Structural and functional changes in the mitochondrial apparatus of cortical tubules of the solitary kidney in chronic blockade of cholinergic mediation

In 15, 30 and 90 days the effect of continuous atropine pharmacological blockade of parasympathetic innervation on morphometrical characteristics of epithelial mitochondria in the cortical segments of the canaliculi has been studied in a single kidney of Wistar rats. The maximal degree of the alternative changes has been determined in the proximal canaliculi. In the distal canaliculi epithelium a compensatory increase of the main quantitative parameters in mitochondria has been registered. The plasticity of the mitochondrial apparatus, specific for the collecting tubules under compensatory hypertrophy, is inhibited under conditions of deparasympathization.     

Changes in the local blood flows of the single kidney with partial impairment of the autonomic innervation

The changes of cortical and intramedullary blood flow of the remaining after nephrectomy kidney under the condition of guanethidine sympathectomy and continuous pharmacological blockade of parasympathetic mediation by atropine were studied in chronic experiments on Wistar line rats in dynamics at 4, 7, 15, 30, 60, 90 and 120 days. Decrease in cortical and increase of intramedullary peritubular blood flow were noted in both experimental series, that is both blockade of sympathetic and parasympathetic nerves after 15 days. The conclusion was made that blood flow redistribution is a universal mechanisms of single kidney adaptation to its neurogenic impairments.     

Changes in the pool and spectrum of adenine nucleotides in the cortex of the solitary kidney in chronic denervation

Chronic energy-++-deficient condition of nephron cortical portions manifested in a two ware pool decrease and spectrum impairment of the adenyl system components was revealed as a result of the long-term studies in tissue contents of ATP, ADP, AMP in the rat renal cortex under conditions of experimental combination of compensatory hypertrophy and chronic nervous decentralization. A negative trophic effect of chronically overloaded cortex tissue de-mediation is responsible for energy metabolism at the early phase while at the later stage, beginning two months after the experiment, the progressing hypoperfusion of the cortical tubular system of a single denervated kidney is.     

Compensatory Growth of Congenital Solitary Kidneys in Pigs Reflects Increased Nephron Numbers Rather Than Hypertrophy

Background

Patients with unilateral MultiCystic Kidney Dysplasia (MCKD) or unilateral renal agenesis (URA) have a congenital solitary functioning kidney (CSFK) that is compensatory enlarged. The question whether this enlargement is due to increased nephron numbers and/or to nephron hypertrophy is unresolved. This question is of utmost clinical importance, since hypertrophy is associated with a risk of developing hypertension and proteinuria later in life with consequent development of CKD and cardiovascular disease.

Methodology/Principal Findings

In a cohort of 32,000 slaughter pigs, 7 congenital solitary functioning kidneys and 7 control kidneys were identified and harvested. Cortex volume was measured and with a 3-dimensional stereologic technique the number and volume of glomeruli was determined and compared. The mean total cortex volume was increased by more than 80% and the mean number of glomeruli per kidney was 50% higher in CSFKs than in a single control kidney, equaling 75% of the total nephron number in both kidneys of control subjects. The mean total glomerular volume in the CSFKs was not increased relative to the controls.

Conclusions/Significance

Thus, in pigs, compensatory enlargement of a CSFK is based on increased nephron numbers. Extrapolation of these findings to the human situation suggests that patients with a CSFK might not be at increased risk for developing hyperfiltration-associated renal and cardiovascular disease in later life due to a lower nephron number.     

Endothelial dysfunction promotes the transition from compensatory renal hypertrophy to kidney injury after unilateral nephrectomy in mice

Loss of functional nephrons associated with chronic kidney disease induces glomerular hyperfiltration and compensatory renal hypertrophy. We hypothesized that the endothelial nitric oxide synthase (eNOS) [soluble guanylate cyclase (sGC)] protein kinase G (PKG) pathway plays an important role in compensatory renal hypertrophy after unilateral nephrectomy. Analysis of mice subjected to unilateral nephrectomy showed increases in kidney weight-to-body weight and total protein-to-DNA ratios in wild-type but not eNOS knockout (eNOSKO) mice. Serum creatinine and blood urea nitrogen increased after nephrectomy in eNOSKO but not in wild-type mice. Furthermore, Bay 41-2272, an sGC stimulator, induced compensatory renal hypertrophy in eNOSKO mice and rescued renal function. The NO donor S-nitrosoglutathione (GSNO) and Bay 41-2272 stimulated PKG activity and induced phosphorylation of Akt protein in human proximal tubular cells. GSNO also induced phosphorylation of eukaryotic initiation factor 4E-binding protein and ribosomal protein S6. Our results highlight the importance of the eNOS-NO-PKG pathway in compensatory renal hypertrophy and suggest that reduced eNOS-NO bioavailability due to endothelial dysfunction is the underlying mechanism of failure of compensatory hypertrophy and acceleration of progressive renal dysfunction.     

