Vasorelaxant Mechanism of Herbal Extracts from Mentha suaveolens, Conyza canadensis, Teucrium polium and Salvia verbenaca in the Aorta of Wistar Rats.

Mentha suaveolens (MS), Conyza canadensis (CC), Teucrium polium (TP) and Salvia verbenaca (SV) are used in Morocco to treat hypertension. Our aim was to characterize the composition and vasoreactivity of extracts of MS, CC, TP and SV. The chemical compositions of aqueous extracts of MS, SV and TP, and of a hydromethanolic extract of CC, were identified by HPLC-DAD. The vasoreactive effect was tested in rings of the thoracic aorta of female Wistar rats (8-14 weeks-old) pre-contracted with 10 µM noradrenaline, in the absence or presence of L-NAME 100 µM, indomethacin 10 µM or atropine 6 µM, to inhibit nitric oxide synthase, cyclooxygenase or muscarinic receptors, respectively. L-NAME and atropine decreased the vasorelaxant effect caused by low concentrations of MS. Atropine and indomethacin decreased the vasorelaxant effect of low concentrations of SV. High concentrations of MS or SV and the effect of SV and TP were not altered by any antagonist. The activation of muscarinic receptors and NO or the cyclooxygenase pathway underlie the vasorelaxant effect of MS and SV, respectively. Neither of those mechanisms underlines the vasorelaxant effect of CC and TP. These vasorelaxant effect might support the use of herbal teas from these plants as anti-hypertensives in folk medicine.

Milk Formula Enriched with Sodium Butyrate Influences Small Intestine Contractility in Neonatal Pigs.

Butyrate, a by-product of gut bacteria fermentation as well as the digestion of fat in mother's milk, exerts a wide spectrum of beneficial effects in the gastrointestinal tissues. The present study aimed to determine the effects of sodium butyrate on small intestine contractility in neonatal piglets. Piglets were fed milk formula alone (group C) or milk formula supplemented with sodium butyrate (group B). After a 7-day treatment period, isometric recordings of whole-thickness segments of the duodenum and middle jejunum were obtained by electric field stimulation under the influence of increasing doses of Ach (acetylocholine) in the presence of TTX (tetrodotoxin) and atropine. Moreover, structural properties of the intestinal wall were assessed, together with the expression of cholinergic and muscarinic receptors (M1 and M2). In both intestinal segments (duodenum and middle jejunum), EFS (electric field stimulation) impulses resulted in increased contractility and amplitude of contractions in group B compared to group C. Additionally, exposure to dietary butyrate led to a significant increase in tunica muscularis thickness in the duodenum, while mitotic and apoptotic indices were increased in the middle jejunum. The expression of M1 and M2 receptors in the middle jejunum was significantly higher after butyrate treatment. The results indicate increased cholinergic signaling and small intestinal growth and renewal in response to feeding with milk formula enriched with sodium butyrate in neonatal piglets.

Antihypertensive Activity in High Salt-Induced Hypertensive Rats and LC-MS/MS-Based Phytochemical Profiling of Melia azedarach L. (Meliaceae) Leaves.

Melia azedarach L. leaves have been traditionally used but not scientifically evaluated for antihypertensive activity. The focus of the present work was to carry out the detailed phytochemical profiling and antihypertensive potential of methanolic extract and subsequent fractions of this plant. The tandem mass spectrometry-based phytochemical profiling of M. azedarach extract (Ma.Cr) and fractions was determined in negative ionization mode while molecular networking was executed using the Global Natural Product Social (GNPS) molecular networking platform. This study resulted in the identification of 29 compounds including flavonoid O-glycosides, simple flavonoids, triterpenoidal saponins, and cardenolides as the major constituents. Ma.Cr at the concentration of 300 mg/kg resulted in a fall in blood pressure (BP), i.e., 81.44 ± 2.1 mmHg in high salt-induced hypertensive rats in vivo, in comparison to normotensive group, i.e., 65.36 ± 1.8 mmHg at the same dose. A decrease in blood pressure was observed in anaesthetized normotensive and hypertensive rats treated with extract and various fractions of M. azedarach. A reasonable activity was observed for all fractions except the aqueous fraction. The highest efficacy was shown by the ethyl acetate fraction, i.e., 77.06 ± 3.77 mmHg in normotensive and 88.96 ± 1.3 mmHg in hypertensive anaesthetized rats. Ma.Cr and fractions showed comparatively better efficacy towards hypertensive rats as compared to rats with normal blood pressure. Blood pressure-lowering effects did not change upon prior incubation with atropine. In vitro testing of Ma.Cr and polarity-based fractions resulted in L-NAME sensitive, endothelium-dependent vasodilator effects on aortic tissues. Pretreatment of aorta preparations with Ma.Cr and its fractions also blocked K+-induced precontractions indicating Ca2+ channel blocking activity comparable to verapamil. The extract and polarity-based fractions did not reveal a vasoconstrictor response in spontaneously beating isolated rat aorta. Ma.Cr and fractions when used in atrial preparations resulted in negative inotropic and chronotropic effects. These effects in atrial preparations did not change in the presence of atropine. These effects of extract and fractions explained the antihypertensive potential of M. azedarach and thus provided a scientific basis for its ethnopharmacological use in the treatment of hypertension. Among the constituents observed, flavonoids and flavonoid O-glycosides were previously reported for antihypertensive potential.

