Characteristic alterations in adrenal catecholamine contents in SHR, SHRSP, and WKY during development of hypertension and stroke

Esaxerenone: blood pressure reduction and cardiorenal protection without reflex sympathetic activation in salt-loaded stroke-prone spontaneously hypertensive rats

Mineralocorticoid receptor (MR) is involved in the mechanisms of blood pressure elevation, organ fibrosis, and inflammation. MR antagonists have been used in patients with hypertension, heart failure, or chronic kidney disease. Esaxerenone, a recently approved MR blocker with a nonsteroidal structure, has demonstrated a strong blood pressure-lowering effect. However, blood pressure reduction may lead to sympathetic activation through the baroreflex. The effect of esaxerenone on the sympathetic nervous system remains unclear. We investigated the effect of esaxerenone on organ damage and the sympathetic nervous system in salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP), a well-established model of essential hypertension with sympathoexcitation and organ damage. Three-week administration of esaxerenone or hydralazine successfully attenuated the blood pressure elevation. Both esaxerenone and hydralazine comparably suppressed left ventricular hypertrophy and urinary albumin excretion. However, renal fibrosis and glomerular sclerosis were suppressed by esaxerenone but not hydralazine. Furthermore, plasma norepinephrine level, a parameter of systemic sympathetic activity, was significantly increased by hydralazine but not by esaxerenone. Consistent with these findings, the activity of the control centers of sympathetic nervous system, the parvocellular region of the paraventricular nucleus in the hypothalamus and the rostral ventrolateral medulla, was enhanced by hydralazine but remained unaffected by esaxerenone. These results suggest that esaxerenone effectively lowers blood pressure without inducing reflex sympathetic nervous system activation. Moreover, the organ-protective effects of esaxerenone appear to be partially independent of its blood pressure-lowering effect. In conclusion, esaxerenone demonstrates a blood pressure-lowering effect without concurrent sympathetic activation and exerts organ-protective effects in salt-loaded SHRSP. Esaxerenone has antihypertensive and cardiorenal protective effects without reflex sympathetic activation in salt-loaded stroke-prone spontaneously hypertensive rats.

Adrenal α2-adrenergic receptors in the aging normotensive and spontaneously hypertensive rat

This study investigates α(2)-adrenergic receptor (α(2)AR) mediated feedback inhibition of catecholamine release from the adrenal medulla of adult (52 weeks) and old (98 weeks) spontaneously hypertensive rats (SHR) and normotensive controls Wistar Kyoto (WKY) rats. Adrenal epinephrine content as well as the spontaneous and the nicotinic-evoked release of epinephrine were similar between adult SHR and WKY rats. Aging produced a significant reduction in epinephrine synthesis in WKY rats. In contrast, in SHR aging produced a significant increase in epinephrine release without significant changes in epinephrine synthesis. The α(2)AR agonist medetomidine abolished (80-90% inhibition) the nicotinic-evoked release of epinephrine in adult SHR and WKY rats. With aging, this effect was unaltered in WKY rats but was significantly decreased in SHR (30% inhibition). Adrenal α(2A)AR mRNA levels were significantly reduced in old SHR compared with age matched WKY rats. In conclusion, in aging the α(2)AR mediated feedback inhibition of epinephrine release from the adrenal medulla is preserved in WKY rats but compromised in SHR, resulting in increased epinephrine release.

Fasudil attenuates sympathetic nervous activity in the adrenal medulla of spontaneously hypertensive rats

We investigated the effects of fasudil, a Rho kinase inhibitor, on hypertension in spontaneously hypertensive rats and on the catecholamine synthetic pathway. Ten-week-old male SHR and Wistar-Kyoto rats were administered fasudil (10 mg/kg/day s.c.) for 4 days. Systolic blood pressure was measured using the tail-cuff method. Catecholamine levels were measured with high-performance liquid chromatography-ECD methods. Tyrosine hydroxylase protein levels were measured in Western blot analysis. The tyrosine hydroxylase mRNA level was measured using real-time PCR methods. Fasudil significantly decreased systolic blood pressure in spontaneously hypertensive rats, but not in Wistar-Kyoto rats. Fasudil also significantly decreased catecholamine, tyrosine hydroxylase protein, and tyrosine hydroxylase mRNA levels in the adrenal medulla of spontaneously hypertensive rats. These results suggest that the depressor effects of fasudil on hypertension in spontaneously hypertensive rats may be related to inhibition of the catecholamine synthetic pathway.

