Plasma concentrations of endothelin-1 in spontaneously hypertensive rats and DOCA-salt hypertensive rats

To investigate the possible involvement of endothelin-1 (ET-1), an endothelium-derived potent vasoconstrictor peptide, in the pathophysiology of hypertension, plasma ET-1 levels in 15-week-old spontaneously hypertensive rats (SHR) and DOCA-salt hypertensive rats were measured with a sandwich-type enzyme immunoassay. The vasocontractile effect of ET-1 in aortic helical preparations was significantly more sensitive in DOCA-salt hypertensive rats than in control sham-operated rats, but plasma levels of ET-1 did not differ between them. Plasma ET-1 levels in genetically hypertensive rats (SHR and stroke-prone SHR) were significantly lower than those in age-matched normotensive Wistar-Kyoto (WKY) rats. The plasma concentrations of big ET-1, a precursor of ET-1, in both SHR and SHR-SP were significantly lower than those of WKY, suggesting that the production of ET-1 is decreased in rats of genetic hypertension. Although the vascular reactivity to ET-1 increased in both DOCA-salt hypertensive and genetically hypertensive rats, present findings of the plasma ET-1 levels suggest that the role of ET-1 in the vascular control system may be different in DOCA-salt hypertensive rats and genetically hypertensive rats.     

Tissue catecholamine concentrations in spontaneously hypertensive rats

Tissue concentrations of noradrenaline (NA), dopamine (DA) and adrenaline (A) were compared in spontaneously hypertensive (SHR) and normotensive (NCR) rats, aged 1, 3, 8, 14 and 24 weeks The organs analyzed included the brain, subdivided into prosencephalon and rhombencephalon, heart, adrenal glands and kidney. Brain catecholamines were significantly lower in SHR than in NCR, and the difference appeared already at the age of 3 weeks. Concomitant increase was found in the adrenal NA and A concentrations of the SHR. Concentration of NA in the heart decreased in the SHR following onset of hypertension. It is concluded that the diminished NA, DA and A concentrations in the brain as well as the augmented adrenal NA and A levels in the SHR may be causally related to the development of hypertension, while the heart NA level reflects the secondary, hypertension -- related changes.     

Elevated vertebrobasilar artery resistance in neonatal spontaneously hypertensive rats

Erythropoietin (Epo) is produced primarily in the kidneys upon low blood oxygen availability and stimulates erythropoiesis in the bone marrow. Recombinant human Epo (rHuEpo), a drug developed to increase arterial oxygen content in patients, is also illicitly used by athletes to improve their endurance performance. Therefore, a robust and sensitive test to detect its abuse is needed. The aim of the present study was to investigate potential human serum biomarkers of Epo abuse employing a proteomic approach. Eight healthy male subjects were injected subcutaneously with rHuEpo (5,000 IU) every second day for a 16-day period. Serum was collected before starting the treatment regime and again at days 8 and 16 during the treatment period. Samples were homogenized and proteins separated by two-dimensional gel electrophoresis (2DE). Spots that changed significantly in response to rHuEpo treatment were identified by mass spectrometry. Both the number of reticulocytes and erythrocytes increased throughout the study, leading to a significant increase in hematocrit and hemoglobin content. In addition, transferrin levels increased but the percentage of iron bound to transferrin and ferritin levels decreased. Out of 97 serum proteins, seven were found to decrease significantly at day 16 compared with pre-Epo administration, and were identified as four isoforms of haptoglobin, two isoforms of transferrin, and a mixture of hemopexin and albumin. In support, total serum haptoglobin levels were found to be significantly decreased at both days 8 and 16. Thus a 2DE proteomic approach for discovery of novel markers of Epo action appears feasible.     

