Renal Denervation in Patients with Resistant Hypertension-Assessment by 3T Renal 23Na-MRI: Preliminary Results

BACKGROUND/AIM

Renal denervation (RDN) has been considered a promising therapy option for patients suffering from therapy-resistant hypertension. Besides, in blood-pressure regularization, the kidneys play a fundamental role in sodium ((23)Na) homeostasis. This study assesses the effect of RDN on renal (23)Na concentration using (23)Na magnetic resonance imaging (MRI).

PATIENTS AND METHODS

Two patients with therapy-resistant hypertension underwent RDN. (23)Na-MRI, (1)H-MRI, including diffusion weighted imaging (DWI), as well as endothelial dysfunction assessment, were performed 1 day prior, as well as 1, 30 and 90 days after RDN.

RESULTS

The renal corticomedullary (23)Na gradient did not change after RDN for all time points. Additionally, functional imaging and retinal vessel parameters were not influenced by RDN. Results regarding blood pressure changes and arterial stiffness, as well as patients' clinical outcome, were heterogeneous.

CONCLUSION

RDN does not seem to alter renal (23)Na concentration gradients, as measured by MRI.

Alveolar epithelial barrier functions in ventilated perfused rabbit lungs

We employed ultrasonic nebulization for homogeneous alveolar tracer deposition into ventilated perfused rabbit lungs. (22)Na and (125)I-albumin transit kinetics were monitored on-line with gamma detectors placed around the lung and the perfusate reservoir. [(3)H]mannitol was measured by repetitive counting of perfusion fluid samples. Volume of the alveolar epithelial lining fluid was estimated with bronchoalveolar lavage with sodium-free isosmolar mannitol solutions. Sodium clearance rate was -2.2 +/- 0.3%/min. This rate was significantly reduced by preadministration of ouabain/amiloride and enhanced by pretreatment with aerosolized terbutaline. The (125)I-albumin clearance rate was -0.40 +/- 0.05%/min. The appearance of [(3)H]mannitol in the perfusate was not influenced by ouabain/amiloride or terbutaline but was markedly enhanced by pretreatment with aerosolized protamine. An epithelial lining fluid volume of 1.22 +/- 0.21 ml was calculated in control lungs. Fluid absorption rate was 1.23 microl x g lung weight(-1) x min(-1), which was blunted after pretreatment with ouabain/amiloride. We conclude that alveolar tracer loading by aerosolization is a feasible technique to assess alveolar epithelial barrier properties in aerated lungs. Data on active and passive sodium flux, paracellular solute transit, and net fluid absorption correspond well to those in previous studies in fluid-filled lungs; however, albumin clearance rates were markedly higher in the currently investigated aerated lungs.

Quality management program and misadministrations--Nuclear Regulatory Commission. Final rule

The Nuclear Regulatory Commission (NRC) is amending regulations governing therapeutic administrations of byproduct material and certain uses of radioactive sodium iodide to require implementation of a quality management program to provide high confidence that the byproduct material or radiation from byproduct material will be administered as directed by an authorized user physician. The Commission believes this performance-based amendment will result in enhanced patient safety in a cost-effective manner while allowing the flexibility necessary to minimize intrusion into medical judgments. This amendment also modifies the notification, reporting, and recordkeeping requirements related to the quality management program and misadministrations.

Changes in sodium-22 turnover and total body potassium in two-kidney, one-clip renovascular hypertension

Changes in sodium-22 turnover and total body potassium (TBK) were studied during acute (within 2 weeks after clipping) and chronic (12-14 weeks after clipping) phases in two-kidney, one-clip (2k, 1c) hypertensive rabbits by using a whole body counter. Sodium-22 injected intravenously was eliminated more rapidly in hypertensive rabbits than in controls. The biological half-life (BHL) of sodium-22 was shorter in hypertensive rabbits during both acute (p less than 0.05) and chronic phases (p less than 0.001). A significant negative correlation was obtained between the BHL of sodium-22 and blood pressure (r = -0.588, p less than 0.05) in hypertensive rabbits. TBK decreased significantly at the chronic phase in hypertensive rabbits (p less than 0.05), while TBK showed no significant change in controls. Serum sodium and potassium did not change during the observation period. Increased plasma aldosterone concentration was observed during the acute phase in hypertensive rabbits. These results suggested that sodium retention was not a major factor in the acute and chronic phases of 2k, 1c hypertension in rabbits and that pressure natriuresis could explain, at least in part, the lack of sodium retention. Furthermore, there appears to be a derangement in the intracellular potassium metabolism which may be associated with the maintenance rather than the development of hypertension.

Sodium-24 studies in postmastectomy lymphedema

Seven patients were studied with 24Na to determine the relative disappearance time of the isotope from the postmastectomy lymphedematous arm as compared to the normal side. The results tend to confirm previously held convictions that the edema is usually confined to the subcutaneous fat and skin. The disappearance time (T1/2) of the radioactive sodium from the muscle of the edematous side was usually comparable to that of the control side. The data also indicate that the impairment of fluid drainage from other areas, such as the lateral chest wall, that normally drain into the axilla, is impaired similarly to that of the subcutaneous fat of the arm. Operative procedures designed to relieve the edema of the arm by providing an alternate route of drainage should provide a conduit for the fluid to an area that does not normally drain to the axilla of the affected side.

Loss of mouse testis mass after X-irradiation or injection of 22Na

Mass loss in the mouse testis per unit of absorbed dose was used as a means of comparing acute external with protracted internal whole body irradiation. The external and internal sources were X-rays and 22Na respectively. Estimates of the absolute dose to the testis from 22Na were made. The effects of acute and protracted radiation on the integrated loss in mass in the testis per unit of absorbed dose are similar.

Capillary permeability in cat choroid, studied with the single injection technique (II)

Transcapillary movements of 22Na, 51Cr-EDTA and 125I-myoglobin were studied in the cat choroid by means of the single injection technique, using labelled albumin as the reference tracer. By an external shunting of blood, recirculation of tracer was delayed and complete venous outflow curves became available for analysis. The initial extractions observed were 0.66, 0.35 and 0.08 respectively. The extractions decreased with time. Within 20--25 s the extracted fractions of the tracers had almost completely returned to the blood. The results indicate high permeability coefficients and small extravascular volumes of distribution. The retinal pigment epithelium seems to have a very low permeability to all three substances. Extraction of tritiated water at 20--25 s was about 0.30 probably due to rapid penetration of labelled water into the retina. Evidence for a stereo-specific transport system for glucose in the retinal pigment epithelium was found in experiments with labelled D-glucose and 3-O-methyl-D-glucose. The total amount of glucose delivered by the choroid was calculated from measurements of the a-v differences for unlabelled glucose.