Expression of nitric oxide synthase isoforms in hypothalamo–pituitary–adrenal axis during the development of spontaneous hypertension in rats

This study was performed to investigate the expression of the major isoforms of nitric oxide synthase mRNA and protein in the hypothalamo-pituitary-adrenal axis (HPA axis) of spontaneously hypertensive rats (SHR) at two different postnatal ages corresponding to the development of genetic hypertension. Using RT-PCR and Western blot techniques, the mRNA and protein levels of neuronal (nNOS), endothelial (eNOS) and inducible (iNOS) isoforms were measured in 3- to 4-week-old (prehypertensive phase) and 12- to 13-week-old (established hypertension phase) SHR and age-matched normotensive Wistar-Kyoto (WKY) rats. nNOS but not eNOS mRNA levels were increased at prehypertensive and hypertensive phases in SHR HPA axis. Compared to age-matched WKY rats, significantly higher levels of nNOS protein were found in the hypothalamus, lower levels in the adrenal glands and no changes were observed in the pituitary gland. At both ages tested, there was no significant change in eNOS protein expression in SHR HPA axis. The expression of iNOS mRNA and protein was under detection limit. In the HPA axis, the expression of nNOS isoform appears to be differentially controlled at the transcriptional and translational levels in SHR. Increased mRNA levels and differential nNOS protein expression from birth in SHR HPA axis may contribute in the pathogenesis of genetic hypertension.

Sympathetic Hyperfunction Causes Increased Sensitivity of the Autonomic Nervous System to Whole-Body X Irradiation

Although the etiology of radiation sickness is still unknown, disturbance of the autonomic nervous system is suggested to be a factor. This study was designed to compare the radiosensitivity of spontaneously hypertensive rats possessing sympathetic hyperfunction and control Wistar-Kyoto rats, and to analyze the effects of radiation on the autonomic nervous system in both strains. After a 7.5-Gy dose of whole-body X irradiation, the blood pressure decreased significantly at 8 h and 2 days in the spontaneously hypertensive rats, but not in the Wistar-Kyoto rats. Epinephrine levels in the adrenal gland of spontaneously hypertensive rats decreased at 4, 8 and 24 h, unlike the Wistar-Kyoto rats. Radiation evoked a stronger increase in norepinephrine in the jejunum and colon of spontaneously hypertensive rats than in Wistar-Kyoto rats. Acetylcholine levels in the jejunum of spontaneously hypertensive rats decreased, in contrast to the increase in Wistar-Kyoto rats within 24 h after irradiation. The survival rate of spontaneously hypertensive rats was lower than that of Wistar-Kyoto rats and weight loss, appetite loss and morphological changes in the jejunum were greater in spontaneously hypertensive rats than in Wistar-Kyoto rats after irradiation. These results indicated that X irradiation caused greater activities in autonomic nervous function and severe radiation injury in spontaneously hypertensive rats. Sympathetic hyperfunction may be associated with a higher sensitivity to radiation, including radiation injury and radiation sickness.

Biochemical and morphological characterization of spontaneously hypertensive hyperlipidaemic rats

1. To develop and characterize a new animal model of hypertension and hyperlipidaemia, we cross-bred spontaneously hypertensive rats (SHR) with spontaneously hyperlipidaemic rats (HLR). 2. A new strain of spontaneously hypertensive hyperlipidaemic rats (SHHR) was established at generation 10 through selective mating of brothers and sisters (systolic blood pressure > 150 mmHg, plasma cholesterol > 150 mg/dL). Cross-bred Wistar-Kyoto (WKY) rats and Sprague-Dawley (SD) rats (SDWKY rats) were used as a control. 3. Adrenaline and noradrenaline levels in the plasma and adrenal medulla of male SHHR were significantly higher than those of male SDWKY rats. The tyrosine hydroxylase activity in the adrenal medulla of male SHHR was significantly higher than that of male SDWKY rats. Low-density lipoprotein expression was found in the plasma of male and female SHHR and HLR. Cholesterol 7alpha-hydroxylase mRNA expression in the liver of male SHHR was lower than that of male SDWKY rats. Endothelium lesions and lipid deposition under the endothelium were observed in the aorta of 24-month-old SHHR, especially female SHHR, but not in age-matched HLR and SDWKY rats. 4. The hypertension of this new animal model of hypertension and hyperlipidaemia may be related to increased catecholamine activity and the hyperlipidaemia may be related to changes in the expression of cholesterol 7alpha-hydroxylase mRNA and lipoprotein profiles. The SHHR may be valuable in the study of mechanisms of atherosclerosis and the evaluation of anti-atherosclerosis drugs as a new strain of cardiovascular disease.

