Impairment of vasodilator function in basilar arteries from aged rats

Characterization of Endothelium-Dependent Relaxation in the Saphenous Artery and Its Caudal Branches in Young and Old Adult Sprague Dawley Rats

Ageing is associated with reduced endothelium-derived nitric oxide (NO) production in the femoral artery of Sprague Dawley (SD) rats. In the current study, we examined endothelium-dependent relaxation (EDR) in the saphenous artery and its caudal branches. We used acetylcholine and the Proteinase-Activated receptor-2 (PAR2)-specific agonist (2fLIGRLO) with nitroarginine methylester (L-NAME) to assess EDR in two groups of male SD rats (age in weeks: young, 10–12; old, 27–29). Acetylcholine and 2fLIGRLO were potent NO-dependent relaxant agents in all arteries. For all arteries, EDR by acetylcholine decreased significantly in old compared to young SD rats. Interestingly, PAR2-induced EDR of proximal saphenous artery segments and caudal branches decreased significantly in old compared to young, but did not differ for the in-between middle and distal ends of the saphenous artery. L-NAME treatment increased subsequent contractions of proximal and middle segments of saphenous arteries by phenylephrine and U46619 in young, but not in old, SD rats. We conclude the SD saphenous artery and caudal branches exhibit regional characteristics that differ in response to specific EDR agonists, endothelial NO synthase inhibitor, and changes to endothelium function with increased age, which are, in part, attributed to decreased sensitivity of vascular smooth muscle to the gaseous transmitter NO.

From Newborn to Senescence Morphological and Functional Remodeling Leads to Increased Contractile Capacity of Arteries

Aging induces substantial morphological and functional changes in vessels. We hypothesized that due to morphological remodeling the total contractile forces of arteries increase, especially in older age as a function of age. Mean arterial blood pressure of rats and morphological and functional characteristics of isolated carotid arteries rats, from newborn to senescent, were assessed. The arterial blood pressure of rats increased significantly from 0.25 to the age of 6 months, and then it reached a level, which was maintained until age of 30 months. Wall lumen and wall thickness increased with age, mostly due to media (smooth muscle) thickening, whereas wall tension gradually reduced with age. Contractions of arteries to nonreceptor-mediated vasomotor agent (KCl, 60mM) increased in three consecutive age groups, whereas contractility first increased (until 2 months), then it did not change further with aging. Norepinephrine-induced contractions initially increased in young age and then did not change further in older age. These findings suggest that during normal aging due to remodeling of arterial wall (smooth muscle) the contractile capacity of arteries increases, which seems to be independent from systemic blood pressure. Thus, arterial remodeling can favor the development of increased circulatory resistance in older age.

The effects of aging on the functional and structural properties of the rat basilar artery

Aging leads to progressive pathophysiological changes in blood vessels of the brain and periphery. The aim of this study was to evaluate the effects of aging on cerebral vascular function and structure. Basilar arteries were isolated from male Fischer 344 cross Brown Norway (F344xBN) rats at 3, 8, and 24 months of age. The basilar arteries were cannulated in the pressurized system (90 cm H₂O). Contractile responses to KCl (30–120 mmol/L) and endothelin‐1 (10⁻¹¹–10⁻⁷ mol/L) were evaluated. Responses to acetylcholine (ACh) (10⁻¹⁰–10⁻⁴ mol/L), diethylamine (DEA)‐NONO‐ate (10⁻¹⁰–10⁻⁴ mol/L), and papaverin (10⁻¹⁰–10⁻⁴ mol/L) were assessed to determine both endothelium‐dependent and endothelium‐independent responsiveness. Advanced aging (24 months) decreased responses of the basilar artery to both the contractile and relaxing agents; whereas, DEA‐induced dilation was significantly higher in the 8‐month‐old group compared with the younger and older groups. The arterial wall‐to‐lumen ratio was significantly increased in 24‐month‐old rats. Smooth muscle cell count was also decreased in old rats. These findings indicate that aging produces dysfunction of both the endothelium and the vascular smooth muscle in the basilar artery. Aging also alters wall structure of the basilar artery, possibly through decreases in smooth muscle cell number and concomitant hypertrophy.

