Compensatory renal growth in the mouse. I. Allometric approach to the effect of age

Relationships between organ weight and body/brain weight in the rat: what is the best analytical endpoint?

Analysis of organ weight in toxicology studies is an important endpoint for identification of potentially harmful effects of chemicals. Differences in organ weight between treatment groups are often accompanied by differences in body weight between these groups, making interpretation of organ weight differences more difficult. Using data from control rats that were part of 26 toxicity studies conducted under similar conditions, we have evaluated the relationship between organ weight and body/brain weight to determine which endpoint (organ weight, organ-to-body weight ratio, or organ-to-brain weight ratio) is likely to accurately detect target organ toxicity. This evaluation has shown that analysis of organ-to-body weight ratios is predictive for evaluating liver and thyroid gland weights, and organ-to-brain weight ratios is predictive for evaluating ovary and adrenal gland weights. Brain, heart, kidney, pituitary gland, and testes weights are not modeled well by any of the choices, and alternative analysis methods such as analysis of covariance should be utilized.

Chromosomal mapping of a major quantitative trait locus regulating compensatory renal growth in the rat

Despite extensive research conducted over the past century, the mechanisms of compensatory renal growth (CRG) remain a mystery. Insight into the mechanisms that regulate CRG might be gained by identifying genetic factors that influence this complex phenotype. In a large set of recombinant inbred strains derived from the spontaneously hypertensive rat and the Brown Norway rat, a genome scan for quantitative trait loci (QTL) that regulate CRG was performed. The CRG score was expressed as a ratio of the weight of the remnant right kidney at 8 wk of age to the weight of the left kidney at 5 wk of age, both adjusted for body weight. QTL mapping was performed using Map Manager QT and the strain distribution patterns of more than 600 genetic markers. It was found that CRG after unilateral nephrectomy is a multifactorially determined trait with a substantial genetic component. The heritability of CRG approached 40%. Genome wide scan analysis revealed significant evidence of linkage to a region of rat chromosome 4 designated Crg 1 that accounted for more than 50% of the additive genetic variance of CRG in the recombinant inbred strains. The detection of a major QTL influencing CRG in the rat should provide new opportunities for identifying mechanisms that regulate this historically enigmatic phenomenon and may also have implications for research on the pathogenesis of end-stage kidney disease.

Compensatory renal growth: modulation by calcium PTH and 1,25-(OH)2D3

To further elucidate the mechanisms by which compensatory renal growth (CRG) can be influenced by calcium and calcium regulating hormones, the influence of dietary calcium and phosphorus, parathyroid hormone (PTH) or 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) was evaluated in unilaterally nephrectomized (UNI-NX) rats. These animals were sacrificed three days after UNI-NX and CRG of the remaining kidney was assessed by kidney wt, RNA and DNA gains, and by 3H-thymidine incorporation. The degree of CRG was enhanced in animals given a low dietary calcium and, conversely, was decreased in those receiving a phosphorus-poor diet. In thyroparathyroidectomized (TPTX) rats, PTH administration resulted in a dose proportional stimulation of CRG. When 1,25-(OH)2D3 was given to vitamin D deficient animals, the degree of CRG was enhanced in a dose proportional manner. In another experiment, TPTX-vitamin D deficient rats were given the same amount of 1,25-(OH)2D3 by miniosmotic pump infusion. In these animals, dietary calcium restriction, instead of stimulating, inhibited CRG. From these observations we conclude that calcium and calcium regulating hormones modulate CRG, and hypothesize that the effects observed are mediated through changes in cell calcium.