Testosterone increased blood pressure and decreased renal tyrosine hydroxylase activity in SHR/y and Wistar-Kyoto rats

The present study evaluated the association between a testosterone-induced elevation in blood pressure (BP) and renal tyrosine hydroxylase activity in SHR/y and Wistar-Kyoto male rats. The SHR/y rat is a consomic strain having the Y chromosome of the Spontaneously Hypertensive Rat and autosomes and the X chromosome from normotensive Wistar-Kyoto (WKY). Rats were castrated at 4-6 weeks and divided into control and sham groups (n = 6/group) with testosterone and blank sham implants respectively. BP and blood were taken every 2 weeks for estimation of serum testosterone and catecholamines. The animals were terminated at 16-18 weeks and kidneys were removed for the estimation of tyrosine hydroxylase activity. The testosterone treated rats had higher BP, plasma testosterone levels, kidney weights, but lower renal tyrosine hydroxylase activity than the sham treated controls. Hence, chronic testosterone treatment inhibits renal tyrosine hydroxylase activity in WKY and SHR/y rats.

Tyrosine hydroxylase antisense gene therapy causes hypotensive effects in the spontaneously hypertensive rats

We investigated the effect of antisense oligodeoxynucleotides (AS ODN) against tyrosine hydroxylase (TH) on hypertension and sympathetic nervous system activity in spontaneously hypertensive rats (SHR). Systolic blood pressure (SBP) in SHR treated with TH AS ODN (50, 200 microg/rat, i.v.) was significantly lower than that of control SHR. Epinephrine and norepinephrine levels, TH activity, and TH protein levels in the adrenal medulla of SHR were reduced concomitant with TH AS ODN treatment-induced changes in SBP. In contrast, TH AS ODN (200 microg/rat) had no effect on SBP in Wistar-Kyoto rats (WKY), despite significantly decreased catecholamine levels, TH activity, and TH protein levels. These findings suggest that peripheral systemic injection of TH AS ODN may be effective as hypotensive therapy in SHR.

Effects of nitric oxide synthase inhibitor on tyrosine hydroxylase mRNA in the adrenal medulla of spontaneously hypertensive and Wistar Kyoto rats

We studied the effects of N(G)-nitro-l-arginine methyl ester (L-NAME) on catecholamine levels, tyrosine hydroxylase (TH) activity, and TH mRNA levels in the adrenal medulla of spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). L-NAME (100 mg/L in drinking water) and atropine (10 mg/L in drinking water) were administered for 2 weeks. Epinephrine and norepinephrine levels, TH activity, and TH mRNA levels in the adrenal medulla of L-NAME-treated WKY were significantly decreased. These parameters were not significantly altered in the adrenal medulla of L-NAME-treated SHR. Nitrite/nitrate levels in the adrenal medulla of L-NAME-treated WKY were significantly decreased; however, no significant change in L-NAME-treated SHR was observed. Ca(2+)-dependent nitric oxide synthase (NOS) activity in the adrenal medulla of SHR was significantly decreased compared to that of WKY. TH mRNA levels in L-NAME + atropine-treated and L-NAME-treated WKY were significantly lower than TH mRNA levels in control WKY. These results suggest that nitric oxide in the adrenal medulla may enhance the catecholamine biosynthetic pathway via increased TH mRNA expression. Our results also suggest that this effect is suppressed in SHR due to decreased NOS activity in the adrenal medulla.

Enhancement of the affinity of androgen receptor in the adrenal medulla of spontaneously hypertensive rats

We investigated the alteration of tyrosine hydroxylase (TH) mRNA expression and androgen receptor in the adrenal medulla of spontaneously hypertensive rats (SHR). The TH mRNA expression in the adrenal medulla of SHR was higher than that of Wistar Kyoto rats (WKY). The testosterone increased the TH mRNA expression of SHR, but not WKY. The affinity of androgen receptor in the adrenal medulla of SHR was higher than that of WKY; however, the number of androgen receptor was not different. These results suggested that the increased binding affinity of the androgen receptor of SHR may be related to TH gene transcription in the adrenal medulla.

Different susceptibility of stress-induced gastric ulcer and the autonomic nervous function in the hereditary hypertensive rats

Susceptibility of stress-induced ulcer by restraint water immersion (RWI) was examined in Wistar Kyoto rats (WKY), spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SHRSP). Ulcer formation was slight in SHR, and very slight in SHRSP. The ulcer index and blood pressure showed a significant inverse correlation (P < 0.001). Acid secretion was lowest in SHRSP, and hypergastrinemia was present in SHRSP. Gastric motility was suppressed during RWI in SHR and SHRSP. The noradrenaline content of the gastric mucosa and muscle layer was significantly greater in these hypertensive strains, and histologically noradrenergic innervation in the mucosa was also denser in SHRSP and SHR. Choline acetyltransferase activity in the stomach was significantly lower in SHR and SHRSP than WKY (P < 0.01). These findings suggest that susceptibility of stress-induced ulcer is inversely correlated with systemic blood pressure and that the alteration of autonomic nervous function contributes to inhibition of stress ulcers by suppressing acid secretion and motility in the hereditary hypertensive rats.

