Effect of injection of L-NAME on drinking response

Central interaction between nitric oxide, lactate and glial cells to modulate water and sodium intake in rats

The "astrocyte-to-neuron lactate shuttle" (ANLS) mechanism is part of the central inhibitory pathway to modulate sodium intake. An interaction between the GABAergic neurons and nitric oxide (NO) in the subfornical organ (SFO) in salt-appetite inhibition has been suggested. In addition, NO is a key molecule involved in astrocytic energy metabolism and lactate production. In the present study, we hypothesized there is an interaction between astrocytic lactate and central NO to negatively modulate water and sodium intake through the ANLS mechanism. The results showed that central Nω-nitro-L-arginine methyl ester (L-NAME, NO-synthase inhibition) induced an increase in water and sodium intake. These responses were attenuated by previous central microinjection of fluorocitrate (FCt, a reversible glial inhibitor). Interestingly, L-NAME-induced water and sodium intake were also decreased by previous microinjection of lactate but did not change after inhibition of the ANLS mechanism by α-cyano 4-hydroxycinnamic acid (α-CHCA), an inhibitor of the MCT lactate transporter. Our results suggest a central interaction between NO, glial cells, and lactate to modulate water and sodium intake.

Effects of hydrogen sulfide (H2S) on water intake and vasopressin and oxytocin secretion induced by fluid deprivation

During dehydration, responses of endocrine and autonomic control systems are triggered by central and peripheral osmoreceptors and peripheral baroreceptors to stimulate thirst and sodium appetite. Specifically, it is already clear that endocrine system acts by secreting vasopressin (AVP), oxytocin (OT) and angiotensin II (ANG II), and that gaseous molecules, such as nitric oxide (NO) and carbon monoxide (CO), play an important role in modulating the neurohypophyseal secretion as well as ANG II production and thirst. More recently, another gas-hydrogen sulfide (H2S)-has been studied as a neuronal modulator, which is involved in hypothalamic control of blood pressure, heart frequency and temperature. In this study, we aimed to investigate whether H2S and its interaction with NO system could participate in the modulatory responses of thirst and hormonal secretion induced by fluid deprivation. For this purpose, Wistar male rats were deprived of water for 12 and 24h, and the activity of sulfide-generating enzymes was measured. Surprisingly, 24-h water deprivation increased the activity of sulfide-generating enzymes in the medial basal hypothalamus (MBH). Furthermore, the icv injection of sodium sulfide (Na2S, 260nmol), a H2S donor, reduced water intake, increased AVP, OT and CORT plasma concentrations and decreased MBH nitrate/nitrite (NOX) content of 24-h water-deprived animals compared to controls. We thus suggest that H2S system has an important role in the modulation of hormonal and behavioral responses induced by 24-h fluid deprivation.

Role of angiotensin AT2 receptors and nitric oxide in the cardiopulmonary baroreflex control of renal sympathetic nerve activity in rats

OBJECTIVES

This study investigated the hypothesis that angiotensin II (type 2) (AT2) receptor activation to modulate the renal sympatho-inhibition to saline volume expansion was dependent on nitric oxide production.

METHODS

Renal sympatho-inhibition to a saline volume expansion (VEP, 0.25% body weight/min i.v. for 30 min) was studied following intracerebroventricular (ICV) saline, CGP42112 (CGP, AT2 agonist), PD123319 (AT2 antagonist), and losartan (AT1 antagonist), and then in combination with N-nitro-L-arginine methyl ester (L-NAME) (nitric oxide synthase inhibitor).

