Histomorphometric study of the enhancement of renal compensatory hypertrophy by ACTH in the rat

In the female adult rat, renal compensatory hypertrophy is greatly enhanced by hyperadrenocorticism elicited by the administration of ACTH given at a dose of 18 Y/100 g BW/d for 7 days after uninephrectomy (UN). This renotrophic effect of ACTH is particularly prominent in rats drinking a NaCl solution (9 g/l). In the present experiments, we performed histomorphometrical measurements of the glomerular tuft (GT) and the proximal tubule (PT) in the hypertrophying kidney (HK) remaining 7 days after UN in 10 rats treated with ACTH and 7 control animals. The histologic preparations were examined under light microscopy with the "Kontron" image analyzer. ACTH increased the weight of the HK (1213.8 +/- 20.3 mg versus 1037.3 +/- 13.3, p less than 0.001) and determined an enlargement of the cross sectional area of the GT (12559 +/- 3351.3 mu2 versus 10486 +/- 407.5, p less than 0.01) and of the epithelial area of the PT (1751 +/- 40.8 mu2 versus 1586 +/- 41.5, p less than 0.025). These morphometrical data are consistent with the increased Protein/DNA ratio - a marker of cellular hypertrophy - found in other rats studied under the same experimental conditions. The increased weight gain of the HK elicited by ACTH is related to the hypertrophy of the epithelial cells of the PT and possibly to an enlargement of the glomeruli.     

Impairment of renal compensatory hypertrophy by hypothyroidism in the rat

Renal compensatory hypertrophy (RCH) occurs in hypothyroid rate, but it is impaired when compared to RCH found in euthyroid controls. It is due to cellular hypertrophy as the DNA content does not change and the Protein/DNA ratio increases in the compensating kidney. RCH is enhanced by thyroxine (T4) with a rise in the DNA content of the compensating kidney, but the Protein/DNA ratio does not change indicating that hypertrophy is as important as hyperplasia. Corticotrophin (ACTH) given to eu and hypothyroid rats enhances RCH with an increase in the protein content of the compensating kidney without any change in its DNA content. In the hyperthyroid rats, the enhanced RCH is not further increased by ACTH and the rise in the kidney DNA content elicited by T4 is suppressed by ACTH. The Protein/DNA ratio is increased by ACTH in hypo, eu and hyperthyroid rats. The renotrophic action of ACTH is due to hyperadrenocorticism: it is related to an increased plasma testosterone level and to a disturbed Na+, K+ and glucose metabolism.     

Enhancement of compensatory renal hypertrophy by beta-1-24 corticotropin in the rat]

In the rat, the administration of beta1-24-corticotrophin during 7 days following an uninephrectomy enhances significantly the compensatory hypertrophy of the remaining kidney. There is no increase in renal compensatory hypertrophy when ACTH is injected to previously adrenalectomized rats. This action of ACTH could be related to the diabetes mellitus induced by this hormone or to an increase in sodium reabsorption by the tubular epithelial cells.     

Effects of glucagon on physiologic and compensatory renal growth in the rat

Glucagon has been implicated as a growth-promoting hormone in the kidneys of diabetic animals, but its role in the nondiabetic state is unknown. We evaluated the effect of subcutaneous glucagon administration on renal growth in intact rats with two kidneys and after 50% reduction in renal mass. The relative kidney weight was increased in intact rats treated with a glucagon infusion for 7 days (p less than 0.01), but decreased in uninephrectomized rats treated with glucagon (p less than 0.05). Absolute kidney weight gain and rates of renal DNA synthesis were also significantly blunted by glucagon infusion in uninephrectomized rats. These data suggest that 'physiologic' and 'compensatory' renal growth are governed by separate processes. Furthermore, the observation that glucagon promotes renal growth in intact nondiabetic animals supports its possible role as a growth factor in the early stages of diabetes.     

Influence of nutritional factors on the renotrophic action of ACTH in the uninephrectomized rat.

In the rat, renal compensatory hypertrophy (RCH) was apparent 48 h after uninephrectomy; it was significantly enhanced by long-acting beta1-24-corticotrophin (ACTH) when the animals had free access to food and a NaCl solution (9 g/l). In rats starved after uninephrectomy but drinking the NaCl solution freely, RCH was suppressed: the weights of the body, heart, liver, and solitary kidney were reduced. In similarly starved rats treated with ACTH, the weights of the heart and the solitary kidney were normal. RCH was also impaired in rats fed only a glucose solution (30 g/dl) after uninephrectomy, but it is restored by ACTH, which significantly increases the weight of the remaining kidney. This renotrophic action of ACTH may be related to hyperglycemia and, perhaps, elevated urinary K excretion, which occur in hyper-adrenocorticism and increase the work load of the nephron.     

Glomerular metabolic changes in compensatory renal hypertrophy.

In compensatory hypertrophy, 7 days after unilateral nephrectomy, an increase in respiration and glucose-6-P dehydrogenase activity are observed in the glomeruli of the hypertrophied kidney. It is suggested that is is related to the clearing of an increased amount of filtration residues by the glomerular cells.     

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.