Day-night variation in the in vitro contractility of aorta and mesenteric and renal arteries in transgenic hypertensive rats

TGR(mREN2)27 (TGR) rats develop severe hypertension and an inverted circadian blood pressure profile with peak blood pressure in the daytime rest phase. The present study investigated the in vitro responsiveness of different arteries of TGR rats during day and night. Twelve-week-old TGR rats and normotensive Sprague-Dawley (SPRD) controls, synchronized to 12h light, 12h dark (LD 12:12) (light 07:00 19:00), were killed at 09:00 (during rest) and 21:00 (during activity), and endothelium-dependent relaxation by acetylcholine and vascular contraction by angiotensin II were studied by measuring isometric force in ring segments of abdominal aorta and mesenteric and renal arteries. In SPRD rats, consistent day-night variation was found, with greater responses to angiotensin II during the daytime rest span. In TGR rats, biological time-dependent differences were found in the renal vasculature, but not in the aorta and mesenteric artery. Relaxation of SPRD rat aorta and mesenteric artery by acetylcholine was greater at 09:00, whereas in TGR rats, day-night variation was absent (mesenteric artery) or inverted (aorta). In conclusion, based on the study of two time points, daynight variation in vascular contractility of aorta and mesenteric artery is blunted in TGR rats, whereas renal artery segments showed an unchanged daynight pattern compared to SPRD controls. (Chronobiology International, 18(4), 665 681, 2001)     

ROK contribution to endothelin-mediated contraction in aorta and mesenteric arteries following intermittent hypoxia/hypercapnia in rats

We reported previously that intermittent hypoxia with CO(2) to maintain eucapnia (IH-C) elevates plasma endothelin-1 (ET-1) and arterial pressure. In small mesenteric arteries (sMA; inner diameter = 150 microm), IH-C augments ET-1 constrictor sensitivity but diminishes ET-1-induced increases in intracellular Ca(2+) concentration, suggesting IH-C exposure increases both ET-1 levels and ET-1-stimulated Ca(2+) sensitization. Because Rho-associated kinase (ROK) can mediate Ca(2+) sensitization, we hypothesized that augmented vasoconstrictor sensitivity to ET-1 in arteries from IH-C-exposed rats is dependent on ROK activation. In thoracic aortic rings, ET-1 contraction was not different between groups, but ROK inhibition (Y-27632, 3 and 10 microM) attenuated ET-1 contraction more in IH-C than in sham arteries (50 +/- 11 and 78 +/- 7% vs. 41 +/- 12 and 48 +/- 9% inhibition, respectively). Therefore, ROK appears to contribute more to ET-1 contraction in IH-C than in sham aorta. In sMA, ROK inhibitors did not affect ET-1-mediated constriction in sham arteries and only modestly inhibited it in IH-C arteries. In ionomycin-permeabilized sMA with intracellular Ca(2+) concentration held at basal levels, Y-27632 did not affect ET-1-mediated constriction in either IH-C or sham sMA and ET-1 did not stimulate ROK translocation. In contrast, inhibition of myosin light-chain kinase (ML-9, 100 microM) prevented ET-1-mediated constriction in sMA from both groups. Therefore, IH-C exposure increases ET-1 vasoconstrictor sensitivity in sMA but not in aorta. Furthermore, ET-1 constriction is myosin light-chain kinase dependent and mediated by Ca(2+) sensitization that is independent of ROK activation in sMA but not aorta. Thus ET-1-mediated signaling in aorta and sMA is altered by IH-C but is dependent on different second messenger systems in small vs. large arteries.     

