The mechanism of relaxation in response to magnesium by the aorta of pregnant rats with salt-induced hypertension

Vascular Response to Graded Angiotensin II Infusion in Offspring Subjected to High-Salt Drinking Water during Pregnancy: The Effect of Blood Pressure, Heart Rate, Urine Output, Endothelial Permeability, and Gender

Introduction. Rennin-angiotensin system and salt diet play important roles in blood pressure control. We hypothesized that the high-salt intake during pregnancy influences the degree of angiotensin-dependent control of the blood pressure in adult offspring. Methods. Female Wistar rats in two groups (A and B) were subjected to drink tap and salt water, respectively, during pregnancy. The offspring were divided into four groups as male and female offspring from group A (groups 1 and 2) and from group B (groups 3 and 4). In anesthetized matured offspring mean arterial pressure (MAP), heart rate and urine output were measured in response to angiotensin II (AngII) (0-1000 ng/kg/min, iv) infusion. Results. An increase in MAP was detected in mothers with salt drinking water (P < 0.05). The body weight increased and kidney weight decreased significantly in male offspring from group 3 in comparison to group 1 (P < 0.05). MAP and urine volume in response to AngII infusion increased in group 3 (P < 0.05). These findings were not observed in female rats. Conclusion. Salt overloading during pregnancy had long-term effects on kidney weight and increased sex-dependent response to AngII infusion in offspring (adult) that may reveal the important role of diet during pregnancy in AngII receptors.

Orchidectomy attenuates impaired endothelial effects of a high-salt diet in Sprague–Dawley rats

The effect of sex hormones on vascular reactivity is considered one of the underlying factors contributing to gender differences in cardiovascular functions and diseases. Experiments were designed to investigate the role of androgens in salt-induced hypertension by assessing the relaxation response of isolated aortic rings to acetylcholine and sodium nitroprusside in the presence or absence of l-nitroarginine methyl ester in Sprague–Dawley rats. The rats were either orchidectomized or sham-operated, with or without testosterone replacement, and were placed on a normal or high-salt diet for 6 weeks. The results indicate a significant increase (p < 0.001) in the mean arterial blood pressure of rats on the high-salt diet, when compared with control or orchidectomized rats. Orchidectomy elicited a reduction in mean arterial blood pressure (p < 0.01), while testosterone replacement normalized mean arterial blood pressure to values seen in intact rats on the high-salt diet. The high-salt diet reduced the relaxation response to acetylcholine both in the presence and absence of inhibition of endothelial nitric oxide synthase with l-nitroarginine methyl ester. Bilateral orchidectomy attenuated the impaired endothelial function induced by the high-salt diet in rats, but this was reversed by concomitant administration of testosterone, suggesting a role for androgens in enhancing long-term vascular smooth muscle tone and hence maintenance of high blood pressure in salt-induced hypertension.

Modulation of renal CNG-A3 sodium channel in rats subjected to low- and high-sodium diets

In this work, we studied the mRNA distribution of CNG-A3, an amiloride-sensitive sodium channel that belongs to the cyclic nucleotide-gated (CNG) family of channels, along the rat nephron. The possible involvement of aldosterone in this process was also studied. We also evaluated its expression in rats subjected to diets with different concentrations of sodium or to alterations in aldosterone plasma levels. Total RNA isolated from whole kidney and/or dissected nephron segments of Wistar rats subjected to low- and high-sodium diets, furosemide treatment, adrenalectomy, and adrenalectomy with replacement by aldosterone were analyzed by the use of Western blot, ribonuclease protection assay (RPA) and/or reverse transcription followed by semi-quantitative polymerase chain reaction (RT-PCR). CNG-A3 sodium channel mRNA and protein expression, in whole kidneys of rats subjected to high-Na+ diet, were lower than those in animals given a low-salt diet. Renal CNG-A3 mRNA expression was also decreased in adrenalectomized rats, and was normalized by aldosterone replacement. Moreover, a CNG-A3 mRNA expression study in different nephron segments revealed that aldosterone modulation is present in the cortical thick ascending loop (cTAL) and cortical collecting duct (CCD). This result suggests that CNG-A3 is responsive to the same hormone signaling as the amiloride sensitive sodium channel ENaC and suggests the CNG-A3 may have a physiological role in sodium reabsorption.

