Salvinorin A Produces Cerebrovasodilation through Activation of Nitric Oxide Synthase, ␬ Receptor, and Adenosine Triphosphate–sensitive Potassium Channel Diansan Su, M.D., Ph.D.,* John Riley, B.A.,† Willis J. Kiessling, B.A.,† William M. Armstead, Ph.D.,‡ Renyu Liu, M.D., Ph.D.§ ABSTRACT Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/114/2/374/253404/0000542-201102000-00025.pdf by guest on 02 October 2021 What We Already Know about This Topic • Salvinorin A is a nonopioid selective ␬ opioid receptor agonist. Background: Salvinorin A is a nonopioid, selective ␬ opioid– receptor agonist. Despite its high potential for clinical applica- tion, its pharmacologic profile is not well known. In the current study, we hypothesized that salvinorin A dilates pial arteries via What This Article Tells Us That Is New activation of nitric oxide synthase, adenosine triphosphate–sen- • Salvinorin A is an efficacious cerebral vascular dilator in the sitive potassium channels, and opioid receptors. newborn piglet, under normal conditions and with constriction from endothelin and hypocarbia. Methods: Cerebral artery diameters and cyclic guanosine • Salvinorin A acts via the ␬ opioid receptor, nitric oxide gener- monophosphate in cortical periarachnoid cerebrospinal fluid ation, and adenosine triphosphate–sensitive potassium chan- were monitored in piglets equipped with closed cranial win- nel to produce cerebral vasodilatation. dows. Observation took place before and after salvinorin A administration in the presence or absence of an opioid antag- onist (naloxone), a ␬ opioid receptor–selective antagonist istration every 2 min. Vasodilatation and the associated cy- (norbinaltorphimine), nitric oxide synthase inhibitors clic guanosine monophosphate elevation in cerebrospinal (N(G)-nitro-L-arginine and 7-nitroindazole), a dopamine fluid were abolished by preadministration N(G)-nitro-L-ar- ginine, but not 7-nitroindazole. Although naloxone, norbin- receptor D2 antagonist (sulpiride), and adenosine triphos- ϩ phate–sensitive potassium and Ca2 -activated K channel an- altorphimine, and glibenclamide abolished salvinorin A–in- tagonists (glibenclamide and iberiotoxin). The effects of duced cerebrovasodilation, this response was unchanged by salvinorin A on the constricted cerebral artery induced by iberiotoxin and sulpiride. Hypocarbia and endothelin-con- hypocarbia and endothelin were investigated. Data were an- stricted pial arteries responded similarly to salvinorin A, to alyzed by repeated measures ANOVA (n ϭ 5) with statistical the extent observed under resting tone. significance set at a P value of less than 0.05. Conclusions: Salvinorin A dilates cerebral arteries via acti- Results: Salvinorin A induced immediate but brief vasodi- vation of nitric oxide synthase, adenosine triphosphate–sen- ␬ latation that was sustained for 30 min via continual admin- sitive potassium channel, and the opioid receptor. * Visiting Scholar from Department of Anesthesiology, Renji ALVINORIN A is an active component of Salvia divino- Hospital, Shanghai Jiaotong University, School of Medicine, Shang- rum, a perennial herb of the Lamiaceae (mint) family, in- hai, China, and Assistant Professor, † Research Assistant, ‡ Professor, S § Assistant Professor, Department of Anesthesiology and Critical digenous to Mexico. Salvia divinorum has long been tradition- Care, Hospital of University of Pennsylvania, Philadelphia, ally used by local people to produce hallucinogenic experiences Pennsylvania. essential for spiritual divination.1,2 Salvinorin A is a highly effi- Received from the Department of Anesthesiology and Critical cacious, naturally occurring nonpeptide, and it is the only Care, Hospital of University of Pennsylvania, Philadelphia, Pennsyl- ␬ 1,3 vania. Submitted for publication May 20, 2010. Accepted for publi- known nonnitrogenous opioid receptor (KOR) agonist. cation October 12, 2010. Support was provided from institutional Similar to the history of opium, Salvia divinorum is a and/or departmental sources as well as the Foundation for Anes- naturally abundant plant that has been used by human be- thesia Education and Research (Rochester, Minnesota) Grant no. MRTG-02/15/2008, and the National Institutes of Health (Bethesda, ings for recreational purposes for several centuries. Salvinorin Maryland) Grant no. HD57355. A has been proposed as a new opioid receptor agonist for Address correspondence to Dr. Liu: Department of Anesthesiol- clinical use.4–6 However, none of KOR agonists have been ogy and Critical Care, University of Pennsylvania School of Medi- used clinically because of their known adverse effects. Al- cine, 336 John Morgan Building, 3620 Hamilton Walk, Philadelphia, Pennsylvania 19104. [email protected]. Information on