Ventromedial hypothalamus lesions increase the dipsogenic responses and reduce the pressor responses to median preoptic area activation

In this study, we investigated the participation of adrenergic receptors of the median preoptic area (MnPO) and the participation of ventromedial hypothalamus (VMH) in angiotensin II- (ANG II)-induced water intake and presser responses. Male rats with sham or electrolytic VMH lesions and a stainless steel cannula implanted into the MnPO were used. Noradrenaline, clonidine (an alpha(2)-adrenergic receptor agonist), or phenylephrine (an alpha(1)-adrenergic receptor agonist) injected into the MnPO of sham-lesioned rats reduced water ingestion induced by ANG II injected into the same area. In VMH-lesioned rats ANG II-induced water intake increased with a previous injection of noradrenaline, phenylephrine, or isoproterenol. The presser response induced by ANG II injected into the MnPO was reduced in VMH-lesioned rats, whereas the presser response induced by clonidine was abolished. Previous treatment with noradrenaline and phenylephrine into the MnPO of sham-lesioned rats produced a presser response, and a hypotensive response was obtained with the previous administration of noradrenaline, phenylephrine or isoproterenol into the MnPO of VMH-lesioned rats. These results show that VMH is essential for the dipsogenic and presser responses induced by adrenergic and angiotensinergic activation of the MnPO in rats. (C) 1997 Elsevier B.V.

DIFFERENT EFFECTS ON RAT ARTERIAL-PRESSURE AND HEART-RATE WHEN LOSARTAN IS INJECTED INTO THE 3RD-VENTRICLE OR 4TH-VENTRICLE

Cardiovascular 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 +/- 3 mmHg and 343 +/- 9 bpm (N = 23), respectively. LOS (50, 100 or 200 nmol/2 mu l) injected into the 3rdV induced presser (peak of 25 +/- 3 mmHg) and tachycardic (peak of 60 +/- 25 bpm) responses. LOS injected into the 4thV had no effect on MAP, but it induced bradycardia (peak of -35 +/- 15 bpm). KCl (200 nmol/2 mu l) injected into the 3rdV or into the 4thV had no effect on either MAP or HR compared to 0.9% saline injection. The results indicate that LOS injected into the third ventricle acts on forebrain structures to induce its presser and tachycardic effects and that bradycardia, likely dependent on hindbrain structures, is obtained when LOS is injected into the fourth ventricle.

ROLE OF ADRENERGIC PATHWAYS OF THE MEDIAL PREOPTIC AREA IN ANGII-INDUCED WATER-INTAKE AND RENAL EXCRETION IN RATS

In this study, we investigated the participation of adrenergic neurotransmission in angiotensin II- (ANGII)-induced water intake and urinary electrolyte excretion by means of injection of the alpha(1)-, alpha(2)-, and beta-adrenoceptor antagonists and ANGII into the medial preoptic area (MPOA) in rats. Prazosin (an alpha(1)-adrenergic antagonist) antagonized the water ingestion, Na+, K+ and urine excretion induced by ANGII, whereas yohimbine (an alpha(2)-adrenergic antagonist) enhanced the Na+, K+ and urine excretion induced by ANGII. Propranolol (a nonselective beta-adrenoceptor blocker) antagonized the water ingestion and enhanced the Na+ and urine excretion induced by ANGII. Previous treatment with prazosin reduced the presser responses to ANGII, whereas yohimbine had opposite effects. Previous injection of propranolol produced no effects in the presser responses to ANGII. These results suggest that the adrenergic neurotransmission in the MPOA may actively participate in ANGII-induced dipsogenesis, natriuresis, kaliuresis and diuresis in a process that involves alpha(1)-, alpha(2)-, and beta-adrenoceptors.

Fmoc-POAC: [(9-fluorenylmethyloxycarbonyl)-2,2,5,5-tetramethylpyrrolidine-N-oxyl-3-amino-4-carboxylic acid]: A novel protected spin labeled beta-amino acid for peptide and protein chemistry

