Bruno A. Carillo

Oxidative Stress in the Sympathetic Premotor Neurons Contributes to Sympathetic Activation in Renovascular Hypertension

BACKGROUND Based on previous data, we hypothesized that an increase of angiotensin II (Ang II)-via the Ang II type 1 (AT-1) receptor-in the rostral ventrolateral medulla (RVLM) and the paraventricular nucleus (PVN) of the hypothalamus could activate NAD(P)H oxidase that will produce superoxides resulting in increased sympathetic activity and hypertension. METHODS The mRNA expression of AT-1 receptors, NAD(P)H oxidase subunits (p47phox and gp91phox), and CuZnSOD were analyzed in the RVLM and PVN of male Wistar rats (Goldblatt hypertension model, 2K-1C). In addition, we administered Tempol 1 and 5 nmol into the RVLM, PVN, or systemically. The mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) were analyzed. RESULTS The AT-1 mRNA expression and NAD(P)H oxidase subunits was greater in the RVLM and PVN in 2K-1C compared to the control group. Furthermore, the CuZnSOD expression was similar in both groups. Tempol 1 nmol into the RVLM reduced MAP (15 +/- 1%) and RSNA (11 +/- 2%) only in 2K-1C rats. Tempol (5 nmol) in the same region decreased the MAP (12 +/- 4%) and RSNA (20 +/- 7%), respectively, only in 2K-1C. In the PVN, Tempol 5 nmol resulted in a significant fall in the MAP (24 +/- 1%) and in the RSNA (7.9 +/- 2%) only in the 2K-1C. Acute intravenous (IV) infusion of Tempol decreased MAP and RSNA in the 2K-1C but not in the control rats. CONCLUSIONS The data suggest that the hypertension and sympathoexcitation in 2K-1C rats were associated with an increase in oxidative stress within the RVLM, the PVN and systemically.

Perinatal Salt Restriction: A New Pathway to Programming Insulin Resistance and Dyslipidemia in Adult Wistar Rats

Several studies support the hypothesis that chronic diseases in adulthood might be triggered by events that occur during fetal development. This study examined the consequences of perinatal salt intake on blood pressure (BP) and carbohydrate and lipid metabolism in adult offspring of dams on high-salt [HSD; 8% (HSD2) or 4% (HSD1)], normal-salt (NSD; 1.3%), or low-salt (LSD; 0.15% NaCl) diet during pregnancy and lactation. At 12 wk of age, female Wistar rats were matched with adult male rats that were fed NSD. Weekly tail-cuff BP measurements were performed before, during, and after pregnancy. After weaning, the offspring received only NSD and were housed in metabolic cages for 24-h urine collection for sodium and potassium and nitrate and nitrite excretion measurements. At 12 wk of age, intra-arterial mean BP was measured, a euglycemic-hyperinsulinemic clamp was performed, and plasma lipids and nitrate and nitrite concentrations were determined. Tail-cuff BP was higher during pregnancy in HSD2 and HSD1 than in NSD and LSD dams. Mean BP (mm Hg) was also higher in the offspring of HSD2 (110 ± 5) and HSD1 (107 ± 5) compared with NSD (100 ± 2) and LSD (92 ± 2). Lower glucose uptake and higher plasma cholesterol and triacylglycerols were observed in male offspring from LSD dams (glucose uptake: HSD2 17 ± 4, HSD1 15 ± 3, NSD 11 ± 3, LSD 4 ± 1 mg · kg−1 · min−1; cholesterol: HSD2 62 ± 6, HSD1 82 ± 11, NSD 68 ± 10, LSD 98 ± 17 mg/dL; triacylglycerols: HSD2 47 ± 15, HSD1 49 ± 12, NSD 56 ± 19, LSD 83 ± 11 mg/dL). In conclusion, maternal salt intake during pregnancy and lactation has long-term influences on arterial pressure, insulin sensitivity, and plasma lipids of the adult offspring.

