An increase in the sympathoadrenal medullary function in stroke-prone spontaneously hypertensive rats under anesthetized and resting conditions

Effects of a Single Session of Acupuncture Treatment on Blood Pressure and Heart Rate Variability in Patients with Mild Hypertension

Objective: The aim of the present study was to compare the effects of acupuncture treatment on arterial blood pressure (BP) and heart rate (HR) in patients with mild hypertension with high sympathetic tone with those of normotensive patients and to examine the effects on cardiac sympathetic nerve activity (CSNA) and vagal activity using heart rate variability (HRV) analysis. Design: Eight male patients with prehypertension or stage I hypertension and eight normotensive age-matched patients were included in this study. All patients had their systolic BP (SBP), diastolic BP (DBP), HR, and HRV measured. In addition, the ratio of low-frequency (LF) to high-frequency (HF) HRV and the power of the HF of the HRV were recorded. The study was conducted at Kansai University of Health Sciences in Japan. Interventions: Each patient underwent a single, 15-min-long acupuncture session. Acupuncture was applied to PC6, LI4, ST36, LR3 on both sides, and GV20. Results: SBP and HR decreased significantly in the hypertensive group during and after acupuncture compared with the baseline SBP and HR (p < 0.05). LF/HF was significantly reduced during acupuncture (p < 0.05), and HF was significantly increased after acupuncture in the hypertensive group (p < 0.05). However, there were no significant changes in LF/HF or HF in the control group. Conclusions: Acupuncture may reduce the BP and HR in patients with mild hypertension. An HRV analysis suggests that acupuncture may suppress the enhanced basal CSNA activity and increase the vagal nerve activity in patients with mild hypertension. Clinical Trial Registration number: UMIN000041249.

Neural mechanisms of reflex inhibition of heart rate elicited by acupuncture-like stimulation in anesthetized rats

We briefly review our recent studies on the neural mechanisms of the reflex effects of acupuncture-like stimulation on heart rate in rats. In pentobarbital anesthetized rats, acupuncture-like stimulation of one of various segmental areas of the body (forelimb, chest, abdomen, hindlimb) invariably induces a decrease in heart rate. In the case of the hindlimb, the effect can be produced by stimulation of the muscles alone but not of skin alone, and is abolished by severance of the hindlimb somatic nerves. Electrical stimulation of groups III and IV nerve fibers (in the tibial nerve) decreases heart rate. Decrease in heart rate by acupuncture-like stimulation of a hindlimb is accompanied by a decrease in cardiac sympathetic nerve activity, and is abolished by cardiac sympathectomy but not by vagotomy. High spinal cord transection or infusion of the GABA(A) receptors antagonist, bicuculline, into the cisterna magna is effective in disrupting the reflex bradycardia. Opioid receptor blockade does not disrupt the reflex arc. We conclude that the reflex pathway involved in the decrease of heart rate by acupuncture-like stimulation comprises groups III and IV muscle afferent nerves whose activation stimulates GABAergic neurons in the brainstem and inhibits sympathetic outflow to the heart. When the sympathetic tone is high due to hypercapnia, the induced reduction in both cardiac sympathetic nerve activity and heart rate is not augmented, suggesting that the magnitude of sympatho-inhibitory response to acupuncture-like stimulation does not depend on pre-existing sympathetic tone.

Sympatho-inhibitory response of the heart as a result of short-term acupuncture-like stimulation of the rat hindlimb is not augmented when sympathetic tone is high as a result of hypercapnia

This study examined whether the sympatho-inhibitory response of the heart to acupuncture-like stimulation of a hindlimb in anesthetized rats depends on the sympathetic tone. Observed reductions in both cardiac sympathetic nerve activity and heart rate following short-term acupuncture-like stimulation of a hindlimb were not augmented when the sympathetic tone was high as a result of hypercapnia.

