Effect of angiotensin-converting enzyme inhibitor on salt appetite and thirst of BALB/c mice

Arterial blood pressure and renal sodium excretion in dopamine D3 receptor knockout mice

Alterations in the dopaminergic system may contribute to the development of hypertension. Recently, it has been reported that pentobarbital-anesthetized mice with deficient dopamine D(3) receptors showed renin-dependent elevation in blood pressure. In a series of experiments, we evaluated the contribution of the dopamine D(3) receptor to the renal sodium excretion and arterial blood pressure behavior in conscious as well as anesthetized dopamine D(3) receptor knockout (-/-) mice. The blood pressure measuring study was designed as a cross-over trial to investigate the influence of different sodium loads. The animals were fed a normal salt diet (0.6% NaCl, NS) for 1 week and afterwards a low (0.2% NaCl, LS) or a high salt diet (4.6% NaCl, HS) for 2 weeks. After the third week, the animals were switched to the corresponding protocol. Systolic blood pressure in conscious (-/-) mice measured by tail-cuff plethysmography was not different from that of wild-type (+/+) animals, irrespective of the time course or the salt diet. In another experiment, challenge of an acute sodium loading per gavage in conscious D(3) receptor (-/-) and (+/+) animals on HS or NS diet did not show significant differences in renal sodium excretion between the two genotypes. Additionally, animals were fed an NS diet for 1 week and an HS diet for another week. As expected, sodium excretion significantly increased after the change from the NS to the HS diet. A slightly lower urinary sodium excretion was observed when comparing D(3) receptor (-/-) mice to their corresponding (+/+) mice, both on an HS diet. Clearance experiments with anesthetized D(3) receptor (-/-) and (+/+) mice were performed to investigate the renal sodium excretion capacity, when exposed to a moderate volume expansion (VE). Urinary sodium excretion increased in response to the VE; however, no difference were observed between the two genotypes. Taking these results together, we conclude that in the present animal model renal dopamine D(3) receptors are not significantly involved in the regulation of blood pressure associated with a deficiency in renal sodium elimination.

Role of angiotensin in body fluid homeostasis of mice: effect of losartan on water and NaCl intakes

It is known that mice injected peripherally with ANG II do not show a drinking response but that cFos immunoreactivity (ir) is induced in brain regions similar to those in rats. We now show in Crl:CD1(ICR) mice that peripheral injection of the ANG II type 1 receptor antagonist losartan was sufficient to prevent this induction of Fos-ir in the subfornical organ (SFO). Injection of ANG II into the lateral cerebral ventricle produced a robust water intake in mice and induced Fos-ir in SFO, as well as in median preoptic (MnPO) and paraventricular (PVN) nuclei. Peripheral injection of losartan blocked this drinking response and prevented the induction of Fos-ir in each of these brain regions. Hypovolemia produced by polyethylene glycol (PEG) produced a robust water intake but no evidence of sodium appetite, and it induced Fos-ir in SFO, MnPO, and PVN. Peripheral injection of losartan did not affect this drinking response. Fos-ir induced by PEG in SFO and MnPO was reduced by treatment with losartan, while that induced in the PVN was further increased by losartan. Sodium depletion with furosemide and low-sodium diet produced a strong sodium appetite and induced Fos-ir in SFO and MnPO. Treatment with losartan completely blocked the sodium appetite, as well as the induction of Fos-ir in these brain regions. These data indicate that endogenous production of ANG II and action at forebrain receptors is critically involved in depletion-related sodium appetite in mice. The absence of an effect of losartan on PEG-induced drinking suggests the critical involvement of other factor(s) such as arterial or venous baroreceptor input, and we discuss how this factor could also explain why peripheral ANG II is not dipsogenic in mice.

Sodium deficiency and salt appetite in ICR: CD1 mice

Using an outbred strain of mouse, we examined several characteristics of sodium appetite induced by depletion. We found that an appetite for 0.15 M NaCl solution was stimulated 24 h after injection of furosemide and access to a low-sodium diet, but not by low-sodium diet alone. When the duration of exposure to low-sodium diet was increased from 1 to 7 days, there was no additional effect on either the appetite or the blood plasma changes including elevated hematocrit ratio, protein and aldosterone concentrations, and plasma renin activity (PRA). Mice also showed an appetite for hypertonic (0.5 M) NaCl in solutions or in a gel matrix; the intakes of these two were comparable but the gel measurement was gravimetric so maybe more accurate. In the same study, we showed that single injections of either 10 or 40 mg/kg furosemide followed by a 24-h low-sodium diet produced similar appetites, but that 2.5 mg/kg had a submaximal effect. Lastly, we further validated the use of the gel matrix by showing in chronically depleted mice that intake was inversely related to NaCl concentration in the range 0.5-1.5 M, and that appetite was selective for sodium but not the anion with which it was paired.

