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Thomas E Lohmeier

Publications and source records attributed to Thomas E Lohmeier.

11 recordsLinked to original sources
PubMed2006

Renal denervation does not abolish sustained baroreflex-mediated reductions in arterial pressure.

Recent studies indicate that suppression of renal sympathetic nerve activity and attendant increments in renal excretory function are sustained baroreflex-mediated responses in hypertensive animals. Given the central role of the kidneys in long-term regulation of arterial pressure, we hypothesized that the chronic blood pressure-lowering effects of the baroreflex are critically dependent on intact renal innervation. This hypothesis was tested in 6 dogs by bilaterally activating the carotid baroreflex electrically for 7 days before and after bilateral renal denervation. Before renal denervation, control values for mean arterial pressure and plasma norepinephrine concentration were 95+/-2 mm Hg and 96+/-12 pg/mL, respectively. During day 1 of baroreflex activation, mean arterial pressure decreased 13+/-1 mm Hg, and there was modest sodium retention. Daily sodium balance was subsequently restored, but reductions in mean arterial pressure were sustained throughout the 7 days of baroreflex activation. Activation of the baroreflex was associated with sustained decreases in plasma norepinephrine concentration ( approximately 50%) and plasma renin activity (30% to 40%). All of the values returned to control levels during a 7-day recovery period. Two weeks after renal denervation, control values for mean arterial pressure, plasma norepinephrine concentration, plasma renin activity, and sodium excretion were comparable to those measured when the renal nerves were intact. Moreover, after renal denervation, all of the responses to activation of the baroreflex were similar to those observed before renal denervation. These findings demonstrate that the presence of the renal nerves is not an obligate requirement for achieving long-term reductions in arterial pressure during prolonged activation of the baroreflex.

Animals↗
PubMed2006

Baroreflex activation for the treatment of hypertension: principles and practice.

This article reviews the history and current status of an innovative nonpharmacological approach for the treatment of resistant hypertension - chronic electrical activation of the afferent limb of the carotid baroreflex. Recent studies in both normotensive and hypertensive canine models have unambiguously demonstrated sustained and clinically relevant reductions in arterial pressure and sympathetic activity in the course of prolonged baroreflex activation. Clinical trials designed to evaluate the efficacy and safety of this therapy in patients with resistant hypertension are now underway in both Europe and the USA.

Animals↗
PubMed2005

Influence of prolonged baroreflex activation on arterial pressure in angiotensin hypertension.

Despite recent evidence indicating sustained activation of the baroreflex during chronic infusion of angiotensin II (Ang II), sinoaortic denervation does not exacerbate the severity of the hypertension. Therefore, to determine whether Ang II hypertension is relatively resistant to the blood pressure-lowering effects of the baroreflex, the carotid baroreflex was electrically activated bilaterally for 7 days in 5 dogs both in the presence and absence of a continuous infusion of Ang II (5 ng/kg per minute) producing high physiological plasma levels of the peptide. Under control conditions, basal values for mean arterial pressure (MAP) and plasma norepinephrine concentration (NE) were 93+/-1 mm Hg and 99+/-25 pg/mL, respectively. By day 7 of baroreflex activation, MAP and NE were reduced to 72+/-4 mm Hg (-21+/-3 mm Hg) and 56+/-15 pg/mL, respectively, but PRA was unchanged (control=0.41+/-0.06 ng ANG I/mL per hour). All values returned to basal levels by the end of a 7-day recovery period. After 7 days of Ang II infusion, MAP increased from 93+/-3 to 129+/-3 mm Hg, whereas NE fell from 117+/-15 to 86+/-23 pg/mL. During the next 7 days of baroreflex activation/Ang II infusion, further reductions in NE were not statistically significant, and on the final day of baroreflex activation, the reduction in MAP was only 5+/-1 mm Hg, compared with 21+/-3 mm Hg in the control normotensive state. These findings indicate that long-term baroreflex-mediated reductions in arterial pressure are markedly diminished, but not totally eliminated, in the presence of hypertension produced by chronic infusion of Ang II.

Angiotensin II↗
PubMed2005

Prolonged activation of the baroreflex: a viable approach for the treatment of hypertension?

In most patients with hypertension, arterial pressure is above the target level for control, even in those individuals taking multiple antihypertensive drugs. In this article, we review the history and current status of a nonpharmacologic approach for the treatment of hypertension--chronic electrical activation of the afferent limb of the carotid baroreflex. Recent studies in normotensive and hypertensive dogs have clearly demonstrated impressive and sustained reductions in arterial pressure and sympathetic activity during prolonged baroreflex activation. Clinical trials are now underway in Europe, and clinical investigation in the United States will begin this year to evaluate the efficacy of this therapy in patients with resistant hypertension.

Animals↗
PubMed2005

Recent insights into the interactions between the baroreflex and the kidneys in hypertension.

Recent findings in chronically instrumented animals challenge the classic concept that baroreflexes do not play a role in the chronic regulation of arterial pressure. As alterations in renal excretory function are of paramount importance in the chronic regulation of arterial pressure, several of these recent studies have focused on the long-term interactions between the baroreflex and the kidneys during chronic perturbations in arterial pressure and body fluid volumes. An emerging body of evidence indicates that the baroreflex is chronically activated in several experimental models of hypertension, but in most cases, the duration of these studies has not exceeded 2 wk. Although these studies suggest that the baroreflex may play a compensatory role in attenuating the severity of the hypertension, possibly even in primary hypertension with uncertain causes of sympathetic activation, there has been only limited assessment of the quantitative importance of this interaction in the regulation of arterial pressure. In experimental models of secondary hypertension, baroreflex suppression of renal sympathetic nerve activity is sustained and chronically promotes sodium excretion. This raises the possibility that the renal nerves may be the critical efferent link for baroreceptor-induced suppression of central sympathetic output through which long-term compensatory reductions in arterial pressure are produced. This contention is supported by strong theoretical evidence but must be corroborated by experimental studies. Finally, although it is now clear that pressure-induced increases in baroreflex activity persist for longer periods of time than previously suggested, studies using new tools and novel approaches and extending beyond 2 wk of hypertension are needed to elucidate the true role of the baroreflex in the pathogenesis of clinical hypertension.

