Antagonism of clonidine injected intracerebroventricularly in different models of salt intake

Clonidine, and alpha2-adrenergic agonist, injected into the brain inhibits salt intake of animals treated by the diuretic model of sodium depletion. In the present study, we address the question of whether central injection of clonidine also inhibits salt intake in animals deprived of water or in the need-free state. Saline or clonidine (30 nmol) was injected into the anterior third ventricle of 24-h sodium-depleted (furosemide + removal of ambient sodium), of 24-h water-deprived and of normovolemic (need-free state) adult male rats. Clonidine injected intracerebroventricularly (icv) inhibited the 1.5 per cent NaCl intake for 120 min by 50 to 90 per cent in every model tested. Therefore, different models of salt intake are inhibited by icv injection of clonidine. Idazoxan, an alpha2-adrenergic antagonist, injected icv at a dose of 160 nmol, inhibited the effect of clonidine only in the furosemide + removal of ambient sodium model of salt intake. This indicates that the antagonism of this effect by idazoxan is dependent on the body fluid/sodium status of the animal.

Central interaction between atrial natriuretic peptide and angiotensin II in the control of sodium intake and excretion in female rats

We investigated the effects of estrogen on sodium intake and excretion induced by angiotestin II (ANG II), atrial natriuretic peptide (ANP) or ANG II plus ANP injected into median preoptic nucleus MnPO). Female Holtzman rats weighing 250-300 g were used. Sodium ingestion and excretion 120 min after the injection of 0.5 mul of 0.15 M NaCl into the MnPO were 0.3 + 7 muEq in intact rats, 0.5 + 0.2 ml (N = 10) and 27 + 6 muEq in ovariectmized rats, and 0.2 + 0.08 (N = 11) and 36 + 8 muEq in estrogen-treated ovariectomized (50 mug/day for 21 days) rats, respectively. ANG II (21 muM) injection in intact, ovariectomized, and estrogen-treated ovariectomized rats increased sodium intake (3.8 + 0.4, 1.8 + 0.3 and 1.2 + 0.2 ml/120 min, respectively) (N = 11) and increased sodium excretion (166 + 18,82 + 22 and 86 + 22 and 86 + 12 muEq/120 min, respectively (N = 11). ANP (65 muM) injection in intact (N = 11), ovariectomized (N = 10) and estrogen-treated ovariectomized (N = 10) rats increased sodium intake (1.4 + 0.2, 1.8 + 0.3, and 1.7 + 0.3 ml/120 min, respectively) and sodium excretion (178 + 19, 187 + 9, and 232 + 29 muEq/120 min, respectively). Concomitant injection of ANG II and ANP into the MnPO of intact (N = 12), ovariectomized (N = 10) and estrogentreated ovariectomized (N = 10) rats caused smaller effects than those produced by each peptide given alone: 1.3 + 0.2, 0.9 + 0.2 and 0.3 + 0.1 ml/120 min for sodium intake, respectively, and 86 + 9,58 + 7, and 22 + 4 muEq/120 min for sodium excretion, respectively. Taken together, these results demonstrate that there is an antagonistic interaction of ANP and ANG II on sodium intake and excretion, and that reproductive hormones affect this interaction.

Paraventricular nucleus administration of DuP753 or PD123319 inhibits the effects of angiotensin on water and sodium intake

We determined the effects of DuP753 and PD123319 (both nonpeptides and selective antagonists of the AT1 and AT2 angiotensin receptors, respectively), and [Sar(l), Ala(8)]ANG II (a non-selective peptide antagonist of angiotensin receptors)on water and 3 per cent NaCl intake induced by administration of angiotensin II (ANG II) into the paraventricular nucleus (PVN) of sodium-depleted Holtzman rats weighing 250-300 g. Twenty hours before the experiments, the rats were depleted of sodium using furosemide (10 ng/rat, sc). The volume of drug solution injected was 0.5 mul over a period of 10-15 sec. Water and sodium intake were measured at 0.25, 0.5, 1.0 and 2.0 h. Pre-treatment with DuP753 (l4 rats) at a dose of 60 ng completely abolished the water intake induced by injection of 12 ng of ANG II (15 rats) (6.4 ñ 0.6 vs 1.4 ñ 0.3 ml/2 h), whereas [Sar(l), Ala(8)]ANG II (l2 rats) and PDl23319 (10 rats) at the doses of 60 ng partially blocked water intake (6.4 ñ 0.6 vs 2.9 ñ 0.5 and 2.7 ñ 0.2 ml/2 h, respectively). In the same animals, [Sar(l), Ala(8)]ANG II, DuP753, and PDl23319 blocked the sodium intake induced by ANG II (9.2 ñ 1.6 vs 3.3 ñ 0.6, 1.8 ñ 0.3, and 1.4 ñ 0.2 ml/2 h, respectively). These results indicate that both DuP753 and PD123319, administered into the PVN, blocked the water and sodium intake induced by administration of ANG II into the same site.

