Hemmung der Natriumresorption im proximalen und distalen Konvolut adrenalektomierter Ratten

Summary In 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 Eq/mm² × sec in the proximal convolution and from 1.7 to 1.2×10^–5 Eq/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.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Micropuncture studies on the influence of antidiuretic hormone on tubular fluid reabsorption in rats with hereditary hypothalamic diabetes insipidus

Summary Micropuncture studies were carried out on rats with hereditary hypothalamic diabetes insipidus, in order to measure net sodium and water reabsorption in proximal convolutions and short loops of Henle during water diuresis and ADH-induced antidiuresis. Intravenous infusion of 0.15 mU ADH per minute reduced urine flow from 74.5 l per kidney per minute to 10.8 l, and increased urine osmolality from 117 to 605 mOsm/kg. These changes could be reversed by stopping ADH.ADH did not alter the fractional reabsorption of fluid or the reabsorptive capacity for sodium in the proximal tubules. Nor did it change glomerular filtration rates of single superficial nephrons or of the entire kidney.Fractional reabsorption of the glomerular filtrate up to the early distal convolution was significantly higher (82.0%) in water diuresis than in antidiuresis (74.4%). Since this reabsorption remained unchanged in the proximal convolutions, the decreased reabsorption during antidiuresis must have occurred in the short loops. Fractional reabsorption of sodium up to the early distal tubule was essentially identical during water diuresis and antidiuresis, indicating that ADH does not enhance urinary concentration by increasing the reabsorption of sodium from short loops.On leave of absence from the Department of Physiology, Dartmouth Medical School, Hannover, N. H., from January to June, 1967. Recipient of USPHS Research Career Program Award 5-K3-GM-21, 786.     

Effects of aldosterone on lipid metabolism and renal oxygen consumption in the rat

Summary The plasma level of free fatty acids (FFA) in adrenalectomized rats increases by 50% after treatment with aldosterone (2 g/100 g rat).Lipolytic activity in peripheral fat tissue is lowered after adrenalectomy and doubles after in vivo administration of aldosterone to adrenalectomized rats (measured as free fatty acid release in vitro from epididymal fat tissue).Lypolysis of adipose tissue stimulated by the in vitro presence of ACTH also increases after in vivo administration of aldosterone.Incorporation of intravenously administered label from U¹⁴C-palmitate into total extractable lipid of renal tissue is augmented 3 h after aldosterone administration to adrenalectomized rats, while no increase of the radioactivity is observed in total lipid from liver tissue. Treatment with aldosterone does not affect the total lipid content of kidney or liver in adrenalectomized rats.The oxygen consumption rate of kidney cortex slices with lactate, -hydroxybuterate or acetoacetate as substrates is lowered after in vivo administration of aldosterone to adrenalectomized rats. With succinate, however, the respiratory rate of kidney slices increases after aldosterone treatment of adrenalectomized rats, the ouabain-sensitive respiration being more affected than the ouabain-insensitive respiration. An interpretation of the O₂ consumption data implicating competition of lipid metabolism for CoA-SH is discussed.     

Tubular transport processes in proximal tubules of hypothyroid rats. Lack of relationship between thyroidal dependent rise of isotonic fluid reabsorption and Na+−K+-ATPase activity