Effect of nifedipine on calcium-induced contractions to potassium in the aorta and mesenteric arteries of spontaneously hypertensive and normotensive rats

Graded contractions to cumulative additions of calcium in the presence of KCl were obtained in strips of aorta and mesenteric arteries of normotensive (WKY) and spontaneously hypertensive (SHR) rats. In calcium-free medium, a maximally effective concentration of KCl produced a response that was larger in the mesenteric arteries (43-51% of control) than in the aorta (12-14% of control). The calcium channel blocker nifedipine (NFD, up to 10(-7) M) did not significantly alter these calcium-insensitive responses. The Ca2+-induced responses were inhibited by NFD, in a concentration-dependent fashion, in both vessel types of WKY and SHR rats. The aortic responses were more sensitive to inhibition by NFD than the responses of mesenteric arteries. Moreover, the aortic responses of WKY were inhibited to a greater extent than those of the SHR. The results suggest: (a) a differential calcium dependence of contractions to KCl in the vessels studied; (b) that aortic responses are dependent on NFD-sensitive voltage-sensitive Ca2+ channels to a greater extent than the responses of mesenteric arteries; and (c) that hypertension results in a decreased sensitivity of the aorta Ca2+ channels to NFD.     

Tempol improves vascular function in the mesenteric vascular bed of senescent rats

Ageing is associated with structural and functional alterations of the vasculature. The nature of age-related vascular disorders is not completely understood. Oxidative stress is hypothesized to play a crucial role in the pathophysiology of vascular complications. We investigated the effects of chronic treatment with the superoxide dismutase mimetic tempol (4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl) on vascular function in the mesenteric vasculature of aged rats. Young (3 weeks) and old (40 weeks) Sprague-Dawley rats were treated with tempol (1 mM in drinking water) or vehicle for 3 weeks. Arterial blood pressure was slightly, but significantly, higher in old than in young rats. Tempol had no effect on arterial blood pressure. The vasoconstrictor responses to norepinephrine (NE) and serotonin (5-HT) were exaggerated in the mesenteric vascular bed (MVB) removed from old rats. Vasodilator responses to acetylcholine (ACh), papaverine (PPV), and isoprenaline (ISO) were reduced in the MVB of old rats in comparison with young rats. Chronic treatment of old rats with tempol normalized their responses to NE and 5-HT. The dilator responses to ACh, PPV, and ISO were similar between old rats receiving tempol and young rats. The present findings suggest that oxidative stress contributes to vascular dysfunction in the mesentery of old rats. The vasculoprotective effects of tempol remain to be elucidated.     

Blood flow responses in celiac and superior mesenteric arteries in the initial phase of digestion

Blood flow (BF) responses in the celiac artery (CA) and superior mesenteric artery (SMA) during and immediately after a meal are poorly understood. We characterized postprandial BF responses in these arteries in the initial phase of digestion. After a baseline measurement in the overnight fasting state, healthy subjects ingested solid food (300 kcal) and water ad libitum within 5 min (4.6 +/- 0.2 min, means +/- SE), and then rested for 60 min in the postprandial state. Mean blood velocities (MBVs) in CA (n = 7) and SMA (n = 9) and mean arterial pressure (MAP) were measured throughout the procedure. The MAP was divided by the MBV to yield the resistance index (RI). The MBV in CA and SMA started increasing within a minute after beginning the meal. The MBV in CA rapidly reached its peak increase (60 +/- 8% change from baseline) at 5 +/- 1 min after the start of the meal, whereas the MBV in SMA gradually reached its peak increase (134 +/- 14%) at 41 +/- 4 min after the start of the meal, reflecting a decrease in the RI for both CA and SMA. These findings suggested an earlier increase in CA and SMA MBV, implying that the increase of BF in some parts of the small intestine precedes the arrival of chyme.     

Chewing and taste increase blood velocity in the celiac but not the superior mesenteric arteries

To investigate the role of chewing and taste in the meal-induced rapid increase in splanchnic blood flow, we compared the blood flow responses in the celiac artery (CA) and superior mesenteric artery (SMA) to chewing solid food with a chocolate taste (FOOD) and paraffin wax without taste (WAX). After 5 min of baseline measurement, 15 healthy subjects repeated chewing and expectorating the FOOD or WAX every 20 s for 4 min followed by 10 min of recovery measurement. We measured the mean blood velocity (MBV) in the CA and SMA. The baseline MBVs in the CA and SMA did not differ between the FOOD and WAX trials. The MBV in the CA was lower than baseline at the 1st min of chewing in both trials. It was higher than baseline at the 3rd min of FOOD chewing, whereas it did not increase during and after WAX chewing. The MBV in the CA was higher in the FOOD trial than in the WAX trial at the 3rd min of chewing and thereafter. In contrast, the MBV in the SMA did not change throughout the protocols. These results suggest that the taste of food plays a role in meal-induced hyperemia in the CA but not the SMA.     