Differential sympathetic and angiotensinergic responses in rats submitted to low- or high-salt diet.

The present study was designed to evaluate, in Wistar rats, the effect of high- or low-salt diet on the hemodynamic parameters and on the renal and lumbar sympathetic nerve activity. The renal gene expression of the renin angiotensin system components was also evaluated, aiming to find some correlation between salt intake, sodium homeostasis and blood pressure increase. Male Wistar rats received low (0.06% Na, TD 92141-Harlan Teklad), a normal (0.5% Na, TD 92140), or a high-salt diet (3.12% Na, TD 92142) from weaning to adulthood. Hemodynamic parameters such as cardiac output and total peripheral resistance, and the renal and lumbar sympathetic nerve activity were determined (n=45). Plasma renin activity, plasma and renal content of angiotensin (ANG) I and II, and the renal mRNA expression of angiotensinogen, renin, AT1 and AT2 receptors were also measured (n=24). Compared to normal- and low-salt diet-, high-salt-treated rats were hypertensive and developed an increase (P<0.05) in total peripheral resistance and lumbar sympathetic nerve activity. A decrease in renal renin and angiotensinogen-mRNAs and in plasma ANG II and plasma renin activity was also found in salt overloaded animals. The renal sympathetic nerve activity was higher (P<0.05) in low- compared to high-salt-treated rats, and was associated with an increase (P<0.05) in renal ANG I and II and with a decrease (P<0.05) in AT2 renal mRNA. Plasma ANG I and II and plasma renin activity were higher in low- than in normal-salt rats. Our results show that increased blood pressure is associated with increases in lumbar sympathetic nerve activity and total peripheral resistance in high-salt-treated rats. However, in low-salt-treated rats an increase in the renal sympathetic nerve was correlated with an increase in the renal content of ANG I and II and with a decrease in AT2 renal mRNA. These changes are probably in favor of the antinatriuretic response and the sodium homeostasis in the low-salt group.

Role of the caudal pressor area in the regulation of sympathetic vasomotor tone

It is well known that the ventrolateral medulla contains neurons involved in the tonic and reflex control of the cardiovascular system. Two regions within the ventrolateral medulla were initially identified: the rostral ventrolateral medulla (RVLM) and the caudal ventrolateral medulla (CVLM). Activation of the RVLM raises arterial blood pressure and sympathetic nerve activity, and activation of the CVLM causes opposite effects. The RVLM premotor neurons project directly to sympathetic preganglionic neurons and are involved in the maintenance of resting sympathetic vasomotor tone. A significant proportion of tonic activity in the RVLM sympathetic premotor neurons is driven by neurons located in a third region of the ventrolateral medulla denominated caudal pressor area (CPA). The CPA is a pressor region located at the extreme caudal part of the ventrolateral medulla that appears to have an important role controlling the activity of RVLM neurons. In this brief review, we will address the importance of the ventrolateral medulla neurons for the generation of resting sympathetic tone related to arterial blood pressure control focusing on two regions, the RVLM and the CPA.

Changes in GABAergic inputs in the paraventricular nucleus maintain sympathetic vasomotor tone in chronic heart failure

The paraventricular nucleus (PVN) of the hypothalamus is an important region of the brain involved in the regulation of sympathetic vasomotor tone. Accumulating evidence supports the idea that a change in hypothalamic γ-aminobutyric acid (GABA)-ergic inhibitory and glutamatergic excitatory inputs contribute to the exacerbated sympathetic drive in chronic heart failure (HF). The purpose of this study was to determine whether a possible imbalance between glutamatergic and GABAergic inputs to the PVN contributes to increased sympathetic outflow in HF in two different sympathetic territories. Renal (RSNA) and splanchnic sympathetic nerve activity (SSNA), mean arterial blood pressure (MAP) and heart rate were recorded from urethane-anesthetized HF or sham rats. The NMDA-glutamate and GABA-A receptor densities within the PVN were quantified in HF and sham rats by autoradiography. Bilateral microinjection of kynurenic acid (4nmol) into the PVN decreased MAP and RSNA and SSNA in HF but not in sham rats. Furthermore, in response to GABA-A blockade in the PVN by bicuculline (400 pmol), hypertension and SSNA were reduced in HF compared to sham. The quantification of ionotropic NMDA receptors and GABA-A receptors in the PVN showed a significant reduction of GABA-A in HF rats; however, the NMDA density in the PVN did not differ between groups. Thus, this study provides evidence that the sympathoexcitation is maintained by an imbalance between GABAergic and glutamatergic inputs in the PVN in HF. The reduced GABAergic input results in relatively augmented glutamatergic actions in the PVN of HF rats.