RESULTS

ICV saline, PD123319, CGP, and losartan did not change baseline mean arterial pressure, heart rate, or renal sympathetic nerve activity (RSNA). VEP decreased RSNA in all groups by 58-62% (P<0.05). CGP enhanced the decrease in RSNA compared to saline (74 vs. 60%; P<0.05), whereas PD123319 was without effect (58 vs. 57%). L-NAME only increased baseline RSNA when co-administered with PD123319 (P<0.05). VEP-induced reduction in RSNA following L-NAME was less than during ICV saline (46 vs. 62%; P<0.05). In the group where PD123319 preceded L-NAME, the fall in RSNA was smaller than when PD123319 was infused alone (40 vs. 63%; P<0.05), but not if PD123319 followed L-NAME (52 vs. 44%). L-NAME did not change the magnitude of VEP-induced sympatho-inhibition following CGP (67 vs. 60%). Losartan enhanced the renal sympatho-inhibition to VEP (70 vs. 62%; P<0.05), the magnitude of which was unchanged when L-NAME was present (70 vs. 65%).

CONCLUSION

AT2 receptor activation enhances the VEP-induced reduction in RSNA. Although nitric oxide is important in allowing the normal renal sympatho-inhibitory response to VEP, this is not dependent on AT2 receptors.

Functional relationship between subfornical organ cholinergic stimulation and nitrergic activation influencing cardiovascular and body fluid homeostasis

We have studied the effects of L-NG-nitro arginine methyl esther (L-NAME), L-arginine (LAR), inhibitor and a donating nitric oxide agent on the alterations of salivary flow, water intake, arterial blood pressure (MAP) and heart rate (HR) induced by the injection pilocarpine into the subfornical organ (SFO). Rats (Holtzman 250-300 g) were anesthetized with 2, 2, 2-tribromoethanol (20 mg/100 kg b. wt.) and a stainless steel cannula were implanted into their SFO. The volume of injection was 0.2 microl. The amount of saliva secretion was studied over a 5-min period. Pilocarpine (40 microg), L-NAME (40 microg) and LAR (30 microg) were used in all experiments for the injection into the SFO. Pilocarpine (10, 20, 40, 80 and 160 microg) injected into SFO elicited a concentration-dependent increase in salivary secretion. L-NAME injected prior to pilocarpine into the SFO increased salivary secretion and water intake due to the effect of pilocarpine. LAR injected prior to pilocarpine into the SFO attenuated the salivary secretion and water intake. Pilocarpine, injected into the SFO increased the MAP and decreased heart rate (HR). L-NAME injected prior to pilocarpine into the SFO potentiated the pressor effect of pilocarpine with a decrease in HR. LAR injected into the SFO prior to pilocarpine attenuated the increase in MAP with no changes in HR. The present study suggests that the SFO nitrergic cells interfere in the cholinergic pathways implicated in the control of salivary secretion, fluid and cardiovascular homeostasis.

Lateral hypothalamus lesions influences water and salt intake, and sodium and urine excretion, and arterial blood pressure induced by L-NAME and FK 409 injections into median preoptic nucleus in conscious rats

Male Holtzman rats weighting 200-250 g were anesthetized with zoletil 50 mg/Kg (tiletamine chloridrate 125,0 mg and zolazepan chloridrate 125,0 mg) into quadriceps muscle and submitted an electrolytic lesion of the lateral hypothalamus (LH) and a stainless steel cannula was implanted into their median preoptic nucleus (MnPO). We investigated the effects of the injection into the (MnPO) of FK 409 (20 microg/0.5 microl), a nitric oxide (NO) donor, and N(W)-nitro-L-arginine methyl ester (L-NAME) 40 microg/0.5 microl, a nitric oxide synthase inhibitor (NOSI), on the water and sodium appetite and the natriuretic, diuretic and cardiovascular effects induced by injection of L-NAME and FK 409 injected into MnPO in rats with LH lesions. Controls were injected with a similar volume of 0.15 M NaCl. L-NAME injected into MnPO produced an increase in water and sodium intake and in sodium and urine excretion and increase de mean arterial pressure (MAP). FK 409 injected into MnPO did not produce any change in the hydro electrolytic and cardiovascular parameters in LH-sham and lesioned rats. FK 409 injected before L-NAME attenuated its effects. These data show that electrolytic lesion of the LH reduces fluid and sodium intake as well as sodium and urine excretion, and the pressor effect induced by L-NAME. LH involvement with NO of the MnPO excitatory and inhibitory mechanisms related to water and sodium intake, sodium excretion and cardiovascular control is suggested.