The stable free radical 2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxylic acid (TOAC) is the only spin labeled amino acid that has been used to date to successfully label peptide sequences for structural studies. However, severe difficulty in coupling the subsequent amino acid has been the most serious shortcoming of this paramagnetic marker. This problem stems from the low nucleophilicity of TOAC's amine group towards the acylation reaction during peptide chain elongation. The present report introduces the alternative beta -amino acid 2,2,5,5-tetramethylpyrrolidine-N-oxyl-3-amino-4-carboxylic acid (POAC), potentially useful in peptide and protein chemistry. Investigations aimed at addressing the stereochemistry of this cyclic molecule through X-ray diffraction measurements of crystalline and bulk samples revealed that it consists only of the trans conformer. The 9-fluorenylmethyloxyearbonyl group (Fmoc) was chosen for temporary protection of the POAC amine function, allowing insertion of the probe at any position in a peptide sequence. The vasoactive octapeptide angiotensin II (AII, DRVYIHPF) was synthesized by replacing Pro(7) with POAC. The reaction of Fmoc-POAC with the peptidyl-resin occurred smoothly, and the coupling of the subsequent amino acid showed a much faster reaction when compared with TOAC. POAC(7)-AII was obtained in good yield, demonstrating that, in addition to TOAC, POAC is a convenient amino acid for the synthesis of spin labeled peptide analogues. The present findings open the possibility of a wide range of chemical and biological applications for this novel beta -amino acid derivative, including structural investigations involving its differentiated bend-inducing characteristics.

Central moxonidine on water and NaCl intake

In this study we investigated: (a) the effects of intracerebroventricular (i.c.v.) injections of moxonidine (an alpha(2)-adrenergic and imidazoline receptor agonist) on the ingestion of water and NaCl induced by 24 h of water deprivation; (b) the effects of i.c.v. injection of moxonidine on central angiotensin II (ANG II)- and carbachol-induced water intake; (c) the effects of the pre-treatment with i.c.v, idazoxan (an alpha(2)-adrenergic and imidazoline receptor antagonist) and RX 821002 (a selective alpha(2)-adrenergic antagonist) on the antidipsogenic action of central moxonidine. Male Holtzman rats had stainless steel cannulas implanted in the lateral cerebral ventricle. Intracerebroventricular injection of moxonidine (5 and 20 nmol/1 mu l) reduced the ingestion of 1.5% NaCl solution (4.1 +/- 1.1 and 2.9 +/- 2.5 ml/2 h, respectively vs. control = 7.4 +/- 2.1 ml/2 h) and water intake (2.0 +/- 0.6 and 0.3 +/- 0.2 ml/h, respectively vs. control = 13.0 +/- 1.4 ml/h) induced by water deprivation, Intracerebroventricular moxonidine (5 nmol/1 mu l) also reduced i.c.v. ANG Ii-induced water intake (2.8 +/- 0.9 vs. control = 7.9 +/- 1.7 ml/1 h) and i.c.v. moxonidine (10 and 20 nmol/1 mu l) reduced i.c.v. carbachol-induced water intake (4.3 +/- 1.7 and 2.1 +/- 0.9, respectively vs. control = 9.2 +/- 1.0 ml/1 h). The pre-treatment with i.c.v. idazoxan (40 to 320 nmol/1 mu l) abolished the inhibitory effect of i.c.v, moxonidine on carbachol-induced water intake. Intracerebroventricular idazoxan (320 nmol/1 mu l) partially reduced the inhibitory effect of moxonidine on water deprivation-induced water intake and produced only a tendency to reduce the antidipsogenic effect of moxonidine on ANG Ii-induced water intake. RX 821002 (80 and 160 nmol/1 mu l) completely abolished the antidipsogenic action of moxonidine on ANG Ii-induced water intake. The results show that central injections c: moxonidine strongly inhibit water and NaCl ingestion. They also suggest the involvement of central alpha(2)-adrenergic receptors in the antidipsogenic action of moxonidine. (C) 1999 Elsevier B.V.

Congenic strains reveal the effect of the renin gene on skeletal muscle angiogenesis induced by electrical stimulation

Previous studies have indicated the importance of angiotensin II (ANG II) in skeletal muscle angiogenesis. The present study explored the effect of regulation of the renin gene on angiogenesis induced by electrical stimulation with the use of physiological, pharmacological, and genetic manipulations of the renin-angiotensin system (RAS). Transfer of the entire chromosome 13, containing the physiologically regulated renin gene, from the normotensive inbred Brown Norway (BN) rat into the background of an inbred substrain of the Dahl salt-sensitive (SS/Mcwi) rat restored renin levels and the angiogenic response after electrical stimulation. This restored response was significantly attenuated when SS-13BN/Mcwi consomic rats were treated with lisinopril or high-salt diet. The role of ANG II on this effect was confirmed by the complete restoration of skeletal muscle angiogenesis in SS/Mcwi rats infused with subpressor doses of ANG II. Congenic strains derived from the SS-13BN/Mcwi consomic were used to further verify the role of the renin gene in this response. Microvessel density was markedly increased after stimulation in congenic strains that contained the renin gene from the BN rat (congenic lines A and D). This angiogenic response was suppressed in control strains that carried regions of the BN genome just above (congenic line C) or just below (congenic line B) the renin gene. The present study emphasizes the importance of maintaining normal renin regulation as well as ANG II levels during the angiogenesis process with a combination of physiological, genetic, and pharmacological manipulation of the RAS.

