Effects of a reversible 'nephrectomy' on renal sympathetic activity and blood pressure in the rat: evidence for an acute angiotensin-mediated hypertension

Effectiveness of renal denervation therapy for resistant hypertension: a systematic review and meta-analysis

OBJECTIVES

This study sought to determine the current effectiveness and safety of sympathetic renal denervation (RDN) for resistant hypertension.

BACKGROUND

RDN is a novel approach that has been evaluated in multiple small studies.

METHODS

We performed a systematic review and meta-analysis of published studies evaluating the effect of RDN in patients with resistant hypertension. Studies were stratified according to controlled versus uncontrolled design and analyzed using random-effects meta-analysis models.

RESULTS

We identified 2 randomized controlled trials, 1 observational study with a control group, and 9 observational studies without a control group. In controlled studies, there was a reduction in mean systolic and diastolic blood pressure (BP) at 6 months of -28.9 mm Hg (95% confidence interval [CI]: -37.2 to -20.6 mm Hg) and -11.0 mm Hg (95% CI: -16.4 to -5.7 mm Hg), respectively, compared with medically treated patients (for both, p < 0.0001). In uncontrolled studies, there was a reduction in mean systolic and diastolic BP at 6 months of -25.0 mm Hg (95% CI: -29.9 to -20.1 mm Hg) and -10.0 mm Hg (95% CI: -12.5 to -7.5 mm Hg), respectively, compared with pre-RDN values (for both, p < 0.00001). There was no difference in the effect of RDN according to the 5 catheters employed. Reported procedural complications included 1 renal artery dissection and 4 femoral pseudoaneurysms.

CONCLUSIONS

RDN resulted in a substantial reduction in mean BP at 6 months in patients with resistant hypertension. The decrease in BP was similar irrespective of study design and type of catheter employed. Large randomized controlled trials with long-term follow-up are needed to confirm the sustained efficacy and safety of RDN.

Uninephrectomy reduces 11β-hydroxysteroid dehydrogenase type 1 and type 2 concomitantly with an increase in blood pressure in rats

Renal allograft donors are at risk of developing hypertension. Here, we hypothesized that this risk is at least in part explained by an enhanced intracellular availability of 11β-hydroxyglucocorticoids due to an increased 11β-hydroxysteroid dehydrogenase type 1 enzyme (11β-HSD1), an intracellular prereceptor activator of biologically inactive 11-ketocorticosteroids in the liver, and/or a diminished 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), an inactivator of 11β-hydroxyglucocorticoids in the kidney. To test this hypothesis, uninephrectomized (UNX) (n=9) and sham-operated (n=10) adult Sprague-Dawley rats were investigated. Mean arterial blood pressure and heart rate were measured continuously by telemetry for 6 days in week 5 after UNX. The mRNA of 11β-Hsd1 and 11β-Hsd2 in liver and kidney tissues were assessed by RT-PCR and the 11β-HSD activities were directly quantified in their corresponding tissues by determining the ratios of (tetrahydrocorticosterone+5α-tetrahydrocorticosterone)/tetrahydrodehydrocorticosterone ((THB+5α-THB)/THA) and of corticosterone/dehydrocorticosterone (B/A) by gas chromatography-mass spectrometry. The apparent total body activities of 11β-HSD1 and 11β-HSD2 were estimated using the urinary and plasma ratios of (THB+5α-THB)/THA and B/A. Mean arterial blood pressure was increased after UNX when compared with sham operation. Hepatic mRNA content of 11β-Hsd1 and hepatic, plasma, and urinary ratios of (THB+5α-THB)/THA were decreased after UNX, indicating diminished access of glucocorticoids to its receptors. In renal tissue, 11β-Hsd2 mRNA was reduced and B/A ratios measured in kidney, plasma, and urine were increased, indicating reduced 11β-HSD2 activity and enhanced access of glucocorticoids to mineralocorticoid receptors. Both 11β-HSD1 and 11β-HSD2 are downregulated after UNX in rats, a constellation considered to induce hypertension.

A thermodynamic model of the sympathetic and parasympathetic nervous systems

In light of the nonequilibrium thermodynamics by I. Prigogine, the autonomic nervous system as a whole may be viewed as a dissipative structure progressively assembled in the course of evolution, plastically and rhythmically interfaced between forebrain, internal and external environments, to regulate energy, matter and information exchanges. In the present paper, this hypothesis is further pursued to verify whether the two main divisions of the autonomic nervous system, the sympathetic and parasympathetic systems, may support different types of exchange with the external environment. Previous data from hypothalamic stimulation experiments, studies of locus coeruleus function and available data on behavioral functional organization indicate that (1) tight engagement with the external environment, (2) high level of energy mobilization and utilization and (3) information mainly related to exteroceptive sensory stimulation characterize a behavioral prevalence of sympathoadrenal activation. On the other hand, (1) disengagement from the external environment, (2) low levels of internal energy and (3) dominance of proprioceptive information characterize a behavioral prevalence of vagal tone. Behavioral matter exchanges such as feeding, drinking, micturition and defecation are equally absent at the extreme of sympathoadrenal and vagally driven behaviors. The autonomic nervous system as a whole is genetically determined, but the sympathoadrenal system has been mainly designed to organize the visceral apparatus for an action to be performed by the biological system in the external environment and to deal with the novelty of task and of the environment, while the functional role of the parasympathetic is to prepare the visceral apparatus for an action to be performed by the biological system on itself, for recovery and self-protection (homeostasis), and is reinforced by repetition of phylo- and ontogenetically determined patterns. The available clinical data further support this interpretation indicating that an increased sympathetic and a decreased vagal tone may represent a consistent risk factor for cardiovascular diseases.