Direct evidence for imidazoline (I1) receptor modulation of ethanol action on norepinephrine-containing neurons in the rostral ventrolateral medulla in conscious spontaneously hypertensive rats

BACKGROUND

Enhancement of the rostral ventrolateral medulla (RVLM) presympathetic (norepinephrine, NE) neuronal activity represents a neurochemical mechanism for the pressor effect of ethanol. In this study, we tested the hypothesis that ethanol action on RVLM presympathetic neurons is selectively influenced by the signaling of the local imidazoline (I1) receptor. To support a neuroanatomical and an I1-signaling selectivity of ethanol, and to circumvent the confounding effects of anesthesia, the dose-related neurochemical and blood pressure effects of ethanol were investigated in the presence of selective pharmacological interventions that cause reduction in the activity of RVLM or nucleus tractus solitarius (NTS) NE neurons via local activation of the I1 or the alpha2-adrenergic receptor in conscious spontaneously hypertensive rats.

RESULTS

Local activation of the I1 receptor by rilmenidine (40 nmol) or by the I1/alpha2 receptor mixed agonist clonidine (1 nmol), and local activation of the alpha2-adrenergic receptor (alpha2AR) by the pure alpha2AR agonist alpha-methylnorepinephrine (alpha-MNE, 10 nmol) caused reductions in RVLM NE, and blood pressure. Intra-RVLM ethanol (1, 5, or 10 microg), microinjected at the nadir of the neurochemical and hypotensive responses, elicited dose-dependent increments in RVLM NE and blood pressure in the presence of local I1--but not alpha2-receptor activation. Only intra-NTS alpha-MNE, but not rilmenidine or clonidine, elicited reductions in local NE and blood pressure; ethanol failed to elicit any neurochemical or blood pressure responses in the presence of local activation of the alpha2AR within the NTS.

CONCLUSION

The findings support the neuroanatomical selectivity of ethanol, and support the hypothesis that the neurochemical (RVLM NE), and the subsequent cardiovascular, effects of ethanol are selectively modulated by I1 receptor signaling in the RVLM.

Kidney denervation combined with elimination of adrenal-renal portal circulation prevents the development of hypertension in spontaneously hypertensive rats

1. Kidney denervation in spontaneously hypertensive rats (SHR) during the prehypertensive stage delays and attenuates the development of hypertension. The same results have been obtained after elimination of the adrenal-renal portal circulation (ARPC). The aim of the present study was to investigate the influence of concomitant kidney denervation and elimination of ARPC on hypertension in SHR. 2. Experiments were performed on 6-week-old male SHR and Wistar-Kyoto (WKY) rats. In the first group of animals (group I), the ARPC was eliminated by removing the left adrenal gland and the right kidney. In the second group of rats (group II), the right kidney and the right adrenal gland were removed and the left kidney was denervated. In the third group of rats (group III), the right adrenal gland and the left kidney were removed and the right kidney was denervated. In the fourth group of rats (group IV), the right adrenal gland and the right kidney were removed. Group IV served as the control group. Denervations were repeated every 3 weeks. Systolic blood pressure was measured indirectly. 3. Elimination of ARPC (group I) and kidney denervation (group II) delayed and attenuated hypertension to the same degree (163 +/- 5 and 157 +/- 4 mmHg, respectively). Application of the these two methods concomitantly (group III) prevented the development of hypertension (130 +/- 6 mmHg). 4. We conclude that both intact efferent sympathetic renal nerves and adrenal hormones reaching the kidney through the ARPC may be mandatory factors for the development of arterial hypertension in SHR.