Anti-epidermal growth factor antibody inhibits compensatory renal hyperplasia but not hypertrophy after unilateral nephrectomy in mice.

The effect of anti-epidermal growth factor (EGF) antibody on the compensatory renal growth including hyperplasia and hypertrophy was investigated. The antibody used in this study blocked the stimulatory effect of EGF on the DNA synthesis of cultured rat hepatocytes. When this antibody was injected into mice intravenously after unilateral nephrectomy, the labeling index of the renal cortical tubular cells decreased significantly at the second day after uninephrectomy, but the antibody caused no decrease in remaining kidney weight. Immunohistochemical study revealed that injected anti-mouse EGF rabbit IgG was positively stained at the renal cortical tubular cells. EGF would thus appear importantly essential to compensatory renal hyperplasia.     

Aldosterone Binding by Compensatory Hypertrophied Kidney with Disturbed Neurotrophic Supply in Rats

We studied certain aspects of interaction between (³H)aldosterone and the cytoplasmic as well as nuclear receptors of renal cells in the rats during compensatory renal hypertrophy at the background of reflex renal dystrophy. The dystrophy developing in the kidney after cutting the sciatic nerve blocks the compensatory increase in specific accumulation of (³H)aldosterone in the cytoplasm of the renal tubular cells. (³H)Aldosterone transport from the cytoplasmic receptors to the nuclear receptors during rat reflex dystrophy of compensatory hypertrophied kidney is lower as compared to the control. The reflex dystrophy induced by a sciatic nerve injury proved to have no effect on the degree of hypertrophy of the only kidney.     

Compensatory renal hypertrophy after nephrectomy in newborn rats]

The process of the kidney compensatory hypertrophy in young rats has been studied after nephrectomy on the 2nd day of life. The intact kidney was investigated by morphometrical and electron microscopical methods from the 1st day till the 3rd month after operation. The kidney compensatory hypertrophy in the early postnatal ontogenesis is accompanied by the acceleration of growth and differentiation of renal structures. The hypertrophy involves three successive steps: (1) functional tension of ultrastructures; (2) expressed hyperplasia and hypertrophy of cells; (3) structural-functional specialization. Among the cellular factors of the kidney compensatory growth at this age, the main role is played by the process of cell hyperplasia.     

Conservation of ribosomal RNA during compensatory renal hypertrophy. A major mechanism in RNA accretion

After removal of one mouse kidney, compensatory hypertrophy in the remaining kidney is marked in 2 days by a 20% average increase in ribosomal RNA (rRNA) per cell. Both 28S and 18S RNA are conserved during the initial stages of compensatory renal hypertrophy to an extent sufficient to account for the rest of the observed accumulation of rRNA. Like some cultured cells, the kidney conserves rRNA during physiological growth.     

Comparative characteristics of compensatory renal hypertrophy following unilateral nephrectomy in mature and old rats]

One of the kidneys was removed in rats from 35 to 900 g in weight; they were then sacrificed 2, 14, 30 and 60 days after the operation. The degree of compensatory hypertrophy of the remaining kidney varied greatly in rats of different age, without decreasing in old age, however. Sixty days after the operation the weight of the hypertrophic kidney in old rats was equal to 55--93% of the weight of both kidneys in control. Hypertrophy of the kidney at any age was accompanied by an increased proliferation of the tubular cells, particularly in their proximal portion. An increase in the size of renal bodies during kidney hypertrophy was characteristic of rats of any age. However, with the advance of age this process developed more rapidly and was stronger. At any periods of investigation the hypertrophic kidney in rats of any age contained a greater number (1 1/2--2 times more) of "open" renal bodies in comparison with the kidney of intact rats.     

