Effect of brain serotonin on the arterial pressure and plasma renin in normal and hypertensive rats]

The effects of changes in brain serotonin content after injections of p-chlorophenylalanine (p-CPA), L-5-hydroxytryptophan (L-5HTP) and 5-6-dihydroxytryptamine (5-6DHT) on the mean arterial pressure (MAP), plasma renin activity (PRA) and peripheral levels of atrial natriuretic peptide (ANP) have been studied in normal and hypertensive (2K:1C model) male Wistar rats. The p-CPA (250 mg/kg) and L-5HTP (200 mg/kg) were injected i.p., while 5-6 DHT (15 micrograms/animal in 10 mu/animal vehicle) was injected into lateral brain ventricles. The effects were studied 24 h after the p-CPA injection, 2 h after L-5HTP and 10 or 20 days after 5-6DHT administration. The fall in brain serotonin produced by p-CPA and 5-6DHT did not modify the MAP values in the normal and hypertensive rat model, whereas the increase induced after L-5HTP injection only caused a slight decrease in arterial pressure in normotensive animals. The ARP experimented remarkable rises in the normal and hypertensive rats, these values increasing after L-5HTP and falling after p-CPA and 5-6 DHT injections. Similar changes are detected in the normal group after administration of these substances related to serotoninergic brain activity. The ANP levels rose after renal artery constriction, and they are not affected by the above mentioned substances. Only p-CPA and 5-6DHT reduced a low decrease in the ANP levels 10 days after their administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of high calcium diet on magnesium, catecholamines, and blood pressure of stroke-prone spontaneously hypertensive rats

To test the effect of a high dietary calcium intake on blood pressure, we fed stroke-prone spontaneously hypertensive (SHR-SP) and Wistar-Kyoto rats (WKY) diets containing (a) 0.25% Ca/0.08% Mg, (b) 4.0% Ca/0.02% Mg, and (c) 4.0% Ca/0.08% mg, beginning at 6 weeks of age. SHR-SP and WKY rats receiving 4% Ca with the lower Mg content had lower blood pressures, hypomagnesemia, and hypomagnesuria, and grew poorly. SHR-SP receiving 4% Ca and the higher Mg diet had blood pressures no different from those of rats receiving the 0.25% Ca diet, in spite of having lower body weights. Rubidium flux studies in erythrocytes were not influenced by Ca or Mg in the diets. Plasma phosphate values were moderately reduced in rats receiving 4% Ca diets. Epinephrine and norepinephrine values were higher in SHR-SP than in WKY rats. Norepinephrine increased with stress in both strains, independent of diet. Epinephrine values were lower in SHR-SP receiving the 4% Ca diets and showed less of an increase with stress compared to SHR-SP receiving the 0.25% Ca diet. After 26 weeks of diets, SHR-SP and WKY rats were given 0.9% NaCl in their drinking water. NaCl increased blood pressure in SHR-SP irrespective of Ca content of the diet. These data suggest that a high Ca diet influences Mg homeostasis and adrenal medullary function in SHR-SP. Further, SHR-SP appear resistant to any blood pressure lowering effect of Ca irrespective of NaCl intake.     

Effect of physical training by swimming on the arterial pressure, plasma and hypothalamo-post-hypophyseal vasopressin in genetically hypertensive rats of the Lyon strain

The effect of a 5-week swimming training on systolic blood pressure (PAS) and vasopressin (AVP) and Neurophysins (NpT) concentration in the blood and content in the pituitary and the hypothalamus was studied in Lyon genetically hypertensive rats [LH] and in their controls: the normotensive [LN] and low blood pressure [LL] rats belonging to the 28th generation. Nine female rats of each group were trained 5 days a week for 5 weeks, starting with 2 h a day, with a 15 min increase every day, up to 6 h a day. The PAS was measured using an indirect plethysmographic technique one time a week during the whole training session. At the end of the training, the rats were decapitated. AVP and NpT were measured in blood, pituitary and hypothalamus, by radioimmunoassay (RIA). Hematocrit as well as plasma Na+, K+, protein and osmotic content were also measured. Results show that the training did not affect any of the studied parameters: mainly, there was no decrease in PAS or plasma AVP level in the hypertensive rats compared to the normotensive ones. The only difference was a lower AVP content in the pituitary of LH rats compared to LN (p less than 0.01), which is difficult to interpret. Our results shed doubt on the efficiency of a swimming training on the evolution of hypertension in the Lyon rat model.     

Effect of a low-frequency magnetic field on systemic arterial pressure in spontaneously hypertensive rats

The effect of low-frequency magnetic field (MF) on systemic blood pressure has been studied in chronic experiments on 21 spontaneously hypertensive rats. The animals' kidney area was exposed to MF (induction value 30T). Direct blood pressure measurements have revealed an antihypertensive effect.     