Cardiac tolerance to ischemia in neonatal spontaneously hypertensive rats

Hypertension is the risk factor of serious cardiovascular diseases, such as ischemic heart disease and atherosclerosis. The aim of the present study was to analyze the development of cardiac tolerance to ischemia in neonatal spontaneously hypertensive rats (SHR) and possible protective effect of ischemic preconditioning (IP) or adaptation to intermittent high-altitude hypoxia (IHAH). For this purpose we used 1- and 10-day-old pups of SHR and their normotensive control Wistar Kyoto rats (WKY). Isolated hearts were perfused in the Langendorff mode with Krebs-Henseleit solution at constant pressure, temperature and rate. Cardiac tolerance to ischemia was expressed as a percentage of baseline values of developed force (DF) after global ischemia. IP was induced by three 3-min periods of global ischemia, each separated by 5-min periods of reperfusion. IHAH was simulated in barochamber (8 h/day, 5000 m) from postnatal day 1 to 10. Cardiac tolerance to ischemia in 1-day-old SHR was higher than in WKY. In both strains tolerance decreased after birth, and the difference disappeared. The high cardiac resistance in 1- and 10-day-old SHR and WKY could not be further increased by both IP and adaptation to IHAH. It may be concluded that hearts from newborn SHR are more tolerant to ischemia/reperfusion injury as compared to age-matched WKY; cardiac resistance decreased in both strains during the first ten days, similarly as in Wistar rats.     

Plasma catecholamines and dopamine-beta-hydroxylase activity in spontaneously hypertensive rats.

Levels of plasma norepinephrine and total catecholamines in spontaneously hypertensive rats bred from a normotensive Kyoto strain of Wistar rats increase between their 8th to 12th week post utero concomitant with the development of hypertension, but levels of plasma norepinephrine are not significantly different between the spontaneously hypertensive strain, a normotensive Kyoto strain and a N.I.H. strain of Wistar rats at either 8 or 12 weeks of age. Plasma total catecholamine levels in the spontaneously hypertensive strain are significantly higher at 12 weeks of age than those in either control strain, while plasma levels of dopamine-β-hydroxylase show no consistant relationship between the three strains. It, therefore, appears unlikely that increased sympathetic neuronal activity is an etiological factor in this form of hypertension.     

Plasma catecholamine concentrations in normotensive rats of different strains and in spontaneously hypertensive rats under basal conditions and during cold exposure

Under basal conditions, the levels of circulating norepinephrine (NE) and epinephrine (E) were higher in normotensive Wistar rats of different origins than in Sprague-Dawley rats. Since the decline of ³H-NE concentration in the plasma after i.v. injection was similar in Wistar and in Sprague-Dawley rats, the higher levels of endogenous NE in the former strain probably reflect greater NE release from sympathetic nerve terminals. In normotensive Sprague-Dawley and Wistar rats, plasma NE rose to various extents during cold exposure (4°C), depending on the basal plasma NE levels. Compared with normotensive Wistar Kyoto rats (WKY), spontaneously hypertensive rats (SHR) had similar basal plasma E and NE concentrations, similar rates of ³H-NE disappearance, but more rapid increases to higher values of plasma NE during cold exposure. It is concluded that the basal rate of peripheral catecholamine release does not seem to be the main determining factor for arterial blood pressure in the various rat strains and that the sympathetic neuronal system of SHR is more responsive to cold exposure than that of WKY rats.     

Effect of high calcium diet on the development of high blood pressure in intact spontaneously hypertensive rats and in adrenalectomized spontaneously hypertensive rats treated with aldosterone

The current investigation was designed to study the effect(s) of high calcium diet on the development of high blood pressure (BP) in both young intact spontaneously hypertensive rats (SHRs) and in young adrenalectomized (ADX) male SHRs treated with aldosterone (ALDO). Weaned SHRs were fed either a control calcium diet (0.5% Ca as PO4) (CCaDiet), a high calcium diet (2.5% Ca, 0.5% as PO4 and 2% as CO3) (HCaDiet), or Agway ProLab rat food containing 2.5% Ca (HCaPLDiet). The HCaDiet significantly blunted the development of high BP in young intact SHRs (P less than 0.001; n = 8 to 10). At 6 weeks of age, BP was 117 +/- 2 mm Hg (HCaDiet) compared with 135 +/- 3 mm Hg (CCaDiet); by 12.7 weeks of age, BP was 192 +/- 4 mm Hg (HCaDiet) compared with 233 +/- 3 mm Hg (CCaDiet). Similar results were observed in age-matched SHRs fed the HCaPLDiet. The results show that subcutaneous infusion of ALDO (1.0 microgram/d, osmotic pumps) for 2 weeks to young ADX male SHRs raised on the CCaDiet caused a significant increase in systolic BP when compared with SHRs implanted with Sham pumps (P less than 0.001). High BP associated with ALDO infusion was attenuated by the HCaDiet (BP after 2 weeks was 138 +/- 8 mm Hg for the HCaDiet group compared with 200 +/- 5 mm Hg for the CCaDiet group, P less than 0.001; n = 4 to 6). The results show that the HCaDiet blunts the development of high BP in intact SHRs and may protect against the development of ALDO hypertension in ADX young SHRs.     