Beneficial Effects of Black Cardamom (Amomum subulatum) on Hemodynamic Parameters in Normotensive and Spontaneously Hypertensive Rats.

<b>Background and Objectives:</b> <i>Amomum subulatum</i> (AS) is used to improve cardiac health in traditional medicine practice. The present study evaluates the pharmacological effect of AS aqueous extract on blood pressure in Normotensive (NR) and Spontaneously Hypertensive Rats (SHR). <b>Materials and Methods:</b> Blood pressure, Heart Rate (HR) and Heart Rate Variability (HRV), was recorded in catheterized Sprague-Dawley rats before and after AS intravenous administration by using Mikro-Tip Pressure-Volume System (MPVS), PowerLab. The receptor activity was assessed by using the drugs Acetylcholine (ACh) and Atropine (Atr). <b>Results:</b> Preliminary phytochemistry of AS suggests that it contains tannins, flavonoids and saponins. Mean Arterial Pressure (MAP) was found to decrease significantly in NR and SHR as compared with the control. The lowest dose (1 mg kg¹) produced the least (16%) while 30 mg kg¹ caused the maximum reduction (40%) in MAP. Electrocardiograph analysis revealed a significant increase in RR interval (decreased heart rate), time-domain Standard Deviation of Interbeat Interval (SDNN) and the Root Mean Square of the Successive Differences (RMSSD) and High-frequency Domain (HF%) parameters and a decrease in the Low-Frequency (LF) range, suggesting the activation and involvement of the parasympathetic limb. It was also observed that the cardiovascular effects of AS were comparable to Acetylcholine (ACh) and both were completely blocked by Atropine (1 µg kg¹). <b>Conclusion:</b> The obtained results suggest that AS has a hypotensive effect, with an impact on the HRV of NR and SHR. <i>Amomum subulatum</i> might cause an augmented effect on the cholinergic limb of the Autonomic Nervous System (ANS) and decrease the blood pressure and heart rate significantly.

Antihypertensive Activity of Sauromatum guttatum Mediated by Vasorelaxation and Myocardial Depressant Effects. / O Efeito Anti-Hipertensivo de Sauromatum Guttatum Mediado por Efeitos Vasorrelaxante e Depressivos Miocárdicos.

BACKGROUND: Sauromatum guttatum (S. guttatum) is used in the treatment of blood disorders and reportedly has a spasmolytic activity through Ca2+ channel inhibition. OBJECTIVES: The aim of this study was to investigate the antihypertensive potential of S. guttatum in high salt-induced hypertensive Sprague-Dawley (SD) rat model (HSHRs). METHODS: SD rats were divided into normotensive, hypertensive, S. guttatum and verapamil treated groups. S. guttatum crude extract (Sg.Cr) (100, 150 and 300 mg/kg/day) and verapamil (5, 10 and 15 mg/kg/day) were administered orally along with NaCl. Aortic rings and right atrial strips from normotensive rats were used to investigate the underlying mechanisms. The level of statistical significance was set at 5%. RESULTS: Mean arterial pressure decreased in the Sg.Cr and verapamil-treated hypertensive groups in a dose-dependent manner (p < 0.001). In the vascular reactivity study, acetylcholine induced relaxations with an EC50 value of 0.6 µg/mL (0.3-1.0) in Sg.Cr-treated hypertensive rats (300 mg/kg), suggesting endothelial preservation. In isolated normotensive rat aorta, Sg.Cr-treated rats showed vasorelaxation with an EC50 value of 0.15 mg/mL (0.10-0.20), ablated by endothelial denudation or pretreatment with L-NAME and atropine. Sg.Cr treatment caused relaxation against high K+-induced contractions, like verapamil. Sg.Cr showed negative inotropic (82%) and chronotropic effects (56%) in isolated rat atrial preparations reduced with atropine. The phytochemical investigation indicated presence of alkaloids, flavonoids and tannins. CONCLUSION: S. guttatum has a vasodilatory effect through endothelial function preservation, muscarinic receptor-mediated NO release and Ca2+ movement inhibition, while atrial myocardial depressant effect can be linked to the muscarinic receptor. These findings provide pharmacological base for using S. guttatum extract as an antihypertensive medication.

