Factors affecting the maturation of glomerular filtration rate and renal plasma flow in the new-born dog

1. The maturation of glomerular filtration rate was studied by comparison of thirty-six new-born mongrel dogs aged 1-35 days with six adult dogs.2. Under mannitol diuresis, glomerular filtration rate (GFR) rose from 0.16 ml. min(-1).g kidney(-1) at 1 day of age to 0.34 ml. min(-1).g kidney(-1) at 1 month of age. Adult GFR averaged 0.68 ml. min(-1).g(-1). There was good correlation of GFR with arterial blood pressure (r = 0.76, P < 0.001). Part of the statistical correlation of GFR with blood pressure was found to be independent of the relationship between blood pressure and age.3. Acute increases or decreases in blood pressure resulted in parallel changes in GFR in the puppies. There was no change of GFR with change of blood pressure in adult dogs. Carotid artery clamping, independent of blood pressure changes, produced increased renal vascular resistance and decreased GFR in the pups.4. Renal plasma flow (RPF) increased from 0.70 ml. min(-1).g(-1) at 1 day of age to 1.80 ml. min(-1).g(-1) at 1 month and showed good correlation with blood pressure (r = 0.67, P < 0.001). Filtration fraction (GFR/RPF) and renal vascular resistance did not vary with age in the pup and were the same as those for the adult.5. These results support the hypothesis that maturation of GFR and RPF are closely related to maturation of arterial blood pressure in the mongrel dog. The factors other than blood pressure which also affect renal maturation in the dog still need to be more clearly defined.     

Mechanism of the glucocorticoid-induced increase in glomerular filtration rate

In order to investigate the mechanism(s) by which glucocorticoids increase GFR the determinants of glomerular ultrafiltration were measured in two groups of seven Munich-Wistar rats. Group 1 rats were normal controls and group 2 rats were pretreated with methylprednisolone (MP), 15 mg/kg per day for 4 days prior to study. In rats given MP mean values for SNGFR were about 25% higher than in the control group, averaging 33.6 +/- 1.6 (SE) vs. 27.0 +/- 1.0 nl/min. Mean values for initial glomerular plasma flow rate (QA) were also about 25% higher in MP-treated rats, averaging 83.4 +/- 3.9 vs. 65.9 +/- 1.9 nl/min in controls. Mean values of the transglomerular hydraulic pressure difference (deltaP) as well as afferent (IIA) and efferent (IIE) oncotic pressures were essentially similar between control and MP-treated rats. Filtration pressure equilibrium, i.e., equality between IIE and deltaP, obtained in both groups and the mean minimum estimates of the ultrafiltration coefficient (Kf) were also similar between control and MP-treated rats. Thus, the rise in SNGFR following MP is entirely due to the increase in AQ, rather than to changes in the other determinants of ultrafiltration.     

Role of glomerular prostanoid in control of glomerular filtration rate in rats

Summary It is generally accepted that the main action of glomerular prostanoids (GPs) on glomerular filtration rate (GFR) is to modulate the activity of different vasoconstrictors, specially in states of renal hypoperfusion. However it was also suggested that GPs may directly affect GFR. The present study was focused on this last hypothesis, in different experimental models, in rats.In adriamycin induced acute renal failure, the transient decrease of GFR is associated with higher levels of thromboxane B₂. Later on, when GFR returns to normal, vasodilator prostaglandins synthesis was also increased.In captopril induced renal failure in Na depleted rats (where GPs synthesis remained normal), stimulation of PGE₂ and PGI₂ production by K and NaCl was associated with a significant improvement of GFR. Furthermore, the increase in GFR induce by NaCl was prevented by inhibition of prostaglandin synthesis.Infusion of atrial natriuretic peptide in euvolemic rats induce a marked elevation both of GFR and PGE₂ synthesis. It was abolished by previous administration of prostaglandin synthesis inhibitor.In conclusion, glomerular prostanoids may influence GFR, either directly, or as mediator or modulator of other vasoactive hormones.Abbreviations GPs glomerular prostanoids - PG prostaglandin - TX thromboxane - ANP atrial natriuretic peptide - GFR glomerular filtration rate - PE polyethylene Nachtrag zu den Hauptreferaten des 19. Kongresses der Gesellschaft für Nephrologie in Göttingen (Klin Wochenschr 66/18)     