Brain opiate receptor concentrations are increased in adult spontaneously hypertensive rats.

The saturable binding of 3H-naltrexone in the brains of eight week old spontaneously hypertensive rats (SHR) is about twice that measured in corresponding normotensive WKY rats. This increase is dependent on age since in three and four week old SHR and WKY rats no difference in binding is observed. Scatchard analysis of the saturation curves for the adult animals revealed that the change in binding is due to an increase in the number of binding sites and does not reflect a difference in binding affinity. The increase in opiate receptor content of SHR rats coincides with the appearance of elevated blood pressure in these animals, and supports a concept in which an interaction between the endorphins and the endocrine system may be involved in the mechanisms controlling hypertension.     

Additive effects of combined valsartan and spironolactone on cardiac aldosterone escape in spontaneously hypertensive rats

The additive effects of combined valsartan and spironolactone on plasma and cardiac aldosterone escape were evaluated in spontaneously hypertensive rats (SHRs). Twenty-four SHRs were treated with valsartan (30 mg/kg body weight per day), spironolactone (20 mg/kg body weight per day) and a combination of both for 4 months. Blood was collected and plasma aldosterone (PA) was estimated with radioimmunoassay (RIA). Ex vivo heart perfusion was performed, the ex vivo cardiac aldosterone (EXCA) was assessed by RIA after high-performance liquid chromatography separation. PA and EXCA were significantly decreased after one month but increased after 4 months in valsartan administration group. The combined valsartan and spironolactone therapy normalized cardiac aldosterone levels. This study provides the first evidence that the long-term treatment with Angiotensin II type 1 receptor antagonist (AT1A) induces local aldosterone escape in cardiovascular tissue, whereas the combined AT1A and spironolactone therapy inhibits the escape in hypertensive rats.     

Calpastatin level in spontaneously hypertensive rats

We studied calpastatin activity in erythrocytes of Milan hypertensive and prehypertensive rats, in their normotensive controls, in F1 and F2 hybrids, and in two inbred strains derived from F2, one hypertensive and the other normotensive. Our results show that the decrease in calpastatin activity observed in Milan hypertensive rats was not caused by hypertension, it was transmitted in a recessive way in heterozygous, and it was not correlated to hypertension.     

StAR expression and the long-term aldosterone response to high-potassium diet in Wistar-Kyoto and spontaneously hypertensive rats

Most of the current medical treatments for endometriosis aim to downregulate estrogen activity. However, a high recurrence rate after medical treatment has been the most significant problem. BAY 11-7085, a soluble inhibitor of NK-kappaB activation, has been shown to inhibit cell proliferation and induce apoptosis of a variety of cells. To examine the potential application of BAY 11-7085 in the treatment of endometriosis, we investigated the effects of this agent on the cell proliferation and apoptosis of cultured ovarian endometriotic cyst stromal cells (ECSCs) by a modified methylthiazole tetrazolium assay, a 5-bromo-2'-deoxyuridine incorporation assay, and internucleosomal DNA fragmentation assays. The effect of BAY 11-7085 on the cell cycle of ECSCs was also determined by flow cytometry. The expression of apoptosis-related molecules was examined in ECSCs with Western blot analysis. BAY 11-7085 significantly inhibited the cell proliferation and DNA synthesis of ECSCs and induced apoptosis and the G0/G1 phase cell cycle arrest of these cells. Additionally, downregulation of the B-cell lymphoma/leukemia-2 (Bcl-2) and Bcl-X(L) expression with simultaneous activation of caspase-3, -8, and -9 was observed in ECSCs after treatment with BAY 11-7085. These results suggest that BAY 11-7085 induces apoptosis of ECSCs by suppressing antiapoptotic proteins, and that caspase-3-, -8-, and -9-mediated cascades are involved in this mechanism. Therefore, BAY 11-7085 could be used as a therapeutic agent for the treatment of endometriosis.     