FUNDAMENTO: A Sauromatum guttatum (S. guttatum) é utilizado no tratamento de doenças do sangue e supostamente tem atividade espasmolítica através da inibição dos canais de Ca2+. OBJETIVOS: O objetivo deste estudo foi investigar o potencial anti-hipertensivo de S. guttatum em modelo de rato Sprague-Dawley (SD) com hipertensão induzida por dieta com alto teor de sal (HIDATS). MÉTODOS: Ratos SD foram divididos em normotensos, hipertensos e grupos tratados com verapamil e S. guttatum. Extrato bruto de S. guttatum (Sg.B) (100, 150 e 300 mg/kg/dia) e verapamil (5, 10 e 15 mg/kg/dia) foram administrados por via oral junto com NaCl. Anéis aórticos e faixas do átrio direito de ratos normotensos foram utilizados para investigar os mecanismos subjacentes. O nível de significância estatística adotado foi de 5%. RESULTADOS: A pressão arterial média diminuiu nos grupos hipertensos tratados com Sg.B e verapamil de forma dose-dependente (p <0,001). No estudo de reatividade vascular, a acetilcolina induziu relaxamentos com valor CE50 de 0,6 µg/mL (0,3­1,0) em ratos hipertensos tratados com Sg.B (300 mg/kg), sugerindo preservação endotelial. Em aorta isolada de rato normotenso, o Sg.B exibiu vasorrelaxamento com valor de CE50 de 0,15 mg/mL (0,10-0,20), após ablação por desnudamento endotelial ou pré-tratamento com L-NAME e atropina. O tratamento com Sg.B causou relaxamento contra contrações induzidas por K+ alto, como o verapamil. O Sg.B mostrou efeitos inotrópicos (82%) e cronotrópicos (56%) negativos em preparações isoladas atriais de ratos reduzidas com atropina. A avaliação fitoquímica indicou a presença de alcaloides, flavonoides e taninos. CONCLUSÃO: O S. guttatum possui efeito vasodilatador através da preservação da função endotelial, liberação de NO mediada pelo receptor muscarínico e inibição do movimento de Ca2+, enquanto o efeito depressor do miocárdio atrial pode estar ligado ao receptor muscarínico. Esses achados fornecem a base farmacológica para o uso do extrato de S. guttatum como um medicamento anti-hipertensivo.

Linalool-rich rosewood oil induces vago-vagal bradycardic and depressor reflex in rats.

Cardiovascular effects of the linalool-rich essential oil of Aniba rosaeodora (here named as EOAR) in normotensive rats were investigated. In anesthetized rats, intravenous (i.v.) injection of EOAR induced dose-dependent biphasic hypotension and bradycardia. Emphasis was given to the first phase (phase 1) of the cardiovascular effects, which is rapid (onset time of 1-3 s) and not observed in animals submitted to bilateral vagotomy or selective blockade of neural conduction of vagal C-fibre afferents by perineural treatment with capsaicin. Phase 1 was also absent when EOAR was directly injected into the left ventricle injection, but it was unaltered by i.v. pretreatment with capsazepine, ondansetron or HC030031. In conscious rats, EOAR induced rapid and monophasic hypotensive and bradycardiac (phase 1) effects that were abolished by i.v. methylatropine. In endothelium-intact aortic rings, EOAR fully relaxed phenylephrine-induced contractions in a concentration-dependent manner. The present findings reveal that phase 1 of the bradycardiac and depressor responses induced by EOAR has a vago-vagal reflex origin resulting from the vagal pulmonary afferents stimulation. Such phenomenon appears not to involve the recruitment of C-fibre afferents expressing 5HT3 receptors or the two chemosensory ion channels TRPV1 and TRPA1 . Phase 2 hypotensive response appears resulting from a direct vasodilatory action.