The purpose of this study was to determine the effects of advancing age on the structure and vasomotor responses of the basilar artery as well as the serum antioxidant capacity. Advanced aging (24 months) decreased responses of the basilar artery to both the contractile and relaxing agents, whereas, DEA‐induced dilation was significantly higher in the 8‐month‐old group compared with the younger and older rats. The arterial wall‐to‐lumen ratio was significantly increased in 24‐month‐old rats. Smooth muscle cell count was also decreased in old rats. Our findings demonstrate that aging is associated with functional impairment in endothelium‐dependent and ‐independent relaxation responses and contractility in the basilar arteries, and these diminished responses are accompanied by structural remodeling and decreased antioxidant capacity of the serum.

Exercício físico, receptores β-adrenérgicos e resposta vascular

O exercício aeróbio promove efeitos benéficos na prevenção e tratamento de doenças como hipertensão arterial, aterosclerose, insuficiência venosa e doença arterial periférica. Os receptores β-adrenérgicos estão presentes em várias células. No sistema cardiovascular, promovem inotropismo e cronotropismo positivo cardíaco e relaxamento vascular. Embora os efeitos do exercício tenham sido investigados em receptores cardíacos, estudos focados nos vasos são escassos e controversos. Esta revisão abordará os efeitos do exercício físico sobre os receptores β-adrenérgicos vasculares em modelos animais e humanos e os mecanismos celulares envolvidos na resposta relaxante. Em geral, os estudos mostram resultantes conflitantes, onde observam diminuição, aumento ou nenhum efeito do exercício físico sobre a resposta relaxante. Assim, os efeitos do exercício na sensibilidade β-adrenérgica vascular merecem maior atenção, e os resultados mostram que a área de fisiopatologia vascular é um campo aberto para a descoberta de novos compostos e avanços na prática clínica.

Mechanisms Underlying Hypertrophic Remodeling and Increased Stiffness of Mesenteric Resistance Arteries From Aged Rats

The mechanisms associated with structural and mechanical alterations of mesenteric resistance arteries from aged rats were investigated by using pressure myography, confocal microscopy, immunofluorescence, and picrosirius red staining. Arteries from old rats showed: (i) increased wall and media thickness, greater number of smooth muscle cell (SMC) layers but decreased density of SMC; (ii) increased number of adventitial cells; (iii) hypertrophy of nuclei of SMC and endothelial cells; (iv) increased stiffness associated with increased total collagen content and collagen I/III deposition in the media; and (v) similar content but changes in elastin structure in the internal elastic lamina. Hypertrophic outward remodeling in aged rat resistance arteries involve adventitial cells hyperplasia, reorganization of the same number of hypertrophied SMC in more SMC layers leading to thickened media and endothelial cell hypertrophy. Fibrosis associated with collagen deposition and changes in elastin structure might be responsible for the increased stiffness of resistance arteries from aged rats.

A role for cyclooxygenase in aging-related changes of beta-adrenoceptor-mediated relaxation in rat aortas