Differential baroreceptor modulation mediated by the ventrolateral medulla

Previous studies have shown that pharmacological stimulation of a region denominated caudal pressor area (CPA), located in the caudal end of the ventrolateral medulla, induces increases in arterial blood pressure (BP). The aim of this study was to compare the responses on renal sympathetic nerve activity (rSNA) and BP responses mediated by stimulation of CPA or rostral ventrolateral medulla (RVLM), in intact or sino-aortic barodenervated rats. Male Wistar rats (300-350 g, n=15) were anesthetized (urethane 1.2 to 1.4 g/kg, i.v.) and artificially ventilated. The mean arterial pressure (MAP) and rSNA were measured during bilateral glutamate microinjection (10 nmo/100 nl) into the CPA or into the RVLM. Glutamatergic stimulation of the RVLM increased MAP (46+/-7 mm Hg) and rSNA (82+/-21%); during CPA stimulation, MAP and rSNA increased 60+/-7 mm Hg and 93+/-9%, respectively. However, despite the similarity of responses mediated by both regions, the duration of rSNA and blood pressure responses mediated by the CPA were significantly longer than the duration of the responses mediated by the RVLM. After barodenervation, there was an increase in the time-course and magnitude of sympathetic response only in response to RVLM stimulation but not in response to CPA. The results suggest a differential baroreceptor modulation on rSNA mediated by the ventrolateral medulla neurons. Glutamatergic activation of CPA neurons can cause large increases in the rSNA and BP with a weaker baroreceptor modulation when compared to responses mediated by the RVLM neurons.

Cardioprotective effect of ornitho-kinin in an anesthetized, open-chest chicken model of acute coronary occlusion

The generation of bradykinin (BK; Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) in blood and kallidin (Lys-BK) in tissues by the action of the kallikrein-kinin system has received little attention in non-mammalian vertebrates. In mammals, kallidin can be generated by the coronary endothelium and myocytes in response to ischemia, mediating cardioprotective events. The plasma of birds lacks two key components of the kallikrein-kinin system: the low molecular weight kininogen and a prekallikrein activator analogous to mammalian factor XII, but treatment with bovine plasma kallikrein generates ornitho-kinin [Thr6,Leu8]-BK. The possible cardioprotective effect of ornitho-kinin infusion was investigated in an anesthetized, open-chest chicken model of acute coronary occlusion. A branch of the left main coronary artery was reversibly ligated to produce ischemia followed by reperfusion, after which the degree of myocardial necrosis (infarct size as a percent of area at risk) was assessed by tetrazolium staining. The iv injection of a low dose of ornitho-kinin (4 microg/kg) reduced mean arterial pressure from 88 +/- 12 to 42 +/- 7 mmHg and increased heart rate from 335 +/- 38 to 402 +/- 45 bpm (N = 5). The size of the infarct was reduced by pretreatment with ornitho-kinin (500 microg/kg infused over a period of 5 min) from 35 +/- 3 to 10 +/- 2% of the area at risk. These results suggest that the physiological role of the kallikrein-kinin system is preserved in this animal model in spite of the absence of two key components, i.e., low molecular weight kininogen and factor XII.