Hypothyroid rats reconstituted with 10 g/kg b.w. per day of tri-iodothironine (T₃) for 4 days resulted in normal free T₃ and TSH levels. FT₃ levels were: 0.53±0.3 pg/ml in hypothyroid rats; 2.78±1.21 pg/ml in hormone reconstituted rats and 2.90±0.90 pg/ml in euthyroid rats. TSH levels were 3,508±513 g/ml in hypothyroid rats; 1,008±204 g/ml in reconstituted rats and 270±184 ng/ml in euthyroid rats.When hypothyroid rats were reconstituted with 50 g T₃/kg b.w. per day, TSH levels were nearly normal after 4 days (1,157±621 ng/ml). However FT₃ levels after 1–4 days were always higher than in euthyroid rats.Hypothyroid rats show a decrease in isotonic fluid reabsorption (J _v) in the proximal tubule (1.50±0.08 versus 4.96±0.23 10^–2 nl·mm^–1·s^–1 in euthyroid animals). 1 day after T₃ (10 g/kg b.w./day) injectionJ _v was increased significantly to 2.05±0.20 10^–2 nl·mm^–1·s^–1 and continued to increase during 4 days of T₃ reconstitution.When 50 g T₃/kg b.w./day was used,J _v increased to 2.75±0.07 after 1 day and to 3.10±0.42 10^–2 nl·mm^–1·s^–1 after 4 days.J _v was never reaching a value close to that of euthyroid rats because the tubular radius in hypothyroid rats (14.7±1.8 m) is less than that of euthyroid rats (19.2±0.5 m). The radius in hypothyroid rats treated with T₃ was unchanged over a 4 day course with either high or low doses of T₃.Na⁺–K⁺-ATPase activity was found to be 2.91±0.16 M P_i/h×mg protein in homogenates of kidney cortex from hypothyroid rats. Treatment of hypothyroid rats with 10 g or 50 g of T₃ resulted in an initial decrease in ATPase activity, followed by an increase to base level in hypothyroid rats with 10 g and a significantly higher level with 50 g. This decrease in ATPase activity was contrasted to the increase inJ _v.These data indicate that there is a dissociation between the effects of physiological doses of thyroid hormones on proximal tubular reabsorption and the effects of T₃ on Na⁺–K⁺-ATPase activity of kidney cortex. This leads to question the relationship between sodium transport and ATPase activity under physiological doses of thyroid hormones. An early effect of physiological doses of thyroid hormones on brush border Na⁺ permeability is suggested.     

Sodium conductance changes by aldosterone in the rat kidney

Summary To asses passive permeability properties of distal, and proximal tubules of the rat kidney the tubular lumen was perfused with solutions of 1.5 and 150 mM Na/l while transtubular potential differences were recorded. Sodium transport numbers (T _Na) were calculated.T _Na in the distal tubule of adrenalectomized rats was acutely increased from 0.21 to 0.27 by aldosterone (5 g/100 g B.W.). This effect of aldosterone could not be reduced by concomitant injection of cycloheximide (100 g/100 g B.W.). Aldosterone was also effective in control rats. In the proximal tubule similar data were obtained. However, the aldosterone-induced increase of conductance was slightly reduced with cycloheximide.These measurements of transepithelial sodium conductance indicate that aldosterone, in addition to the already known stimulation of active sodium transport, increases overall permeability of the tubular wall to sodium. In the distal tubule this effect indicates an increase of the luminal membrane permeability whereas in the proximal tubule aldosterone may facilitate the diffusion of sodium through the intercellular shunt path and/or the luminal membrane. The passive components of transepithelial electrolyte transfer seem to be less sensitive to inhibition of protein synthesis than the active transport components.Supported by Deutsche Forschungemeinschaft.     

Increase of cytochromes a and a3 in rat kidney mitochondria in response to administration of aldosterone in vivo

Summary The influence of aldosterone in vivo on cytochromes in rat kidney mitochondria is studied, comparing rats in normal state, adrenalectomized state, and adrenalectomized rats 2 hours after administration of adlosterone (7.5 g per 100 g rat as single dose plus infusion of 0.125 g per hour and 100 g rat).No significant changes between these states are observed of either cytochrome b, cytochrome c₁, or cytochrome c content.Cytochrome a, as estimated from the 605 m band of the difference spectrum (reduced vs. oxidized), decreases from 508±51 nanomoles per g protein (n=12) in the controls to 273±65 (n=12) nanomoles per g protein in the adrenalectomized state.After administration of aldosterone to adrenalectomized rats the concentration of cytochrome a increased to 464±38 nanomoles per g protein (n=12).The difference spectrum (anaerob vs aerob+Antimycin A) shows that the absorbancy maximum at 444 m (more specific for cytochrome a₃) is also considerably decreased after adrenalectomy, and increased after administration of aldosterone to adrenalectomized rats. Hence the contents of both compounds of cytochrome oxidase, cytochrome a and cytochrome a₃, appear to be controlled by aldosterone.The molar ratio of cytochrome c to cytochrome a is 1.1 in the controls, 1.8 after adrenalectomy, and 1.1 after administration of aldosterone to adrenalectomized rats.Possible relations of this effect to the previously observed increase of tricarboxylic acid cycle enzyme activities under aldosterone are discussed.The 46% decrease of the cytochrome a content in mitochondria from the whole kidney of adrenalectomized rats, which is restored to the normal level in response to aldosterone, is difficult to reconcile with the concept that the hormone acts on distal tubules only, as these constitute only about 10% of the material used. Therefore, the present result is considered to support the concept that the hormone acts on both distal and proximal tubules.     

