Clonidine and phenylephrine injected into the lateral hypothalamus inhibits water intake in rats.

It has been demonstrated that peripheral or intracerebroventricular (i.c.v.) administration of the alpha 2-adrenoceptor agonist, clonidine, blocks the water intake induced by several dipsogenic stimuli in rats. In the present investigation we studied the effect of the injection of clonidine, phenylephrine, prazosin or yohimbine into the lateral hypothalamic area (LHA) on the water intake induced by water deprivation or central angiotensin II (AII) in rats. Rats with chronic cannulas implanted into the lateral ventricle and LHA were used. Injection of clonidine or phenylephrine into the LHA reduced the water intake produced by both water deprivation and i.c.v. injection of AII. Previous injection of the alpha 1- or alpha 2-adrenoceptor antagonists, prazosin or yohimbine, into the LHA reduced the antidipsogenic effect of clonidine or phenylephrine injected into the same area. These results suggest that the alpha 1- and alpha 2-adrenergic receptors of the hypothalamus are part of the central inhibitory system for the thirst produced by dehydration or central AII.

Lesion of the anteroventral third ventricle region abolishes the beneficial effects of hypertonic saline on hemorrhagic shock in rats.

The effect of intravenous infusion of hypertonic saline (HS, 7.5% NaCl) on the recovery of mean arterial pressure (MAP) during hemorrhage was studied in sham-operated rats and in rats with electrolytic lesion in the anteroventral third ventricle (AV3V) region. After intravenous infusion of 7.5% NaCl (4 ml/kg b.wt.), MAP increased from about 60 to 90 mmHg in sham rats and became stable at this level during all the time of observation (30 min). In AV3V-lesioned rats, after the same infusion, the MAP increased to 80 mmHg, but returned to the pre-infusion levels within 30 min. These results show that the integrity of the AV3V region is important for the beneficial effect of HS during hemorrhagic shock in rats. The AV3V lesion disrupts neural pathways involved in the maintenance of fluid balance and these changes probably abolish the effect of hypertonic saline.

Lesion of the anteroventral third ventricle region impairs the recovery of arterial pressure induced by hypertonic saline in rats submitted to hemorrhagic shock.

The effect of intravenous infusion of hypertonic saline (HS, 7.5% NaCl) on the recovery of mean arterial pressure (MAP) after hemorrhage was studied in sham-operated rats and in rats with electrolytic lesion of the anteroventral third ventricle (AV3V) region (4 h, 4 and 20 days). Rats anesthetized with thiopental sodium were bled (about 2.8 ml/100 g) until the MAP was stabilized at the level of 60 mmHg for 30 min. In sham-lesioned rats, MAP increased to 90 mmHg and became stable near this level after intravenous infusion of 7.5% NaCl (4 ml/kg b.wt.). In AV3V-lesioned rats, the same infusion induced a smaller increase in MAP (80 mmHg) and the MAP returned to pre-infusion levels within 30 min. These results show that the AV3V region plays an important role in the recovery of arterial pressure induced by hypertonic saline in rats submitted to hemorrhagic shock.

AV3V lesion suppresses the pressor, dipsogenic and natriuretic responses to cholinergic activation of the septal area in rats.

In the present study we investigated the effect of anteroventral third ventricle (AV3V) lesion on pressor, dipsogenic, natriuretic and kaliuretic responses induced by the injection of carbachol (a cholinergic agonist) into the medial septal area (MSA) of rats. Male rats with sham or AV3V lesion and a stainless-steel cannula implanted into the MSA were used. Carbachol (2 nmol) injected into the MSA in sham lesion rats produced pressor (43 +/- 2 mmHg), dipsogenic (9.6 +/- 1.2 ml/h), natriuretic (531 +/- 82 microEq/120 min) and kaliuretic (164 +/- 14 microEq/120 min) responses. In AV3V-lesioned rats (1-5 days and 14-18 days), the pressor (11 +/- 2 and 14 +/- 2 mmHg, respectively), dipsogenic (1.9 +/- 0.7 and 1.4 +/- 0.6 ml/h), natriuretic (21 +/- 5 and 159 +/- 44 microEq/120 min) and kaliuretic (124 +/- 14 and 86 +/- 13 microEq/120 min) responses induced by carbachol injection into the MSA were reduced. These results show that the AV3V region is essential for the pressor, dipsogenic, natriuretic and kaliuretic responses induced by cholinergic activation of the MSA in rats.