Interval bisection in spontaneously hypertensive rats

An interval bisection procedure was used to study time discrimination in spontaneously hypertensive rats (SHR), which have been proposed as an animal model for the attention deficit hyperactivity disorder (ADHD); Wistar Kyoto and Wistar rats were used as comparison groups. In this procedure, after subjects learn to make one response (S) following a short duration stimulus, and another (L) following a long duration stimulus, stimuli of intermediate durations are presented, and the percentage of L is calculated for each duration. A logistic function is fitted to these data, and different parameters that describe the time discrimination process are obtained. Four conditions, with different short and long durations (1-4, 2-8, 3-12, 4-16s) were used. The results indicate that time discrimination is not altered in SHR, given that no difference in any of the parameters obtained were significant. Given that temporal processing has been proposed as a fundamental factor in the development of the main symptoms of ADHD, and that deficits in time discrimination have been found in individuals with that disorder, the present results suggest the necessity of exploring time perception in SHR with other procedures and sensory modalities, in order to assess its validity as an animal model of ADHD.     

Abnormal functional development of sympathetic nerve terminal-smooth muscle complex in neonatal spontaneously hypertensive rats

In neonatal and young adult SH and WK rats, maturation of a functional unit consisting of sympathetic nerve terminals and smooth muscle (levator palpebrae) was assessed $\text{in vivo}$ by measuring the contractile response to tyramine, an agent which releases endogenous norepinephrine from sympathetic nerve terminals. Responses in SH are comparable to WK at 5–6 days postnatally, smaller from the 8th through 19th day and larger in young adults (41–46 days old). Results indicate that functional maturation of the nerve terminal-smooth muscle complex is retarded in SH relative to WK during the 2nd and 3rd postnatal weeks. It is suggested that retardation in the neonatal SH rat is an expression of a genetic defect in the growth of the complex and that the enhanced response in young adult SH is a consequence of the neonatal abnormality.     

Effect of varying concentrations of linoleic acid on alpha-adrenoceptor responses in spontaneously hypertensive rats

The effect of increased intake of linoleic acid on the alpha-adrenergic system was assessed by safflower oil supplementation to spontaneously hypertensive rats. Linoleic acid-enriched intake at 5%, 15% and 30% by weight of total food intake for 12 wk was associated with a reduction in resting arterial blood pressure, while heart rate and heart to body weight ratios were similar to control group values. A dose-response analysis to norepinephrine bitartrate administered intravenously indicated a significant reduction in the vascular reactivity to this alpha-adrenergic agonist in all groups given linoleic acid. Direct assessment of alpha-adrenoceptor number (Bmax) and affinity (KD) in cardiac sarcolemma with [3H]-prazosin indicated that receptor binding properties were not affected by linoleic acid intake. Our results suggest that short-term linoleic acid supplementation in the established hypertensive state may lower blood pressure through effects upon alpha-adrenergic reactivity in vascular tissue, without associated effects in cardiac tissue.     

Glutathione system in young spontaneously hypertensive rats

Glutathione (GSH) forms a part of the antioxidant system that plays a vital role in preventing oxidative stress, and an imbalance in the oxidant/antioxidant system has been linked to the pathogenesis of hypertension. The aim of this study was to investigate the status of the GSH system in the kidney of spontaneously hypertensive rats (SHR). Components of the GSH system, including glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST), and total GSH content, were measured in the kidneys of 4, 6, 8, 12, and 16 weeks old SHR and Wistar–Kyoto (WKY) rats. Systolic blood pressure of SHR was significantly higher from the age of 6 weeks onwards compared with age-matched WKY rats. GPx activity in the SHR was significantly lower from the age of 8 weeks onwards when compared to that in age-matched WKY rats. No significant differences were evident in the GPx-1 protein abundance, and its relative mRNA levels, GR, GST activity, and total GSH content between SHR and age-matched WKY rats. The lower GPx activity suggests of an impairment of the GSH system in the SHR, which might be due to an abnormality in its protein rather than non-availability of a cofactor. Its role in the development of hypertension in SHR however remains unclear.     