beta-Adrenoceptor-mediated vasorelaxation decreases with age in various vascular beds. The present study investigated the roles of cyclooxygenase (COX) on beta-adrenoceptor vasorelaxation by isoprenaline in 8- and 54-week-old rat aortas. The vasorelaxation responses by isoprenaline (0.03-3 microM) were significantly reduced in 54-week-old aortas compared to 8-week. Addition of the non-selective COX inhibitors indomethacin (10 microM) or aspirin (10 microM) restored isoprenaline vasorelaxation of 54-week-old aortas to levels found in 8-week-old aortas. This suggests the involvement of COX prostanoids in the age-related reduction of beta-adrenoceptor vasorelaxation. Immunohistochemistry revealed greater levels of COX-1 and COX-2 staining in 54-week-old aortas compared to 8-week with expression located mainly in medial smooth muscle. An age-linked increase in COX-1 and COX-2 protein was found in cremaster arterioles of 54-week-old rats (compared to 8-week) mainly in the endothelial layer. The age-related increase in COX-1 and COX-2 protein led to elevation of prostacyclin (measured as 6-keto prostaglandin F(1alpha)) and thromboxane A(2) (measured as thromboxane B(2)) in 54-week compared to 8-week-old aortas. Endothelium removal in 54-week aortas markedly reduced the 6-keto prostaglandin F(1alpha) level, thus suggesting an endothelial source for elevated prostacyclin. These findings in combination with the effects of COX inhibitors suggest that the age-related decrease in beta-adrenoceptor vasorelaxation by isoprenaline is due to an age-linked increase in COX expression, which elevates production of COX-derived vasoactive prostanoids.

Testosterone augments endotoxin-mediated cerebrovascular inflammation in male rats

Activation of inflammatory mechanisms contributes to cerebrovascular pathophysiology. Male gender is associated with increased stroke risk, yet little is known about the effects of testosterone in the cerebral circulation. Therefore, we explored the impact of testosterone treatment on cerebrovascular inflammation with both in vivo and in vitro models of inflammation. We hypothesized that testosterone would augment the expression of two vascular markers of cellular inflammation, cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). Using four groups of male rats [intact, orchiectomized (ORX), and ORX treated with either testosterone (ORXT) or the testosterone metabolite 17β-estradiol (ORXE)], we determined effects of the sex hormones on cerebrovascular inflammation after intraperitoneal LPS injection. Western blot analysis showed that induction of inflammatory markers was increased in cerebral blood vessels from ORXT rats compared with intact or ORX rats. In contrast, in cerebral blood vessels from ORXE rats, there was a significant decrease in endotoxin-induced COX-2 and iNOS protein levels. Confocal microscopy of cerebral blood vessels from ORXT rats showed increased COX-2 and iNOS immunoreactivity in both endothelial and smooth muscle cells after LPS treatment. In vitro incubation with LPS also induced COX-2 in pial vessels isolated from the four animal treatment groups, with the greatest induction observed in ORXT vessels compared with the ORX and ORXE groups. Production of PGE2, a principal COX-2-derived prostaglandin end product, was also greatest in cerebral vessels isolated from ORXT rats. In conclusion, testosterone increases cerebrovascular inflammation; this effect may contribute to stroke differences between men and women.

Estrogen suppresses IL-1beta-mediated induction of COX-2 pathway in rat cerebral blood vessels

Interleukin (IL)-1beta is a potent inducer of inflammatory prostaglandins, which are important mediators of vascular response to cerebral injury, whereas estrogen reduces brain injury in models of ischemic stroke. Thus we examined the effects of in vivo IL-1beta exposure on cerebrovascular cyclooxygenase (COX)-2 expression and function in an animal model of chronic estrogen replacement. Estrogen-treated and nontreated ovariectomized female rats received IL-1beta injections (10 microg/kg i.p.), and then cerebral vessels were isolated for biochemical and contractile measurements. In estrogen-deficient rats, IL-1beta induced cerebrovascular COX-2 protein expression; a peak response occurred 3 h after injection. COX-2 was localized to arterial endothelium using confocal microscopy. IL-1beta increased PGE2 but not PGI2 production and decreased vascular tone as measured in isolated cerebral arteries; the latter effect was partially reversed by treatment with the selective COX-2 inhibitor NS-398 (10 micromol/l). In contrast, in animals treated with estrogen, IL-1beta had no significant effect on COX-2 protein levels, PGE2 production, or vascular tone. Combined treatment with 17beta-estradiol and medroxyprogesterone acetate also prevented increases in PGE2 production after IL-1beta treatment, but treatment with 17alpha-estradiol had no effect. IL-1beta induction of COX-2 protein was prevented by treatment with the nuclear factor-kappaB inhibitor caffeic acid phenethyl ester (20 mg/kg i.p.), and estrogen treatment reduced cerebrovascular nuclear factor-kappaB activity. Estrogen thus has potent anti-inflammatory effects with respect to cerebral vascular responses to IL-1beta. These effects may have important implications for the incidence and severity of cerebrovascular disease.