Noradrenaline and mixed alpha 2-adrenoceptor/imidazoline-receptor ligands: effects on sodium intake.

The effect of noradrenaline, and mixed ligands to alpha 2-adrenoceptors (alpha 2-AR) and imidazoline receptors (IR), injected intracerebroventricularly (i.c.v.), on sodium intake of sodium depleted rats, was tested against idazoxan, a mixed antagonist ligand to alpha 2-AR and IR. The inhibition of sodium intake induced by noradrenaline (80 nmol) was completely reversed by idazoxan (160 and 320 nmol) injected i.c.v. The inhibition of sodium intake induced by mixed ligands to alpha 2-AR and IR, UK14,304, guanabenz and moxonidine, was antagonized from 50 to 60% by idazoxan i.c.v. The results demonstrate that noradrenaline, a non-ligand for IR, acts on alpha 2-AR inhibiting sodium intake. The possibility that either alpha 2-AR or IR mediate the effect of mixed agonists on sodium intake remains an open question.

Effects of central alpha-adrenergic agonists on hormone-induced 3% NaCl and water intake.

Male rats received intracerebroventricular (ICV) renin (600 ng) or daily subcutaneous injections of deoxycorticosterone (5 mg) to induce 3% NaCl and water intake. Noradrenaline (NOR; 40-160 nmol) and clonidine (CLO; 5-20 nmol) injected ICV induced 70 to 100% inhibition of the intakes. Phenylephrine (PHE; 40-160 nmol) injected ICV induced 60 to 95% inhibition of the intakes. NOR and PHE induced a stronger inhibition on the 3% NaCl intake induced by renin than on the intake induced by deoxycorticosterone (DOC), and CLO did the opposite. CLO was always more effective than PHE to induce inhibition of the intakes. The results suggest that NOR inhibits hormone (angiotensin II, aldosterone)-induced NaCl intake by acting mainly on alpha 2-adrenergic receptors.

Pressor, dipsogenic, natriuretic and kaliuretic response to central carbachol in rats with lesion of the medial septal area.

In the present study we investigated the effect of electrolytic lesion of the medial septal area (MSA) on the dipsogenic, natriuretic, kaliuretic and pressor responses elicited by intracerebroventricular (i.c.v.) injection of the cholinergic agonist carbachol. Freely moving rats with sham or MSA lesion (1-7 days and 14-18 days) and a stainless steel cannula implanted into the lateral ventricle were studied. In sham rats, i.c.v. injection of carbachol (7.5 nmol) produced an increase in water intake (10.2 +/- 1.5 ml/h), mean arterial pressure (MAP) (35 +/- 5 mmHg) and urinary Na+ and K+ excretion (551 +/- 83 and 170 +/- 17 muEq/120 min, resp.). The pressor (18 +/- 3 and 14 +/- 4 mmHg, resp.) and natriuretic responses (178 +/- 58 and 172 +/- 38 muEq/120 min) produced by i.c.v. carbachol in acute or chronic MSA-lesioned rats were reduced. No change was observed in urinary K+ excretion and a reduced water intake (5 +/- 1.3 ml/h) was observed only in acute MSA-lesioned rats. These results suggest that the MSA plays an important role for the pressor and natriuretic responses induced by central cholinergic activation in rats. A small influence of this structure on water intake may also be suggested.

The anteroventral third ventricle (AV3V) region is essential for pressor, dipsogenic and natriuretic responses to central carbachol.