Noradrenaline synthesis after sympathetic nerve activation in rat atria and its dependence on calcium but not CAM kinase II and protein kinases A or C

1. The biosynthesis of noradrenaline following sympathetic nerve activation was investigated in rat atria. In particular the time course of noradrenaline synthesis changes, the relationship of changes in synthesis to transmitter release and the possible roles of second messengers and protein kinases were examined. 2. Rat atria incubated with the precursor [3H]-tyrosine synthesized [3H]-noradrenaline. Synthesis was enhanced following pulsatile electrical field stimulation (3 Hz for 5 min) with the bulk of the increase occurring in the first 45 min after the commencement of electrical stimulation. In separate experiments rat atria were pre-incubated with [3H]-noradrenaline and the radioactive outflow in response to electrical field stimulation (3 Hz for 5 min) was taken as an index of noradrenaline release. 3. Stimulation-induced (S-I) noradrenaline synthesis was significantly correlated to S-I noradrenaline release for a variety of procedures which modulate noradrenaline release by mechanisms altering Ca2+ entry into the neurone (r2 = 0.99): those which decreased release: tetrodotoxin (0.3 microM), Ca(2+)-free medium, lowering the frequency of nerve activation to 1 Hz, and those which increased release, tetraethylammonium (0.3 mM), phentolamine (1 microM) and the combination of phentolamine (1 microM) and adenosine (10 microM). On the strength of this relationship we suggest that Ca2+ entry is a determining factor in S-I synthesis changes rather than the amount of noradrenaline released. Indeed the reduction in noradrenaline release with the calmodulin-dependent protein (CAM) kinase II inhibitor KN-62 (10 microM) which acts subsequent to Ca2+ entry, did not affect S-I synthesis. 4. The cell permeable cyclic AMP analogue, 8-bromoadenosine 3',5'-monophosphate (BrcAMP, 90 and 270 microM), dose-dependently increased basal [3H]-noradrenaline synthesis in unstimulated rat atria. This effect was antagonized by the selective protein kinase A (PKA) antagonist, Rp-8-chloroadenosine 3',5'-cyclic monophosphorothioate (RClcAMPS, 300 microM), suggesting that PKA activation enhances basal noradrenaline biosynthesis in sympathetic nerve terminals. 5. The protein kinase inhibitors, KN-62 (CAM kinase II, 10 microM), RClcAMPS (PKA, 300 microM), polymyxin B (protein kinase C (PKC), 21 microM) and staurosporine (PKC, PKA and CAM kinase II, (0.1 microM) did not affect S-I synthesis, although KN-62, polymyxin B and staurosporine decreased S-I release. We conclude that S-I synthesis is triggered by Ca2+ entering the neurone but that the signalling pathway does not involve classical protein kinases and appears distinct from the steps involved in transmitter release.

Direct vascular connection between adrenal gland and kidney may play an important role in pathogenesis of hypertension

A direct vascular connection between adrenal gland and kidney exists in various species. Thereby kidney function might be modified by the adrenal gland more precisely. In addition, the impact of adrenal hormones on the kidney function due to this circulatory 'by-pass' might be much stronger than judged from the relevant hormone concentrations in the circulating blood. Because overactivity of the sympatho-adrenal system is evident in essential hypertension we hypothesize that the adrenal-renal vascular connection plays an important role in the pathogenesis of arterial hypertension.

2-Deoxy-D-glucose-induced central glycopenia differentially influences renal and adrenal nerve activity in awake SHR rats

2-deoxy-D-glucose (2-DG) evokes an increase in the efferent discharge rate of the adrenal nerve in narcotized rats and rabbits. The study reported here was undertaken to determine the sympathetic nerves and blood pressure responses to i.v. 2-DG administration in awake SHR rats. An increase in adrenal sympathetic nerve activity (adrSNA) by 63% was observed 15 min after 125 mg/kg 2-DG administration, but there were no changes in the renal sympathetic nerve activity (renSNA), blood pressure (BP) or the heart rate (HR). Additional administration of 375 mg/kg 2-DG (cumulative dose was 500 mg/kg) led to the increase in the adrSNA by more then 120%, and in BP by 20 mm Hg, whereas renSNA was increased only by 30%. These results indicate that 2-DG-induced neuroglycopenia evokes highly differential changes in adrenal and renSNA in awake SHR rats. Whether this explains the marked response in BP in SHR to 2-DG is to be established.