Acute arteriolar vasoconstriction following furosemide in conscious spontaneously hypertensive rats

Involvement of the effect of renal hypoperfusion medications on vancomycin trough concentration: A secondary analysis using a retrospective observational data

This study examined the association between vancomycin (VCM) trough concentration and confounding factors including renal hypoperfusion medications which include angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, loop/thiazide diuretics, or non-steroidal anti-inflammatory drugs. This secondary analysis included patients aged >15 years who were administered VCM intravenously between June 2015 and August 2017 at the Tokyo Women's Medical University Medical Center East. We investigated predictors for three (initial, mean, and final) dose-normalized VCM trough concentration (dose-normalized VCM_trough ) as outcome using a multiple linear regression analysis. In total, 208 patients were analysed (use of loop/thiazide diuretics: 48 [23%]). Multiple linear regression analysis revealed that the initial dose-normalized VCM_trough was negatively correlated with estimated glomerular filtration rate (eGFR) (p = 0.028) and positively correlated with the use of loop/thiazide diuretics (p = 0.003). Meanwhile, there was a positive correlation between the mean dose-normalized VCM_trough and age (p = 0.023). The mean dose-normalized VCM_trough was negatively correlated with eGFR (p < 0.001) and serum albumin (p < 0.001). The final dose-normalized VCM_trough was positively associated with age (p = 0.034) and negatively associated with eGFR (p = 0.032) and serum albumin (p = 0.007). Clinicians should closely monitor VCM trough concentration while receiving VCM and loop/thiazide diuretics.

Benefits and risks of furosemide in acute kidney injury

Furosemide, a potent loop diuretic, is frequently used in different stages of acute kidney injury, but its clinical roles remain uncertain. This review summarises the pharmacology of furosemide, its potential uses and side effects, and the evidence of its efficacy. Furosemide is actively secreted by the proximal tubules into the urine before reaching its site of action at the ascending limb of loop of Henle. It is the urinary concentrations of furosemide that determine its diuretic effect. The severity of acute kidney injury has a significant effect on the diuretic response to furosemide; a good 'urinary response' may be considered as a 'proxy' for having some residual renal function. The current evidence does not suggest that furosemide can reduce mortality in patients with acute kidney injury. In patients with acute lung injury without haemodynamic instability, furosemide may be useful in achieving fluid balance to facilitate mechanical ventilation according to the lung-protective ventilation strategy.

Furosemide increases water content in renal tissue

The present study was designed to evaluate the short-term effects of intravenous administration of furosemide on key functions in the kidney cortex and the outer and inner medulla of rats by using magnetic resonance imaging (MRI). Renal tissue water content, renal tissue oxygenation (in relation to the magnetic resonance spin-spin relaxation rate), the apparent diffusion coefficient (ADC) of water, and volume of renal blood flow were measured. Furosemide administration resulted in an increased water content in all regions of the kidney. In parallel with this, we found a significant reduction in ADC in the cortex (2.7 +/- 0.1 x 10(-3) to 2.3 +/- 0.1 x 10(-3) mm(2)/s; P < 0.01) and in the outer medulla (2.3 +/- 0.1 x 10(-3) to 2.0 +/- 0.1 x 10(-3) mm(2)/s; P < 0.01), indicating that the intra- to extracellular volume fraction of water increased in response to furosemide administration. Furosemide also decreased the blood oxygenation in the cortex (49.1 +/- 2.9 to 40.9 +/- 2.0 s(-1); P < 0.01), outer medulla (41.9 +/- 2.8 to 33.2 +/- 1.6 s(-1); P < 0.01) and in the inner medulla (37.1 +/- 2.9 to 26.7 +/- 1.8 s(-1); P < 0.01), indicating an increased amount of oxygenated Hb in the renal tissue. Moreover, renal blood flow decreased in response to furosemide (6.9 +/- 0.2 to 4.4 +/- 0.2 ml/min; P < 0.001). In conclusion, furosemide administration was associated with increased renal water content, an increase in the intra- to extracellular volume fraction of water, an increased oxygen tension, and a decrease in the renal blood flow. Thus MRI provides an integrated evaluation of changes in renal function, leading to decreased renal water and solute reabsorption in response to furosemide, and, in addition, MRI provides an alternative tool to monitor noninvasively changes at the cellular level.