Evaluation of Vmax as an index of myocardial contractility during afterload and preload elevations

In order to test if the maximal velocity of shortening (V(max)TP) reflects the level of inotropism and is affected by preload and afterload, the behavior of this index was compared in two groups of anesthetized, atropinized dogs when preload and afterload were raised with an angiotensin II infusion. In seven dogs (group I), the arterial pressure elevation was allowed to inhibit reflectively the sympathetic tone and depress contractility. In eleven dogs (group II), the adrenergic activity was abolished by previous administration of reserpine. In group I, there was a significant decrease in V(max)TP during the angiotensin infusion. In group II, there was no significant change in the value of this index when the drug was infused. In six animals of this group, a further increase of arterial pressure was induced, but the values of V(max)TP remained similar to control. These results suggest that this index reflects the inotropic state of the myocardium and does not suffer significantly from the influence of preload and afterload elevations within our experimental limits.

Interaction between areas of the central nervous system in the control of water intake and arterial pressure in rats

1. Water intake induced by injection of 0.2 M-NaCl into the lateral preoptic area was increased by the injection of angiotensin II into the subfornical organ of rats. The injection of hypertonic saline solution into the subfornical organ increased water intake. However, the increase was lower than when the solution was injected into the lateral preoptic area. The injection of 4 μg angiotensin II into the lateral preoptic area further augmented this effect. 2. Injection of angiotensin II into the subfornical organ caused a rise in blood pressure which preceded the thirst-inducing effect. The injection of 0.2 M NaCl into the subfornical organ caused no changes in blood pressure, whereas the injection of angiotensin II into the lateral preoptic area caused some increase. 3. Dehydration of the lateral preoptic area by means of 0.2 M NaCl in combination with intravenous infusion of angiotensin II caused a summation of effects in terms of the water intake, without changing cardiovascular alterations induced by the infusion of angiotensin II. A summation of effects in the water intake, but not in blood pressure, was also observed when 0.5 M NaCl was infused intravenously in combination with the injection of angiotensin II into the subfornical organ and into the lateral preoptic area. 4. The results indicate that there are interactions between the subfornical organ and lateral preoptic area in the regulation of cardiovascular and thirst mechanisms.

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

Cardiovascular 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±3 mmHg and 343±9 bpm (N=23), respectively. LOS (50, 100 or 200 nmol/2 μl) injected into the 3rdV induced pressor (peak of 25±3 mmHg) and tachycardic (peak of 60±25 bpm) responses. LOS injected into the 4thV had no effect on MAP, but it induced bradycardia (peak of -35±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% 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.

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

Noradrenaline (NOR) is a neurotransmitter presenl 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. 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. 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 facililates fluid intake by acting on postsynaptic receptors, but we do not know how it inhibits fluid infake. The inhibitory and facilitatory effects of NOR on ingestive behavior suggest a dual role for this neurotransmitter in the control of hydromineral fluid intake.

Effects of intracerebroventricular injections of losartan or PD123319 on arterial pressure and heart rate of sodium replete and sodium deplete rats

Angiotensin II (Ang II) non-peptide antagonists were injected i.c.v. (6.25-200 nmol, n = 5-8 rats/group): In sodium replete rats, losartan (AT1 receptor antagonist) induced an increase in mean arterial pressure (MAP) and in heart rate (HR) by 3rd ventricular (3rdV) injection, and a weaker pressor response and bradycardia by 4th ventricular (4thV) injection. PD123319 (AT2 receptor antagonist) induced an increase in MAP and in HR by 3rdV injection, and an increase in MAP and no alteration in HR by 4thV injection. In sodium deplete (furosemide plus removal of ambient sodium for 24 h) rats, losartan induced an increase in MAP and no alteration in HR by 3rdV injection, and no alteration in MAP and bradycardia by 4thV injection. PD123319 induced an increase in MAP and in HR by 3rdV injection, and an increase in MAP and bradycardia by 4thV injection. Thus, there was no fall in MAP by central injections of Ang II antagonists. Intravenous injection of losartan, but not of PD123319, induced a fall in MAP in both sodium replete and sodium deplete animals. Therefore, losartan and PD123319 can have similar effects on MAP and HR when injected intracerebroventricularly, although some differences are also present. The bradycardia is consistent with an withdrawal of Ang II inhibitory action on baroreflex.