Autoregulation of the glomerular filtration rate and the single-nephron glomerular filtration rate despite inhibition of tubuloglomerular feedback in rats chronically volume-expanded by deoxycorticosterone acetate

Tubuloglomerular feedback (TGF) function and autoregulation (renal blood flow RBF; glomerular filtration rate, GFR; single-nephron glomerular filtration rate, SNGFR) were examined in rats chronically treated with deoxycorticosterone acetate (DOCA) and given isotonic saline to drink. DOCA treatment depressed arterial plasma renin activity, expanded plasma volume by 25% and increased arterial blood pressure. Autoregulation of RBF and GFR was maintained in the DOCA animals above 90 mm Hg and 110 mm Hg respectively, whereby both GFR and RBF were lower than in controls. Micropuncture experiments demonstrated the absence of TGF in the DOCA animals. There was no difference between SNGFR values measured in the distal and proximal tubules, nor was there a significant response of SNGFR when loops of Henle were perfused with Ringer's solution at 20 nl/min. Loop perfusion in control rats with tubular fluid collected in DOCA rats elicited a normal TGF response, showing that TGF inhibition in the DOCA animals is due to changes in the function of the juxtaglomerular apparatus. In contrast to control rats, proximal SNGFR was perfectly autoregulated. These results suggest that TGF is not primarily responsible for autoregulation and that the vasodilatation normally resulting from acute TGF interruption is therefore compensated by some other mechanism such that RBF and GFR are lower than in controls.     

Reduction of the glomerular filtration rate by the efferent blood from a kidney taken from a previously dehydrated dog

Summary The two kidneys of one dog were perfused separately with the same blood pool and at a constant arterial pressure. After the control periods, one of the kidneys was replaced by another one taken from a dehydrated dog. The presence of the dehydrated kidney resulted in significant and almost immediate decreases of creatinin clearance, urine flow and sodium excretion by the contralateral kidney, without any change in the overall renal blood flow. These changes disappeared, after the removal of the dehydrated kidney. They were not observed if the dehydrated kidney was replaced either by a kidney taken from a salt-depleted, non water-deprived dog, or by a simple arterio-venous shunt. These results suggest that in the status of dehydration, the kidney releases some humoral material which might be responsible for the decrease of the measured GFR (C creat) perhaps by the way of permeability changes.     

An integral approach to the measurement of glomerular filtration rate

The paper presents a method for the accurate clinical measurement of kidney glomerular filtration rate using a single injection of tracer and the collection of plasma and urine samples. The method is based on an integral-equation approach and is implemented by computerised curve fitting of the plasma-concentration data. The urine-collection procedures are simplified, and errors are reduced. Plasma-only methods are shown to be special cases of the general integral equation, and their limitations are stated.     

Changes in the glomerular filtration rate after unilateral nephrectomy in rats

Changes in the glomerular filtration rate (GFR) were studied in rats, 4 h to 4 weeks after unilateral nephrectomy (NX). The GFR was determined with a technique using⁵¹Cr-EDTA and a single timed blood sample. The GFR determined in this way corresponded with the GFR calculated by two compartment analysis and with the plasma levels of creatinine and urea.Increases in the GFR, compared with half the GFR of sham operated rats, were observed as early as 4 h after NX. This increase was entirely due to an increase in the GFR per gram of kidney, since no increase in kidney weight was observed at that time. After the initial increase, the GFR remained at that level during the first 48 h after NX. At 48 h a significant increase in kidney weight per 100 g body weight had taken place. The longterm changes in the GFR amounted to an increase of about 80% of that of sham operated rats after 3–4 weeks. After 4 weeks, the increase in the GFR of the remaining kidney was due to an increase in kidney weight of 35% as well as an increase in the GFR per gram of kidney of 20%.These data indicate that the increase in the GFR of the remaining kidney after unilateral NX occurs rapidly and is independent of an increase in kidney weight. Compensatory hypertrophy develops at a later stage and helps to maintain the increased function of the single remaining kidney.Supported by the Sophia Foundation for Medical Research