1-Nitro-2-phenylethane, the main constituent of the essential oil of Aniba canelilla, elicits a vago-vagal bradycardiac and depressor reflex in normotensive rats.

Previously, it was shown that intravenous (i.v.) treatment with the essential oil of Aniba canelilla (EOAC) elicited a hypotensive response that is due to active vascular relaxation rather than to the withdrawal of sympathetic tone. The present study investigated mechanisms underlying the cardiovascular responses to 1-nitro-2-phenylethane, the main constituent of the EOAC. In pentobarbital-anesthetized normotensive rats, 1-nitro-2-phenylethane (1-10mg/kg, i.v.) elicited dose-dependent hypotensive and bradycardiac effects which were characterized in two periods (phases 1 and 2). The first rapid component (phase 1) evoked by 1-nitro-2-phenylethane (10mg/kg) was fully abolished by bilateral vagotomy, perineural treatment of both cervical vagus nerves with capsaicin (250 microg/ml) and was absent after left ventricle injection. However, pretreatment with capsazepine (1mg/kg, i.v.) or ondansetron (30 microg/kg, i.v.) did not alter phase 1 of the cardiovascular responses to 1-nitro-2-phenylethane (10mg/kg, i.v.). In conscious rats, 1-nitro-2-phenylethane (1-10mg/kg, i.v.) evoked rapid hypotensive and bradycardiac (phase 1) effects that were fully abolished by methylatropine (1mg/kg, i.v.). It is concluded that 1-nitro-2-phenylethane induces a vago-vagal bradycardiac and depressor reflex (phase 1) that apparently results from the stimulation of vagal pulmonary rather than cardiac C-fiber afferents. The transduction mechanism of the 1-nitro-2-phenylethane excitation of C-fiber endings is not fully understood and does not appear to involve activation of either Vanilloid TPRV(1) or 5-HT(3) receptors. The phase 2 hypotensive response to 1-nitro-2-phenylethane seems to result, at least in part, from a direct vasodilatory effect since 1-nitro-2-phenylethane (1-300 microg/ml) induced a concentration-dependent reduction of phenylephrine-induced contraction in rat endothelium-containing aorta preparations.

Cardiovascular autonomic dysfunction in a novel rodent model of polycystic kidney disease.

Autonomic dysfunction, hypertension and cardiovascular morbidity in end stage renal disease are critically linked, however there are limited models available to investigate this relationship and develop clinical interventions. This study aimed to define the relationship between hypertension and autonomic function in a new rodent model of polycystic kidney disease (PKD). Using measures of heart rate and systolic blood pressure variability (HRV, SBPV), and time domain analysis of cardiac and sympathetic baroreflex function, we compared the Lewis PKD model (LPK) to a Lewis control. Systolic BP and SBPV were significantly higher in LPK vs. Lewis (168+/-7 vs. 131+/-8mm Hg, P

Antinociceptive effects of the novel spirocyclopiperazinium salt compound LXM-10 in mice.