Interaction between supraoptic nucleus and septal area in the control of water, sodium intake and arterial blood pressure induced by injection of angiotensin II

We investigated the effects of injection into the supraoptic nucleus (SON) of losartanand PD 123319 (nonpeptide AT(1) and AT(2)-angiotensin II [ANG II] receptor antagonists, respectively); d(CH(2))(5)-Tyr(Me)-AVP (AVPA; an arginine-vasopressin [AVP] V(1) receptor antagonist), FK 409 (a nitric oxide [NO] donor), and N(W)-nitro-l-arginine methyl ester (l-NAME; an NO synthase inhibitor) on water intake, sodium chloride 3% (NaCl) intake and arterial blood pressure induced by injection of ANG II into the lateral septal area (LSA). Male Holtzman rats (250-300 g) were implanted with cannulae into SON and LSA unilaterally. The drugs were injected in 0.5 microl over 30-60 s. Controls were injected with a similar volume of 0.15 M NaCl. ANG II was injected at a dose of 10 pmol. ANG II antagonists and AVPA were injected at doses of 80 nmol. FK 409 and l-NAME were injected at doses of 20 and 40 microg, respectively. Water and NaCl intake was measured over a 2-h period. Prior administration of losartan into the SON decreased water and NaCl intake induced by injection of ANG II. While there was a decrease in water intake, ANG II-induced NaCl intake was significantly increased following injection of AVPA. FK 409 injection decreased water intake and sodium intake induced by ANG II. l-NAME alone increased water and sodium intake and induced a pressor effect. l-NAME-potentiated water and sodium intake induced by ANG II. PD 123319 produced no changes in water or sodium intake induced by ANG II. The prior administration of losartan or AVPA decreased mean arterial pressure (MAP) induced by ANG II. PD 123319 decreased the pressor effect of ANG II to a lesser degree than losartan. FK 409 decreased the pressor effect of ANG II while l-NAME potentiated it. These results suggest that both ANG II AT(1) and AVP V(1) receptors and NO within the SON may be involved in water intake, NaCl intake and the pressor response were induced by activation of ANG II receptors within the LSA. These results do not support the involvement of LSA AT(2) receptors in the mediation of water and NaCl intake responses induced by ANG II, but influence the pressor response.

Nitric oxide of the supraoptic nucleus influences the salivary secretion, sodium renal excretion, urinary volume and arterial blood pressure induced by pilocarpine

Male Holtzman rats weighting 200-250 g were anesthetized with zoletil 50 mg/Kg (tiletamine chloridrate 125.0 mg and zolazepan chloridrate 125.0 mg) into quadriceps muscle and stainless steel cannulas were implanted into their supraoptic nucleus (SON). We investigated the effects of the injection into the supraoptic nucleus (SON) of FK 409, a nitric oxide donor, and NW-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor (NOS), on the salivary secretion, arterial blood pressure, sodium excretion and urinary volume induced by pilocarpine, which was injected into SON. The drugs were injected in 0.5 microl volume over 30-60 s. Controls was injected with a similar volume of 0.15 M NaCl. FK 409 and L-NAME were injected at doses of 20 microg/0.5 microl and 40 microg/0.5 microl respectively. The amount of saliva secretion was studied over a five-minute period after injection of pilocarpine into SON. Injection of pilocarpine (10, 20, 40, 80, 160 microg/microl) into SON produced a dose-dependent increase in salivary secretion. L-NAME was injected into SON prior to the injection of pilocarpine into SON, producing an increase in salivary secretion due to the effect of pilocarpine. FK 409 injected into SON attenuating the increase in salivary secretion induced by pilocarpine. Mean arterial pressure (MAP) increase after injections of pilocarpine into the SON. L-NAME injected into the SON prior to injection of pilocarpine into SON increased the MAP. FK 409 injected into the SON prior to pilocarpine attenuated the effect of pilocarpine on MAP. Pilocarpine (0.5 micromol/0.5 microl) injected into the SON induced an increase in sodium and urinary excretion. L-NAME injected prior to pilocarpine into the SON increased the urinary sodium excretion and urinary volume induced by pilocarpine. FK 409 injected prior to pilocarpine into the SON decreased the sodium excretion and urinary volume induced by pilocarpine. All these roles of pilocarpine depend on the release of nitric oxide into the SON. In summary the present results show: a) SON is involved in pilocarpine-induced salivation; b) that mechanism involves increase in MAP, sodium excretion and urinary volume.

