Ovarian failure induced by 4-vinylcyclohexene diepoxide worsens the autonomic cardiovascular response to chronic unpredictable stress in rats.

AIMS: After menopause, women are more responsive to stress and more prone to exhibit hypertension, which elevates the risk of cardiac diseases. This vulnerability is due, in part, to the decline of ovarian steroids plasma levels. The 4-vinylciclohexane diepoxide (VCD) causes a gradual depletion of ovarian follicles causing loss of the normal ovarian function and a hormonal profile comparable to menopause in humans. We aimed to verify whether the ovarian failure (OF) worsens the cardiovascular autonomic response to stress. MAIN METHODS: Rats were treated with VCD (160 mg/kg) or oil for 15 days, exposed to chronic unpredictable stress (CUS) for 10 days and studied 80 and 180 days after VCD treatment. KEY FINDINGS: 80 days after VCD-treatment, stressed rats showed increased sympathetic nerve activity, reduced parasympathetic activity and an increase in the overall spontaneous baroreflex sensitivity (BRS). 180 days after VCD treatment, BRS was impaired and the vascular sympathetic activity was increased, independently of stress exposure. SIGNIFICANCE: Neither 80 nor 180 days after the onset of VCD-treatment the hypertensive effects of stress were enhanced in rats. However, OF led to a worsening on different aspects of the cardiovascular response to stress, which can cause cardiovascular complications when associated with ovarian aging.

Cardiovascular Autonomic Responses in the VCD Rat Model of Menopause: Effects of Short- and Long-Term Ovarian Failure.

After menopause, hypertension elevates the risk of cardiac diseases, one of the major causes of women's morbidity. The gradual depletion of ovarian follicles in rats, induced by 4-vinylcyclohexene diepoxide (VCD), is a model for studying the physiology of menopause. 4-Vinylcyclohexene diepoxide treatment leads to early ovarian failure (OF) and a hormonal profile comparable to menopause in humans. We have hypothesized that OF can compromise the balance between sympathetic and parasympathetic tones of the cardiovascular system, shifting toward dominance of the former. We aimed to study the autonomic modulation of heart and blood vessels and the cardiovascular reflexes in rats presenting short-term (80 days) or long-term (180 days) OF induced by VCD. Twenty-eight-day-old Wistar rats were submitted to VCD treatment (160 mg/kg, intraperitoneally) or vehicle (control) for 15 consecutive days and experiments were conducted at 80 or 180 days after the onset of treatment. Long-term OF led to an increase in the sympathetic activity to blood vessels and an impairment in the baroreflex control of the heart, evoked by physiological changes in arterial pressure. Despite that, long-term OF did not cause hypertension during the 180 days of exposure. Short-term OF did not cause any deleterious effect on the cardiovascular parameters analyzed. These data indicate that long-term OF does not disrupt the maintenance of arterial pressure homeostasis in rats but worsens the autonomic cardiovascular control. In turn, this can lead to cardiovascular complications, especially when associated with the aging process seen during human menopause.

Exaggerated sympathoexcitatory reflexes develop with changes in the rostral ventrolateral medulla in obese Zucker rats.

Obesity leads to altered autonomic reflexes that reduce stability of mean arterial pressure (MAP). Sympathoinhibitory reflexes such as baroreflexes are impaired, but reflexes that raise MAP appear to be augmented. In obese Zucker rats (OZR) sciatic nerve stimulation evokes larger increases in MAP by unknown mechanisms. We sought to determine the autonomic underpinnings of this enhanced somatic pressor reflex and whether other sympathoexcitatory reflexes are augmented. We also determined whether their final common pathway, glutamatergic activation of the rostral ventrolateral medulla (RVLM), was enhanced in male OZR compared with lean Zucker rats (LZR). Sciatic nerve stimulation or activation of the nasopharyngeal reflex evoked larger rises in splanchnic sympathetic nerve activity (SNA) (79% and 45% larger in OZR, respectively; P < 0.05) and MAP in urethane-anesthetized, ventilated, paralyzed adult OZR compared with LZR. After elimination of baroreflex feedback by pharmacological prevention of changes in MAP and heart rate, these two sympathoexcitatory reflexes were still exaggerated in OZR (167% and 69% larger, respectively, P < 0.05). In adult OZR microinjections of glutamate, AMPA, or NMDA into the RVLM produced larger rises in SNA (∼61% larger in OZR, P < 0.05 for each drug) and MAP, but stimulation of axonal fibers in the upper thoracic spinal cord yielded equivalent responses in OZR and LZR. In juvenile OZR and LZR, sympathoexcitatory reflexes and physiological responses to RVLM activation were comparable. These data suggest that the ability of glutamate to activate the RVLM becomes enhanced in adult OZR and may contribute to the development of exaggerated sympathoexcitatory responses independent of impaired baroreflexes.