The compound LXM-10 (2,4-dimethyl-9-beta-phenylethyl-3-oxo-6, 9-diazaspiro [5.5]undecane chloride) is a new spirocyclopiperazinium salt compound. This is the first article to evaluate its antinociceptive effect in the abdominal constriction test induced by acetic acid and the hot-plate test. In the abdominal constriction test, LXM-10 had a significant dose-response effect, and the maximal inhibition ratio was 79.2%. In the hot-plate test, LXM-10 had significant dose-response and time-response effects. The antinociceptive effect began at 1.0 h, peaked at 2.0 h, and persisted 3.0 h after s.c. administration. The hot-plate latency was increased by 126.8% at the dose of 12.0 mg/kg. The antinociceptive effect of LXM-10 was blocked by mecamylamine (a central and peripheral neuronal nicotinic acetylcholine receptor antagonist, 0.25, 0.5, 1.0 mg/kg, i.p.), hexamethonium (a peripheral neuronal nicotinic acetylcholine receptor antagonist, 0.2, 1.0, 5.0 mg/kg, i.p.), atropine (a central and peripheral muscarinic acetylcholine receptor antagonist, 0.2, 1.0, 5.0 mg/kg, i.p.), and atropine methylnitrate (a peripheral muscarinic acetylcholine receptor antagonist, 0.2, 1.0, 5.0 mg/kg, i.p.) in a dose-dependent fashion. In contrast, the effect was not blocked by naloxone (a non-selective opioid receptor antagonist, 2.0 mg/kg, i.p.) or yohimbine (a alpha(2)-adrenergic receptor antagonist, 1.0, 2.5, 5.0 mg/kg, i.p.) in the hot-plate test. Therefore, the antinociceptive effects of LXM-10 involve the peripheral neuronal nicotinic and muscarinic acetylcholine receptors; they are not related to opioid receptors or alpha(2)-adrenergic receptors. LXM-10 did not affect motor coordination, spontaneous activity, or body temperature. These findings with LXM-10 suggest that spirocyclopiperazinium derivatives could provide insight on new analgesics.

Sympathetic and parasympathetic component of bradycardia triggered by stimulation of NTS P2X receptors.

We have previously shown that activation of P2X purinoceptors in the subpostremal nucleus tractus solitarius (NTS) produces a rapid bradycardia and hypotension. This bradycardia could occur via sympathetic withdrawal, parasympathetic activation, or a combination of both mechanisms. Thus we investigated the relative roles of parasympathetic activation and sympathetic withdrawal in mediating this bradycardia in chloralose-urethane anesthetized male Sprague-Dawley rats. Microinjections of the selective P2X purinoceptor agonist alpha,beta-methylene ATP (25 pmol/50 nl and 100 pmol/50 nl) were made into the subpostremal NTS in control animals, after atenolol (2 mg/kg i.v.), a beta1-selective antagonist, and after atropine methyl bromide (2 mg/kg i.v.), a muscarinic receptor antagonist. The bradycardia observed with activation of P2X receptors at the low dose of the agonist is mediated almost entirely by sympathetic withdrawal. After beta1-adrenergic blockade, the bradycardia was reduced to just -5.1 +/- 0.5 versus -28.8 +/- 5.1 beats/min in intact animals. Muscarinic blockade did not produce any significant change in the bradycardic response at the low dose. At the high dose, both beta1-adrenergic blockade and muscarinic blockade attenuated the bradycardia similarly, -37.4 +/- 6.4 and -40.6 +/- 3.7 beats/min, respectively, compared with -88.0 +/- 11 beats/min in control animals. Double blockade of both beta1-adrenergic and muscarinic receptors virtually abolished the response (-2.5 +/- 0.8 beats/min). We conclude that the relative contributions of parasympathetic activation and sympathetic withdrawal are dependent on the extent of P2X receptor activation.

Cardiovascular effects of methyleugenol, a natural constituent of many plant essential oils, in normotensive rats.

Cardiovascular effects of intravenous (i.v.) treatment with methyleugenol (ME), a natural constituent of many plant essential oils, were investigated in normotensive rats. Additionally this study examined (I) whether the autonomic nervous system is involved in the mediation of ME-induced changes in mean aortic pressure (MAP) and heart rate (HR), and (II) whether the hypotensive effects of ME could result from its vasodilatory effects directly upon vascular smooth muscle. In both pentobarbital-anesthetized and conscious rats, i.v. bolus injections of ME (1 to 10 mg/kg) elicited similar and dose-dependent decreases in MAP. In anesthetized rats, ME decreased HR only at the highest dose (10 mg/kg), while changes of this parameter were not uniform in conscious rats. Pretreatment of anesthetized rats with bilateral vagotomy significantly reduced the bradycardia response to ME (10 mg/kg) without affecting the hypotension. In conscious rats, i.v. pretreatment with methylatropine (1 mg/kg) or hexamethonium (30 mg/kg) had no significant effect on ME-induced hypotension. In rat isolated thoracic aorta preparations, ME (0.006-1.68 mM) induced a concentration-dependent reduction of potassium (60 mM)-induced contraction. This is the first physiological evidence that i.v. treatment with ME in either anesthetized or conscious rats elicits hypotension; an effect that seems related to an active vascular relaxation rather than withdrawal of sympathetic tone.