Impaired angiotensin-induced drinking in spontaneously hypertensive rats

The drinking response during the 30 minutes following intracerebroventricular injection of angiotensin II (AII) (1 to 200 ng) was compared in male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto control rats (WK). SHR drank significantly less than WK at the 10, 50 and 100 ng doses. In contrast, responses to intracerebroventricular carbachol and intraperitoneal hypertonic saline were not different between SHR and WK. These agents are believed to induce drinking by mechanisms independent of angiotensin. Binding of I¹²⁵-labelled AII to particles prepared from the hypothalamus, thalamus, septum and midbrain (HTSM) region was measured in one month old male and two month old female SHR and their respective age matched WK controls. No differences were found in binding between SHR and WK of either sex. These data demonstrate an impairment of drinking responses in the SHR which seem to be specific for angiotensin. This finding supports the hypothesis that the CNS angiotensin system might be abnormal in these animals.     

Angiotensin stimulates respiration in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) have an activated brain angiotensin system. We hypothesized 1) that ventilation (V) would be greater in conscious SHR than in control Wistar-Kyoto (WKY) rats and 2) that intravenous infusion of the ANG II-receptor blocker saralasin would depress respiration in SHR, but not in WKY. Respiration and oxygen consumption (VO(2)) were measured in conscious aged-matched groups (n = 16) of adult female SHR and WKY. For protocol 1, rats were habituated to a plethysmograph and measurements obtained over 60-75 min. After installation of chronic intravenous catheters, protocol 2 consisted of 30 min of saline infusion ( approximately 14 microliter. kg(-1). min(-1)) followed by 40 min of saralasin (1.3 microgram. kg(-1). min(-1)). V, tidal volume (VT), inspiratory flow [VT/inspiratory time (TI)], breath expiratory time, and VO(2) were higher, and breath TI was lower in "continuously quiet" SHR. In SHR, but not in WKY rats, ANG II-receptor block decreased V, VT, and VT/TI and increased breath TI. During ANG II-receptor block, an average decrease in VO(2) in SHR was not significant. About one-half of the higher V in SHR appears to be accounted for by an ANG II mechanism acting either via peripheral arterial receptors or circumventricular organs.     

G-proteins in kidneys of spontaneously hypertensive rats

G(s alpha)-, total G(i alpha)- and G(q/11alpha)-protein concentrations were investigated by quantitative immunoblotting in membranes of total kidney, renal cortex and medulla as well as in cortical tubules and glomeruli of Spontaneously Hypertensive Rats (SHR) and normotensive Wistar Kyoto rats (WKY), aged 5 weeks, 3 or 8 months. We found that total kidney of 5 week old SHR possess less G(s alpha)-, G(i alpha)- and G(q/11alpha)-proteins than controls. For G(s alpha)-proteins, differences found in total kidney were mirrored both in cortex (tubules and glomeruli) and in medulla. Decreased G(i alpha)-concentrations were accompanied by lower tubular but higher glomerular levels, while medullar levels were also increased. Decreased G(q/11alpha)-concentrations were reflected in decreased glomerular and medullary concentrations. Kidneys of 3 month old SHR and WKY possessed similar concentrations of all G(alpha)-species. In 8 month old SHR similar G(i alpha)-, but decreased G(s alpha)-and G(q/11alpha)-concentrations were observed. The G(s alpha)-decrease was reflected in cortex and medulla, the G(q/11alpha)-decrease in the medulla. We conclude that the main strain-related differences in G(alpha)-concentrations are seen in prehypertensive SHR.     

Delayed development of hypertension and increased aortic relaxation in spontaneously hypertensive rats after neonatal sympathectomy

The effect of neonatal sympathectomy on vasodilator responses to acetylcholine (ACh) and cAMP has been studied in aortic rings of spontaneously hypertensive rats (SHR) and normotensive animals. The relaxation of intact SHR aorta in response to ACh and cAMP was 20-35% lower than that of normotensive rats. Sympathectomy in normotensive rats did not affect the level of blood pressure and aorta reactivity to Ach. In SHR, sympathectomy caused a decrease in blood pressure, while relaxation in response to ACh and cAMP increased, as compared to intact SHR, but remained lower than in normotensive rats. The data obtained suggest that the decrease in arterial pressure of sympathectomized SHR is a result not only of the reduction in sympathetic effects but also of the increase in smooth muscle relaxation.