Genetic mapping of two pairs of linked ribosomal protein genes in Saccharomyces cerevisiae

Summary We have used the 2 mapping method described by Falco and Botstein (1983) and tetrad analysis to map four ribosomal protein genes (two linked pairs) in S. cerevisiae. One pair (rp28–rp55 copy 1) is on chromosome XV, 14 cM proximal to ARG8. The other pair (rp55–rp28 copy 2) is 19 cM from the centromere on the left arm of chromosome XIV. To map copy 1 we used the E. coli -galactosidase gene rather than a yeast gene to mark the ribosomal protein chromosomal locus. This provided a more sensitive color screening assay for chromosome loss in the 2 method. It also removed the restriction that the mapping tester strains must be mutant for the plasmid marker.     

Glucocorticoid induction of angiotensin converting enzyme

Angiotensin converting enzyme (ACE) converts angiotensin I (Angio I) to angiotensin II (Angio II) and inactivates bradykinin (BK).Glucocorticoids in the physiological range increase ACE in rabbit alveolar macrophages and bovine endothelial cells in culture. Since Angio I and BK are cleaved by ACE catalysis during passage through the pulmonary vasculature we have studied the steroid modulation of ACE in the rat lung.The conversion of Angio I to Angio II by isolated lungs from normal or adrenalectomized male Wistar rats has been evaluated.The initial conversion of Angio I to Angio II in lungs from normal rats was about 60%. In contrast the initial converting activity in lungs from adrenalectomized rats was about 30%.In both groups the converting activity progressively decreased. After 3 h it was about 30% in normal lungs and virtually undetectable in lungs from adrenalectomized rats.Dexamethasone infusion (1 g/ml) prevented the decrease in ACE activity observed in normal lungs and induced a gradual enhancement of converting activity in lungs from adrenalectomized animals up to the control level. The effect of dexamethasone was abolished by simultaneous infusion of cycloheximide (1 g/ml).These results demonstrate that glucocorticoids induce ACE synthesis in the rat lung.By this induction glucocorticoids promote the increase of both Angio II formation and BK degradation. Thus ACE induction may represent a possible mechanism whereby glucocorticoids might control vascular tone and permeability according to the general mode of action of steroid hormones.     

Maleic acid induced aminoaciduria,studied by free flow micropuncture and continuous microperfusion

The injection of 200 mg/kg BW maleic acid was found to be a suitable dose for exploring the experimental Fanconi syndrome by micropuncture techniques in rats. In clearance experiments, the fractional excretion of glycine,l-alanine,l-aspartate and taurine was measured. After intraperitoneal administration of maleic acid the excretion of these amino acids was increased in the range between the 20-fold and the 230-fold. Free flow micropuncture experiments showed that the reabsorption of these amino acids is reduced drastically along the whole proximal tubule. Continuous microperfusion experiments lead to the result that, in maleic acid pretreated rats, the reabsorption of¹⁴C-glycine from the proximal convolution was strongly inhibited. It was found, furthermore, that after blocking the saturable glycine transport byl-phenylalanine, the remaining reabsorption of glycine (corresponding to passive diffusion) was exactly the same with and without maleic acid. Microinfusion experiments with 8 mol·l^–1 l-³H-alanine into the early distal tubule showed a fractional recovery of 103±4.2% (S.D.) in the control and of 101±6.5% in presence of maleic acid. It is concluded that maleic acid inhibits the saturable reabsorption mechanism of amino acids along the proximal tubule. Passive permeability of the tubular membrane does not seem to be altered by maleic acid.Part of this work was presented at the 49th Meeting of the German Physiological Society in Göttingen, March, 7–10, 1978 [22]