Vagal and sciatic nerve stimulation have complex, time-dependent effects on chemically-induced seizures: a controlled study.

Previous studies of the effects of electrical vagus stimulation on experimental seizures were without suitable controls or statistical validation, and ignored the potential role of vagally-induced hemodynamic depression on seizure expression. This study addresses these limitations. The effects of periodic left vagus nerve stimulation (LVNS) on chemically-induced seizures in rats were compared with control groups receiving no stimulation (NoS), left sciatic nerve stimulation (LSNS) and LVNS after pretreatment with methyl atropine (MA-LVNS). Stimulation followed a 30 s on-120 s off cycle over 130 min. Seizures were scored visually and the temporal variation of their probability P(s) across the stimulation cycle was measured statistically. P(s) was significantly different (P<0.01) for all groups: LSNS had the highest and MA-LVNS the lowest seizure probability; LVNS and NoS had intermediate values. While LVNS blocked seizures, it also precipitated them, explaining why its anti-seizure effect was only slightly greater than NoS. Neither LVNS nor MA-LVNS induced changes in cortical rhythms ('activation') associated with decreased P(s), unlike LSNS which increased cortical rhythm synchrony and with it, P(s). LVNS alone induced marked bradycardia and moderate hypoxemia. In conclusion, cranial and peripheral nerve stimulation have complex, time-varying effects on cerebral excitability: low frequency LSNS facilitated seizures, while LVNS both suppressed and facilitated them. The anti-seizure effect of LVNS was small and may have, in part, been due to a hemodynamically-induced deficit in energy substrates. The effects of MA-LVNS on seizure duration and P(s) raise the possibility that, in the absence of hemodynamic depression, stimulation of this nerve does not have a strong anti-seizure effect.

Muscarinic depression of synaptic transmission in the epileptogenic GABA withdrawal syndrome focus.

The GABA withdrawal syndrome (GWS) is a model of local status epilepticus consecutive to the interruption of a prolonged GABA infusion into the rat somatomotor cortex. Bursting patterns in slices from GWS rats include intrinsic bursts of action potentials (APs) induced by intracellular depolarizing current injection and/or paroxysmal depolarization shifts (PDSs) induced by white matter stimulation. Possible changes in the effects of cholinergic drugs after in vivo induction of GWS were investigated on bursting cells (n = 30) intracellularly recorded in neocortical slices. In GWS slices, acetylcholine (Ach, 200-1000 microM) or carbachol (Cch, 50 microM) applications increased the number of bursts induced by depolarizing current injection while synaptically induced PDSs were significantly diminished (by 50-60%) or even blocked independently of the cholinergic-induced depolarization. The intrinsic burst facilitation and PDS depression provoked by Ach or Cch were mimicked by methyl-acetylcholine (mAch, 100-400 microM, n = 11), were reversed by atropine application (1-50 microM, n = 3), and were not mimicked by nicotine (50-100 microM, n = 4), indicating the involvement of muscarinic receptors. In contrast, in nonbursting cells from the same epileptic area (n = 42) or from equivalent area in control rats (n = 24), a nonsignificant muscarinic depression of EPSPs was induced by Cch and Ach. The mAch depression of excitatory postsynaptic potential (EPSPs) was significantly lower than that seen for PDSs in GWS rats. None of the cholinergic agonists caused bursting appearance in these cells. Therefore the present study demonstrates a unique implication of muscarinic receptors in exerting opposite effects on intrinsic membrane properties and on synaptic transmission in epileptiform GWS. Muscarinic receptor mechanisms may therefore have a protective role against the development and spread of epileptiform activity from the otherwise-activated epileptic focus.

Cardiovascular responses evoked by carbachol microinjection into the posterior hypothalamus involves ganglionic nicotinic and muscarinic mechanisms.

