Effect of diuretics in newborn rats and puppies

Evidence of induction of new nephrons in immature kidneys undergoing hypertrophy

Unilateral nephrectomy performed during the first days or weeks of life may or may not induce the development of new nephrons in the remaining kidney. Such an increase has been reported to occur, as discussed in this review, in newborn rats and mice, but not in guinea pigs. These observations are consistent with other data suggesting different patterns of compensatory adaptation in young and in old animals.

Number of glomeruli in normal and hypertrophied kidneys of mice and guinea-pigs

1. In mice and guinea-pigs, the number of glomeruli was counted in kidneys during normal growth and in hypertrophy induced by unilateral nephrectomy. 2. In mice, the number of glomeruli increased sharply during the first 2 weeks in life, and more slowly afterwards. Unilateral nephrectomy, when performed during this period of natural increase, induced the formation of supplementary nephrons in the contralateral kidney. 3. In guinea-pigs, the number of glomeruli was almost complete at birth. No evidence of a supplementary increase in the number of nephrons was found in hypertrophied kidneys following unilateral nephrectomy. 4. These results, together wit previous data obtained in the rat, suggest that the ability to induce new nephrons after unilateral nephrectomy in different species would depend more on the state of kidney maturity at birth than on differences in the renal mechanisms which lead to hypertrophy.

Postnatal changes in renal glomerular blood flow distribution in puppies

The intrarenal distribution of radionuclide microspheres injected into the thoracic aorta was used to examine glomerular blood flow distribution (GBFD) in 26 healthy, unanesthetized puppies, ranging in age from 5 h to 42 days, and in 5 adult dogs. For analysis, the cortex was divided into four equally thick zones designated zone I (subcapsular) to zone IV (juxtamedullary). During the first 36 h of life, the highest flow rate was in zone II, which received 35.5+/-2.0%/g, compared with 26.8+/-1.4% to zone I, 23.7+/-1.4% to zone III, and 13.4+/-1.4% to zone IV. At age 6 wk, zone I had the highest rate of perfusion (48.6+/-2.1%, compared with 28.8+/-1.4% in zone II, 15.8+/-0.8%, in zone III, and 6.8+/-0.6% in zone IV). The 6-wk old animals resembled the adult animals, except for relatively greater perfusion per gram of zone I in the former group. Changes in relative GBFD did not correlate with those in arterial pressure or peripheral hematocrit. The distribution of glomeruli among the four zones of the cortex followed its own pattern of development. At birth and at 6 wk, the greatest density of glomeruli was in zone I (50.6+/-5.4 and 42.7+/-3.9%/g respectively, as compared with 24.1+/-2.9% in adults); in adults zone II contained the greatest density (39.1+/-1.6%). At birth the relative perfusion of glomeruli in zone I was only one-fifth that of glomeruli in zone IV, with intermediate values in zones II and III. By 6 wk of age, increased perfusion of the outer cortical glomeruli resulted in rates of flow in the four zones that did not differ significantly from each other. Relative perfusion in zone I continued to increase, so that in the adult animals perfusion in that zone was significantly greater than in the three deeper zones. These data demonstrate the marked hemodynamic changes that take place within the kidney during the first few weeks of life. The relatively greater blood flow of the most deeply situated nephrons in the early postnatal period suggests ascendancy of this population of nephrons and may have important functional implications.

Compensatory renal growth after unilateral nephrectomy in the new-born rat

1. The right kidney in a series of control rats aged between 5 days and 115 days was weighed. The kidney weight/body weight ratio was greater in young than in older rats, but decreased linearly with increasing age.2. After unilateral nephrectomy of rats 5 days old, the remaining kidney underwent compensatory growth. The rate and extent of this growth were greater than in adult rats.3. The concentrations of RNA and DNA in the renal cortex and medulla of rats 5 days old were higher than in adult animals. The concentrations of the two nucleic acids fell with age, and reached adult levels after approximately 6 weeks.4. After unilateral nephrectomy of rats 5 days old, the concentrations of RNA and DNA in the medulla were not significantly different from those in control animals. In the cortex, however, there was a delayed increase in the RNA/DNA ratio, which reached a level some 12% higher than that in control rats. This increase was smaller than that observed in unilaterally nephrectomized adult rats.5. The cortical Q(O2) of the remaining kidney of unilaterally nephrectomized new-born rats was elevated by some 20% within 1 day of unilateral nephrectomy. Cortical Q(O2)'s remained higher than those of control animals for 3-4 weeks.6. Since after unilateral nephrectomy, the increase in renal mass in new-borns was greater than that in adults, whereas the degree of cortical cellular hypertrophy (as estimated by the RNA/DNA ratio) was smaller than in adults, it is likely that in new-born animals a significant contribution to compensatory growth comes from cellular hyperplasia.

Action potentials of the pyramidal neurones in the hippocampus of the rabbit

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