Effect of intracerebroventricular injection of ramipril on the drinking response caused by injection of noradrenaline into the third ventricle

We studied the effect of ramipril injected into the third ventricle (3rdV) on the control of water intake induced by injection of noradrenaline into the 3rdV of adult male Holtzman rats (250-300 g) implanted with a chronic stainless steel cannula into the 3rdV. The injection volume was always 1mul and was injected over a period of 30-60 sec. Control animals were injected with 0.15 M NaCl. After the injection of isotonic saline (control, O.15 M NaCl) into the 3rdV, water ingestion was 0.3 ñ 0.1 ml/h. Ramipril(l mug/mul)injected into the 3rdV prior to isotonic saline produced no changes in water ingestion (0.4 ñ 0.2 ml/h). The injection of noradrenaline (40 nmol/mul) after isotonic saline induced an increase in water intake (3.0 ñ 1.1 ml/h). The prior injection of ramipril decreased this ingestion to 1.8 + 0.3 ml/ h. These data show that the inhibition of converting enzyme in the brain reduces the water intake induced by catecholaminergic stimulation. We conclude that the brain is able to transform the prodrug ramipril into the active drug ramiprilat.

Inhibitory effect of DUP-753 on the drinking responses of rats to central administration of noradrenaline and angiotensin II and to dehydration

We investigated the effect of losartan (DUP-753) on the dipsogenic responses produced by intracerebroventricular (icv) injection of noradrenaline (40 nmol/mul) and angiotensin II (ANG II (2 ng/mul) in male Holtzman rats weighing 250-300g. The effect of DUP-753 was also studied in animals submitted to water deprivation for 30 h. After control injections of isotonic saline (0.15 M NaCl, 1 mul) into the lateral ventricle (LV) the water intake was 0.2 ñ 0.01 ml/h. DUP-753 (50 nmol/mul) when injected alone into the LV of satiated animals had no significant effect on drinking (0.4 ñ 0.02 ml/h) (N = 8). DUP-753 (50 nmol/mul) injected into the LV prior to noradrenaline reduced the water intake from 2.4 ñ 0.8 to 0.8 ñ 0.2 ml/h (N = 8). The water intake induced by injection of ANG II and water deprivation was also reduced from 9.2+ 1.4 and 12.7 ñ 1.4 ml/h to 0.8 ñ 0.2 and 1.7 ñ 0.3 ml/h (N = 6 and N=8), respectively. These data indicate a correlation between noradrenergic pathways and angiotensinergic receptors and lead us to conclude that noradrenaline-induced water intake may be due to the release of ANG II by the brain. The finding that water intake was reduced by DUP-753 in water-deprived animals suggests that dehydration releases ANG II and, that AT1 receptors of the brain play an important role in the regulation of water intake induced by deprivation.

Losartan (DUP-753) blocks the natriuretic, kaliuretic and antidiuretic effect of intracerebroventricular injection of carbachol in water-loaded rats

We determined the effect of intracerebroventricular (icv) administration of losartan, an angiotensin II NG II), subtype I receptor (AT1) antagonist, on icv carbachol-induced natriuresis, kaliuresis and antidiuresis in water-loaded male Holtzman rats (250-300 g) with a cannula implanted into the lateral ventricle (LV). The rats were water loaded with 5 per cent of their body weight by gavage twice, with the second gavage one hour after the first. Carbachol (2 nmol in mul) was injected icv immediately after the second load. When losartan (DUP753, 50 nmol in 1 mul) was administered icv, it was given 3 min before carbachol. Previous icv treatment with losartan significantly reduced the icv carbachol-induced natriuresis (324 ñ 17 muEq/120 min), kaliuresis (103ñ15muEq /120min) and antidiuresis(13.5ñ2.1 ml/120 min) compared to the effects of previous icv injection of saline (Na+ excretion = 498 ñ 22 muEq/120 min; K+ excretion = 167 ñ 20 muEq/120 min; urine volume = 5.2 ñ 1.2 ml/l20 min). These results, reported as means ñ SEM for 12 rats in each group, are consistent with the hypothesis that AT1 subtype receptors participate in the regulation of body electrolyte balance.