Effect of chronic denervation on blood flow and ultrastructural and functional status of the tubule system of the solitary kidney

The sodium kidney treatment, local blood flow in the cortex and medulla as well as ultrametric parameters of mitochondria of different regions of the rat kidney duct system were studied under compensatory hypertrophy of kidneys (CHK) and against a background of aftereffects of single kidney decentralization (SKD). In all 120 experiments have been conducted. In the course of the first two weeks of the experiment the local blood flows in the cortex of SKD increased by 30% as compared to those under CHK and natriuresis+ was thrice as high (due to a decrease in proximal reabsorption). In this case coefficients of structural organization Km and of energy efficiency (Ke) of mitochondria lowered in cells of proximal ducts. Later on the intensity of local blood flows in the cortex of SKC was not only lower progressively than that under CHK but also of the control, simultaneously local blood flows in medulla being increased. The complete equalization of the sodium transport parameters of SKD up to their values under CHK did not occur. The rise of ultrametric parameters of the medullary ducts of SKD segments is associated with the intensification of their hemoperfusion.     

Renal cortical remodelling by NO-synthesis blockers in rats is prevented by angiotensin-converting enzyme inhibitor and calcium channel blocker

The cortical remodelling was studied when chronically nitric oxide synthesis (NOs) blockade (L-NAME-induced) hypertensive rats are simultaneously treated, or not, with angiotensin-converting enzyme inhibitor or calcium channel blocker. Four groups of eight rats each were studied as follows: Control (C), L-NAME (L), L-NAME+Enalapril (L+E) and L-NAME+Verapamil (L+V). The systolic blood pressure (SBP) was weekly recorded. The cortex of the left kidneys was analysed according to the vertical section design. The volume-weighted mean glomerular volume (VWGV) was made through the "point-sampled intercepts" method. Enalapril and verapamil were efficient in reducing the SBP in rats submitted to NOs blockade. Glomeruli had considerable alterations in L group rats (glomerular hypertrophy or sclerosis) and tubular atrophy. The VWGV was 100% greater in L group rats than in the C group rats, while it was 30% smaller in L+E and L+V groups than in L group. The tubular volume was 30–50% greater, while the tubular lenght was 20–30% smaller in L group than in the other groups. The renal cortical region showed glomerular sclerosis/hypertrophy and tubular remodelling in rats with NOs blockade that was efficiently prevented with the simultaneous treatment with enalapril or verapamil.     

Compensatory hypertrophy in radiothyroidectomized dwarf rats.

The aim of the study was to clarify whether growth hormone and thyroid hormones play a role in compensatory organ hypertrophy. Radiothyroidectomized dwarf rats with serious disorder of growth hormone production due to the loss of thyroid function were used in the experiments. As regards growth hormone production these animals may be considered as having been "hypophysectomized". The loss of thyroid function and growth hormone deficiency did not affect the degree of compensatory hypertrophy of the kidney, the adrenal and the gonad. The observation indicates that the hormones under study are not of decisive importance in the mechanism of compensatory organ enlargement. Further investigations are needed to clarify whether organ enlargement in the hypometabolic rat occurring at the level observed in the controls is associated with enhanced function.     

Ultrastructural changes in nucleoli and fibrillar centers under the effect of local ultraviolet microbeam irradiation of interphase culture cells

As shown previously, ultraviolet (uv) microbeam irradiation of one of the two mature nucleoli within an interphase cell nucleus causes significant diminution and inactivation of the irradiated nucleolus and compensatory growth and activation of the nonirradiated one. In the present work we describe the results of an ultrastructural study of this phenomenon. The changes in the nucleoli were examined by means of complete series of ultrathin sections obtained from seven irradiated pig kidney cells. The compensatory hypertrophy of the nonirradiated nucleoli is shown to be accompanied by a nearly twofold increase in the number of fibrillar centers (FCs) and by a decrease in their linear dimensions compared with the control cells of the same ploidy. In the degraded nucleoli the number of FCs decreases, but their dimensions increase. Ultraviolet microbeam irradiation causes dramatic diminution of the dense fibrillar component within the irradiated nucleoli as well. The nucleolar capacity for compensatory hypertrophy indicates that in addition to active ribosomal genes, mature nucleoli also contain "silent" genes capable of being activated under extreme conditions to sustain the required level of rRNA synthesis. It is assumed that activation of latent ribosomal genes is accompanied by FC "fragmentation" without a considerable increase in their total volume per cell.     

Changes in quantitative characteristics of mitochondria of the cortical tubules of the kidneys with compensatory hypertrophy in the blocking of autonomic mediation

To elucidate the significance of neuromediators in ergotrophic provision of duct cells of the compensatory-hypertrophying kidney mitochondrial apparatuses of cortical nephron segments epithelium in a single kidney of Wistar rats have been morphometrically studied under conditions of continuous 90-day blockade of vegetative nerves by administration of both guanetidine and atropine. It is shown that distal duct mitochondria have undergone the most pronounced regressive changes in the experimental series that is accounted for by specificity and power capacity of the transport processes in this segment. Lagging of the principal morpho-functional mitochondrial characteristics in other cortical nephron portions behind those of a single kidney is a direct evidence of the active trophic influence of the vegetative nervous system mediators on adaptive reconstruction of compensatory-hypertrophying kidney metabolism.     