Angiotensin II↗
PubMed2004

Prolonged activation of the baroreflex produces sustained hypotension.

The role of baroreflexes in long-term control of arterial pressure is unresolved. To determine whether chronic activation of the baroreflex produces sustained hypotension, we developed a method for prolonged activation of the carotid baroreflex in conscious dogs. This was achieved by chronically implanting electrodes around both carotid sinuses and using an externally adjustable pulse generator to electrically activate the carotid baroreflex. Control values for mean arterial pressure (MAP) and heart rate were 93+/-3 mm Hg and 64+/-4 bpm, respectively. After control measurements, the carotid baroreflex was activated bilaterally for 7 days at a level that produced a prompt and substantial reduction in MAP, and for day 1 MAP was reduced to 75+/-4 mm Hg. Moreover, this hypotensive response was sustained throughout the entire 7 days of baroreflex activation (day 7, MAP=72+/-5 mm Hg). During prolonged baroreflex activation, heart rate decreased in parallel with MAP, although the changes were not as pronounced (day 7, heart rate=51+/-3 bpm). Prolonged baroreflex activation was also associated with approximately 35% reduction in plasma norepinephrine concentration (control=87+/-15 pg/mL). After baroreflex activation, hemodynamic measures and plasma levels of norepinephrine returned to control levels. Interestingly, despite the pronounced fall in MAP, plasma renin activity did not increase during prolonged baroreflex activation. These data indicate that prolonged baroreflex activation can lead to substantial reductions in MAP by suppressing the sympathetic nervous system. Furthermore, sustained sympathoinhibitory effects on renin secretion may play an important role in mediating the long-term hypotensive response.

Animals↗
PubMed2003

Sustained activation of the central baroreceptor pathway in obesity hypertension.

The major goal of this study was to determine whether there is increased activation of medullary neurons that participate in the central baroreceptor reflex pathway in dogs with obesity-induced hypertension, a model of hypertension that is associated with increased sympathetic activity. We used Fos-like (Fos-Li) protein immunohistochemical methods to determine activation of neurons in the nucleus tractus solitarius (NTS), caudal ventrolateral medulla (CVLM), and rostral ventrolateral medulla (RVLM). Dogs were fed either a regular diet or an identical diet with the addition of 0.5 to 0.9 kg of cooked beef fat. After approximately 6 weeks of the high fat diet, body weight (36.3+/-0.4 vs 21.5+/-0.5 kg), mean arterial pressure (105+/-4 vs 91+/-3 mm Hg), and heart rate (97+/-4 vs 70+/-3 bpm) were significantly greater in obese than in control dogs, respectively. There was little Fos-Li immunoreactivity in medullary neurons of control dogs but marked reactivity in obese dogs. Specifically, the number of Fos-Li-positive cells in the NTS and CVLM was 3 to 5 times greater in obese than in control dogs. Furthermore, despite sustained activation of these baroreceptor-sensitive neurons, there was a significantly greater number of Fos-Li positive cells in the RVLM of dogs fed the high fat diet. As baroreceptor suppression of sympathoexcitatory cells in the RVLM is mediated by activation of neurons in the NTS and CVLM, these results support recent findings indicating that baroreflex suppression of sympathetic activity is a long-term compensatory response in hypertension. However, sympathoexcitatory inputs onto RVLM neurons would appear to predominate over the inhibitory effects of the baroreflex in obesity hypertension.

Animals↗
PubMed2002

Sustained activation of the central baroreceptor pathway in angiotensin hypertension.

Recent studies indicate that renal sympathetic nerve activity is chronically suppressed in angiotensin (Ang II) hypertension and that baroreflexes play a critical role in mediating this response. To support these findings, we determined whether the hypertension associated with chronic infusion of Ang II at 4.8 pmol/kg per minute (5ng/kg per minute) produces sustained activation of medullary neurons that participate in the central baroreceptor reflex pathway. We used Fos-like (Fos-Li) protein immunohistochemical methods to determine activation of neurons in the nucleus tractus solitarius (NTS), caudal ventrolateral medulla (CVLM), and rostral ventrolateral medulla (RVLM). Results were compared in three groups of chronically instrumented dogs subjected to infusion of: 1) saline (control); 2) Ang II-2 hours (acute); and 3) Ang II-5 days (chronic). Mean arterial pressure increased 22 +/- 3 and 35 +/- 3 mm Hg during acute and chronic Ang II infusion, respectively. There was little Fos-Li immunoreactivity in medullary neurons in control dogs. In contrast, during acute Ang II infusion there was a 2- to 3-fold increase in Fos-Li staining in the NTS and CVLM, but no increase in staining in RVLM neurons. As baroreceptor suppression of sympathoexcitatory cells in the RVLM is mediated by activation of neurons in the NTS and CVLM, these results were expected. More importantly, this same pattern of central neuronal activation was observed during chronic Ang II hypertension. Therefore, these results support recent findings indicating that baroreflex suppression of renal sympathetic nerve activity is a long-term compensatory response in Ang II hypertension.

Angiotensin II↗