In the present study we investigated the effect of anteroventral third ventricle (AV3V) lesion on pressor, dipsogenic and natriuretic responses produced by the intracerebroventricular (i.c.v.) injection of a cholinergic agonist (carbachol). Freely moving rats with AV3V or sham lesion (1-2 days and 9-12 days) and a delay cannula implanted into the lateral ventricle were studied. Changes in mean arterial pressure (MAP, 1 h record), water intake (1 h) and Na+ excretion (2 h) were analysed after i.c.v. injection of carbachol (7.5 nmol). In sham rats, i.c.v. injection of carbachol produced an increase in MAP (35 +/- 2 mmHg), water ingestion (7.7 +/- 1.2 ml/h) and Na+ excretion (626 +/- 42 microEq/120 min). The effects of i.c.v. carbachol injection were reduced 1-2 days after AV3V lesion (delta MAP = 6 +/- 2 mmHg, water ingestion = 0.3 +/- 0.3 ml/h and Na+ excretion = 31 +/- 11 microEq/120 min) and 9-12 days (delta MAP = 11 +/- 3 mmHg, water ingestion = 3.3 +/- 0.9 ml/h and Na+ excretion = 37 +/- 11 microEq/120 min). These results show that the AV3V region is essential for the full development of the pressor, dipsogenic and natriuretic responses produced by central cholinergic receptors.

Effect of furosemide treatment on the central and peripheral pressor responses to cholinergic and adrenergic agonists, angiotensin II, hypertonic solution and vasopressin.

The present study was performed to investigate the effect of treatment with furosemide on the pressor response induced by intracerebroventricular (i.c.v.) injections of cholinergic (carbachol) and adrenergic (norepinephrine) agonists, angiotensin II (ANGII) and hypertonic saline (HS, 2 M NaCl). The changes induced by furosemide treatment on the pressor response to intravenous (i.v.) norepinephrine, ANGII and arginine vasopressin (AVP) were also studied. Rats with a stainless-steel cannula implanted into the lateral ventricle (LV) were used. Two injections of furosemide (30 mg/kg b.wt. each) were performed 12 and 1 h before the experiments. Treatment with furosemide reduced the pressor response induced by carbachol, norepinephrine and ANGII i.c.v., but no change was observed in the pressor response to i.c.v. 2 M NaCl. The pressor response to i.v. ANGII and norepinephrine, but not AVP, was also reduced after treatment with furosemide. These results show that the treatment with furosemide impairs the pressor responses induced by central or peripheral administration of adrenergic agonist or ANGII, as well as those induced by central cholinergic activation. The results suggest that the treatment with furosemide impairs central and peripheral pressor responses mediated by sympathetic activation and ANGII, but not those produced by AVP.

Alterations in the water intake caused by central inhibition of angiotensin-converting enzyme in the rat.

In the present study we investigated the effects of central (i.c.v.) and subcutaneous (s.c.) injections of a 2 micrograms dose of lisinopryl, an inhibitor of angiotensin I(ANGI)-converting enzyme (CE), on water intake. I.c.v. but not s.c. injection of lisinopryl abolished drinking in response to s.c. isoprenaline (100 micrograms/kg) and significantly reduced drinking in response to 24 h water deprivation or s.c. polyethylene glycol (30% w/v, 10 ml/kg). Lisinopryl had no effect on water intake induced by cellular dehydration (s.c. injection of hypertonic saline (2 M NaCl)). These results are consistent with the hypothesis that lisinopryl acts as a CE blocking agent in the brain. The thrist challenge induced by hypotension using isoprenaline acts primarily by generating ANGII systemically and centrally. The other thirst challenges such as cellular dehydration are independent of the ANGII in the brain. This conclusion was made possible by utilizing a new CE blocking agent at a smaller dose than normally used for other ANG I-CE inhibitors.

Carbachol injection into the medial preoptic area induces natriuresis, kaliuresis and antidiuresis in rats.

