor agonists were devoid of any vasomotor effect. 4. In bovine pial vessels, 5-HT and sumatriptan elicited potent constrictions (respective pD(2) of 7.2+/-0.1 and 6.6+/-0.1), a weak dilation being occasionally observed at low sumatriptan concentrations. 5. A significant negative correlation was observed between pial and intracortical vessels diameter and the extent of the dilatory response to 10(-9) M sumatriptan. Together, these results indicate that sumatriptan, most likely via activation of distinctly localized microvascular 5-HT(1B) receptors, can induce a constriction and/or a dilation which is sensitive to inhibition of NO synthesis and dependent on the size and, possibly, the existing tone of the vessels.
authors.affiliation: Laboratory of Cerebrovascular Research, Montreal Neurological Institute, 3801 University Street, McGill University, Montréal, QC, Canada H3A 2B4.
authors.forename: A
authors.initials: A
authors.lastname: Elhusseiny
authors.forename: E
authors.initials: E
authors.lastname: Hamel
mesh_terms: D000818:Animals; D001160:Arterioles / Q000187:drug effects; D001578:Benzopyrans / Q000494:pharmacology; D002227:Carbazoles / Q000494:pharmacology; D002417:Cattle; D002540:Cerebral Cortex / Q000098:blood supply*; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005464:Fluorobenzenes / Q000494:pharmacology; D006801:Humans; D009129:Muscle Tonus / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D052250:Nitric Oxide Synthase Type III; D019335:Nitroarginine / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011985:Receptors, Serotonin / Q000187:drug effects; D044263:Receptors, Serotonin, 5-HT1; D012701:Serotonin / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D018170:Sumatriptan / Q000494:pharmacology*; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D001578:Benzopyrans; D002227:Carbazoles; D004791:Enzyme Inhibitors; D005464:Fluorobenzenes; C109453:LY 344864; C112854:PNU 109291; D010879:Piperazines; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D019335:Nitroarginine; D012701:Serotonin; D018170:Sumatriptan; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III