Effet d'une déshydratation sur le monoxyde d'azote, l'axe vasopressinergique et l'axe corticotrope chez le rat

Effect of dehydration on nitric oxide, corticotropic and vasopressinergic axis in rat. The purpose of our work is to study, in the male 'Wistar' rat, the effects of a chronic dehydration, by deprivation of water for three days out of four, during four repeated cycles, on the evolution of certain blood variables, on the activities of both corticotropic and vasopressinergic axis and on the synthesis of nitric oxide. The chronic dehydration causes a considerable reduction of the body weight, an activation of the vasopressinergic axis and an increase in the circulating rates of the nitrates/nitrites, which represent the final metabolites of the reaction of oxidation of nitric oxide. The pituitary-adrenal axis is not statistically affected by the chronic dehydration. This seems to be in favour of a possible adaptation of corticotropic axis to chronic water deprivation. The activation of synthesis of nitric oxide shows its implication in the regulation of the water balance and its buffer effect on vasoconstriction and hypertension induced by water stress.

Role of nitric oxide of the median preoptic nucleus (MnPO) in the alterations of salivary flow, arterial pressure and heart rate induced by injection of pilocarpine into the MnPO and intraperitoneally

We investigated the effect of L-NAME, a nitric oxide (NO) inhibitor and sodium nitroprusside (SNP), an NO-donating agent, on pilocarpine-induced alterations in salivary flow, mean arterial blood pressure (MAP) and heart rate (HR) in rats. Male Holtzman rats (250-300 g) were implanted with a stainless steel cannula directly into the median preoptic nucleus (MnPO). Pilocarpine (10, 20, 40, 80, 160 g) injected into the MnPO induced an increase in salivary secretion (P<0.01). Pilocarpine (1, 2, 4, 8, 16 mg/kg) ip also increased salivary secretion (P<0.01). Injection of L-NAME (40 g) into the MnPO prior to pilocarpine (10, 20, 40, 80, 160 g) injected into the MnPO or ip (1, 2, 4, 8, 16 mg/kg) increased salivary secretion (P<0.01). SNP (30 g) injected into the MnPO or ip prior to pilocarpine attenuated salivary secretion (P<0.01). Pilocarpine (40 g) injection into the MnPO increased MAP and decreased HR (P<0.01). Pilocarpine (4 mg/kg body weight) ip produced a decrease in MAP and an increase in HR (P<0.01). Injection of L-NAME (40 g) into the MnPO prior to pilocarpine potentiated the increase in MAP and reduced HR (P<0.01). SNP (30 g) injected into the MnPO prior to pilocarpine attenuated (100%) the effect of pilocarpine on MAP, with no effect on HR. Administration of L-NAME (40 g) into the MnPO potentiated the effect of pilocarpine injected ip. SNP (30 g) injected into the MnPO attenuated the effect of ip pilocarpine on MAP and HR. The present study suggests that in the rat MnPO 1) NO is important for the effects of pilocarpine on salivary flow, and 2) pilocarpine interferes with blood pressure and HR (side effects of pilocarpine), that is attenuated by NO.