Spontaneous renal blood flow autoregulation curves in conscious sinoaortic baroreceptor-denervated rats

These experiments examined whether the conscious sinoaortic baroreceptor-denervated (SAD) rat, owing to its high spontaneous arterial pressure (AP) variability, might represent a model for renal blood flow (RBF) autoregulation studies. In eight SAD and six baroreceptor-intact rats, AP and RBF were recorded (1-h periods) before and after furosemide (10 mg/kg followed by 10 mg. kg(-1). h(-1) iv) administration. In control conditions, AP variability was markedly enhanced in SAD rats (coefficient of variation: 16.0 +/- 1.2 vs. 5.4 +/- 0.5% in intact rats), whereas RBF variability was only slightly increased (8.7 +/- 0.6 vs. 6.1 +/- 0.5% in intact rats), suggesting buffering by autoregulatory mechanisms. In SAD rats, but not in intact rats, the AP-RBF relationships could be modeled with a four-parameter sigmoid Weibull equation (r(2) = 0.24 +/- 0.07, 3,600 data pairs/rat), allowing for estimation of an autoregulatory plateau (10.1 +/- 0.7 ml/min) and a lower limit of RBF autoregulation (P(LL) = 93 +/- 6 mmHg, defined as AP at RBF 5% below the plateau). After furosemide treatment, autoregulation curves (r(2) = 0.49 +/- 0.07) in SAD rats were shifted downward (plateau = 8.6 +/- 0.8 ml/min) and rightward (P(LL) = 102 +/- 5 mmHg). In five of six intact rats, P(LL) became measurable (104 +/- 1 mmHg), albeit with limited accuracy (r(2) = 0.09 +/- 0.03). In conclusion, the conscious SAD rat offers the possibility of describing RBF autoregulation curves under dynamic, unforced conditions. The tubuloglomerular feedback and myogenic mechanisms cooperate in setting P(LL) and thus in stabilizing RBF during spontaneous depressor episodes.

Furosemide elicits immediate sympathoexcitation via a renal mechanism independent of angiotensin II

This investigation aimed at examing the hypothesis that furosemide elicits renal sympathoexcitation through stimulation of renal renin release, which in turn produces increased plasma angiotensin II levels, causing centrally mediated sympathoexcitation. In addition, direct central nervous actions of furosemide on central control of mean arterial pressure, heart rate, and efferent renal sympathetic nerve activity were examined. Furosemide (300 mg/kg intravenously) was administered to four groups of rats: (1) control; (2) nephrectomized; (3) with intravenous losartan blockade (10 mumol/kg); and (4) with intracerebroventricular losartan blockade (10 nmol). In a fifth group of rats, furosemide was administered intracerebroventricularly (0, 2.5, 25 or 250 micrograms). To eliminate reflex control of mean arterial pressure, heart rate and efferent renal sympathetic nerve activity, all experiments were performed in rats with sinoaortic denervation and bilateral vagotomy. Experiments were performed during Saffan anaesthesia (0.9% alphaxalone/0.3% alphadolone), and rats were paralyzed with pancuronium and artifically ventilated. Furosemide produced an immediate 40% increase in efferent renal sympathetic nerve activity while the furosemide vehicle, 2 vol.% ethanolamine, did not affect efferent renal sympathetic nerve activity. The furosemide-induced increase in efferent renal sympathetic nerve activity was abolished in rats with bilateral nephrectomy but it was not affected by intravenous or intracerebroventricular losartan blockade. Intracerebroventricular angiotensin II produced an increase in mean arterial pressure and efferent renal sympathetic nerve activity whereas intravenous angiotensin II produced a pressor response in absence of increased efferent renal sympathetic nerve activity. Losartan effectively blocked responses to intravenous or intracerebroventricular angiotensin II. Intracerebroventricular administration of furosemide produced no changes in mean arterial pressure, heart rate or efferent renal sympathetic nerve activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of renal vasoconstriction following furosemide in conscious rats

Regional hemodynamics following intravenous injection of furosemide were studied in conscious rats instrumented with Doppler flowprobes. Furosemide caused a dose-dependent acute (within 3 min) transient increase in renal resistance (RR) followed by a later generalized vasoconstriction in the renal, mesenteric and hindquarter (HQR) vascular bed. With in vitro experiments a possible direct effect of furosemide on renal artery segments was excluded. The acute rise in RR was partly (approximately 40%) attenuated by pretreatment with phentolamine or prazosin, but not prevented by renal denervation, volume repletion or pretreatment with captopril, losartan, indomethacin, aminophylline, nifedipine, or a vasopressin V1A-receptor-antagonist. However, the acute renal vasoconstriction was absent in water diuretic rats. The later vasoconstriction was blunted by captopril (RR+HQR), losartan (RR) and phentolamine (HQR) pretreatment. We conclude that the later generalized vasoconstriction following furosemide involves regional specific stimulation of angiotensin II and alpha-adrenoceptors. The mechanism of the acute renal vasoconstriction could not be fully determined. Because of its absence in water diuretic rats, its rapid onset, transient nature and relative insensitivity for pharmacological tools in euvolemic rats, the acute increase in RR following furosemide may be caused by cell swelling as a result from dissipation of the renal medullary gradient.