Effect of diisopropylfluorophosphate on muscarinic and gamma-aminobutyric acid receptors in visual cortex of cats.

Administration of diisopropylfluorophosphate (DFP), an organophosphorus (OP) compound, irreversibly inhibits acetylcholinesterase (AChE) and results in cholinergic hyperactivity. This study investigated muscarinic and gamma-aminobutyric acid (GABA) receptor changes in visual cortex of cats following an acute exposure to DFP. A single acute administration of DFP (4 mg/kg) decreased the number of muscarinic receptors at 2, 10, and 20 hours after treatment. GABA receptors were elevated at 2 and 10 hours but returned to within control levels at 20 hours. No significant alteration in muscarinic or GABA receptor affinity was noted. In all cases cortical AChE activity was inhibited 60-90%. These findings show a down regulation of muscarinic receptors after DFP associated with low AChE activity. GABA receptors also are altered, and may be part of a compensatory mechanism to counteract excess cholinergic stimulation.     

Cholinergic Control of Nerve Growth Factor in Adult Rats: Evidence from Cortical Cholinergic Deafferentation and Chronic Drug Treatment

Abstract: It is well documented that nerve growth factor (NGF) plays an important role in maintaining functions of cholinergic basal forebrain neurons. In the present study, we tested the hypothesis that cholinergic activity controls NGF levels in cholinoceptive neurons of the cerebral cortex and hippocampus. To address that question, we used both cholinergic deafferentation of cerebral cortex and hippocampus by cholinergic immunolesion with 192IgG-saporin and chronic pharmacological treatment of sham-treated and immunolesioned rats with the cholinergic agonist pilocarpine and the cholinergic antagonist scopolamine. We observed an increase in NGF protein levels in the cortex and hippocampus after cholinergic immunolesions and also after muscarinic receptor blockade by chronic intracerebroventricular scopolamine infusion in sham-treated rats after 2 weeks. There was no further increase in the accumulation of NGF after scopolamine treatment of immunolesioned rats. Chronic infusion of pilocarpine had no effect on cortical and hippocampal NGF protein levels in sham-treated rats. In rats with cholinergic immunolesions, however, pilocarpine did prevent the lesion-induced accumulation of NGF. There was no effect of cholinergic lesion and drug treatment on cortical or hippocampal NGF mRNA levels, consistent with the importance of NGF retrograde transport as opposed to its de novo synthesis. This study provides strong evidence for the hypothesis that there is cholinergic control of cortical and hippocampal NGF protein but not mRNA levels in adult rats.     

Excretion of water, sodium, and potassium during the compensatory renal hypertrophy in hypothyroid rats]

Renal compensatory hypertrophy is studied in age matched euthyroid and radiothyroidectomized female rats. 7 days after uninephrectomy, the hypertrophy of the remaining kidney is equally small in both groups. But 60 days after this operation, the hypothyroid animals show only a 12% increase in the wet weight of the remaining kidney whereas the euthyroid controls increase this weight by 21%. The excretion of water, Na and K are determined in the urine excreted in 5 h after a small water load. The results are related to 1 gram of kidney wet weight. These outputs increase in all animals after uninephrectomy. They are significantly higher in the hypothyroid rats than in the euthyroid controls as well before than 60 days after uninephrectomy. The reduction in tubular Na reabsorption found in the hypothyroid rat may account for the impairment of compensatory renal hypertrophy in hypothyroidism.     

Participation of the cholinergic nervous mechanism in regulating adequate blood supply to the rabbit cerebral cortex

Dilatation of the pial arteries and their active segments (sphincters of the offshots and precortical arteries) was studied in rabbits under the conditions of enhanced neuronal activity of the brain cortex, induced by application of 0.5% strychnine to its surface. The blockade of the cholinergic transmission by microapplication of atropine to vessel walls caused a significant inhibition of the dilatatory responses of the study microvessels. Reduction of functional dilatation was most demonstrable in the precortical arteries, less marked in the sphincters of the offshots and still less marked in the small pial arteries. No differences in the responses of the large pial arteries were discovered either before or after atropine microapplications. The author suggests that the cholinergic mechanism plays an important part in regulation of adequate brain blood supply and that such a regulation may be performed locally within the area of a single radial artery occupying ca. 1/5 mm2 of the brain surface in rabbits.