Responses of glomerular filtration, renal blood flow and salt-water handling to acute cardioselective and non-selective beta-adrenoceptor blockade in essential hypertension

Physiological confounders of renal blood flow measurement

OBJECTIVES

Renal blood flow (RBF) is controlled by a number of physiological factors that can contribute to the variability of its measurement. The purpose of this review is to assess the changes in RBF in response to a wide range of physiological confounders and derive practical recommendations on patient preparation and interpretation of RBF measurements with MRI.

METHODS

A comprehensive search was conducted to include articles reporting on physiological variations of renal perfusion, blood and/or plasma flow in healthy humans.

RESULTS

A total of 24 potential confounders were identified from the literature search and categorized into non-modifiable and modifiable factors. The non-modifiable factors include variables related to the demographics of a population (e.g. age, sex, and race) which cannot be manipulated but should be considered when interpreting RBF values between subjects. The modifiable factors include different activities (e.g. food/fluid intake, exercise training and medication use) that can be standardized in the study design. For each of the modifiable factors, evidence-based recommendations are provided to control for them in an RBF-measurement.

CONCLUSION

Future studies aiming to measure RBF are encouraged to follow a rigorous study design, that takes into account these recommendations for controlling the factors that can influence RBF results.

Dynamic tissue perfusion assessment reflects associations between antihypertensive treatment and renal cortical perfusion in patients with chronic kidney disease and hypertension

PURPOSE

Renal cortical perfusion measured in noninvasive, dynamic ultrasonic method is connected with the hemodynamic cardiac properties and renal function. Antihypertensive drugs affect the functioning of the heart and kidneys. The aim of the study was to evaluate the effect of a chronic use of antihypertensive drugs on ultrasound parameters of renal cortical perfusion.

METHODS

The study included 56 consecutive patients (49 M + 7 F, age 54.0 ± 13.3) with stable chronic kidney disease and hypertension. Color Doppler dynamic tissue perfusion measurement was used to assess renal cortical perfusion.

RESULTS

Patients were treated with a mean of 2.7 ± 1.4 antihypertensive drugs, of which diuretics accounted for 25%, angiotensin-converting enzyme inhibitors (ACE-I) together with angiotensin receptor blockers (ARB) 24%, beta-blockers (BB) 23%, calcium channel blockers 16%, alpha-1 blockers (α1B) 9% and centrally acting drugs 3%. All investigated groups of drugs correlated significantly with parameters of renal perfusion. In multivariable regression analyses adjusted to age, diuretics were connected with the decrease (r = - 0.473) and ACE-I + ARB (r = 0.390) with the improvement of proximal and whole renal cortex perfusion (R² = 0.28; p < 0.001), whereas BB (r = - 0.372) and α1B (r = - 0.280) independently correlated with worsened perfusion of renal distal cortex (R² = 0.21, p < 0.01).

CONCLUSIONS

The type of antihypertensive therapy had a significant influence on the ultrasound parameters of renal cortical perfusion. Noninvasive, ultrasonic dynamic tissue perfusion measurement method appears to be an adequate tool to assess the impact of drugs on renal cortical perfusion.

Clearance and beyond: the complementary roles of GFR measurement and injury biomarkers in acute kidney injury (AKI)

Acute kidney injury (AKI) is a common and frequently fatal illness in critically ill patients. The reliance on daily measurements of serum creatinine as a surrogate of glomerular filtration rate (GFR) not only delays diagnosis and development of successful therapies but also hinders insight into the pathophysiology of human AKI. Measurement of GFR under non-steady-state conditions remains an elusive gold standard against which biomarkers of renal injury need to be judged. Approaches to the rapid (near real-time) measurement of GFR are explored. Even if real-time GFR was available, absent baseline information will always limit diagnosis of AKI based on GFR or serum creatinine to a detection of change. Biomarkers of renal cellular injury have provided new strategies to facilitate detection and early intervention in AKI. However, the diagnostic and predictive performance of urinary biomarkers of injury vary, depending on both the time after renal injury and on the preinjury GFR. Progress in understanding the role of each novel biomarker in the causal pathways of AKI promises to enhance their diagnostic potential. We predict that combining rapid measures of GFR with biomarkers of renal injury will yield substantive progress in the treatment of AKI.

Renal and limb vasodilatation during acute beta-adrenoceptor blockade with indenolol

Indenolol is a noncardioselective beta-adrenoceptor blocking drug with partial agonist activity. The mechanism of its acute antihypertensive activity has been evaluated in a double-blind, inpatient, crossover, randomized study versus placebo in 12 patients (eight men, four women, mean age 53 +/- 13 yr) with I and II WHO grade essential hypertension. Patients discontinued all antihypertensive and diuretic drugs at least 4 weeks before entry into the study. The effects of indenolol (120 mg) and placebo (2 weeks apart) were measured, in the same patient, 2 hours after a single oral administration. Variations of cardiac function were assessed by radionuclide angiocardiography, renal blood flow by sequential scintigraphy, and leg blood flow by strain-gauge plethysmography. Compared with placebo, indenolol reduced systolic blood pressure by 27.9 mm Hg and diastolic blood pressure by 17.1 mm Hg. Heart rate was also significantly decreased. The hemodynamic profile of indenolol activity was characterized by a decrease of cardiac index, without significant changes in systemic vascular resistance. Both renal and leg blood flow were increased by indenolol, and vascular resistance in these districts was considerably reduced. The percent reduction of renal vascular resistance was correlated significantly with the percent reduction of mean blood pressure. In conclusion, acute administration of indenolol exerts a considerable antihypertensive activity associated with a marked vasodilation in vascular districts involved in the progression of hypertensive disease such as the renal and muscular vasculature.

Effects of acute beta-adrenoceptor blockade with metoprolol on the renal response to dopamine in normal humans

The present study investigated the contribution of adrenergic beta 1-receptor stimulation to the cardiovascular and renal effects of low-dose dopamine in eight normal, water-loaded humans. Metoprolol (100 mg) or placebo was administered orally at 08.00 h in a randomized, double-blind fashion on two different days. Renal clearance studies were performed during a 1 h baseline period, two 1 h periods with dopamine infusion (3 micrograms kg-1 min-1), and a 1 h recovery period. Cardiac output was measured by an ultrasonic Doppler method, and lithium clearance (CLLi) was used to estimate proximal tubular outflow. Baseline values of heart rate, systolic pressure and mean arterial pressure decreased with metoprolol compared with placebo, but cardiac output, effective renal plasma flow (ERPF) and glomerular filtration rate (GFR) were not significantly changed. Metoprolol significantly decreased baseline CLLi and sodium clearance (CLNa) by 19% (P < 0.01) and 34% (P < 0.01), respectively. Metoprolol blunted the dopamine-induced increases in heart rate and systolic pressure, but cardiac output increased to the same extent on both study days by 26% (placebo, P < 0.05) and by 31% (metoprolol, P < 0.01), respectively. With and without metoprolol, dopamine did not significantly change GFR, and the percentage increases in ERPF were similar on the two study days (40% (P < 0.001) and 42% (P < 0.001), respectively). Dopamine increased CLLi and CLNa by 31% (P < 0.01) and 114% (P < 0.01), respectively, with placebo, and by 36% (P < 0.01) and 114% (P < 0.01), respectively, with metoprolol. Values during infusion remained significantly lower with metoprolol compared with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)