Multifactorial control of water and saline intake: Role of α2-adrenoceptors

Water and saline intake is controlled by several mechanisms activated during dehydration. Some mechanisms, such as the production of angiotensin II and unloading of cardiovascular receptors, activate both behaviors, while others, such as the increase in blood osmolality or sodium concentration, activate water, but inhibit saline intake. Aldosterone probably activates only saline intake. Clonidine, anα2-adrenergic agonist, inhibits water and saline intake induced by these mechanisms. One model to describe the interactions between these multiple mechanisms is a wire-block diagram, where the brain circuit that controls each intake is represented by a summing point of its respective inhibiting and activating factors. The α2-adrenoceptors constitute an inhibitory factor common to both summing points.

Importância da região anteroventral do terceiro ventrículo (AV3V) no controle cardiovascular e do equilíbrio hidroeletrolítico

The maintenance of the arterial pressure in normal levels is important for the homeostasis of body fluids. The central nervous system regulating sympathetic and parasympathetic autonomic efferent can adjust arterial pressure which allows animals or human to face different daily activities with the best performance. Different central areas are responsible for the control of autonomic discharges to cardiovascular system and many of them are also involved in the control of fluid electrolyte balance. One of these areas is the tissue surrounding the anteroventral third ventricle (AV3V region) localized in the forebrain and a main central site for angiotensin II receptors and osmoreceptors. The AV3V lesions impair the development of many models of experimental hypertension in rats and the pressor responses to different stimuli. Lesions of the AV3V region also reduce dipsogenic responses to angiotensin II, central cholinergic activation, water deprivation and increase in plasma osmolarity, atrial natriuretic peptide secretion produced by body fluid expansion and the increase in renal excretion to central cholinergic activation. Recent evidence also suggests the participation of AV3V region in pressor responses produced by the activation of medullary mechanisms.

Nitrergic pathways and L-type calcium channel of MnPO influencing cardiovascular homeostasis

The median preoptic nucleus (MnPO) is one of most important site of the lamina terminalis implicated in the regulation of hydro electrolytic and cardiovascular balance. The purpose of this study was to determine the effect of L-Type calcium channel antagonist, nifedipine, on the increase of median arterial blood pressure (MAP) induce by angiotensin II (ANG II) injected into the MnPO. The influence of nitric oxide (NO) on nifedipine antipressor action has also been studied by utilizing N W-nitro-L-arginine methyl ester (L-NAME) (40 μg 0.2 μL -1) a NO synthase inhibitor (NOSI), 7-nitroindazole (7-NIT) (40 μg 0.2 μL -1), a specific neuronal NO synthase inhibitor (nNOSI) and sodium nitroprusside (SNP) (20 μg 0.2 μL -1) a NO donor agent. We have also investigated the central role of losartan and PD123349 (20 nmol 0.2 μL -1), AT 1 and AT 2, respectively (selective non peptide ANG II receptor antagonists), in the pressor effect of ANG II (25 pmol 0.2 μL -1) injected into the MnPO. Male Wistar rats weighting 200-250 g, with cannulae implanted into the MnPO were utilized. Losartan injected into the MnPO, prior to ANG II, blocked the pressor effect of ANGII. PD 123319 only decreased the pressor effect of ANG II. Rats pre-treated with either 50 μg 0.2 μL -1 or 100 μg 0.2 μL -1 of nifedipine, followed by 25 pmol 0.2 μL -1 of ANG II, decreased ANG II-pressor effect. L-NAME potentiated the pressor effect of ANG II. 7-NIT injected prior to ANG II into the MnPO also potentiated the pressor effect of ANGII but with less intensity than that of L-NAME. SNP injected prior to ANG II blocked the pressor effect of ANG II. The potentiation action of L-NAME and 7-NIT on ANG II-pressor effect was blocked by prior injection of nifedipine. The results described in this study provide evidence that calcium channels play important roles in central ANG II-induced pressor effect. The structures containing NO in the brain, such as MnPO, include both endothelial and neuronal cells, which might be responsible for the influence of nifedipine on the pressor effect of ANG II. These data have shown the functional relationship between L-Type calcium channel and a free radical gas NO in the MnPO, on the control of ANG II-induced pressor effect acting in AT 1 and AT 2 receptors.