The microinjection of carbachol into the medial preoptic area (MPO) of the rat induced natriuresis, kaliuresis and anti-diuresis in a dose-related manner. Atropine blocked all responses to carbachol. Hexamethonium impaired the dose-response effect of carbachol on kaliuresis, but had no effect on natriuresis and enhanced the antidiuretic effect of carbachol. Nicotine alone had no effects, but pre-treatment with nicotine enhanced the responses to carbachol. These data show that activity of the muscarinic receptors of the MPO increases renal electrolyte and reduces water excretion. They also suggest that nicotinic receptors have an inhibitory effect on water excretion. Nicotine could act through mechanisms unrelated to nicotinic receptors to enhance the effect of the carbachol.

Role of the adrenergic pathways of the lateral hypothalamus on water intake and pressor response induced by the cholinergic activation of the medial septal area in rats.

In the present experiments, we investigated a possible involvement of noradrenergic receptors of the lateral hypothalamus (LH) in the water intake and pressor response induced by cholinergic stimulation of the medial septal area (MSA) in rats. The cholinergic agonist carbachol (2 nmol) injected into the MSA induced water intake and pressor response. The injection of an alpha 2-adrenergic agonist, clonidine (20 and 40 nmol), but not of an alpha 1-adrenergic agonist, phenylephrine (80 and 160 nmol), into the LH inhibits the water intake induced by carbachol injected into the MSA. The injection of clonidine or phenylephrine into the LH produced no change in the MAP increase induced by carbachol injected into the MSA. The present results suggest that adrenergic pathways involving the LH are important for the water intake, but not for the pressor response, induced by cholinergic activation of the MSA.

Central muscarinic receptors signal pilocarpine-induced salivation.

Although cholinergic agonists such as pilocarpine injected peripherally can act directly on salivary glands to induce salivation, it is possible that their action in the brain may contribute to salivation. To investigate if the action in the brain is important to salivation, we injected pilocarpine intraperitoneally after blockade of central cholinergic receptors with atropine methyl bromide (atropine-mb). In male Holtzman rats with stainless steel cannulas implanted into the lateral ventricle and anesthetized with ketamine, atropine-mb (8 and 16 nmol) intracerebroventricularly reduced the salivation induced by pilocarpine (4 micro mol/kg) intraperitoneally (133 + 42 and 108 + 22 mg/7 min, respectively, vs. saline, 463 + 26 mg/7 min), but did not modify peripheral cardiovascular responses to intravenous acetylcholine. Similar doses of atropine-mb intraperitoneally also reduced pilocarpine-induced salivation. Therefore, systemically injected pilocarpine also enters the brain and acts on central muscarinic receptors, activating autonomic efferent fibers to induce salivation.

Involvement of the central nervous system in the salivary secretion induced by pilocarpine in rats.

The effect of rats of an anteroventral third ventricle (AV3V) electrolytic lesion on salivary secretion induced by intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) injection of a cholinergic agonist (pilocarpine) was investigated. Sham- or AV3V-lesioned rats anesthetized with urethane and with a stainless steel cannula implanted into the lateral ventricle (LV) were used. The amount of salivary secretion was studied over a seven-minute period after i.c.v. or i.p. injection of pilocarpine. In sham-operated rats, i.p. injection of pilocarpine (1 mg/kg b.w.) (after 6 h, 2, 7, and 15 days) produced salivary secretion (486 +/- 21, 778 +/- 85, 630 +/- 50, and 560 +/- 55 mg/7 min, respectively). This effect was reduced 6 h, 2, and 7 days after an AV3V lesion (142 +/- 22, 113 +/- 32, and 290 +/- 62 mg/7 min, respectively), but not 15 days after an AV3V lesion (516 +/- 19 mg/7 min). I.c.v. injection of pilocarpine (120 micrograms in 1 microL), in sham-operated rats after 6 h, 2, 7, and 15 days also produced salivary secretion (443 +/- 20, 417 +/- 81, 496 +/- 14, and 427 +/- 47 mg/7 min, respectively). The effects of i.c.v. pilocarpine were also reduced 6 h, 2, and 7 days after an AV3V lesion (143 +/- 19, 273 +/- 14, and 322 +/- 17 mg/7 min, respectively), but not after 15 days (450 +/- 28 mg/7 min). The results demonstrate that the central nervous system, and particularly the AV3V region, is important for the effect of pilocarpine on salivary secretion in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

AV3V lesion reduces the pressor, dipsogenic, and natriuretic responses to ventromedial hypothalamus activation.

