Endothelial cells release several compounds, including prostacyclin, NO, and endothelium-derived hyperpolarizing factor (EDHF), that mediate the vascular effects of vasoactive hormones. The identity of EDHF remains unknown. Since arachidonic acid causes endothelium-dependent relaxations of coronary arteries through its metabolism to epoxyeicosatrienoic acids (EETs) by cytochrome P450, we wondered if the EETs represent EDHFs. Precontracted bovine coronary arteries relaxed in an endothelium-dependent manner to methacholine. The cytochrome P450 inhibitors, SKF 525A and miconazole, significantly attenuated these relaxations. They were also inhibited by tetraethylammonium (TEA),an inhibitor of Ca2+-activated K+ channels, and by high [K+]0 (20 mmol/L). Methacholine also caused hyperpolarization of coronary smooth muscle (-27 +/- 3.9 versus -40 +/- 5.1 mV), which was completely blocked by SKF 525A and miconazole. In vessels prelabeled with [3H] arachidonic acid, methacholine stimulated the release of 6-ketoprostaglandin F1alpha, 12-HETE, and the EETs. Arachidonic acid relaxed precontracted coronary arteries, which were also blocked by TEA, charybdotoxin, another Ca2+-activated K+ channel inhibitor, and high [K+]0. 14,15-EET, 11,12-EET, 8,9-EET, and 5,6-EET relaxed precontracted coronary vessels (EC50, 1 X 10(-6) mol/L). The four regioisomers were equally active. TEA, charybdotoxin, and high [K+]0 attenuated the EET relaxations. 11,12-EET hyperpolarized coronary smooth muscle cells from -37 +/- 0.2 to -59 +/- 0.3 mV. In the cell-attached mode of patch clamp, both 14,15-EET and 11,12-EET increased the open-state probability of a Ca2+-activated K+ channel in coronary smooth muscle cells. This effect was blocked by TEA and charybdotoxin. These data support the hypothesis that the EETs are EDHFs.

The use of common surgical procedures varies widely across geographical regions. Differences in illness burden, diagnostic practices, and patient attitudes about medical intervention explain regional variation in surgery rates to only a small degree. Instead, current evidence suggests that surgical variation primarily reflects differences in physician beliefs about the indications for surgery and the extent to which patient preferences are incorporated into treatment decisions. These two components of clinical decision making help explain the “surgical signatures” of specific procedures, as well as why some consistently vary more than others. Variation in clinical decision making is in turn influenced by broader environmental factors, including technology diffusion, specialist supply and local training paradigms, financial incentives, and regulatory factors, which vary across countries. Better scientific evidence about the comparative effectiveness of surgical and non-surgical interventions may help mitigate regional variation, but broader dissemination of shared decision making tools will be essential in reducing variation with preference-sensitive conditions.

Neurochem. 69, 631 -638 (1997).N-Arachidonoylethanolamine (AEA; also called anandamide) has been isolated from brain and shown to bind and activate the brain cannabinoid receptor (Devane et al., 1992). Exogenously administered AEA mimics many of the effects of z9-tetrahydrocannabinol (z9-THC), including the production of hypothermia, decreased spontaneous activity and analgesia in rodents (Fride and Mechoulam, 1993), inhibition of adenylyl cyclase (Vogel et al., 1993), and decreased opening of voltage-operated calcium channels (Mache et al., 1993). Recent studies have demonstrated that AEA is released from neurons in primary culture in response to increased intracellular calcium (DiMarzo et al., 1994), which supports the hypothesis that AEA functions in the brain as a signaling molecule.AEA is rapidly catabolized by brain membranes to arachidonic acid and ethanolamine through the action of an amidohydrolase that is selective for fatty acyl amides (Deutsch and Chin, 1993;Desarnaud et al., 1995;Hillard et al., 1995a;Cravatt et al., 1996). Although AEA amidohydrolase activity is high in crude membrane preparations from brain, it is quite low in tissue preparations that are enriched in plasma membranes (Hillard et al., 1995a). These results suggest that AEA released into the extracellular space is not inactivated by hydrolysis to arachidonic acid. The present experiments explore an alternative mechanism for AEA inactivation, specifically, cellular reuptake of AEA. DiMarzo and coworkers (1994) have reported that cortical neurons in primary culture accumulate AEA in a saturable manner. These investigators further reported that AEA accumulationwas rapid, was temperature sensitive, and was not inhibited by either arachidonic acid or N-palmitoylethanolamine. With the studies reported here, we describe and characterize a similar transport process for AEA in cerebellar granule cells. AEA transport is saturable, temperature dependent, specific, and inhibited by phloretin. The uptake process has the characteristics of facilitated diffusion, that is, it is reversible and not dependent on cellular ATP. These results suggest, first, that AEA distribution between intracellular and extracellular compartments in cerebellar granule cells is dependent on facilitated diffusion and, second, that AEA permeability across

In the brain, pressure-induced myogenic constriction of cerebral arteriolar muscle contributes to autoregulation of cerebral blood flow (CBF). This study examined the role of 20-HETE in autoregulation of CBF in anesthetized rats. The expression of P-450 4A protein and mRNA was localized in isolated cerebral arteriolar muscle of rat by immunocytochemistry and in situ hybridization. The results of reverse transcriptase-polymerase chain reaction studies revealed that rat cerebral microvessels express cytochrome P-450 4A1, 4A2, 4A3, and 4A8 isoforms, some of which catalyze the formation of 20-HETE from arachidonic acid. Cerebral arterial microsomes incubated with [(14)C]arachidonic acid produced 20-HETE. An elevation in transmural pressure from 20 to 140 mm Hg increased 20-HETE concentration by 6-fold in cerebral arteries as measured by gas chromatography/mass spectrometry. In vivo, inhibition of vascular 20-HETE formation with N-methylsulfonyl-12, 12-dibromododec-11-enamide (DDMS), or its vasoconstrictor actions using 15-HETE or 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE), attenuated autoregulation of CBF to elevations of arterial pressure. In vitro application of DDMS, 15-HETE, or 20-HEDE eliminated pressure-induced constriction of rat middle cerebral arteries, and 20-HEDE and 15-HETE blocked the vasoconstriction action of 20-HETE. Taken together, these data suggest an important role for 20-HETE in the autoregulation of CBF.