Development of attenuated baroreflexes in obese Zucker rats coincides with impaired activation of nucleus tractus solitarius.

Adult obese Zucker rats (OZR; >12 wk) develop elevated sympathetic nerve activity (SNA) and mean arterial pressure (MAP) with impaired baroreflexes compared with adult lean Zucker rats (LZR) and juvenile OZR (6-7 wk). In adult OZR, baroreceptor afferent nerves respond normally to changes in MAP, whereas electrical stimulation of baroreceptor afferent fibers produces smaller reductions in SNA and MAP compared with LZR. We hypothesized that impaired baroreflexes in OZR are linked to reduced activation of brain stem sites that mediate baroreflexes. In conscious adult rats, a hydralazine (HDZ)-induced reduction in MAP evoked tachycardia that was initially blunted in OZR, but equivalent to LZR within 5 min. In agreement, HDZ-induced expression of c-Fos in the rostral ventrolateral medulla (RVLM) was comparable between groups. In contrast, phenylephrine (PE)-induced rise in MAP evoked markedly attenuated bradycardia with dramatically reduced c-Fos expression in the nucleus tractus solitarius (NTS) of adult OZR compared with LZR. However, in juvenile rats, PE-induced hypertension evoked comparable bradycardia in OZR and LZR with similar or augmented c-Fos expression in NTS of the OZR. In urethane-anesthetized rats, microinjections of glutamate into NTS evoked equivalent decreases in SNA, heart rate (HR), and MAP in juvenile OZR and LZR, but attenuated decreases in SNA and MAP in adult OZR. In contrast, microinjections of glutamate into the caudal ventrolateral medulla, a target of barosensitive NTS neurons, evoked comparable decreases in SNA, HR, and MAP in adult OZR and LZR. These data suggest that OZR develop impaired glutamatergic activation of the NTS, which likely contributes to attenuated baroreflexes in adult OZR.

Altered regulation of the rostral ventrolateral medulla in hypertensive obese Zucker rats.

Obese Zucker rats (OZR) have elevated sympathetic nerve activity (SNA) and mean arterial pressure (MAP) compared with lean Zucker rats (LZR). We examined whether altered tonic glutamatergic, angiotensinergic, or GABAergic inputs to the rostral ventrolateral medulla (RVLM) contribute to elevated SNA and MAP in OZR. Male rats (14-18 wk) were anesthetized with urethane (1.5 g/kg iv), ventilated, and paralyzed to record splanchnic SNA, heart rate (HR), and MAP. Inhibition of the RVLM by microinjections of muscimol eliminated SNA and evoked greater decreases in MAP in OZR vs. LZR (P < 0.05). Antagonism of angiotensin AT(1) receptors in RVLM with losartan yielded modest decreases in SNA and MAP in OZR but not LZR (P < 0.05). However, antagonism of ionotropic glutamate receptors in RVLM with kynurenate produced comparable decreases in SNA, HR, and MAP in OZR and LZR. Antagonism of GABA(A) receptors in RVLM with gabazine evoked smaller rises in SNA, HR, and MAP in OZR vs. LZR (P < 0.05), whereas responses to microinjections of GABA into RVLM were comparable. Inhibition of the caudal ventrolateral medulla, a major source of GABA to the RVLM, evoked attenuated rises in SNA and HR in OZR (P <0.05). Likewise, inhibition of nucleus tractus solitarius, the major excitatory input to caudal ventrolateral medulla, produced smaller rises in SNA and HR in OZR. These results suggest the elevated SNA and MAP in OZR is derived from the RVLM and that enhanced angiotensinergic activation and reduced GABAergic inhibition of the RVLM may contribute to the elevated SNA and MAP in the OZR.

Attenuated baroreflex control of sympathetic nerve activity in obese Zucker rats by central mechanisms.