Role of nitric oxide and beta-adrenoceptors of the central nervous system on the salivary flow induced by pilocarpine injection into the lateral ventricle

Our studies have focused on the effect of L-NG-nitroarginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), and L-arginine, the substrate of NOS, on salivary secretion induced by the administration of pilocarpine into the lateral cerebral ventricle (LV) of rats. The present study has also investigated the role of the beta-adrenergic agonists and antagonist injected into LV on the salivary secretion elicited by the injection of pilocarpine into LV. Male Holtzman rats with a stainless-steel cannula implanted into the LV were used. The amount of salivary secretion was studied over a 7-min period after injection of pilocarpine, isoproterenol, propranolol, salbutamol, salmeterol, L-NAME and L-arginine. The injection of pilocarpine (10, 20, 40, 80 and 160 microg/microl) into LV produced a dose-dependent increase in salivary secretion. The injection of L-NAME (40 microg/microl) into LV alone produced an increase in salivary secretion. The injection of L-NAME into LV previous to the injection of pilocarpine produced an increase in salivary secretion. L-Arginine (30 microg/microl) injected alone into LV produced no change in salivary secretion. L-Arginine injected into LV attenuated pilocarpine-induced salivary secretion. The isoproterenol (40 nmol/microl) injected into LV increased the salivary secretion. When injected previous to pilocarpine at a dose of 20 and 40 microg/microl, isoproterenol produced an additive effect on pilocarpine-induced salivary secretion. The 40-nmol/microl dose of propranolol injected alone or previous to pilocarpine into LV attenuated the pilocarpine-induced salivary secretion. The injection of salbutamol (40 nmol/microl), a specific beta-2 agonist, injected alone into LV produced no change in salivary secretion and when injected previous to pilocarpine produced an increase in salivary secretion. The 40-nmol/microl dose of salmeterol, a long-acting beta-2 agonist, injected into LV alone or previous to pilocarpine produced no change in salivary secretion. The results have shown that central injections of L-NAME and L-arginine interfere with the salivary secretion, which implies that might participate in pilocarpine-induced salivary secretion. The interaction between cholinergic and beta-adrenergic receptors of the central nervous system (CNS) for the control of salivary secretion can also be postulated.

Novel evidence that nitric oxide of the medial septal area influences the salivary secretion induced by pilocarpine

Our studies have focused on the effect of injection of L-NAME and sodium nitroprussiate (SNP) on the salivary secretion, arterial blood pressure, sodium excretion and urinary volume induced by pilocarpine which was injected into the medial septal area (MSA). Rats were anesthetized with urethane (1.25 g/kg b. wt.) and a stainless steel cannula was implanted into their MSA. The amount of saliva secretion was studied over a five-minute period after injection of pilocarpine into MSA. Injection of pilocarpine (10, 20, 40, 80, 160 microg/microl) into MSA produced a dose-dependent increase in salivary secretion. L-NG-nitro arginine methyl-esther (L-NAME) (40 microg/microl), a nitric oxide (NO) synthase inhibitor, was injected into MSA prior to the injection of pilocarpine into MSA, producing an increase in salivary secretion due to the effect of pilocarpine. Sodium nitroprussiate (SNP) (30 microg/microl) was injected into MSA prior to the injection of pilocarpine into MSA attenuating the increase in salivary secretion induced by pilocarpine. Medial arterial pressure (MAP) increase after injections of pilocarpine into the MSA. L-NAME injected into the MSA prior to injection of pilocarpine into MSA increased the MAP. SNP injected into the MSA prior to pilocarpine attenuated the effect of pilocarpine on MAP. Pilocarpine (40 ug/ul) injected into the MAS induced an increase in sodium and urinary excretion. L-NAME injected prior to pilocarpine into the MSA increased the urinary sodium excretion and urinary volume induced by pilocarpine. SNP injected prior to pilocarpine into the MSA decreased the sodium excretion and urinary volume induced by pilocarpine. All these roles of pilocarpine depend on the release of nitric oxide into the MSA. We may also conclude that the MSA is involved with the cholinergic excitatory mechanism that induce salivary secretion, increase in MAP and increase in sodium excretion and urinary volume.