Multiple forms of estrogen receptor-alpha in cerebral blood vessels: regulation by estrogen

The cerebral vasculature is an important target tissue for estrogen, as evidenced by significant effects of estrogen on vascular reactivity and protein levels of endothelial nitric oxide synthase and prostacyclin synthase. However, the presence, localization, and regulation of estrogen receptors in the cerebral vasculature have not been investigated. In this study, we identified the presence of estrogen receptor-alpha (ER-alpha) in female rat cerebral blood vessels and localized this receptor to both smooth muscle and endothelial cells by use of immunohistochemistry and confocal microscopy. With immunoblot analysis, multiple forms of ER-alpha were detected at 110, 93, 82, 50, and 45 kDa in addition to a relatively weak band corresponding to the 66-kDa putative unmodified receptor. The 82-kDa band was identified as Ser(118)-phosphorylated ER-alpha, whereas the 50-kDa band lacks the normal NH(2) terminus, suggestive of an ER-alpha splice variant. Lower molecular mass bands persisted after in vivo inhibition of 26S proteasome activity with lactacystin, whereas the 110- and 93-kDa bands increased. All forms of ER-alpha in cerebral vessels were decreased after ovariectomy but significantly increased after chronic estrogen exposure in vivo.

Role of calcium-activated potassium channels in impaired acetylcholine vasodilatory responses in diabetic rats

Muscarinic agonists produce endothelium-dependent vasodilatation in the presence of nitric oxide synthase (NOS) inhibition. The importance of this mechanism was assessed in the methoxamine-preconstricted perfused mesenteric vascular bed (MVB) of streptozotocin diabetic Sprague-Dawley rats. At 9 weeks of age, male rats were treated with streptozotocin (55 mg/kg in citrate buffer) or with citrate buffer alone. The superior mesenteric artery was cannulated and the MVB was detached from its intestinal borders. Concentration-response curves to acetylcholine were determined in the presence and in the absence of indomethacin, tetrabutylammonium (a calcium-activated potassium channel blocker), high extracellular potassium, or NOS inhibition with Nomega-nitro-l-arginine and l-NG-nitro-l-arginine. There was a rightward shift in the concentration-response curve with an increase in median inhibitory concentration (p < 0.05) and a reduction in acetylcholine IMAX (p < 0.05) values in 14-week streptozotocin rats. The ability of NOS inhibition to attenuate vasodilatation was reduced in the 14-week streptozotocin group relative to the 2-week streptozotocin treatment group (p < 0.05). However, the ability of tetrabutylammonium to block acetylcholine-mediated vasodilatation remained consistent in streptozotocin rats at both stages. The results demonstrate that an alternate pathway involving calcium-activated potassium channels may compensate for diminished nitric oxide bioactivity. This effect is contingent on the duration of diabetes. This study provides insight into the development and progression of altered diabetic vascular responses.

Aging-associated changes in vascular activity: a potential link to geriatric cardiovascular disease

Ischemic cardiovascular disease is a common cause of morbidity and mortality in the United States population over the age of 65. Prior clinical studies have demonstrated that the severity of cardiovascular pathophysiology is increased in older individuals. Both in vitro and in vivo experimental studies have shown that age-associated clinical events parallel changes in vascular function. Aging is associated with systemic as well as cardiac alterations in three basic vascular regulatory functions: vascular tone, hemostasis, and vascular repair/angiogenesis. This article reviews the molecular and cellular events that may contribute to senescent cardiac pathology. Indeed, a better understanding of the biology of aging-associated vascular dysfunction is fundamental for the development of therapeutics targeted for the treatment of cardiovascular disease in older individuals.