In the present study, we investigated the effect of anteroventral third ventricle (AV3V) lesion on pressor, tachycardic, dipsogenic, natriuretic, and kaliuretic responses induced by the injection of the cholinergic agonist carbachol into the ventromedial hypothalamic nucleus (VMH) of rats. Male rats with sham or AV3V lesion and a stainless steel cannula implanted into the VMH were used. Carbachol (2 nmol) injected into the VMH of sham rats produced pressor (32 +/- 4 mmHg), tachycardic (83 +/- 14 bpm), dipsogenic (8.2 +/- 1.1 ml/h), natriuretic (320 +/- 46 microEq/120 min), and kaliuretic (155 +/- 20 microEq/120 min) responses. In AV3V-lesioned rats (2 and 15 days), the pressor (4 +/- 2 and 15 +/- 2 mmHg, respectively), dipsogenic (0.3 +/- 0.2 and 1.4 +/- 0.7 ml/h), natriuretic (17 +/- 7 and 99 +/- 21 microEq/120 min), and kaliuretic (76 +/- 14 and 79 +/- 7 microEq/120 min) responses induced by carbachol injection into the VMH were reduced. The tachycardia was also abolished (27 +/- 15 and -23 +/- 29 bpm, respectively). These results show that the AV3V region is essential for the pressor, tachycardic, dipsogenic, natriuretic, and kaliuretic responses induced by cholinergic activation of the VMH in rats.

Opiate activation suppresses the drinking, pressor and natriuretic responses induced by cholinergic stimulation of the medial septal area.

The present study investigates the participation and interaction between cholinergic and opiate receptors of the medial septal area (MSA) in the regulation of Na+, K+ and water excretion, drinking and blood pressure regulation. Male Holtzman rats were implanted with stainless steel cannulae opening into the MSA. Na+, K+ and water excretion, water intake and blood pressure were measured after injection of carbachol (cholinergic agonist), FK-33824 (an opiate agonist) + carbachol or naloxone (an opiate antagonist) + carbachol into MSA. Carbachol (0.5 or 2.0 nmol) induced an increase in Na+ and K+ excretion, water intake and blood pressure and reduced the urinary volume. FK-33824 reduced the urinary volume and Na+ and K+ excretion. Previous injection of FK-33824 (100 ng) into the MSA blocked the increases in Na+ and K+ excretion, water intake and blood pressure induced by carbachol. Naloxone (10 micrograms) produced no changes in the effect of 2.0 nmol carbachol, but potentiated the natriuretic effect induced by 0.5 nmol dose of carbachol. These data show an inhibitory effect of opiate receptors on the changes in cardiovascular, fluid and electrolyte balance induced by cholinergic stimulation of the MSA in rats.

Role of cholinergic and adrenergic pathways of the medial septal area in the water intake and pressor response to central angiotensin II and carbachol in rats.

In the present study, we investigated the effect of previous injection of either prazosin (alpha 1-adrenergic antagonist) or atropine (muscarinic cholinergic antagonist) into the medial septal area (MSA) on the pressor and dipsogenic response induced by intracerebroventricular (ICV) injection of carbachol (cholinergic agonist) and angiotensin II (ANGII) in rats. The pressor and dipsogenic responses to ICV carbachol (7 nmol) were reduced after previous treatment of the MSA with atropine (0.5 to 5 nmol), but not prazosin (20 and 40 nmol). The dipsogenic response to ICA ANGII (25 ng) was reduced after prazosin (40 nmol) into the MSA. The pressor response to ICV ANGII was not changed either by previous treatment of the MSA with prazosin or atropine. The present results suggest a dissociation among the pathways subserving the control of dipsogenic and pressor responses to central cholinergic or angiotensinergic activation.

Effect of AV3V lesion on the cardiovascular, fluid, and electrolytic changes induced by activation of the lateral preoptic area.