Effect of a non-peptide angiotensin receptor antagonist on water intake caused by centrally administered carbachol on the rat

Angiotensin II (ANG II) administered centrally produces drinking by acting on subtype 1 ANG II (AT1) receptors. Carbachol, a cholinergic receptor agonist, also induces drinking behavior by a central action. In the present study we determined whether the response to carbachol also involves AT1 receptors. Male Holtzman rats (250-300 g) with stainless steel cannula implanted into the lateral ventricle (LV) were used. Water intake after injection of 0. 15 M NaCl (1.0 microL) into the LV was 0.2 +/- 0.01 ml/h (N = 8). The AT1 receptor antagonist DUP-753 (50 nmol/microL) injected into the LV reduced water intake induced by ANG H (10 nmol/microL) from 9.2 +/- 1.4 to 0.4 +/- 0.1 ml/h (N = 8), and water intake induced by carbachol (2 nmol/microL) from 9.8 +/- 1.4 ml/h to 3.7 +/- 0.8 ml/h (N = 8). These results suggest that AT1 receptors play a role in the drinking behavior observed after central cholinergic stimulation in rats.

The role of angiotensin AT1 receptors in the diuretic, natriuretic, kaliuretic and blood pressure responses induced by angiotensin II activation of the median preoptic nucleus in conscious rats

We determined the effects of two classical angiotensin II (ANG II) antagonists, [Sar1, Ala8]-ANG II and [Sar1, Thr8]-ANG II, and losartan (a nonpeptide and selective antagonist for the AT1 angiotensin receptors) on diuresis, natriuresis, kaliuresis and arterial blood pressure induced by ANG II administration into the median preoptic nucleus (MnPO) of male Holtzman rats weighing 250-300 g. Urine was colected in rats submitted to a water load (5 percent body weight) by gastric gavage, followed by a second water load (5 percent body weight) 1 h later. The volume of the drug solutions injected was 0.5 µl over 10-15 s. Pre-treatment with [Sar1, Ala8]-ANG II (12 rats) and [Sar1, Thr8]-ANG II (9 rats), at the dose of 60 ng reduced (13.7 +/- 1.0 vs 11.0 +/- 1.0 +/- 1.2, respectively), whereas losartam (14 rats) at the dose of 160 ng totally blocked (13.7 +/- 1.0 vs.7.6 +/- 1.5) the urine excretion induced by injection of 12 ng of ANG II (14 rats)...

Progesterone administration to ovariectomized rats reduces water and salt intake induced by central administration of angiotensin II

We tested the effects of estradiol, progesterone and testosterone on water and salt intake induced by angiotensin II (ANG II) injected into the third ventricle of female Holtzman rats weighing 250-300 g. The water and salt ingestion observed after 120 min in the control experiments (injection of 0.5µl of 0.15 M NaCl into the third ventricle) was 1.6 ñ 0.3 ml (N = 10) and 0,3 ñ 0.1 ml (N = 8) in intact rats, respectively, and 1.4 ñ 0.3 ml (N = 10) and 0.2 ñ 0.1 (N = 8) in ovariectomized rats, respectively. ANG II injected in intact rats (4, 6, 12, 25, and 50 ng, icv, in 0,5 µl saline) induced an increase in water intake (4.3 ñ 0.6, 5.4 ñ 0.7, 7.8 ñ 0.8, 10.4 ñ 1.2, 11.2 ñ 1.4 ml/120 min, respectively) ( N = 43). The same doses of icv ANG II in intact increased the 3 per cent NaCl intake (0.9 ñ 0,2, 1.4 ñ 0,3, 2,3 ñ 0.4, 2,2 ñ 0,3, and 2.5 ñ 0.4 ml/120 min, respectively) (N = 42). When administered to ovariectomized rats ANG II induced comparable amounts of water intake (4.0 ñ 0.5, 4.8 ñ 0.6 ñ 0.7, 9.6 ñ 0.8, and 10.9 ñ 1.2 ml/120 min, respectively (