Responsiveness, affinity constants and receptor reserves for serotonin on aortae of aged normotensive and hypertensive rats

We have previously shown that the potency and affinity constants (K(A) values) for serotonin (5-HT) are greater, and the 5-HT2A-receptor reserve is lesser, on the aorta of 6-month-old spontaneously hypertensive rats (SHRs) compared with age-matched Wistar Kyoto normotensive (WKY) rats. The present study was undertaken to investigate whether these parameters are altered on the aorta with ageing and as hypertension progresses to heart failure. The effects of phenoxybenzamine on the serotonergic responses of the aortae of 24-month-old WKY rats and SHRs were determined. On WKY rat aorta, ageing from 6 to 24 months was associated with an increase in sensitivity and affinity for serotonin, and a loss of 5-HT2A-receptor reserve. On SHR aorta, ageing from 6 to 24 months was also associated with an increase in sensitivity and affinity for serotonin, but a loss of 5-HT2A-receptor reserve. The sensitivity to serotonin was greater on the 24-month-old SHR aorta (pD2 6.53) than age-matched WKY rat aorta (pD2 5.89). On the aorta of the 24-month-old WKY rats, the K(A) value for serotonin was 4.5 x 10(-6) M, and the receptor occupancies required for 20 and 50 % maximum responses were 12 and 29%, respectively. There was a similar affinity, but greater receptor reserves, for serotonin on the aorta of age-matched SHRs. In summary, we have shown changes in sensitivity, affinity and 5-HT2A-receptor reserves for serotonin on the aorta with ageing and in hypertension/heart failure.

Functional importance of neuronal nitric oxide synthase in the endothelium of rat basilar arteries

The function of the neuronal isoform of nitric oxide synthase (nNOS) was studied by comparing the effects of the specific nNOS blocker 7-nitro indazole monosodium salt (7-NINA) with that of the general NOS inhibitor N(G)-nitro-L-arginine (L-NA) in isolated rat basilar arteries (BAs). 7-NINA had no significant effect on the resting tone of the vessels, while both L-NA and 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ), a selective inhibitor of the soluble guanylyl cyclase, induced contraction. The relaxant effect of bradykinin was attenuated in the presence of L-NA but was not changed by 7-NINA. In contrast, 7-NINA markedly reduced the acetylcholine-induced, endothelium-dependent relaxation. These results demonstrate that nNOS contributes significantly to the relaxant effect of acetylcholine, indicating the functional importance of this isoenzyme in the cerebrovascular endothelium.

Pharmacological implications of cellular localization of alpha1-adrenoceptors in native smooth muscle cells

1. This study examines the cellular localization of alpha1-adrenoceptors and demonstrates that binding to intracellular receptive binding sites in native smooth muscle cells may influence the pharmacological profile of agonists or antagonists. The example tissue studied was rat basilar artery. 2. An alpha1-adrenoceptor antagonist and fluorescent analogue of prazosin, BODIPY-FL prazosin (QAPB) allowed visualization, with high resolution, of both plasma membrane and cytosolic binding sites on live native cells, as previously shown in cells harbouring recombinant receptors. QAPB-associated fluorescence binding was both time- and concentration-dependent in rat basilar smooth muscle cells and affinity for alpha1-adrenoceptors was calculated from specific binding curves as 1.1 nM. 3. Concentration-dependent binding of QAPB detected in smooth muscle cells dissociated from rat basilar arteries was composed of diffuse and clustered fluorescence. Visually the diffuse component of fluorescence was the more evident up to a concentration of 5 nM QAPB. Confocal visualization of an optical section through the cell showed that the clustered component was located mainly intracellularly. In rat basilar artery smooth muscle cells the intracellular binding sites were located in close proximity to the nuclear membrane. 4. 3D models of QAPB-associated fluorescence demonstrate that a high proportion of effective binding sites are intracellular, showing not only that a high proportion of receptors are located inside the cell but also that in this location they can bind ligands. This has implications for pharmacological analysis in relation to the consequences of intracellular binding per se and for differential effects upon the pharmacology of particular ligands according to whether they can enter the cell.