A comparison between sphygmomanometer-based and ambulatory blood pressure monitoring in acute salt loading and depletion protocol

INTRODUCTION: Ambulatory blood pressure monitors have been used in salt loading and depletion protocols. However, the agreement between measurements made using ambulatory blood pressure monitors and those made with the sphygmomanometer has not been evaluated. OBJECTIVE: The objective of this study was to compare the concordance of the two methods of blood pressure measurements in protocols of acute salt loading and depletion. METHOD: Systolic blood pressure was measured using a sphygmomanometer at the completion of salt infusion (2 L NaCl 0.9%, 4 h) and salt depletion (furosemide, 120mg/day, p.o.) in 18 volunteers. Using the Pearson correlation coefficient (ρ), these readings were compared with the mean systolic blood pressure measured using the ambulatory blood pressure monitoring device during the following periods: 4 h of saline infusion and 12 h of salt depletion; 4 h of saline infusion and the last 6 h of salt depletion; 12 h of salt loading and the last 6 h of depletion; 12 h of salt loading and 12 h of depletion. Salt sensitivity was defined by a difference in the systolic blood pressure between salt loading and salt depletion greater than 10 mmHg when measured with the sphygmomanometer, and the Kappa analysis of concordance (K) was used with a significance level of

Study of the neuronal isoform of nitric oxide synthase present in the peripheral sympathetic nervous system in spontaneously hypertensive rats (SHR) before and after developing arterial hypertension

