Klaus Hierholzer

Micropuncture study of renal transtubular concentration gradients of sodium and potassium in adrenalectomized rats

SummarySamples of proximal and distal tubular fluid were collected from control rats and from adrenalectomized animals maintained on 0.9% NaCl solution. Plasma and tubular fluid were analyzed for Na22 after adequate isotope equilibration and for Na and K by microflamephotometry. Similar analyses were performed in stationary microperfusion experiments in which the magnitude of the limiting concentration gradients for Na and K was estimated. Transtubular electrical potential differences were measured by means of glass-microelectrodes. A comparison of proximal tubular concentration gradients showed no significant differences between the control and the adrenalectomized rats for either Na or K. In contrast, the ability of the distal tubular epithelium to develop concentration gradients for Na and K was significantly reduced by adrenalectomy. This functional impairment could be reversed by the administration of d-aldosterone. No changes in proximal and distal transtubular electrical potential differences were observed in the various experimental conditions.

Hemmung der Natriumresorption im proximalen und distalen Konvolut adrenalektomierter Ratten

SummaryIn adrenalectomized rats rate of net transfer of sodium and fluid has been measured using the split oil droplet method. Net reabsorption of sodium was found to be decreased from 8.9 to 4.5×10−5 μEq/mm2 × sec in the proximal convolution and from 1.7 to 1.2×10−5 μEq/mm2 × sec in the distal convolution of surface tubules. This indicates impairment of the local capacity of the epithelium of both tubular segments to transport sodium in adrenal insufficiency. A second pertinent finding was the decreased transit time of Lissamingreen-stained tubular fluid through the proximal convolution in adrenalectomized animals. In contrast to the inhibition of local fluid and sodium reabsorption fractional reabsorption in the proximal convolution in free flow as estimated from transit time and half time of local fluid reabsorption was found to be increased following adrenalectomy. The possible mechanisms of impairment of sodium transport will be discussed.

The Basic Requirements for the Function of the Isolated Cell Free Perfused Rat Kidney

SummaryWe have attempt to define experimental conditions which would overcome or minimize some of the well known functional limitations of isolated single pass kidney preparations. Rat kidneys were perfused with a Krebs-Henseleit solution containing the gelatine derivative Haemaccel as colloid. Perfusion was initiated in situ via the mesenteric artery. Arterial flow rate was measured continously from the very onset of perfusion. Effective perfusion pressure was recorded distal to the perfusion capillary in the aorta. Aliquots of the venous effluate and of an arterial bypass solution were drawn through an O2 electrode for the calculation of

Mikropunktionsuntersuchungen über den Einfluß von Aldosteron, Cortison und Dexamethason auf die renale Natriumresorption adrenalektomierter Ratten

Q_{{\text{O}}_{\text{2}} }

Einfluß von Adrenalektomie und Glucocorticoiden auf die Wasserpermeabilität corticaler Nephronabschnitte der Rattenniere

.First it was shown that the often observed initial vasoconstriction of the preparation which occurs immediately after cannulation of the kidney can be eliminated by rapid disconnection of the autonomic nerve supply. A more delayed gradual increase of renal resistance, which we observed after 30 min could be prevented by using sterile perfusion solutions. Using glucose as the only substrate fuel, fractional Na-reabsorption decreased to 65% 3 hrs after the onset of perfusion (TNa=27.3 μEq/g·min). When a substrate enriched sterile solution was used containing pyruvate, lactate, oxaloacetate, and glutamate, Na conservation of the isolated kidney could be maintained at a higher level. Fractional Na-reabsorption levelled off and was still 88% after 3 hrs (TNa=64.4 μEq/g·min). The results demonstrate that the transport function of the isolated kidney preparation critically depends on the supply with substrate hydrogen.Thus, the present system meets the basic reqirements necessary for further micropuncture evaluation of renal function under the condition of isolated single pass perfusion.