1. Microinjection of the cholinergic agonist carbachol (3.3, 5.5 and 13.2 nmol) into the posterior hypothalamic nucleus of conscious rats evokes a dose-dependent increase in blood pressure. The pressor response evoked by the lower doses of carbachol was attenuated by pretreatment with the ganglionic nicotinic receptor antagonist pentolinium (10 mg kg(-1), i.v.) while blockade of V1-vasopressin receptors with [d(CH2)5Tyr(Me)]AVP (20 microg kg(-1), i.v.) reduced the pressor response evoked by the highest dose. 2. The combination of pentolinium and the muscarinic receptor antagonist methylatropine (2 mg kg(-1), i.v.) completely blocked the response evoked by the lower doses while the addition of [d(CH2)5Tyr(Me)]AVP to these two antagonists was required for further inhibition of the pressor response to the highest dose of carbachol. Bilateral adrenal demedullation did not affect the pressor response evoked by 5.5 or 13.2 nmol of carbachol. 3. Treatment of intact and adrenal demedullated rats with pentolinium after the pressor response to 13.2 nmol of carbachol was underway reversed the pressor response, but not to the same degree as that provided by the combination of pentolinium and methylatropine, or pentolinium and [d(CH2)5Tyr(Me)]AVP. 4. Methylatropine or [d(CH2)5Tyr(Me)]AVP caused a slight reversal of the carbachol-induced pressor response once it was underway in intact rats. Methylatropine given before or after pentolinium worked with the pentolinium to completely reverse the response. Methylatropine given alone reversed the bradycardia evoked by carbachol to a tachycardia which itself was antagonized by subsequent treatment with pentolinium. 5. These results suggest that the pressor response evoked by carbachol microinjection into the posterior hypothalamic nucleus of conscious rats involves sympathoexcitation and vasopressin release. The sympathoexcitation involves nicotinic and muscarinic receptors in autonomic ganglia.

Autonomic components of the cardiovascular responses to an acoustic startle stimulus in rats.

1. A loud acoustic stimulus was administered to rats prior to and after treatment with autonomic blockers in order to unravel the autonomic mechanisms of the blood pressure (BP) and heart rate (HR) responses to startle. 2. Six rats, implanted with a BP telemetric system, were used in a randomized crossover saline-controlled (saline vs. autonomic blocker) study with a washout period of 7 days between each active session. A first acoustic stimulus (110 dB, 0.7 s) was administered. An autonomic blocker i.e. atropine methylnitrate (15 mg. kg-1), atenolol (15 mg. kg-1) or prazosin HCl (1 mg. kg-1), or physiological saline was administered i.p. 40 min prior to a second identical acoustic stimulus. 3. The average BP rise following the first stimulus was +25 mmHg and the average HR change was +17 bpm. The responses after autonomic blockades were affected as follows: atropine increased the HR rise (+45.1 +/- 1.7 bpm), atenolol reversed the HR changes to a bradycardic response (-21.4 +/- 9.1 bpm), after prazosin treatment the BP rise was reversed into a BP decrease (-11.3 +/- 3.2 mmHg) and the HR increase was amplified (+76.0 +/- 10.0 bpm). Finally, the delay for obtaining the maximal BP change was increased from 1.9 to 2.6 s following prazosin pretreatment. 4. These results indicate that the BP rise resulting from an acute loud noise depends on a vascular sympathetic activation (prevented with prazosin), which is partly blunted by vasodilation (revealed with prazosin). The evoked HR changes combine a sympathetic activation (fully expressed following atropine) and a vagal activation (unmasked with atenolol). Further experiments are necessary to document the vasodilatory component unmasked with prazosin.

Fear potentiation of acoustic startle stimulus-evoked heart rate changes in rats.

The present study examined the extent to which heart rate changes evoked by acoustic startle stimuli are affected by the development of fear during startle testing. The phasic heart rate responses of rats elicited by a 120-dB startle stimulus were characterized by decelerations that habituated across trials and accelerations that developed across trials in a manner that paralleled the development of freezing behavior. A 92-dB stimulus evoked little freezing or tachycardia, yet evoked decelerations of similar magnitude to the 120-dB stimulus. Pharmacological blockade of autonomic activity was used to uncouple freezing from the heart rate accelerations and to show that the accelerations were not an artifact of the habituating decelerations. These results indicate that heart rate responses to nonsignal stimuli depend critically on a rat's previous experience with those stimuli.

Organ-localized hypothalamic-stimulated vasculature changes in the cat.