Neste trabalho, nosso objetivo foi investigar a função e a expressão da isoforma neuronal da enzima sintase de óxido nítrico (nNOS) em ratas Wistar normotensas (N) e espontaneamente hipertensas (SHR) em diferentes fases de desenvolvimento. Estudos a resposta vasoconstritora induzida pela estimulação elétrica de nervos simpáticos periarteriais (EEP) em leito arterial mesentérico (LAM) isolado e perfundido (Krebs, 4ml/min) de ratas N com 30 e 180 dias e SHR de mesma idade. Também foi investigado a influência da hipertensão arterial sobre a modulação nitrérgica da resposta simpática usando um inibidor seletivo para nNOS, S-metil-tiocitrulina (SMTC) (20&micro;M), além de western blot e histoquímica (NADPH-diaforase) do gânglio simpático mesentérico superior. A pressão arterial nos animais de 30 dias foi maior no grupo SHR quando comparada ao grupo N (132,0±1,0 vs 115,9±2,3, SHR; P=0,01) assim como aos 180d (183,0±1,3 vs 126,7±3,1;SHR; P=0,001). Em ambos os animais a pressão arterial se elevou com o envelhecimento (126,7±3,1 vs 115,9±2,3, N; P=0,01); (183,0±1,3 vs 132,0±1,0, SHR; P=0,001). A pressão basal de perfusão dos LAM isolados de N 30d e SHR 30d não apresentaram diferenças (15,5±0,4 vs 13,4±1,0). Entretanto houve um aumento nos animais SHR 180d quando comparados aos N 180d (26,9±0,9 vs 15,7±0,4). A resposta simpática à EEP mostrou que em SHR 30d houve um aumento da resposta vasoconstritora máxima à EEP, quando comparado com N 30d (183,1 [153,3-212,9] vs (78,2 [70,2-86,2] EMAX±EPM, P= 0,001). O mesmo foi observado no grupo SHR 180d em relação ao grupo N 180d (171,1 [165,1-177,2] vs (106,1 [91,1-125,5] EMAX±EPM, P=0,003). Em animais SHR 180d houve um aumento da sensibilidade a EEP em relação ao SHR 30d (14,3 [13,8-14,9] vs (18,7 [15,4-22,0], FE50 [IC95%], P= 0,05). Em contraste, nos animais N 180d foi observado um aumento do efeito máximo em relação ao N 30d (106,1 [91,1-125,5] (78,2 [70,2-86,2] EMAX±EPM, P= 0,002). A perfusão de SMTC não modificou a resposta a EEP em preparações de animais N 30d. Porém, a SMTC produziu um aumento da sensibilidade a EEP em preparações SHR 30d quando comparadas com SHR 30d na ausência do inibidor (15,3 [13, 1-17,5] vs 18,7 [15,4-22,0], FE50 [IC95%], P=0,04). O mesmo foi observado em preparações N 180d (14,8 [12,8-16,7] vs 18,8 [14,4-22,1], FE50 [IC95%], P=0,03), não houve alterações entre as preparações de animais SHR 180d na presença ou na ausência de SMTC. A histoquímica do gânglio mesentérico superior mostrou diminuição significativa de neurônios NADPH-diaforase positivos SHR quando comparadas com N 30 e 180d (0,6±0,2 vs 2,8±0,4, P= 0,001), (0,7±0,46 vs 2,4± 0,4 P= 0.007). O Western blot mostrou uma redução significativa na expressão proteica da nNOS em gânglio mesentérico superior dos animais SHR 180d quando comparados com animais N 180d (0,1 ±0,009 vs 0,3±0,01, P=.0,005). Resumindo, os resultados desse trabalho mostram um menor número de neurônios NADPH-diaforase positivos no gânglio mesentérico superior de ratas SHR, presentes desde a fase de pré-hipertensão e mantidos durante a fase de hipertensão estabelecida, sugerindo uma relação causal entre a redução dos neurônios NADPH-diaforase positivos e o surgimento da hipertensão arterial nesse modelo. A análise dos dados funcionais e da expressão proteica da nNOS mostram que nas fases de pré-hipertensão há uma resposta adrenérgica exacerbada, modulada pelo NO, sugerindo um papel contra-regulador do óxido nítrico sobre a atividade adrenérgica. Nossos dados também mostram que esse mecanismo inicial se esgota com o tempo, uma vez que na fase de hipertensão estabelecida a atividade da enzima, assim como sua expressão encontram-se reduzidas.The objective of the present study was to investigate the function and expression of the nNOS in normotensive (N) and spontaneously hypertensive (SHR) female Wistar rats during different phases of development. We studied the vasoconstrictor response induced by electrical stimulation of periarterial sympathetic nerves (ESP) in a mesenteric arterial bed (MAB) isolated from N rats aged 30 and 180 days and SHR of the same age and perfused with Krebs (4 ml/min). We also investigated the influence of arterial hypertension on the nitrergic modulation of the sympathetic response using the selective nNOS inhibitor S-methyl-thiocitrulline (SMTC, 20&micro;M), as well as Western blot and histochemistry (NADPH-diaphorase) of the superior mesenteric sympathetic ganglion. The arterial pressure of 30d animals was higher for the SHR group compared to the N group (132.0±1.0 vs 115.9±2.3, SHR; P=0.01) as also observed at 180d (183.0±1.3 vs 126.7±3.1, SHR; P=0.001). Arterial pressure increased with aging in both groups (126.7±3.1 vs 115.9±2.3, N; P=0.01); (183.0±1.3 vs 132.0±1.0, SHR; P=0.001). Basal perfusion pressure of MAS isolated from 30d N and SHR did not show differences (15.5±0.4 vs 13.4±1.0). However, there was an increase in 180d SHR animals compared to 180d N animals (26.9±0.9 vs 15.7±0.4). The sympathetic response to ESP revealed an increase of the maximum vasoconstrictor response to ESP in 30d SHR compared to 30d N (183.1 [153.3-212.9] vs (78.2 [70.2-86.2] EMAX±SEM, P= 0.001). The same was observed in 180d SHR animals compared to 180d N animals (171.1 [165.1-177.2] vs (106.1 [91.1-125.5] EMAX±SEM. P=0.003). An increase in sensitivity to ESP occurred in 180d SHR compared to 30d SHR (14.3 [13.8-14.9] vs (18.7 [15.4-22.0], FE50 [95%CI], P<0.05). ln contrast, an increase in maximum effect was observed in 180d N animals compared to 30d N animals (106.1 [91.1-125.5] (78.2 [70.2-86.2] EMAX±SEM, P=0.002). SMTC perfusion did not modify the response to ESP in preparations from 30d N animals. However, SMTC elicited an increase in sensitivity to ESP in 30d SHR preparations compared to 30d SHR preparations in the absence of the inhibitor (15.3 [13.1-17.5] vs 18.7 [15.4-22.0]. FE50 [95%CI], P=0.04). The same was observed in 30d N preparations (14.8 [12.8-16.7] vs 18.8 [14.4-22.1 ], FE50 [95%CI], P=0.03). There was no difference between preparations from 180d SHR animals in the presence or absence of SMTC. Histochemistry of the superior mesenteric ganglion showed a significant reduction of NADPH-diaphorase-positive neurons in 180d SHR compared to 30 and 180d N (0.6 ± 0.2 vs 2.8±0.4, P=0.001). (0.76±0.46 vs 2.4±0.41, P<0.007). Western blot showed a significant reduction in the protein expression of nNOS in the superior mesenteric ganglion of 180d SHR compared to 180d N (0.1±0.009 vs 0.3±0.01, P=0.005). ln summary, the present results show that a smaller number of NADPH-diaphorase-positive neurons was present in the superior mesenteric ganglion of female SHR rats since the pre-hypertensive phase and that this reduction was maintained during the phase of established hypertension, suggesting a causal relation between the reduction of NADPH-diaphorase-positive neurons and the onset of arterial hypertension in this model. Analysis of functional data and of the protein expression of nNOS showed the occurrence of an exacerbated adrenergic response modulated by NO in the pre-hypertensive phases, suggesting a counter-regulatory role of NO in adrenergic activity. The present data also show that this initial mechanism is exhausted with time since the activity of the enzyme and its expression were reduced in the phase of established hypertension