Alpha-adrenergic pathways in the lateral hypothalamus are important for the dipsogenic effect of carbachol injected into the medial septal area

We studied the effect of the Ó1-and Ó2-adrenergic receptors of the lateral hypothalamus (LH) on the control of water intake induced by injection of carbachol into the medial septal area (MSA) of adult male Holtzman rats (250-300g) implanted with chronic stainless steel cannulae into the LH and MSA. The volume of injection was always 1 µl and was injected over a period of 30-60 s. For control, 0.15MNaCl was used. Clonidine (20 nmol) but not phenylephrine (160 nmol) injected into the LH inhibited water intake induced by injection of carbachol (2 nmol) into the MSA, from 5.4 ñ 1.2ml/h to 0.3 ñ 0.1 and 3.0 ñ 0.9 ml/h, respectively (N=26). When we injected yohimbine (80nmol) + clonidine (20nmol) and prazosin (40nmol) + clonidine (20nmol) into the LH, water intake induced by injection of carbachol into the MSA was inhibited from 5.4 ñ 1.2 ml/h to 0.8 ñ 0.5 and 0.3 ñ 0.2 ml/h, respectively (N=19). Water intake induced by carbachol (2nmol) injected into the MSA was decreased by previous injection of yohimbine (80 nmol) + phenylephrine (160 nmol) and prazosin (40 nmol) + phenylephrine (160 nmol) from 5.4 ñ 1.2ml/h to 1.0 ñ 0.7 and 1.8 ml/h, respectively (N = 16). The cannula reached both the medial septal area in its medial portion and the lateral hypothalamus. It has been suggested that the different pathways for induction of drinking converge on a final common pathway. Thus, adrenergic stimulation of Ó2-adrenoceptors of LH can influence this final common pathway

Effect of electrolytic and chemical lesion by ibotenic acid of the amygdala on salt intake

Sodium chloride intake was studied in male Holtzman rats weighing 250-300 g submitted to electrolytic and chemical lesion of the cell bodies, not fibers of the amygdaloid complex. Sodium chloride (1.5 percent) intake increased in animals with electrolytic lesion of the corticomedial nucleus of the amygdala. Sodium chloride (1.5 percent) intake increased after ibotenic acid injection into the corticomedial nucleus of the amygdala to a larger extent (26.6 + or - 9.2 to 147.6 + or - 34.6 ml/5 days). The results indicate that sodium inake response can be induced by lesions, which involved only cell bodies. The fibers of passage of the corticomedial nucleus of the amygdala produce a water intake less consistent than that induced by ibotenic acid, which is more acute. The results show that cell bodies of this region of the amygdala are involved in the control of sodium chloride intake

Injection of ramipril into the lateral ventricle interferes with the drinking response induced by pharmacological and natural thirst stimuli

We investigated the effects of ramipril, an angiotensin I-converting enzyme (ACE) inhibitor, on water intake by male Holtzman rats (250-300 g) with cannulae implanted into the lateral ventricle. Intracerebroventricular (icv) injection of ramipril (1 µg/µl) significantly reduced drinking in response to subcutaneous (sc) injection of isoprenaline (100 µg/kg) from 8.49 + or - 0.69 to 2.96 + or - 0.36 ml/2 h, polyenthyleneglycol (PEG) (30 percent w/v, 10 ml/kg) from 9.51 + or - 2.20 to 1.6 + - 0.34 ml/2 h or water deprivation for 24 h from 12.61 + or - 0.83 to 5.10 + or - 1.37 ml/2 h. Ramipril had no effect on water intake induced by cellular dehydration produced by sc injection of hypertonic saline (2 M NaCl). These results are consistent with the hypothesis that ramipril acts as an ACE-blocking agent in the brain. The possibility that ramipril is transformed to ramiprilat, the active drug, by the brain is suggested

Different effects on rat arterial pressure and heart rate when losartan is injected into the third or fourth ventricle