Stimulation of specific lateral hypothalamic targets in a cat model induces vascular and/or cardiac changes. Evidence is presented that these may consist of discretely localized sympathetically mediated changes taking place in just one or two organs. Moreover, following stimulation of either one of two adjacent lateral hypothalamus sites, pressor effects are induced that superficially look similar, but prove to be mediated by different pathways. To investigate possible synapsing at sympathetic ganglia, e.g. in superior cervical or stellate ganglia, 50 micrograms atropine methyl nitrate, a ganglionic blocker, was applied directly to the ganglia. This was shown to potentiate the pressor effects, in some cases when applied to the superior cervical ganglia, in others to stellate ganglia, presumably by blockade of a ganglionic attenuating mechanism. The contributions made by different sympathetic nerves to the lateral hypothalamus-induced pressor effect were analysed. Stimulation of one of the lateral hypothalamus sites (TAR.I) in eight cats induced a pressor effect that was abolished by severing a nerve branch, from the superior cervical ganglia laterally, shown to innervate neck muscle vasculature. In another group of nine cats stimulation of TAR.II induced a pressor effect abolished by cutting a branch from the superior cervical ganglia medially, shown to be destined to the vasculature of pharyngeal muscles and possibly lower respiratory tract. The hypothesis that central control via the sympathetic nervous system is responsible for differential organ specific regulation of blood flow to individual organs is discussed.

Brain atriopeptin mediates AV3V depressor response.

In urethane-anesthetized rats, sodium L-glutamate (Glu) microinjection into the anteroventral third ventricle region (AV3V) induced a depressor response, but the heart rate remained unchanged, whereas Glu injection into its surrounding areas or normal saline injection into the AV3V had no effect on the arterial pressure and heart rate. Bilateral preinjection of procaine or atriopeptin III antiserum into the nucleus paraventricularis (NPV) and methyl atropine (IV) markedly attenuated the AV3V depressor response, but the hypotensive response was not significantly affected by phentolamine or propranolol (IV), indicating that atriopeptin in the NPV mediates the AV3V depressor response, and excitation of the cardiac vagus is also involved in this response.

Essential role of hypothalamic muscarinic and alpha-adrenergic receptors in atrial natriuretic peptide release induced by blood volume expansion.

Expansion of the blood volume induces natriuresis, which tends to return the blood volume to normal. This response is mediated at least in part by the release of atrial natriuretic peptide (ANP) into the circulation. Previous experiments have shown the participation of the anterior ventral third ventricular (AV3V) region of the hypothalamus in the ANP release that follows volume expansion. When injected into the AV3V region, the cholinergic drug carbachol induces natriuresis and the release of ANP. In the present experiments, microinjection of norepinephrine into the AV3V region induced natriuresis and an increase in plasma ANP. To determine whether cholinergic and alpha-adrenergic pathways are crucial to the volume expansion-induced release of ANP, certain receptor-blocking drugs were injected into the AV3V region of conscious rats. Thirty minutes later blood volume was expanded by intravenous injection of 2.0 ml/100 g of body weight of hypertonic saline (0.3 M NaCl). Microinjection of isotonic saline (2 microliters) into AV3V region of control animals 30 min prior to volume expansion had no effect on the 3-fold increase in plasma ANP concentrations measured 5 min after volume expansion. In contrast, although the receptor-blocking drugs did not alter the initial concentrations of plasma ANP 30 min later, just prior to volume expansion, blockade of muscarinic cholinergic receptors by intraventricular injection of 5 nmol (2 microliters) of atropine sulfate or methylatropine markedly reduced the response to volume expansion but did not obliterate it. Microinjection of the alpha receptor blocker phentolamine (5 nmol) into the AV3V 30 min prior to volume expansion also markedly suppressed the ANP response. Intraperitoneal (i.p.) injection of methylatropine (0.01 mmol/100 g of body weight), which does not cross the blood-brain barrier, also did not affect the basal levels of ANP 30 min after i.p. injection. But, in striking contrast with the blockade of the response to volume expansion induced by intraventricular injection of methylatropine, the response to volume expansion was markedly enhanced by i.p. injection of methylatropine. The results therefore indicate that hypothalamic muscarinic and alpha-adrenergic synapses are essential to release of ANP in response to volume expansion. These results are consistent with a hypothetical pathway for physiological control of ANP release which involves distension of baroreceptors within the right atria, carotid and aortic sinuses, and kidney which alters afferent input to brain stem noradrenergic neurons with axons projecting to the AV3V region. There they activate cholinergic interneurons by an alpha 1-adrenergic synapse. The cholinergic neurons in turn stimulate ANP neurons in this brain region via muscarinic receptors. The stimulation of these neurons activates efferent pathways which induce the release of ANP.