Acetylcholine stimulates the release of endothelium-derived arachidonic acid (AA) metabolites including prostacyclin and epoxyeicosatrienoic acids (EETs), which relax coronary arteries. However, mechanisms of endothelial cell (EC) AA activation remain undefined. We propose that 2-arachidonylglycerol (2-AG) plays an important role in this pathway. An AA metabolite isolated from bovine coronary ECs was identified as 2-AG by mass spectrometry. In ECs pretreated with the fatty acid amidohydrolase inhibitor diazomethylarachidonyl ketone (DAK; 20 micromol/l), methacholine (10 micromol/l)-stimulated 2-AG release was blocked by the phospholipase C inhibitor U-73122 (10 micromol/l) or the diacylglycerol lipase inhibitor RHC-80267 (40 micromol/l). In U-46619-preconstricted bovine coronary arterial rings, 2-AG relaxations averaging 100% at 10 micromol/l were inhibited by endothelium removal, by DAK, by the hydrolase inhibitor methyl arachidonylfluorophosphate (10 micromol/l), by the cyclooxygenase inhibitor indomethacin (10 micromol/l), but not by the CB1 cannabinoid receptor antagonist SR-141716 (1 micromol/l). The cytochrome P-450 inhibitor SKF-525a (10 micromol/l) and the 14,15-epoxyeicosa-5Z-enoic acid EET antagonist (14,15-EEZE; 10 micromol/l) further attenuated the indomethacin-resistant relaxations. The nonhydrolyzable 2-AG analogs noladin ether, 2-AG amide, and 14,15-EET glycerol amide did not induce relaxation. N-nitro-L-arginine-resistant relaxations to methacholine were also inhibited by U-73122, RHC-80267, and DAK. 14,15-EET glycerol ester increased opening of large-conductance K(+) channels 12-fold in cell-attached patches of isolated smooth muscle cells and induced relaxations averaging 95%. These results suggest that methacholine stimulates EC 2-AG production through phospholipase C and diacylglycerol lipase activation. 2-AG is further hydrolyzed to AA, which is metabolized to vasoactive eicosanoids. These studies reveal a role for 2-AG in EC AA release and the regulation of coronary tone.

. Passive stretch inhibits central corelike lesion formation in the soleus muscles of hindlimb-suspended unloaded rats. J Appl Physiol 97: 930 -934, 2004. First published May 7, 2004 10.1152/japplphysiol.00103.2004.-Hindlimb suspension unloading (HSU) is a ground-based model simulating the effects of microgravity unloading on the musculoskeletal system. In this model, gravity causes the hind foot of the rat to drop, opening the front of the ankle to 90 -105°plantar flexion at rest. As HSU proceeds, the normal weight-bearing angle of 30°dorsiflexion is achieved progressively less, and the contraction range of soleus is abbreviated. Our laboratory reported that 12 days of HSU caused central corelike lesions (CCLs) of myofibril breakdown (Riley DA, Slocum GR, Bain JL, Sedlak FR, Sowa TE, and Mellender JW. J Appl Physiol. 69: 58 -66, 1990). The present study investigated whether daily stretch of the calf muscles prevents CCL formation. The soleus muscles of HSU SpragueDawley male rats (ϳ287 g) were lengthened by unilateral ankle splinting at 30°. Compared with the nonsplinted side, splinting for 10 or 20 min per day in awake rats significantly decreased CCLs in soleus by 88 and 91%, respectively (P Ͻ 0.01). Compared with control muscle wet weight, 20-min splinting reduced atrophy by 33%, whereas 10-min splinting ameliorated atrophy by 17% (P Ͻ 0.01). Bilateral soleus electromyograph recording revealed higher levels of contractile activity on the splinted side during splinting. To isolate the effects of stretch from isometric contractile activity, contractions were eliminated by whole animal anesthesia with isoflurane during 10-min daily splinting. The percentage of fibers with CCLs was reduced by 57%, and the average lesion size was 29% smaller in the stretched muscle (P Ͻ 0.05). Soleus muscle wet weight and fiber area were unaltered by stretch alone. Loaded contractions during splinting are necessary to prevent muscle fiber atrophy. Passive muscle stretch acts to maintain myofibril structural integrity. length; countermeasure; splint; atrophy; calcium HINDLIMB SUSPENSION UNLOADING (HSU) of rats is a well-established experimental model for simulating the effects of microgravity unloading on weight-bearing muscles (25). Preventing rats from touching the ground with their hindlimbs causes the antigravity soleus muscles to atrophy due to decreased use, unloading, and shortened working range (29). Central corelike lesions (CCLs), which are areas of focal myofibril dissolution, appear within soleus fibers by day 12 of HSU. For rat solei, the CCLs were postulated to result from the ϳ20% shortened contraction range, which is a consequence of suspensioninduced foot drop posture (plantar flexion) (22,29). Foot drop posture of humans floating in microgravity was first documented in their neutral body position during Skylab missions (26). CCLs also occur in suspension-unloaded rabbits in which soleus shortening is ϳ35% because the large hind feet are weighed down by gravity (2). A shortened length is required for CCL generati...

The incidence of skeletal muscle tendon rupture is increasing. The unloaded, shortened muscle undergoes rapid degeneration. Rehabilitation takes 10-12 weeks and includes stretch therapy. Outcomes may be improved by understanding the pathophysiological changes and stretch mechanisms. We investigated the effects of passive stretch on preventing central core lesions in a rat tenotomy model of simulated Achilles tendon rupture. Adult male rats were tenotomized bilaterally. At 7 days, 39% of the soleus fibers possessed central core lesions. Whole muscle calcium concentration progressively increased and plateaued by 4 days. Dantrolene, a calcium release blocker, injected daily for 7 days, reduced central core lesion formation and calcium build-up. Passive stretch, 20 min/day, inhibited central core lesion formation. Calcium increased at 4 days in mitochondria, and stretch prevented this increase. These findings indicate that stretch therapy reduces central core lesion occurrence by preventing calcium elevation in hypershortened muscles.

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