The control of cell mass and replication. The DNA unit--a personal 20-year study

The deoxyribonucleic acid (DNA) is constant per cell in diploid tissues and in polyploid tissues the DNA content and the cytoplasm increase commensurately. In muscle the DNA unit (protein/DNA) was described on the assumption that each nucleus has jurisdiction over a certain volume of cytoplasm. Such an approach allows a sensible interpretation of metabolic data. Since 66-70% of nuclei are within myofibres muscle represents a reasonably homogeneous tissue. A brief historical review is made concerning the use of DNA as a cell constant. The application of this knowledge to normal human somatic growth and to disease states is considered as well as reduced nutrition and overnutrition. The consequences of reduced nutrition as it related to brain growth are briefly mentioned as is our 7 year study on the fetal primate (Macaca mulatta). Attention is focussed on our work in the early 1960's concerning the role of insulin and growth hormone on the DNA unit. In the last decade this work culminated in the close study of the Little Mouse with isolated growth hormone deficiency--thus exposing the panhypopituitary model (the human pituitary dwarf, Snell Smith mouse or hypophysectomised rat) as non-optimal models. The findings indicate that growth hormone is indeed related to cell replication and insulin to cytoplasmic growth in the postnatal period but the role of other hormones is clearly important, augmenting or opposing these hormones. The concept of constant change of the DNA unit not only applies to major tissues such as muscle but to the study of kidney growth when the contralateral kidney is removed (renal compensatory growth). Species differences are noted in the pattern of cell growth in muscle, but emphasis is placed on cell replication rather than on cytoplasmic growth in the primate. Restriction of protein energy metabolism mainly affects cytoplasmic growth of muscle but restoration of growth to expected levels is the rule. Overnutrition and obesity relate to excessive growth of DNA units in number rather than size. Attention is drawn to factors other than calories, proteins and hormones that influence hormonal actions viz. trace metals such as zinc, chromium and vanadium. The cell mass of the body can readily be reached by relatively non-invasive methods and by monitoring the intracellular water. Muscle mass can be precisely measured by creatinine excretion. The cell mass of muscle constitutes 70% of the entire cell mass.(ABSTRACT TRUNCATED AT 400 WORDS)

Compensatory renal growth in the mouse. III. Growth hormone and insulin deficiency

The effect of combined insulin and growth hormone (GH) deficiency on compensatory renal growth (CRG) was studied in the dwarf mouse, "Little," after insulin suppression with streptozotocin (SZ). Nucleic acid and protein estimations were used to assess changes in cellular hyperplasia and hypertrophy. Mice aged 30 days received SZ while controls received buffers solution alone. Left nephrectomy was performed at 35 days of age with removal of the renoprival kidney 15 days later. In mice with normal GH, renoprival kidney weight was unaffected by SZ, but the total DNA (estimate of cell number) was higher than normal in both sham-operated and renoprival kidneys suggesting that insulin suppression may cause greater cell replication during both normal growth and CRG. The ratio of protein to DNA (estimate of cell size) in the renoprival kidney was not suppressed by SZ as reported in muscle. In GH-deficient mice (lit/lit) given SZ, CRG was significantly diminished (P less than 0.001). Total DNA in the renoprival kidney was slightly greater than the sham-operated control (P less than 0.005) but the protein:DNA ratio (cell size) was unchanged. These results suggest that when both GH and insulin are suppressed, adaptive cellular growth is inhibited. The proposal that GH and insulin are the two primary hormones controlling cellular growth is consistent with these results.

Kidney function after unilateral nephrectomy

Immediately after unilateral nephrectomy ( uNX ) some different mechanisms of compensatory adaptation begin to act followed by a restoration of sufficient kidney function in a short time period. Beside biochemical changes early compensatory hypertrophy of the remaining kidney occurs. Simultaneously, functional adaptations of renal blood flow, glomerular filtration and exertion of electrolyte and xenobiotics take place. With a suitable pretreatment it is principally possible to accelerate the regeneration phase. Thus the phase of reduced excretion capacity of tubularly secreted xenobiotics after removal of one kidney can be shortened or prevented.

Humoral factors in regulation of compensatory renal hypertrophy

Compensatory renal hypertrophy in transplanted kidneys shows that the major regulators are humoral. Crosscirculation experiments are confirmatory indicating further that the regulators are short-lived and must be consistently present during the early phases of hypertrophy. Controls are difficult to achieve in other systems; variables relate to nutrition, means of assay, pharmacokinetics, and abnormalities produced by the experimental model itself. A simple hypothesis to account for the events precipitating renal hypertrophy might integrate the onsets of renal hyperemia soon after contralateral nephrectomy with the activation of pre-existing stimulators specific for the kidney.