Endothelium-dependent relaxation in rabbit aorta after cold storage

Contractile function of smooth muscle retained after overnight storage

The functional responses of different overnight-stored in vitro tissues are not clearly described in any animal model. The influence of overnight storage in an animal model may vary between tissue types. We employed Sprague-Dawley rat as our animal model and investigated the functional changes of rat aorta, trachea, bronchus and bladder that were used (i) immediately after surgical removal (denoted as fresh) and (ii) after storage in aerated (95% O2, 5% CO2) Krebs-Ringer bicarbonate solution at 4 °C for 24 h (denoted as stored). The aorta ring was pre-contracted with phenylephrine, and the functional response of the tissue was investigated using isoprenaline, forskolin and carbachol. Carbachol was also used to increase the tone in trachea, bronchus rings and bladder strips. A clear reduced function of endothelium, with a minor if any effect in the smooth muscle function in rat aorta was observed after overnight storage. The contractile response of overnight-stored rat airway (trachea and bronchus) and bladder smooth muscles remained unchanged. Among all tested tissues, only bronchus showed a reduced response rate (only 40% responded) after storage. In vitro rat tissues that are stored in Krebs solution at 4 °C for 24 h can still be used to investigate smooth muscle responses, however, not endothelium-mediated responses for aorta. The influence of overnight storage on different tissues from an animal model (Sprague-Dawley rat in our study) also provides an insight in maximising the use of sacrificed animals.

Effect of storage duration on the mechanical behavior of mouse carotid artery

Determining arterial mechanical properties is important for understanding the work done by the heart and how it changes with cardiovascular disease. Ex vivo tests are necessary to apply various loads to the artery and obtain data to model and predict the behavior under any load. Most ex vivo tests are performed within 24 h of dissection, so the tissue is still "alive." For large elastic arteries; however, the passive mechanical behavior is attributed mostly to the very stable proteins, elastin, and collagen. If the testing equipment fails, is in use, or is located at another facility, it would be useful to store the vessels and postpone the tests until the equipment is available. The goal of this study is to determine the effects of storage time on the mechanical behavior of the common carotid artery from adult mice. Each artery was tested after storage for 1-28 days in physiologic saline at 4°C. There were no significant effects of storage time on the arterial diameter or force at each pressure, but there were significant effects on the stretch ratio and stress at each pressure. The significant effects on the stretch ratio and stress were due to decreases in the unloaded dimensions with storage time, when measured from cut arterial rings. When the unloaded dimensions were measured instead from histology sections, there were no significant changes with storage time. We conclude that histology sections yield a more consistent measurement of the unloaded dimensions and that there are no significant changes in the mechanical behavior of mouse carotid artery with storage up to 28 days.

The role of arterial smooth muscle in vasorelaxation

The concept of endothelium-derived relaxing factor (EDRF) implies that nitric oxide (NO) produced by NO synthase (NOS) in the endothelium in response to vasorelaxants such as acetylcholine (ACh) acts on the underlying vascular smooth muscle cells (VSMC) inducing vascular relaxation. The EDRF concept was derived from experiments on denuded blood vessel strips and, in frames of this concept, VSMC were regarded as passive recipients of NO from endothelial cells. However, it was later found that VSMC express NOS by themselves, but the principal question remained unanswered, is the NO generation by VSMC physiologically relevant? We hypothesized that the destruction of the vascular wall anatomical integrity by rubbing off the endothelial layer might increase vascular superoxides that, in turn, reduced the NO bioactivity as a relaxing factor. To test our hypothesis, we examined ACh-induced vasorelaxation under protection against oxidative stress and found that superoxide scavengers restored vasodilatory responses to ACh in endothelium-deprived blood vessels. These findings imply that VSMC can release NO in amounts sufficient to account for the vasorelaxatory response and challenge the concept of the obligatory role of endothelial cells in the relaxation of arterial smooth muscle.

Developmental dynamics of endothelial and neurogenic control of canine thoracic aorta

The purpose of the study was to confront the range of endothelial relaxation and neurogenic contraction of the thoracic aorta in fetuses (1 week before birth), puppies (1, 2, 4 and 6 weeks old), and in adult dogs. Isometric tension of aortic rings was monitored in organ bath. Acetylcholine-induced dose-dependent relaxation of aortic rings precontracted by phenylephrine was pronounced already in fetuses and puppies and significantly larger than in adults. Indomethacin, a cyclooxygenase inhibitor, did not affect the magnitude of aortic relaxation to acetylcholine. Transmural nerve stimulation induced but very slight contractions of the thoracic aorta in fetuses, while in puppies the extent of contractions was increasing with increasing age, reaching its maximum in adults. Contractile responses of aortic rings induced by KCl were fully detectable in fetuses and puppies and increased with increasing age of the animals. Thus in ontogenesis, the extent of endothelium-dependent relaxation and neurogenic contraction of the thoracic aorta displayed an opposite trend. The acetylcholine-induced relaxation was fully operative already in fetuses and puppies and its extent was declining toward adulthood, whereas the neurogenic contraction was hardly detectable in fetuses, increasing in puppies, and showed the highest values in adults.

Impairment of nitrergic-mediated relaxation of rat isolated duodenum by experimental diabetes

1. Diabetes mellitus is associated with changes in gastrointestinal motility. The effects of experimental diabetes, induced by streptozotocin administration to rats 3-4 weeks previously, on the nitric oxide (NO)-mediated (nitrergic) relaxation of the duodenum have now been investigated. 2. The non-adrenergic, non-cholinergic (NANC) relaxation of the isolated duodenum induced by nicotine (0.3-10 microM) or the nicotinic agonist, 1,1-dimethyl-4-phenylpiperazinium (DMPP; 10 microM) was inhibited by the NO synthase inhibitor, NG-nitro-L-arginine (3-100 microM). 3. This nitrergic relaxation induced by nicotine or DMPP of the duodenum from diabetic rats was substantially smaller than that of the tissue from control rats. 4. By contrast, the relaxation of the duodenum from diabetic rats to the NO donor, nitroprusside (0.3-10 microM) was similar to that of control tissue, whereas the relaxation to ATP (0.1-3 microM) was enhanced to a small but significant degree. 5. Incubation of duodenal tissue from control rats at 4 degrees C for 72 h, which leads to neuronal disruption, significantly attenuated the relaxation to nicotine or DMPP whereas the relaxation induced by nitroprusside or ATP was not affected. Comparable cold-storage did not affect the endothelium-dependent relaxation of rat aortic rings induced by acetylcholine (0.01-2 microM). 6. The calcium-dependent NO synthase activity in duodenal tissue, determined by the conversion of radiolabelled L-arginine to citrulline, was significantly reduced in cold-stored tissue and in tissue obtained from diabetic rats. 7. These findings in the rat duodenum indicate that a reduction in intestinal NO synthase activity is associated with an impairment of the NANC relaxation. A defect in the intestinal nitrergic innervation could thus contribute to the motility dysfunction observed in diabetes.