摘要:

Present evidence suggests that the renal handling of magnesium is normally a filtration-reabsorption process as evidence for secretion is unsubstantiated. Magnesium reabsorption has distinctive features when compared with that of sodium and calcium. The proximal tubule concentration of magnesium rises to levels about 1.5 times greater than the glomerular filtrate and only 20–30% of the filtered magnesium is reabsorbed in this segment. Although the fractional reabsorption of magnesium is only half that of sodium, it changes in parallel with that of sodium in response to changes in extracellular fluid volume. The major portion of filtered magnesium (some 65%) is reabsorbed in the loop of Henle and evidence indicates that the thick ascending limb is the principal segment involved in magnesium absorption. Recent observations suggests that magnesium reabsorption in the ascending limb may be voltage dependent and secondary to active sodium chloride reabsorption. The loop of Henle appears to be the major nephron site where magnesium reabsorption is regulated possibly by cAMP-mediated hormones including parathyroid hormones, calcitonin, glucagon and antidiuretic hormone. About 10% of the filtered magnesium is delivered into the distal nephron. The distal tubule reabsorbs only a small fraction of the filtered magnesium which may be regulated by the same cAMP-mediated hormones involved in control of magnesium in the loo

ISSN:1420-4096    

DOI:10.1159/000173090

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The effective hydraulic permeability (k) of glomerular capillaries was studied in 2-month-old Wistar rats 4 weeks after uninephrectomy in comparison to age-matched control rats. Isolated kidneys were perfused with a cell-free solution containing 5% albumin. In this preparation the rise of colloid osmotic pressure along the glomerular capillaries can be neglected because the filtration fraction is low (3%) due to high perfusion rates at normal filtration rates. Single nephron filtration rates (SNGFR) and effective filtration pressures were estimated by micropuncture to calculate the ultrafiltration coefficient (Kf). Glomerular capillary surface area was measured morphometrically to obtain k (k = Kf/S). We found that the effective hydraulic permeability in uninephrectomized rats was higher than in rats of comparable age (26.0 vs 18.0 nl/mm Hg · s · cm2). This can contribute to the adaptive rise in SNGFR after uninephrectom

ISSN:1420-4096    

DOI:10.1159/000173091

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The effects of a calcium channel agonist, BAY K-8644, on renin release and renal function were examined in perfused rat kidneys. BAY K-8644 increased renal vascular resistance and reduced glomerular filtration rate, sodium excretion und urine flow in a dose-dependent manner. These actions were prevented by the calcium channel blocker nifedipine. BAY K-8644 had no significant effect on basal renin secretion and failed to prevent renin stimulation by low-perfusion pressure or isoproterenol. The inhibitory effect of high-perfusion pressure on renin secretion was attenuated by the calcium entry blocker verapamil but not by nifedipine. Thus, if voltage-dependent calcium channels in the juxtaglomerular cell membrane participate in the regulation of renin release then these channels appear to be very insensitive to blockade or augmentation by 1,4-dihydropyridines.

ISSN:1420-4096    

DOI:10.1159/000173092

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Autoregulatory efficiency of renal blood flow (RBF) and glomerular filtration rate (GFR) was evaluated in male Sprague-Dawley rats during interference with the renin-angiotensin system by a converting enzyme inhibitor (CEI), captopril (3 mg · h-1 · kg-1 BW). RBF and GFR were approximately 25 (p < 0.01) and 20% (p < 0.02) higher, respectively, in rats infused with CEI than in control rats at spontaneous renal arterial pressure (RAP). A reduction of RAP to 100 mm Hg (within the autoregulatory range) resulted in effective autoregulation of GFR and RBF in control rats. In rats given CEI, however, the autoregulation of GFR was markedly impaired. GFR decreased by 35% (p < 0.001), while RBF remained relatively unchanged. This caused the filtration fraction to decrease from 0.33 ± 0.01 to 0.29 ± 0.01 (p < 0.001). RAP had a consistent effect on the urine flow rate, even though both GFR and RBF were well autoregulated in control rats. No significant decrease in electrolyte excretion was detected within the autoregulatory range in control rats, but during converting enzyme blockade this excretion decreased progressively as RAP was reduced, and the decrease correlated well to the reduction in GFR. In summary, these results suggest that the renin-angiotensin system plays an important intrarenal role in the autoregulation of GFR, probably through an efferent arteriolar mechanism. Furthermore, it is demonstrated that the contra-lateral kidney efficiently compensates in urinary electrolyte excretion for an acute unilateral reduction of RAP, both under control conditions when the perfusion pressure to the contra-lateral kidney increased and during blockade of the renin-angiotensin system when the increase in perfusion pressure was inhibi

ISSN:1420-4096    

DOI:10.1159/000173093

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

To investigate the interaction between arginine-vasopressin (AVP) and the renal kallikrein-kinin system (KKS), urinary excretion rates of bradykinin (BK) and lysyl-brady-kinin (LBK) were monitored in humans following water-loading, and in conscious diabetes insipidus (DI) rats during the infusion of AVP. In humans, the excretion rate of both BK and LBK decreased markedly 90 min after the water load. There was a close positive correlation between plasma AVP levels and urinary BK excretion, while urine flow was correlated negatively with the excretion rates of both kinins. In DI rats infusion of AVP caused a significant, reversible increase (from 14 ± 2.8 to 35 ± 5.1 fmol/min) in BK excretion. These results further implicate AVP in the regulation of the activity of the renal KK

ISSN:1420-4096    

DOI:10.1159/000173094

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The present study was designed to investigate the early hemodynamic and tubular effects of cisplatin administration on dogs. To localize the nephrotoxic actions of cisplatin, we have taken advantage of the lithium clearance method. After infusion of 5 mg of cisplatin per kg, an immediate and significant increase in urinary flow rate (from 0.39 ± 0.07ml/min to 0.73 ± 0.12ml/min), sodium clearance (from 0.33 ± 0.11 ml/min to 0.65 ± 0.14ml/min), potassium clearance (from 9.23 ± 0.48ml/min to 10.77 ± 0.95 ml/min), lithium clearance (from 15.55 ± 2.21 ml/min to 23.76 ± 4.00ml/min) and fractional lithium clearance (from 0.31 ± 0.03 to 0.44 ± 0.04) was seen. This occurred without measurable changes in glomerular filtration rate and renal blood flow. The calculated fractional as well as absolute rates of proximal reabsorption of sodium decreased significantly from 0.68 ± 0.03 to 0.56 ± 0.04 and from 4.76 ± 0.32mmol/min to 3.92 ± 0.23mmol/min, respectively. The results show that administration of cisplatin causes an acute, mainly proximal tubular impairment in dogs without alterations in renal

ISSN:1420-4096    

DOI:10.1159/000173095

出版商:S. Karger AG    

年代:1986

数据来源: Karger