High-salt diet and responses of the pressurized mesenteric artery of the dog to noradrenaline and acetylcholine

A high-salt diet in rats has been shown to result in enhanced vasoconstrictor and/or reduced vasodilator responses of isolated arteries to agonists. The present experiments were designed to investigate the effects of dietary salt on the responses of the pressurized mesenteric resistance artery of the dog to constrictor and dilator agents. Dogs were fed diets containing three different levels of salt with sodium concentrations (in mmol/kg per day) of 0.4 (low salt; LS), 3.0 (intermediate salt; IS) and 6.0 (high salt; HS) for a period of 4 weeks. At the end of the feeding period, animals were killed and lengths of third-order mesenteric artery were obtained and mounted in a perfusion myograph and changes in internal diameter were measured using a microscope and video-tracking device. The responses to noradrenaline (NA), acetylcholine (ACh) and sodium nitroprusside (SNP) were then determined. The vasoconstrictor responses to NA were identical in the three groups. However, the relaxation response of the vessels to ACh was attenuated in HS dogs compared with LS dogs (P < 0.05), but not with IS dogs. The application of N(G)-nitro-l-arginine methyl ester, an inhibitor of nitric oxide synthase, reduced the relaxation responses to ACh comparably in all three groups. The relaxation responses of the vessels to SNP were similar in all groups. These results indicate that, in the dog mesenteric resistance artery, a high-salt diet does not affect vasoconstrictor responses to NA, but does attenuate the vasorelaxant action of ACh, largely by inhibiting the production of endothelium-derived relaxing factor.

Management of autonomic hyperreflexia with magnesium sulfate during labor in a woman with spinal cord injury

Autonomic hyperreflexia, one of the gravest complications of delivery among women with spinal cord injury, has been treated with spinal or epidural anesthesia but not always successfully. We discovered dramatically beneficial effects of magnesium sulfate on autonomic hyperreflexia during labor in a patient with spinal cord injury at a high level.

Rat aorta and mesenteric artery respond differently to serotonin

The sensitivity (EC50) of the ring segment of the mesenteric artery to serotonin (4.84 +/- 0.53 x 10(-7) mol.l-1) was 17x greater than that of the aortic ring segment (5.29 +/- 0.46 x 10(-6) mol.l-1). Incubation of the ring segments in physiological salt solution (PSS) containing methylene blue greatly potentiated the sensitivity of both the aorta and mesenteric artery to serotonin. The degree of potentiation was higher in the aorta than mesenteric artery. L-NAME also increased the sensitivity of both the aorta and mesenteric artery to serotonin and there was no difference in the degree of potentiation of the responses between the aorta and the mesenteric artery. Indomethacin inhibited the contractile responses of the aorta and the mesenteric artery to serotonin. Phenoxybenzamine reduced the contractile responses of both the aorta and the mesenteric artery by the same magnitude. Captopril (10(-4) mol.l-1) significantly attenuated the responses of the mesenteric artery more than the aorta, while methysergide (10(-8) mol.l-1) completely abolished the difference in the responses (EC50 for aorta = 3.50 +/- 0.55 x 10(-5) mol.l-1 vs 5.00 +/- 0.49 x 10(-5) mol.l-1 for mesenteric artery). This study demonstrates that rat aorta and mesenteric artery respond differently to serotonin and the differential response is due to a methylene blue sensitive factor and differences in either the receptor population or sensitivity.

Effect of dietary salt loading and high-calcium diet on vascular smooth muscle responses and endothelium function in rats

1. The present study examined the effects of concurrent manipulation of dietary calcium and salt on contractile responses of vascular smooth muscle (VSM) and endothelial function of aortic rings from Sprague-Dawley rats. 2. Salt loading enhanced the contractile response of the aortic rings to noradrenaline (NA), an effect that was blunted by a high calcium intake. 3. Removal of the endothelium and incubation of aortic rings in physiological salt solution containing methylene blue increased the sensitivity of the rings to NA. 4. The increase in the sensitivity of aortic rings induced by endothelium removal was more pronounced in aortic rings from salt-loaded rats. 5. Acetylcholine caused similar degrees of relaxation in all experimental groups, but the relaxation to histamine was smaller (P < 0.05) in salt-loaded rats than in other groups of rats; however, after removal of the endothelium, the contractile response to histamine was higher in salt-loaded rats. 6. The results indicate that the hypersensitivity of isolated aortic rings to agonists, as observed in salt-loaded rats, is due to altered responses of the VSM and not as a result of changes in the endothelium. In addition, salt loading tends to increase the synthesis of endothelium-dependent relaxing factor. The ability of salt loading to enhance the contractile responses of VSM to agonists can be prevented by supplementing the diet with high calcium.

Hypotensive and vasorelaxing activities of a lectin from the edible mushroom Tricholoma mongolicum

A lectin, which exerted a hypotensive action in rats after intravenous injection via the jugular vein, was isolated from the mycelia of the edible mushroom Tricholoma mongolicum. The lectin possessed a molecular weight of 37 K and its hypotensive activity was dose-dependent. Administration of the lectin at a dose of 10 mg/kg body weight caused a mean arterial blood pressure reduction of 95.3 +/- 7.4 mmHg. The lectin's hypotensive action was not mediated via autonomic ganglion transmission, alpha-adrenoceptors, beta-adrenoceptors, cholinergic receptors, histaminergic receptors, nor the renin-angiotensin system, but it was probably mediated through vasorelaxation via adenosine A2 receptors and/or nitric oxide production.