Increased sympathetic innervation in the cerebral and mesenteric arteries of hypertensive rats

The density of catecholamine-containing nerve fibers was studied in the cerebral and mesenteric arteries from normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR), and stroke-prone SHR (SHRSP) in the growing (SHR, WKY) and adult (SHR, SHRSP, WKY) animals. Cerebral arteries from SHR showed an increased adrenergic innervation from day 1. The nerve plexuses reached an adult pattern earlier in SHR than in WKY. The arteries from adult SHR and SHRSP (22 weeks old) showed a markedly higher nerve density than WKY. There was a positive linear correlation between blood pressure and nerve density for four cerebral arteries. The mesenteric arteries were not innervated at birth. However, hyperinnervation of these arteries in the SHR was already present at 10 days of age as compared with WKY. Sympathectomy with anti-nerve growth factor and guanethidine caused a complete disappearance of fluorescent fibers in the mesenteric arteries from SHR and WKY, and in the cerebral arteries of WKY. The same procedure caused only partial denervation of the cerebral arteries from hypertensive animals. We postulate that the increase in nerve density in the cerebral arteries from the hypertensive rats may contribute to the development of arterial hypertrophy in chronic hypertension through the trophic effect of the sympathetic innervation on vascular structure.     

Adrenergic control of coronary arteries

This review of adrenergic control of coronary arteries is based on studies conducted on isolated vessels. Both alpha- and beta-adrenergic receptors are present in the coronary vasculature but with different distributions. The large coronary arteries have a larger percentage of alpha receptors, which mediate contraction, whereas the small coronary arteries are equipped almost exclusively with beta receptors, which mediate relaxation. The beta receptors are of the subclass beta 1. Both alpha 1 and alpha 2 receptors are present in the large coronaries. The alpha 2 receptors are prejunctional and inhibit neuronal release of norepinephrine (NE), and are also postjunctional and mediate contraction of the vascular smooth muscle. Evidence is reviewed suggesting that coronary alpha and beta receptors may be different conformational states of the same parent macromolecule in which the alpha state predominates at lower temperatures. Contrary to these results we have observed that whereas the response of the large coronary artery to NE at 39 C is predominantly constriction, it is predominantly dilation at 29 C. The characteristic of the adrenergic receptor is clearly temperature dependent.     

Simultaneous presentation of coarctation of the thoracic aorta and aneurysm of the superior mesenteric artery

A 34-year-old woman presented with both coarctation of the thoracic aorta and aneurysm of the superior mesenteric artery. The former was managed by open surgical repair, the latter by stent-graft. This case illustrates the need for facility with both percutaneous and open approaches to diseases of the aorta and its branches.     