Adult obese Zucker rats (OZRs) have reduced sympathetic responses to evoked changes in arterial pressure (AP) compared to lean Zucker rats (LZRs). This study examined whether attenuated sympathetic baroreflexes in OZRs may be due to altered sensory or central mechanisms. The OZRs had elevated baseline splanchnic sympathetic nerve activity (SNA) and mean AP (MAP) compared to age-matched LZRs under urethane anaesthesia (P < 0.05). Aortic depressor nerve activity (ADNA) was measured while AP was altered by infusions of phenylephrine or nitroprusside (+/-60 mmHg over 60-90 s) in rats treated with atropine and propranolol to eliminate changes in heart rate. Although baseline ADNA was higher in the hypertensive OZRs, the relationship between MAP and ADNA was comparable in OZRs and LZRs. In contrast, electrical stimulation of the ADN afferent fibres (5 s train, 2 ms pulses, 4 V, 0.5-48 Hz) produced dramatically smaller reductions in SNA and MAP in OZRs compared to LZRs (P < 0.05). After blockade of alpha-adrenergic receptors to prevent sympathetically mediated depressor responses, OZRs still had reduced sympathetic responses to stimulation of the ADN. In addition, stimulation of vagal afferent nerves electrically or with phenylbiguanide (1, 2, 4 and 8 microg, i.v.) produced smaller inhibitions of SNA in OZRs compared with LZRs (P < 0.05). These data suggest that attenuated sympathetic baroreflexes are the result of altered central mechanisms in OZRs, and not deficits in the responsiveness of aortic baroreceptors to AP. Furthermore, central deficits in the regulation of SNA in OZRs extend to other sympathoinhibitory reflexes initiated by vagal afferent nerves.

Sildenafil acts on the central nervous system increasing sympathetic activity.

Sildenafil induces vasodilation and is used for treating erectile dysfunction. Although its influence on resting heart function appears to be minimal, recent studies suggest that sildenafil can increase sympathetic activity. We therefore tested whether sildenafil injected into the central nervous system alters the autonomic control of the cardiovascular system in conscious rats. The effect of sildenafil citrate injected into the lateral cerebral ventricle was evaluated in conscious rats by means of the recording of lumbar sympathetic nerve activity (LSNA), spectral analysis of systolic arterial pressure and heart rate variability, spontaneous baroreflex sensitivity, and baroreflex control of LSNA. Intracerebroventricular (ICV, 100 microg /5 microl) administration of sildenafil caused remarkable tachycardia without significant change in basal arterial pressure and was associated with a conspicuous increase (47 +/- 14%) in LSNA. Spectral analysis demonstrated that systolic arterial pressure oscillations in the low frequency (LF) range were increased (from 6.3 +/- 1.5 to 12.8 +/- 3.8 mmHg(2)), whereas the high frequency (HF) range was not affected by ICV administration of sildenafil. Sildenafil increased pulse interval oscillations at LF and decreased them at HF. The LF-HF ratio increased from 0.04 +/- 0.01 to 0.17 +/- 0.06. Spontaneous baroreflex sensitivity measured by the sequence method and the baroreflex relationship between mean arterial pressure and LSNA were not affected by ICV administration of sildenafil. In conclusion, sildenafil elicited an increase in sympathetic nerve activity that is not baroreflex mediated, suggesting that this drug is able to elicit an autonomic imbalance of central origin. This finding may have implications for understanding the cardiovascular outcomes associated with the clinical use of this drug.

Aortic depressor nerve function examined in diabetic rats by means of two different approaches.

The present study examined in anesthetized rats, 5 or 120 days after the onset of streptozotocin-induced diabetes, the aortic depressor nerve (ADN) function by means of pressure-nerve activity curve (fitted by sigmoidal regression) and cross-spectral analysis between mean arterial pressure (MAP) and ADN activity. From the sigmoidal regression curve it was calculated the upper and lower ADN activity plateau, range, average gain and MAP halfway between the lower and upper plateau (MAP50). By means of spectral analysis it was calculated the transfer function magnitude (ratio of ADN activity/MAP) as an index of ADN sensitivity (gain) during induced (withdrawal and reinfusion of blood) slow (0.35 Hz) oscillations of MAP simulating Mayer's waves and spontaneous oscillations (approximately 1.5 Hz) caused by respiratory movement. Diabetic rats exhibited, at 5 or 120 days, lower MAP and heart rate. The parameters calculated by means of the sigmoidal regression curve, as well as the ADN activity gain during slow or spontaneous oscillations of MAP, were similar in diabetic and control rats. In conclusion, it was demonstrated that ADN activity was not altered after 5 or 120 days of experimental diabetes, even though the literature documents, at this time frame of diabetes, a conspicuous derangement of the baroreflex.

Peroxidase and lipid peroxidation of soybean roots in response to p-coumaric and p-hydroxybenzoic acids

The scope of the present study was to investigate how the p-coumaric (p-CA) and p-hydroxybenzoic (p-HD) acids affect the peroxidase (POD, EC 1.11.1.7) activity, the lipid peroxidation (LP) and the root growth of soybean (Glycine max (L.) Merr.). Three-day-old seedlings were cultivated in nutrient solution containing p-CA or p-HD (0.1 to 1 mM) for 48 h. After uptake, both compounds (at 0.5 and 1 mM) decreased root length (RL), fresh weight (FW) and dry weight (DW) while increased soluble POD activity, cell wall (CW)-bound POD activity (with 1 mM p-CA and 0.5 mM p-HD) and LP