Factors influencing acute ischaemia-induced renal hypertension in rats

OBJECTIVE

To verify if the acute hypertension that occurs after reversal of complete renal ischaemia is related to the duration of ischaemia, is different in one-kidney (1K) and two-kidney (2K) rats, and is prevented by angiotensin receptor blockade.

METHODS

Four groups of Sprague-Dawley rats anaesthetized with pentobarbitone were studied before, during and after a reversible, complete renal ischaemia achieved by functional right nephrectomy.

RESULTS

In 1K rats (group 1, n = 21), reopening of right renal hilum after functional right nephrectomy of 180, 60 and 30 min was followed by peak increases in systolic blood pressure of 76.0 10.1 mmHg, 36.5 10.0 mmHg and 18.4 4.4 mmHg, respectively (mean SEM). In 2K rats (group 2, n = 21), functional right nephrectomy of 180, 60 and 30 min was followed by smaller increases in blood pressure of 49.8 7.6 mmHg, 5.9 3.3 mmHg and 8.3 2.1 mmHg, respectively. Plasma renin activity was directly related to the duration of functional right nephrectomy, and was greater in 1K rats. In group 3, irbesartan administered to 1K rats (n = 8) during functional right nephrectomy almost completely prevented the development of hypertension upon reopening. In group 4, labetalol injected intravenously in 1K rats (n = 3) did not prevent the blood pressure surge at reopening (49.2 8.5 mmHg).

CONCLUSIONS

An experimental acute renal hypertension may be elicited both in 1K and in 2K rats and for functional right nephrectomy of 30, 60 and 180 min duration. The increase in blood pressure is proportional to the duration of functional right nephrectomy and greater in 1K than in 2K rats. The experimental acute renal hypertension is due to acute release of renin and generation of endogenous angiotensin II, and is specifically prevented by the angiotensin II type 1 receptor blocker, irbesartan, but not by labetalol.

Effects of L-carnosine on renal sympathetic nerve activity and DOCA-salt hypertension in rats

The effects of L-carnosine (beta-alanyl-L-histidine) on the neural activity of the renal sympathetic nerve and on DOCA-salt hypertension in rats were examined. Intravenous injection of 1 microg L-carnosine inhibited renal sympathetic nerve activity in urethane-anesthetized animals, and a diet containing 0.0001% or 0.001% L-carnosine decreased blood pressure elevation in DOCA-salt hypertensive rats. Since L-carnosine is mainly synthesized in the skeletal muscles of mammals, it is not unreasonable to postulate that L-carnosine is an endogenous factor controlling the blood pressure in a manner possibly antagonistic to the obesity-associated hypertensive effect of leptin.

The visceral nervous system and its environments

Starting from the observation of the relationships of the biological system with its environments and of the genetically determined neuronal properties of plasticity and rhythmicity, it is possible to propose a new hypothesis about the functional role and organization of the visceral nervous system based on the physical model of the Dissipative Structure by I. Prigogine. The similarily between the visceral nervous system function and this model is supported by the following observations: (1) The visceral nervous system is a complex system, composed of many interacting units, which works away from thermodynamic equilibrium; (2) the functional organization of the nervous system is strongly dependent on internal and external environmental stimuli; (3) it is characterized by the presence of rhythms and periodic behaviors and (4) the internal order of the system is maintained in the continuous interplay between function, structure and fluctuations. On the basis of the present hypothesis, a few general principles can be formulated: (1) the higher brain centers, the fluid matrix and the external world, are the visceral nervous system natural environments; (2) with which it is plastically interfaced as a thermodynamic dissipative structure; (3) its main functional role is to regulate, distribute and maintain ordered exchanges of matter, energy and information between these environments. The present is a general interpretation of the operations of the visceral nervous system as a whole. In the frame of this interpretation the hypotheses so far formulated, including the homeostatic theory, can be viewed as the description of discrete and complementary aspects of the visceral nervous system functions.

Hypertension after renal transplantation

With current immunosuppression, elevated blood pressure is found in almost 90% of renal graft recipients. Major causes of this are impairment of renal function (secondary to chronic allograft nephropathy or less frequently recurrence of primary renal disease), the use of calcineurin inhibitors as immunosuppressants, uncontrolled renin secretion by the shrunken kidneys of the recipient, stenosing lesions of the transplant artery (or the upstream arteries of the recipient), polycythemia, and genetic predisposition to hypertension of the graft donor. Even minor degrees of blood pressure elevation have a significant impact on survival of the recipient and on graft survival, presumably by amplifying vascular injury to the graft. In this respect, elevation of systolic blood pressure and an abnormal circadian blood pressure profile are of particular relevance. In contrast to previous opinion, angiotensin converting enzyme inhibitors are indicated in treatment, but given the causal role of sodium retention and graft vasoconstriction, diuretics and calcium channel blockers remain mainstays of antihypertensive treatment in the renal allograft recipient.