The role of the sympathetic nervous system in promoting liver cirrhosis induced by carbon tetrachloride, using the essential hypertensive animal (SHR)

The effects of the sympathetic nervous system on liver injury induced experimentally by carbon tetrachloride (CCl4) were examined in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). It was found that the SHR had an elevated catecholamine (CA) content in the adrenal gland without any treatment, and fluorescence histochemistry also revealed dense adrenergic innervations in the liver. Moreover, the SHR showed greater sensitivity to CCl4 stimulation in the sympathetic nervous system than the WKY, resulting in a decreased hepatic blood flow in the acute stage and a depleted CA in the adrenal gland, a lowered blood pressure (BP) and a released non-esterified fatty acid (NEFA) from peripheral adipose tissue in the chronic stage. Upon repetition of the CCl4 treatments twice a week for 4 weeks, the liver injury was more severe in the SHR than in the WKY. Plasma glutamate-pyruvate transaminase (GPT) activity was increased in both strains but more significantly in the SHR than in the WKY. Histological examination of the liver in the SHR showed established cirrhosis, whereas only bridging fibrosis was seen in the WKY. These results suggest that the pathogenesis of the liver damage induced by CCl4 in the SHR, is attributable to the enhanced response of the sympathetic nervous system that releases massive amounts of CA which then lead to vasoconstriction and metabolic changes that promote liver damage.

Role of dopaminergic mechanisms in the kidney for the pathogenesis of hypertension

1. To estimate the role of renal dopaminergic mechanisms in the pathogenesis of hypertension, patients with essential hypertension and animal models of hypertension were investigated. 2. Impaired dopaminergic activity in kidneys for natriuresis was observed in patients with 'salt-sensitive' hypertension and with low-renin hypertension. 3. Decreased dopaminergic activity in kidneys was observed in the Dahl S-rats without salt loading. 4. In spontaneously hypertensive rats, renal dopamine synthesis was enhanced whereas there was a decrease of adenylate cyclase activity in renal tubules. 5. Demonstration of impaired dopaminergic mechanisms in kidneys of human and animal hypertension suggests that renal dopaminergic mechanisms play an important role in development of hypertension.

Effect of decreased dopamine synthesis on the development of hypertension induced by salt loading in spontaneously hypertensive rats

To clarify role of dopamine in the development of hypertension, the effect of a dopamine synthesis inhibitor on blood pressure and urinary output of catecholamines was investigated in spontaneously hypertensive rats (SHR) fed with high sodium diet. Rats were orally given carbidopa, an inhibitor of peripheral DOPA decarboxylase, or the vehicle for 4 weeks. Carbidopa administration accelerated significantly the development of hypertension as compared to the control SHRs with the vehicle. Carbidopa administration resulted in a significant decrease of urinary excreted sodium, urinary dopamine and renal content of dopamine. Conversely, carbidopa administration resulted in a significant increase of urinary excreted norepinephrine, urinary epinephrine and renal content of norepinephrine as compared with control SHRs. These results suggest that decreased dopamine synthesis in kidneys and probably other peripheral tissue accelerates the development of hypertension, mediated by a decrease of natriuresis and an enhancement of sympatho-adrenomedullary activity. Dopamine plays an important role in its protective action against the development of hypertension enhanced by salt loading, and decreased dopaminergic mechanisms accelerated hypertension in SHR.

Peripheral dopamine synthesis and metabolism in spontaneously hypertensive rats

We have studied several parameters of peripheral dopamine synthesis and metabolism in spontaneously hypertensive rats during the development of hypertension. Compared to Wistar-Kyoto rats, there was an increased dopamine content in 8-week-old spontaneously hypertensive rats in the adrenals (1.6 +/- 0.1 vs. 1.2 +/- 0.1 nmol/pair in Wistar-Kyoto rats) and kidneys (97 +/- 12 vs. 63 +/- 7 pmol/g tissue in Wistar-Kyoto rats), but the dopamine content in peripheral organs from normotensive 4-week-old spontaneously hypertensive rats did not differ from Wistar-Kyoto rats. In the heart, the dopamine increase was observed in 14-week-old spontaneously hypertensive rats (systolic blood pressure: spontaneously hypertensive rats, 189 +/- 9; Wistar-Kyoto rats, 106 +/- 2 mm Hg;) in both atrium (spontaneously hypertensive rats, 133 +/- 14; Wistar-Kyoto rats, 86 +/- 20 pmol/g tissue) and ventricle (spontaneously hypertensive rats, 41 +/- 6; Wistar-Kyoto rats, 23 +/- 5 pmol/g tissue). Urinary free dopamine and dihydroxyphenylacetic acid, but not norepinephrine or normetanephrine, in spontaneously hypertensive rats significantly increased between the ages of 7 and 11 weeks, reflecting the dopamine changes in tissue and suggesting a selective increase of the rate of dopamine synthesis and release.(ABSTRACT TRUNCATED AT 250 WORDS)