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K Hierholzer

Publications and source records attributed to K Hierholzer.

At least 37 records · Page 2Linked to original sources
PubMed1987

Corticosteroid metabolism in rat kidney in vitro. IV. Subcellular, sites of 11 beta-hydroxysteroid dehydrogenase activity.

An attempt has been made to identify the subcellular localization of renal corticosteroid metabolism. Subcellular fractions were prepared by differential centrifugation, identified by marker enzymes and incubated under different conditions with corticosterone (B). The NADP+/NADPH dependent metabolism of B could be localized in the nuclear and microsomal fraction. The most prominent metabolite was 11-dehydro-B, which is formed by 11 beta-hydroxysteroid dehydrogenase (EC 1.1.1.146). Enzyme kinetic studies of this enzyme with B as substrate revealed apparent Km-values in the range of 10(-7) M for both the nuclear and microsomal fraction.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1984

Corticosteroid metabolism in isolated rat kidney in vitro. I. Formation of lipid soluble metabolites from corticosterone (B) in renal tissue from male rats.

Kidneys of male Sprague Dawley rats have been isolated and perfused in vitro in order to study the metabolism of corticosterone (B). B is the main endogenous corticosteroid in this species. Using 3H-B and HPLC for the separation of steroid metabolites it has been possible to detect radioactive derivatives of B which have been denoted as met I, II and III. These substances were purified and compared with authentic reference hormones under different isocratic and gradient elution techniques. We observed chromatographic identity of met I with 11-dehydro-20-dihydro-B, of met II with 20-dihydro-B and of met III with 5 alpha-H-4,5-dihydro-B. From the fact that conversion of B can be observed with normal (50 g X l-1 albumin in perfusate) and elevated (75 g X l-1) colloid osmotic pressure of the recirculating perfusate it can be concluded that B gets access to the metabolic site in renal tissue not solely by glomerular filtration and tubular reabsorption. The metabolites identified presently are excreted in the urine. Metopirone increased the concentration of met I and decreased the concentration of met II. This is compatible with the concept of a stimulatory effect of metopirone on a C-20-hydroxysteroid oxidoreductase and a C-11-hydroxysteroid dehydrogenase.

Animals↗
PubMed1984

Corticosteroid metabolism in isolated rat kidney in vitro. II. Sex dependency of metabolism and formation of 11-dehydro-corticosterone.

We have previously demonstrated that isolated kidneys from male rats convert corticosterone (B). The metabolites are formed in renal tissue, released into the recirculating perfusate and excreted in the urine (5). They have been identified as: 11-dehydro-20 zeta-dihydro-B (met I), 20 zeta-dihydro-B (met II) and 5 alpha-H-4,5-dihydro-B (met III), using HPLC. In view of sex dependency of hepatic corticosteroid metabolism we have presently investigated whether or not equivalent sexual differences exist in renal tissue. In applying appropriate HPLC-techniques we could demonstrate a fourth metabolite formed from B, which was chromatographically identical with 11-dehydro-B (= met IV). Female rat kidneys form predominantly the less polar metabolites III and IV, in contrast to kidneys from male rats, which produce met III and the more polar metabolites I and II.

Animals↗
PubMed1984

Corticosteroid metabolism in isolated rat kidney in vitro. III. Structure analysis of lipid soluble metabolites of corticosterone.

We have previously demonstrated that isolated rat kidneys in vitro convert corticosterone (B). Four lipid soluble metabolites (met I, II, III and IV) have been identified which differ in polarity from the parent hormone [2, 5, 6, 11, 15, 16]. In the present experiments these metabolites have been extracted from perfusate after 4 h of recirculation through isolated kidneys of male and female rats. Subsequently they have been separated by HPLC using a polar stationary phase system and n-hexane and isopropanol as eluents. The chromatographic comparison of met II with authentic 20 alpha- and 20 beta-isomers documented that met II is identical with 20 beta-dihydro-B. Measurements of the mass spectra of the purified samples revealed the following structures: met I = 20 beta-dihydro-11-dehydro-B, met II = 20 beta-dihydro-B, met III = 5 alpha-H-4,5-dihydro-B and met IV = 11-dehydro-B.

Animals↗
PubMed1982

Renal metabolism of corticosteroid hormones.

IK and STF from male and female rats have been used to study in vitro the renal metabolism of B. in male rat tissue four lipid soluble metabolites (I-IV) have been found, I + II being more polar and III + IV being less polar than B. I and II have been identified as 11-dehydro-20-hydroxy-B and 20-hydroxy-B. The structure of III and IV remains to be determined. Renal tissue from female rats produced predominantly III indicating sexual variations of steroid metabolism in kidneys.--The literature has been reviewed which documents that the kidneys in addition to B metabolize A, cortisol, progesterone and other corticosteroids.

Adrenal Cortex Hormones↗
PubMed1975

Tubuloglomerular feedback in rat kidneys of different renin contents.

Variations 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 evaluated 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 maneuver 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.

Angiotensin II↗
PubMed1975

A new method for intratubular blockade in micropuncture experiments.

Criteria for a reliable blockade of tubular flow are generally discussed and experimental evidence is presented that solid paraffin meets all the necessary criteria in rat kidney tubules when an immobile and tight sealing intratubular blockade is requested. A special microinjection apparatus for the application of paraffin is described. Furthermore, several alternative methods and materials have been tested and have been found to be inferior to solid paraffin.

Animals↗
PubMed1975

The basic requirements for the function of the isolated cell free perfused rat kidney.

We 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 continuously 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 O-2 electrode for the calculation of Q-o-2. 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 (T Na equals 27.3 muEq/g with 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 (T Na equals 64.4 muEq/g with 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 requirements necessary for further micropuncture evaluation of renal function under the condition of isolated single pass perfusion.

Animals↗
PubMed1971

[Osmotic diuresis].

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Acute Kidney Injury↗