In this study we investigated the effect of the anteroventral third ventricle (AV3V) lesion on the pressor, bradycardic, natriuretic, kaliuretic, and dipsogenic responses induced by the injection of the cholinergic agonist carbachol into the lateral preoptic area (LPOA) in rats. Male Holtzman rats with sham or electrolytic AV3V lesion were implanted with stainless steel cannula directly into the LPOA. Injection of carbachol (7.5 nmol) into the LPOA of sham rats induced natriuresis (405 +/- 66 microEq/120 min), kaliuresis (234 +/- 44 microEq/120 min), water intake (9.5 +/- 1.7 ml/60 min), bradycardia (-47 +/- 11 bpm), and increase in mean arterial pressure (28 +/- 3 mmHg). Acute AV3V lesion (1-5 days) reduced the natriuresis (12 +/- 4 microEq/120 min), kaliuresis (128 +/- 27 microEq/120 min), water intake (1.7 +/- 0.9 ml/60 min), and pressor responses (14 +/- 4 mmHg) produced by carbachol into the LPOA. Tachycardia instead of bradycardia was also observed. Chronic (14-18 days) AV3V lesion reduced only the pressor response (10 +/- 2 mmHg) induced by carbachol. These results showed that acute, but not chronic, AV3V lesion reduced the natriuretic, kaliuretic, and dipsogenic responses to carbachol injection into the LPOA. The pressor response was reduced in acute or chronic AV3V-lesioned rats. The results suggest that the lateral areas may control the fluid and electrolyte balance independently from the AV3V region in chronic AV3V-lesioned rats.

Synergist interaction between angiotensin II and DOCA on sodium and water balance in rats.

Blockade of central angiotensin receptors with the specific antagonist [Leu8]-ANG II abolished water ingestion and water and sodium excretion induced by infusion of angiotensin II (ANGII) into the lateral ventricle (LV) of rats. The antagonist reduced but did not suppress the salt appetite induced by ANGII infusion. Subcutaneous injection of deoxycorticosterone acetate (DOCA) caused increases in water and 3% NaCl ingestion and decreases in sodium excretion. When central ANGII infusion was combined with peripheral DOCA, the water intake was similar to that induced by ANGII alone and the ingestion of 3% NaCl was increased, whereas sodium excretion was inhibited. When ANGII was infused alone, a detailed temporal analysis of fluid and sodium balance showed a negative balance similar those saline controls that persisted throughout the experiment. Combined administration of ANGII and DOCA induce significant changes in water and sodium balance. Sodium and water maintained a positive balance through out the 8-h experiment. The data support an interaction of central ANGII and DOCA on sodium intake and water and sodium balance.

Central alpha-adrenergic agonists and need-induced 3% NaCl and water intake.

In the present study, noradrenaline (NOR, alpha-non-specific adrenergic agonist), clonidine (CLO, alpha 2), phenylephrine (PHE, alpha 1) or isoproterenol (ISO, beta-agonist) was injected in the medial septal area (MSA) of water-deprived, sodium-deplete or food-deprived rats. NOR (80, 160 nmol) inhibited the intake of 3% NaCl, water deprivation-induced and meal-associated water intake. Food deprivation-induced food intake and 10% sucrose intake were not altered by NOR. CLO (10, 20, 30, 40 nmol) inhibited (80-100% inhibition compared to control during 60 min) the intake of 3% NaCl, water deprivation-induced and meal-associated water intake. CLO had a weaker inhibition on food and 10% sucrose intake (30-50% less than the control during 60 and 15 min, respectively). PHE (160 nmol) inhibited 3% NaCl intake and 10% sucrose intake (30% less than the control for 15-30 min). ISO (160 nmol) did not alter water or 3% NaCl intake. NOR induced an increase, CLO and ISO induced a decrease, and PHE no alteration in mean arterial pressure. NOR did not alter water or 3% NaCl intake when injected unilaterally into the caudate nucleus. The results suggest that NOR injected in the MSA acts on alpha 2-adrenergic receptors inducing a specific inhibition of 3% NaCl and water intake.