Influence of a diet rich in fish oil on blood pressure, body weight and cardiac hypertrophy in spontaneously hypertensive rats

The effects of a diet rich in fish oil on arterial blood pressure, body weight, left ventricular weight and heart rate have been investigated in 8 month old spontaneously hypertensive male rats (SHR) as compared to age-matched hypertensive controls. A diet containing 10% fish oil decreased blood pressure by about 40 mmHg within 20 days of starting the experiment, and this effect persisted over the observation period of 80 days. Permitting the animals free access to food, the body weight of the diet group increased by 25%. The degree of hypertrophy as evaluated by relating left ventricular weight to tibial length was significantly reduced (10%) in the diet fed group. Heart rate was increased by 53%. The study demonstrates that a diet rich in fish oil can lower arterial blood pressure over several weeks without a recognizable loss in function despite a considerable increase in body weight. It can be assumed that a more marked regression of left ventricular hypertrophy is counteracted by a reflex increase in sympathetic efferentation to the heart.     

Effect of short-term administration of vasopressin on arterial pressure and norepinephrine turnover in Long-Evans rats

Vasopressin (AVP) in acute experiments has been shown to influence cardiovascular reflexes, but the effect of a more prolonged administration of AVP on the sympathetic nervous system has not been investigated. Long-Evans rats were treated for 7 days with AVP (Pitressin tannate in oil, with single daily doses of 100 or 500 mU.100 g-1, s.c.) to determine whether AVP alters norepinephrine (NE) turnover in kidney, intestine, or skeletal muscle. Control rats were given equal doses of peanut oil daily. NE turnover was determined by measuring the decline in tissue levels of NE for 8 h after inhibition of tyrosine hydroxylase with alpha-methyl-p-tyrosine (300 mg.kg-1, i.p. every 4 h). Measurements of water intake, urine output, and urine osmolality showed that chronic administration of the high dose, but not the low dose, of AVP produced maintained increases in urine osmolality and decreases in water intake and urine output. Body weight, plasma osmolality, plasma electrolytes, and hematocrit were not significantly altered by AVP treatment, but mean arterial pressure was elevated significantly (control, 105 +/- 3 mmHg versus AVP, 119 +/- 4 mmHg, p less than 0.05) (1 mmHg = 133.3 Pa) in the high dose group. Plasma renin activity was decreased slightly, but significantly in rats treated with the high dose of AVP. Compared with results in control animals, there were no statistically significant changes in NE turnover after chronic administration of either the low or the high dose of AVP. The results indicate that administration of AVP for 7 days to rats in normal fluid balance does not result in a decrease in NE turnover in peripheral organs.     

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.     

Cell division in kidneys of rats fed a potassium-deficient diet

Mitoses is stimulated in the kidneys of adult rats fed a potassium-deficient diet. A statistically significant increase in mitotic figures appears first in the collecting ducts of the inner strip of the outer medulla after two days on the K+ deficient diet (P less than 0.05). After six days, mitosis also increases in the collecting ducts in the outer stripe and in the inner medulla (P less than 0.01). After eight days there is a significant rise in mitotic activity in the cells of the proximal convoluted tubule (P less than 0.01). There is a questionable increase in mitosis found only on the fifth day in the distal convoluted tubule. In all other cell types there is no statistically significant increase in cell division over the normal low levels that are observed in the cells of the controls rats.     

Increases in plasma trans-EETs and blood pressure reduction in spontaneously hypertensive rats

Epoxyeicosatrienoic acids (EETs) are vasodilator, natriuretic, and antiinflammatory lipid mediators. Both cis- and trans-EETs are stored in phospholipids and in red blood cells (RBCs) in the circulation; the maximal velocity (V(max)) of trans-EET hydrolysis by soluble epoxide hydrolase (sEH) is threefold that of cis-EETs. Because RBCs of the spontaneously hypertensive rat (SHR) exhibit increased sEH activity, a deficiency of trans-EETs in the SHR was hypothesized to increase blood pressure (BP). This prediction was fulfilled, since sEH inhibition with cis-4-[4-(3-adamantan-1-ylureido)cyclohexyloxy]benzoic acid (AUCB; 2 mg·kg(-1)·day(-1) for 7 days) in the SHR reduced mean BP from 176 ± 8 to 153 ± 5 mmHg (P < 0.05), whereas BP in the control Wistar-Kyoto rat (WKY) was unaffected. Plasma levels of EETs in the SHR were lower than in the age-matched control WKY (16.4 ± 1.6 vs. 26.1 ± 1.8 ng/ml; P < 0.05). The decrease in BP in the SHR treated with AUCB was associated with an increase in plasma EETs, which was mostly accounted for by increasing trans-EET from 4.1 ± 0.2 to 7.9 ± 1.5 ng/ml (P < 0.05). Consistent with the effect of increased plasma trans-EETs and reduced BP in the SHR, the 14,15-trans-EET was more potent (ED(50) 10(-10) M; maximum dilation 59 ± 15 μm) than the cis-isomer (ED(50) 10(-9) M; maximum dilation 30 ± 11 μm) in relaxing rat preconstricted arcuate arteries. The 11,12-EET cis- and trans-isomers were equipotent dilators as were the 8,9-EET isomers. In summary, inhibition of sEH resulted in a twofold increase in plasma trans-EETs and reduced mean BP in the SHR. The greater vasodilator potency of trans- vs. cis-EETs may contribute to the antihypertensive effects of sEH inhibitors.