Investigations on the physiological controls of water and saline intake in C57BL/6 mice

To examine the behavioral and neural control of body fluid homeostasis, water and saline intake of C57BL/6 mice was monitored under ad libitum conditions, after treatments that induce water or salt intake, and after ablation of the periventricular tissue of the anteroventral third ventricle (AV3V). Mice have nocturnal drinking that is most prevalent after the offset and before the onset of lights. When given ad libitum choice, C57BL/6 mice show no preference for saline over water at concentrations up to 0.9% NaCl and a progressive aversion to saline above that concentration. Systemic hypertonic saline, isoproterenol, and polyethylene glycol treatments are dipsogenic; however, systemic ANG II is not. Intracerebroventricular injections of both hypertonic saline and ANG II are dipsogenic, and diuretic treatment followed by a short period of sodium deprivation induces salt intake. After ablation of the AV3V, mice can be nursed to recovery from initial adipsia and, similar to rats, show chronic deficits to dipsogenic treatments. Taken together, the data indicate that mechanisms controlling thirst in response to cellular dehydration in C57BL/6 mice are similar to rats, but there are differences in the efficacy of extracellular dehydration-related mechanisms, especially for systemic ANG II, controlling thirst and salt appetite.

Role of angiotensin in body fluid homeostasis of mice: fluid intake, plasma hormones, and brain Fos

CD1 mice injected peripherally with either ANG I or ANG II failed to drink substantial amounts of water or NaCl, yet showed strong Fos immunoreactivity (ir) in subfornical organ (SFO). Mice injected with furosemide showed modest stimulation of NaCl intake either 3 or 24 h later, were hypovolemic, and showed elevated plasma renin activity (PRA). The pattern of Fos-ir in the brain after furosemide was similar to that seen after peripheral injection of ANG II. Mice became hypovolemic after subcutaneous injection of polyethylene glycol (PEG), showed large increases in PRA, aldosterone, and water intake, but did not show sodium appetite. PEG-treated mice had strong activation of SFO as well as other brain regions previously shown to be related to ANG-associated drinking in rats. ANG II appears to have a modified role in the behavioral response to fluid loss in mice compared with rats.

Localization of angiotensin-converting enzyme, angiotensin II, angiotensin II receptor subtypes, and vasopressin in the mouse hypothalamus

The hypothalamic angiotensin II (Ang II) system plays an important role in pituitary hormone release. Little is known about this system in the mouse brain. We studied the distribution of angiotensin-converting-enzyme (ACE), Ang II, Ang II receptor subtypes, and vasopressin in the hypothalamus of adult male mice. Autoradiography of binding of the ACE inhibitor [125I]351A revealed low levels of ACE throughout the hypothalamus. Ang II- and vasopressin-immunoreactive neurons and fibers were detected in the paraventricular, accessory magnocellulary, and supraoptic nuclei, in the retrochiasmatic part of the supraoptic nucleus and in the median eminence. Autoradiography of Ang II receptors was performed using [125I]Sar1-Ang II binding. Ang II receptors were present in the paraventricular, suprachiasmatic, arcuate and dorsomedial nuclei, and in the median eminence. In all areas [125I]Sar1-Ang II binding was displaced by the AT1 receptor antagonist losartan, indicating the presence of AT1 receptors. In the paraventricular nucleus [125I]Sar1-Ang II binding was displaced by Ang II (Ki = 7.6 X 10(-9)) and losartan (Ki = 1.4 X 10(-7)) but also by the AT2 receptor ligand PD 123319 (Ki = 5.0 X 10(-7)). In addition, a low amount of AT2 receptor binding was detected in the paraventricular nucleus using [125I]CGP42112 as radioligand, and the binding was displaced by Ang II (Ki = 2.4 X 10(-9)), CGP42112 (Ki = 7.9 x 10(-10)), and PD123319 (Ki = 2.2 x 10(-7)). ACE, Ang II, and AT1 as well as AT2 receptor subtypes are present in the mouse hypothalamus. Our data are the basis for further studies on the mouse brain Ang II system.