pur- though Salvinorin A does not belong to the opioid drug class, chasing reprints may be found at www.anesthesiology.org or on the despite its KOR-agonist properties, it is banned in many masthead page at the beginning of this issue. ANESTHESIOLOGY’s counties and much of the United States. articles are made freely accessible to all readers, for personal use only, 6 months from the cover date of the issue. Unlike the KOR agonists, salvinorin A does not produce 2 Copyright © 2011, the American Society of Anesthesiologists, Inc. Lippincott frank hallucinatory effects, and has no dysphoric actions. Williams & Wilkins. Anesthesiology 2011; 114: 374–9 Many intrinsic characters of the compound (e.g., quick on- Anesthesiology, V 114 • No 2 374 February 2011 CRITICAL CARE MEDICINE set, short-acting sedative effect, no respiratory depression)7–9 mmHg. Artificial CSF was warmed to 37–38°C before applica- make it attractive for use in well-controlled perioperative tion to the cerebral cortical surface. Pial arteries were observed settings. Therefore, its physiologic profile and related mech- with a television camera mounted on a dissecting microscope. anism should be well investigated—especially its effects on Vascular diameter was measured from a video monitor that the central nervous system, including cerebral vasculature in connected the camera with a video microscaler (FOR-A, IV550, normal and pathologic conditions. Although some neuro- Tokyo, Japan). logic effects of salvinorin has been well documented,1,10,11 no data exist for the cerebral vasculature effect of salvinorin A. Experimental Protocols We have demonstrated that other KOR agonists Pial artery diameter (small artery, 120–160 ␮m; arteriole, (dynorphin and U50488) can dilate the pial artery 10,12 50–70 ␮m) was monitored and recorded every half minute through the nitric oxide pathway. In the current Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/114/2/374/253404/0000542-201102000-00025.pdf by guest on 02 October 2021 for 10 min after injection of artificial CSF in the presence or study, we hypothesized that salvinorin A might dilate pial arteries under resting and increased tone conditions in- absence of the investigated drug. In general, the window was duced by hypocarbia or endothelin via activation of nitric flushed in 30 s with 1–2 ml CSF through the port connected oxide synthase, adenosine triphosphate–sensitive potas- into the side of the window. CSF samples were collected for sium (K ) channels, and ␬ receptors. cGMP analysis before medication administration and 10 ATP min afterward. We collected the cerebral cortical periarach- Materials and Methods noid CSF by slowly infusing CSF into one port of the win- dow and allowing the CSF to drip freely into a collection Ն Salvinorin A (purity 98%), sodium nitroprusside (SNP), tube on the opposite port. N(G)-nitro-L-arginine (L-NNA), glibenclamide, iberiotoxin, Responses to salvinorin A (10 nM and 1 ␮M, dissolved cromakalim, calcitonin gene–related polypeptide, NS1619, nal- with alcohol) and SNP (10 nM and 1 ␮M), were obtained in oxone, methionine enkephalin, norbinaltorphimine, 7-nitroi- the absence and presence of L-NNA (1 ␮M), a nitric oxide ndazole, sulpiride, and isoproterenol are obtained from Sigma- synthase (NOS) inhibitor, and 7-nitroindazole (100 nM), an Aldrich (St. Louis, MO). All other chemicals were also obtained antagonist of neuronal NOS (nNOS). from Sigma-Aldrich and were of reagent grade. To distinguish the direct versus permissive role of nitric oxide in the salvinorin A–induced dilation response, pial Animals and Surgery artery diameter changes were recorded after SNP (100 pM), Newborn pigs (aged up to 6 days, 1.3–1.8 kg) of both gen- a subthreshold vascular concentration of a nitric oxide do- ders were used for this study. Protocols were approved by the nor, as well as after L-NNA and salvinorin A coadministra- Institutional Animal Care and Use Committee of the Uni- tion. Also determined were the influences of the following on versity of Pennsylvania (Philadelphia, Pennsylvania). Ani- pial artery response: sulpiride (100 nM), a dopamine recep- mals were induced with isoflurane (1–2 minimum alveolar tor D2 antagonist; glibenclamide (100 nM), a KATP channel ␣ ϩ ϩ concentration) and maintained with -chloralose (80–100 antagonist; iberiotoxin (100 nM), a Ca2 -activated K ⅐ ⅐ mg/kg supplemented with 5 mg kg h IV). Both femoral channel antagonist; cromakalim (1 ␮M); calcitonin gene– arteries were catheterized to monitor blood pressure and ␮ related polypeptide (10 nM and 1 M),aKATP agonist; and ϩ ϩ blood gas. A catheter was inserted into the right femoral vein NS1619 (10 nM and 1 ␮M),aCa2 -activated K channel for medication administration. Animals were ventilated with agonist.