Carciovascular responses to central losartan (LOS), a non-peptide angiotensin II (ANG II) receptor antagonist, were investigated by comparing the effects of LOS injection into the 3rd and 4th cerebral ventricles (3rdV, 4thV) on mean arterial pressure (MAP) and heart rate (HR). Adult male Holtzman rats were used (N = 6 animals per group). Average basal MAP and HR were 114 + or - 3 mmHg and 343 + or - 9 bpm (N = 23), respectively. LOS (50, 100 or 200 nmol/2 µl) injected into the 3rdV induced pressor (peak of 25 + or - 3 mmHg) and tachycardic (peak of 60 + or - 25 bpm) responses. LOS injected into the 4thV had no effect on MAP, but it induced bradycardia (peak of -35 + or - 15 bpm). KCl (200 nmol/2 µl) injected into the 3rdV or into the 4thV had no effect on either MAP or HR compared to 0.9 percent saline injection. The results indicate that LOS injected into the third ventricle acts on forebrain structures to induce its pressor and tachycardic effects and that bradycardia, likely dependent on hindbrain structures, is obtained when LOS is injected into the fourth ventricle

Effect of cholinergic stimulation of the amygdaloid complex on water and salt intake

The effect of carbachol (80 nmol/microliters) injection into the amygdaloid nuclear complex (AMG) on sodium appetite and water intake was studied in male Holtzman rats weighing 240-270 g. Twenty-five satiated rats and 38 water-deprived rats were used in the experiment on water intake. In the experiment on sodium intake, 19 rats were injected with atropine+carbachol and 9 rats with hexamethonium+carbachol. After carbachol injection into the AMG, water intake decreased in rats submitted to 30 h of water deprivation (10.28 +/- 1.04 ml/120 min vs 0.69 +/- 0.22 ml/120 min). The decrease in water intake was blocked by prior local injection of atropine (20 nmol/l microliters) (11.66 +/- 1.46 ml/120 min vs 0.69 +/- 0.22 ml/120 min), but not of hexamethonium (30 nmol/1 microliters), into the AMG. In water-deprived animals, carbachol injection into the AMG caused a decrease in sodium chloride intake (6.16 +/- 1.82 ml/h vs 0.88 +/- 0.54 ml/h) which was blocked by previous injection of hexamethonium but not of atropine. These results suggest that the cholinergic system of the AMG plays a role in the control of water and salt intake.

On a possible dual role for central noradrenaline in the control of hydromineral fluid intake

1. Noradrenaline (NOR) is a neurotransmitter present in the central nervous system which is related to the control of ingestive behavior of food and fluids. We describe here the relationship between NOR and intake of water and NaCl solution, fluids that are essential for a normal body fluid-electrolytic balance. 2. Central NOR has an inhibitory effect on fluid intake, but it either induces or not alterations in food intake. Several ways of inducing water intake, such as water deprivation, meal-associated water intake, administration of angiotensinergic, cholinergic or beta-adrenergic agonists, or administration of hyperosmotic solutions, are inhibited by alpha-adrenergic agonists. Need-induced sodium intake by sodium-depleted animals is also inhibited by alpha-adrenergic agonists. 3. NOR can also facilitate fluid intake. Water intake is elicited by NOR and the integrity of central noradrenergic systems is necessary for a normal expression of water or salt intake in dehydrated animals. The angiotensinergic component of either behavior apparently depends on a central noradrenergic system. NOR probably facilitates fluid intake by acting on postsynaptic receptors, but we do not know how it inhibits fluid intake. 4. The inhibitory and facilitatory effects of NOR on ingestive behavior suggest a dual role for this neurotransmitter in the control of hydromineral fluid intake.

Central angiotensin converting enzyme-blockade and thirst

1. The effect of lisinopril, a potent inhibitor of angiotensin converting enzyme (ACE), injected into the medial preoptic area (MPOA) on water intake was investigated in male Holtzman rats (200-250 g). 2. Injection of lisinopril (2 micrograms/microliters) into the MPOA abolished the water intake induced by subcutaneous (sc) injection of isoprenaline (100 per cent ) and water deprivation (90 per cent ) and drastically reduced the water intake induced by sc injection of polyethyleneglycol (60 per cent ). A small reduction of water intake induced by lisinopril was also observed 90 and 120 min after sc hypertonic saline (N = 10 for each group). 3. These results suggest that central ACE activation, particularly in the MPOA, plays an important role in the dipsogenic responses induced by the agents studied