Bile acids and their amidates inhibit 11β-hydroxysteroid dehydrogenase obtained from rat kidney

SummaryVariations in flow rate through the loop of Henle in the range of 0–50 nl/min were induced using pressure controlled microperfusion. Simultaneously, with the aid of a second pressure-microperfusionsystem, the glomerular function of the same nephron was studied by continuous measurement of two parameters, early proximal flow rate (EPFR) and/or stop flow pressure (SFP). Elevation of loop perfusion above physiological values (40 nl/min) resulted in a drop of EPFR and SFP, whereas lowering perfusion rates had no effect. This feedback behaviour was studied in kidneys with different renin contents to test the role of the renin-angiotensin system in the mediation of the macula densa signal to the adjacent glomerular vessels. Renal renin content, measured after micropuncture experiments by incubation with substrate followed by radioimmunoassay of angiotensin I, was unaltered in control (Ia) and heminephrectomized rats (Ib), lowered in contralateral kidneys of 2 kidneys Goldblatt hypertensive rats (IIa), in DOCA- and salt-loaded rats (IIb), and in DOCA-, salt-loaded and heminephrectomized rats (IIc), and it was elevated in clipped kidneys of Goldblatt hypertension rats (IIIa). Micropuncture evaluation of the tubuloglomerular feedback behaviour in these experimental groups revealed the following results: 1. a feedback response under all conditions independent of the widely varying renin contents (1000-fold), 2. an asymmetrical behaviour of the feedback response in all kidneys as demonstrated by suppression of EPFR and SFP at elevated loop flow rates, but no change of these parameters when loop flow was interrupted, 3. compared to controls the decrease of each GFR parameter between 0 and 40 nl/min loop perfusion was lower in DOCA- and salt-loaded rats (IIb, IIc). Additional heminephrectomy (IIc) had no further influence on the reduced feedback response in DOCA- and salt-loaded rats, whereas this manoeuvre reduced the renal renin content drastically. A somewhat higher response than in controls was found in heminephrectomized rats (IIb) and in clipped kidneys of Goldblatt hypertensive rats (IIIa). These different magnitudes of feedback responses do not correlate with the renal renin content. It has been concluded, therefore, that renal renin activity is not the sole determinant of the effectiveness of the tubuloglomerular feedback response.

Filtration in surface glomeruli as regulated by flow rate through the loop of henle

SummaryUsing the split oil droplet method the effects of adrenal cortical steroids on impaired renal Na transport have been tested in adrenalectomized white rats.1. d-aldosterone (dose: 0.125 μg/100 g b.w. intravenously +7.5 μg/100 g b.w. subcutaneously, single dose) after a delay time of about 60 min restored towards normal the local transport capacity for Na of the proximal and distal tubular epithelium.Equal effects were obtained after repeated administration of d-aldosterone (dose: 7.5 μg TMA-aldosterone/100 g b.w. and 24 hrs, intramuscularly) over 3 to 5 days.2. Similarily, cortisone in high doses (2.5 mg/100 g b.w. intramuscularly as single dose or repeated administration over 3 to 5 days) normalized Na transport capacity in both segments.3. Dexamethasone, a synthetic steroid with predominant glucocorticoid activity in a dose equivalent to that of cortisone (50 μg/100 g b.w. and 24 hrs intramuscularly as single dose or repeated administration over 3 to 5 days) did not increase the rate of transtubular net Na transport.4. From the local Na transport capacity and proximal transit time measured with lissamin green fractional NaCl and fluid reabsorption in the proximal convolution has been estimated. Aldosterone, which did not influence proximal transit time, increased fractional reabsorption above control values and above values obtained from adrenalectomized rats without hormone substitution. Fractional reabsorption was normalized by cortisone or was decreased by dexamethasone.

Metabolism of Dexamethasone: Sites and Activity in Mammalian Tissues

Various compounds with steroidal structure were tested for inhibitory effects on enzymatic activity of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) from rat renal microsomes. Most substances exerting inhibitory potency on both the oxidative as well as the reductive activity can be classified into two main groups: pentacyclic triterpenoids of the oleane type and steroidal detergents of the CHAPS-series. Inhibition is competitive, as was shown for one compound of each group. The IC50 values of the various inhibitors range over five orders of magnitude. In all cases, oxidative activity was inhibited more effectively than reductive activity. An attempt has been made to correlate structural properties and inhibitory potency. In brief, inhibition seems to be enhanced by a C11-oxygen function, which is present in all endogenous glucocorticosteroids and a C7-OH function. Inhibition is reduced by a large and polar substituent at C3 in the A-ring. A large D-ring substituent, such as a bisgluconamidopropyl side chain or even an additional E-ring, does not prevent binding to the enzyme, although inhibition seems to be influenced by its steric conformation. The cardiac glycosides and steroidal antibiotics tested exert no inhibitory effect on 11 beta-HSD. Cholesterol and pentacyclic triterpenoids of the lupane type exhibit a very poor inhibition, probably caused by the localization of planar structures in the ring systems, which differs from that of the effective oleane type inhibitors.