Lipid oxidation by heart mitochondria from young adult and senescent rats

1. State-3 (i.e. ADP-stimulated) rates of O(2) uptake with palmitoylcarnitine, palmitoyl-CoA plus carnitine, pyruvate plus malonate plus carnitine and octanoate as respiratory substrate were all diminished in heart mitochondria isolated from senescent (24-month-old) rats compared with mitochondria from young adults (6 months old). By contrast, State-3 rates of O(2) uptake with pyruvate plus malate or glutamate plus malate were the same for mitochondria from each age group. 2. Measurements of enzyme activities in disrupted mitochondria showed a decline with senescence in the activity of acyl-CoA synthetase (EC 6.2.1.2 and 6.2.1.3), carnitine acetyltransferase (EC 2.3.1.7) and 3-hydroxy-acyl-CoA dehydrogenase (EC 1.1.1.35), but no change in the activity of carnitine palmitoyltransferase (EC 2.3.1.21) or acyl-CoA dehydrogenase (EC 1.3.99.3). 3. Measurement of dl-[(3)H]carnitine (in)/acetyl-l-carnitine (out) exchange in intact mitochondria showed decreased rates when the animals used were senescent. However, this followed from a decreased intramitochondrial pool of exchangeable carnitine, such that calculated first-order rate constants for exchange were identical in mitochondria from the two age groups. 4. The decline in acyl-CoA synthetase activity is thought to be the reason for the diminished rate of O(2) uptake with octanoate in senescence. The decline in carnitine acetyltransferase activity is considered to be the cause of the diminished rate of O(2) uptake with acetylcarnitine or with pyruvate plus malonate plus carnitine as substrate. The mechanism of the diminished rate of O(2) uptake with palmitoylcarnitine in senescence is discussed.     

Organ culture of the islets of Langerhans from young and senescent rats

Summary The B-cells of the endocrine pancreas constitute an adequate model for in vitro study of the aging process in highly differentiated cells. In the present study, collagenase-isolated islets of Langerhans from young and senescent rats were cultured up to 28 days. The response of the B-cells to the stimulatory conditions of the culture medium involved the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, and secretory granules. Correlated data from light microscopy, electron microscopy, and insulin radioimmunoassay show that the differentiation and function of senescent B-cells are maintained in culture, as it has been proven for the B-cells of younger animals. On the other hand, signs of cytological deficiency not directly concerned with the specific function of B-cells were observed: abnormal mitochondria and lysosomes are more numerous in the senescent B-cells. The proliferative capacity of the B-cells of aged rats is reduced. Send offprint requests to: Université Catholique de Louvain, Unité de Morphologie animale, Place Croix du Sud, 5, B 1348 Louvain-la-Neuve, BelgiumM.C.M. is currently associated with the Unité d'Histologie, Université de Louvain     

Organization of cells and extracelluar matrix in mesenteric arteries of spontaneously hypertensive rats

Summary Biochemical studies have been used to assess the quantitative changes in elastin and collagen in hypertensive vs. normotensive arteries. However, the relative distribution and organization of these fibrous proteins is likely to be equal in importance to their absolute amounts. In this study we have used scanning electron microscopy in association with selective digestion techniques to assess the organization of cellular and extracellular components of the tunica media of mesenteric arteries of spontaneously hypertensive rats. Superior and small mesenteric arteries were digested with acid, alkali, or bleach to exposure cells, collagen, or collagen and elastin, respectively. We observed that hypertension does not cause a qualitative change in the 3-dimensional arrangement of cells, collagen, or elastin in spontaneously hypertensive arteries when compared to normotensive arteries. However, cells in the superior artery are significantly different in overall shape and surface features when compared to cells of small arteries. These differences in surface morphology of cells are present in hypertensive and normotensive vessels and suggest that superior and small mesenteric artery cells transmit load to the isotropic matrix in different ways. In the elasto-muscular superior artery, force is transmitted across digitations throughout the cell surface. In the muscular small artery, force is transmitted across the tapered, smooth cell surface.     

Endothelial function and myogenic reactivity in small mesenteric arteries of hyperlipidemic pregnant rats