A comparison between sphygmomanometer-based and ambulatory blood pressure monitoring in acute salt loading and depletion protocol

INTRODUCTION: Ambulatory blood pressure monitors have been used in salt loading and depletion protocols. However, the agreement between measurements made using ambulatory blood pressure monitors and those made with the sphygmomanometer has not been evaluated. OBJECTIVE: The objective of this study was to compare the concordance of the two methods of blood pressure measurements in protocols of acute salt loading and depletion. METHOD: Systolic blood pressure was measured using a sphygmomanometer at the completion of salt infusion (2 L NaCl 0.9%, 4 h) and salt depletion (furosemide, 120mg/day, p.o.) in 18 volunteers. Using the Pearson correlation coefficient (&#961;), these readings were compared with the mean systolic blood pressure measured using the ambulatory blood pressure monitoring device during the following periods: 4 h of saline infusion and 12 h of salt depletion; 4 h of saline infusion and the last 6 h of salt depletion; 12 h of salt loading and the last 6 h of depletion; 12 h of salt loading and 12 h of depletion. Salt sensitivity was defined by a difference in the systolic blood pressure between salt loading and salt depletion greater than 10 mmHg when measured with the sphygmomanometer, and the Kappa analysis of concordance (K) was used with a significance level of P<0.05. RESULTS: Only the blood pressure readings obtained using the ambulatory blood pressure device during 4 h of intravenous NaCl and during 12 h of salt depletion showed a high correlation with the variation in the systolic blood pressure measured by the sphygmomanometer, with a full agreement with the salt sensitivity classification (p = 0.71; P = 0.001 and K=1). CONCLUSION: In acute salt loading and depletion protocols, an ambulatory blood pressure monitoring device should be used to record the blood pressure during the 4-h interval of salt infusion and 12-h interval of salt depletion