Lesions of the lateral hypothalamus impair the pressor response to clonidine injected into the medial septal area of conscious rats

The central injection of clonidine (an alpha2-adrenoceptor agonist) in conscious normotensive rats produces hypertensive responses and breadycardia. The present study performed was performed to investigate the effect of electrolytic lesions of the lateral hypothalamus (LH) on the pressor and bradycardiac responses induced by clonidine injected into the medial septal area (MSA) in conscious and unrestrained rats. Male Holtzman rats weighing 250-300 g were used. Mean arterial pressure and heart rate were recorded in sham- or bilateral LH-lesioned rats with a cerebral stainless steel cannula implanted into the MSA. The injection of clonidine (40 nmol/ul) into the MSDA of sham rats (N=8) produced a pressor response (36 ñ 7 mmHg, P<0.05) and bradycardia (-70 ñ 13 bpmm, P<0.05) compared to saline. Fourteen days after LH-lesion (N=9) the pressor response was reduced (9 ñ 10 mmHg, P<0.05) but no change was observed in the bradycardia (-107 ñ 24 bpm). These results show that LH is an important area involved in the pressor response to clonidine injected into the MSA of rats

The effect of phentolamine on the pressor reponse to centrallly administered clonidine in rats

In the present study we investigae the effect of the previous injection of phentolamine (anonspecific alfa-adrenergic antagonist) into the lateral hypothalamus (LH) and lateral ventricle (LV) on the pressor and bradycardic responses produced by the injection of clonidine (an alfa-2 adrenergic agonist) into these same areas of conscious rats. The injections of clonidine into the LH produced pressor (39 ñ 5 and 38 ñ 3 mmHg, respectively) and bradycardic responses (-65 ñ 16 and -94 ñ 13 bpm, respectively). Previous injections of phentalamine into the LH or LV reduced the pressor response to clonidine injected into the same areas (DeltaMAP = 13 ñ 6 mmHg for LH and 1 ñ 3 mmHg for LV). No reduction was observed when clonidine was injected into the LV after the injection of phentalamine into the LH. No changes in bradycardic responses were observed after treatment with phentolamine. The present results show the participation of alfa-adrenergic receptors in the pressor response to centrally administered clonidine but not in the bradycardic reponse. The data also suggest that the pressor effect by the injection of clonidine into the LH is due to the activation of alfa-adrenergic receptors located specifically in this area. The pressor response after injection of clonidine into the LV and of phentolamine into the LH is due to the action of clonidine on other cerebral areas

Effect of dehydration on the increase of arterial pressure and renal electrolyte excretion produced by central cholinergic stimulation in rats

Natriuresis, kaliuresis, diuresis, arterial pressure and heart rate were studied in rats following dehydration and cholinergic stimulation of the medial septal area (MSA). The increase in renal NA+ and K+ excretion produced by the injection of carbachol (2nmol) into the MSA in normal hydrated rats was abolished in 48-h water-deprived rats. Urinary volume was also reduced. Cholinergic stimulation of the MSA produced a smaller mincrease in arterial pressure in 48-h-deprived rats compared to normal hydrated animals. No change was observed in heart rate. These reults show that hydration state is essential for the central cholinergic control of electrolyte excretion and increase in arterial pressure

Interaction between cholinergic and opiate receptors of the lateral hypothalamus in the control of renal excretion in rats

The present study was carried out to investigate the participation and interaction between cholinergic and opiate receptors of the lateral hypothalamus (LH) in the regulation of Na+, K+ and water excretion. Malew Holtzman rats were implanted with chronic cerebral cannulas into the LH. Urine was collected over a period of 2h after injection of carbachol, FK-33824 + carbachol or naloxone + carbachol into the LH. Carbachol (8nmol) reduced urinary volume and increased Na + excretion. Previous injection of FK-333824(100ng) into the LH increased the antidiuretic effect of carbachol, but blocked the increase in Na+ excretion and decreased K+ excretion. Naloxone. Naloxone (10microng) produced no changes in the effect of carbacho9l on renal excretion. These data show an inhibitory effect of opiate receptors on the changes in urinary Na+ and K+ excretion that are induced by chronergic stimulation of the LH in rats, and a potentiating effect on antidiuresis