Supraphysiological increases in serum triglycerides and cholesterol often occur during pregnancy, but their effects on vascular function are poorly understood. Intraperitoneal injection of the nontoxic surfactant poloxamer 407 (P-407) results in sustained elevation of triglycerides and cholesterol. We asked if P-407-induced hyperlipidemia during late pregnancy adversely affects mesenteric resistance artery vasodilator function. On days 13-15 of pregnancy, rats were given a single intraperitoneal injection of P-407, sterile water vehicle, or non-lipid-altering pluronic F-88 (P-88). Four days postinjection, serum triglycerides, cholesterol, free fatty acids, and the lipid peroxidation product malondialdehyde were significantly increased in P-407-treated rats. Mesenteric arteries from P-407-treated rats displayed significant increases in myogenic reactivity (constrictor responses to step increases in intraluminal pressure). The nitric oxide (NO) blocker N(alpha)-methyl-L-arginine increased the myogenic response in control but not in P-407 arteries, normalizing group differences. Endothelial removal increased myogenic reactivity beyond that of prior NO synthase inhibition in controls and potentiated myogenic reactivity in P-407 arteries such that responses again converged. Relaxation responses to the endothelium-dependent vasodilator methacholine did not differ. We conclude that that P-407-induced hyperlipidemia during pregnancy increases myogenic reactivity due to selective attenuation of an NO-mediated vasodilator component of the myogenic response.     

Alterations in EDHF-type relaxation and phosphodiesterase activity in mesenteric arteries from diabetic rats

In isolated superior mesenteric artery rings from age-matched control rats and streptozotocin (STZ)-induced diabetic rats, we investigated the role of cAMP in endothelium-derived hyperpolarizing factor (EDHF)-type relaxation. The ACh-induced EDHF-type relaxation was significantly weaker in STZ-induced diabetic rats than in control rats, and in both groups of rats it was attenuated by 18alpha-glycyrrhetinic acid (18alpha-GA), an inhibitor of gap junctions, and enhanced by IBMX, a cAMP-phosphodiesterase (PDE) inhibitor. These enhanced EDHF-type responses were very similar in magnitude between diabetic and age-matched control rats. The EDHF-type relaxation was enhanced by cilostamide, a PDE3-selective inhibitor, but not by Ro 20-1724, a PDE4-selective inhibitor. The expression levels of the mRNAs and proteins for two cAMP PDEs (PDE3A, PDE3B) were significantly increased in STZ-induced diabetic rats, but those for PDE4D were not. We conclude that the impairment of EDHF-type relaxations in STZ-induced diabetic rats may be attributed to a reduction in the action of cAMP via increased PDE activity.     

Actin in young and senescent fibroblasts.

Long-term exposure of guinea pigs to a diet rich in maize oil caused an increase in adipose-tissue lipoprotein lipase activity. A similar diet rich in beef tallow had no such effect, and neither diet affected the enzyme activity in heart, lung, diaphragm or skeletal muscle.     

Cilostazol improves endothelium-derived hyperpolarizing factor-type relaxation in mesenteric arteries from diabetic rats

We previously reported that in mesenteric arteries from streptozotocin (STZ)-induced diabetic rats that 1) endothelium-derived hyperpolarizing factor (EDHF)-type relaxation is impaired, possibly due to a reduced action of cAMP via increased phosphodiesterase 3 (PDE3) activity (Matsumoto T, Kobayashi T, and Kamata K. Am J Physiol Heart Circ Physiol 285: H283-H291, 2003) and that 2) PKA activity is decreased (Matsumoto T, Wakabayashi K, Kobayashi T, and Kamata K. Am J Physiol Heart Circ Physiol 287: H1064-H1071, 2004). Here we investigated whether chronic treatment with cilostazol, a PDE3 inhibitor, improves EDHF-type relaxation in mesenteric arteries isolated from STZ rats. We found that in such arteries 1) cilostazol treatment (2 wk) improved ACh-, A-23187-, and cyclopiazonic acid-induced EDHF-type relaxations; 2) the ACh-induced cAMP accumulation was transient and sustained in arteries from cilostazol-treated STZ rats; 3) the EDHF-type relaxation was significantly decreased by a PKA inhibitor in the cilostazol-treated group, but not in the cilostazol-untreated group; 4) cilostazol treatment improved both the relaxations induced by cAMP analogs and the PKA activity level; and 5) PKA catalytic subunit (Cat-alpha) protein was significantly decreased, but the regulatory subunit RII-beta was increased (and the latter effect was significantly decreased by cilostazol treatment). These results strongly suggest that cilostazol improves EDHF-type relaxations in STZ rats via an increase in cAMP and PKA signaling.