Functional and morphometric evaluation of offspring kidney after intrauterine undernutrition.

Pregnant rats were subjected to 50% food restriction during the first or the second half of pregnancy, or throughout pregnancy. The effects of intrauterine food restriction, on kidney function and morphometry were studied in newborn and adult (3 months) offspring. No differences in glomerular diameter were observed in newborn restricted rats compared with controls. The number of glomeruli was significantly lower both in newborn and 3-month-old restricted rats. However, glomerular diameter was increased in 3-month-old rats, which suggests that hypertrophic stimuli were present. The medulla/cortex ratio increased in adult rats submitted to food restriction during pregnancy, a finding that agrees with the preserved sodium and acid excretion, and the normal osmolar and free water clearance observed in these groups. These results show that the reduction in glomerular number is still present 3 months after birth in the progeny of mothers submitted to severe food restriction during pregnancy, suggesting impairment of glomerulogenesis even after birth. Intra utero undernutrition can be regarded as an experimental model of glomerular hypertrophy.

Renal effect of gentamicin in diabetic rats.

To evaluate the protective effect of diabetes mellitus (DM) on renal function of rats treated with gentamicin (GM), male Wistar-EPM rats (250-350 g) were treated with streptozotocin (SZ; 45 mg/kg) and starting 10 days after induction of diabetes, GM was given for ten consecutive days at a daily dose of 40 mg/kg. In the GM-treated group (G), a significant fall in inulin and sodium-p-amino-hippurate clearance was obtained (3.57 +/- 0.16 and 12.59 +/- 0.61 ml min-1 kg-1 vs 6.43 +/- 0.21 and 17.98 +/- 0.47 ml min-1 kg-1 in control rats (C), respectively) while in the animals previously injected with SZ (diabetic+gentamicin, DG group) these changes were not observed. The diabetic (D), G and DG groups showed a significant rise in urinary flow compared to C (0.165 +/- 0.009, 0.145 +/- 0.007 and 0.173 +/- 0.009 ml min-1 kg-1 vs 0.109 +/- 0.003 ml min-1 kg-1, respectively); however, only in G was the U/P inulin ratio significantly decreased when compared to C. The fractional excretion (FE) of sodium and potassium was significantly augmented in G when compared to C, D and DG. Thus, diabetes protected against gentamicin nephrotoxicity at both the glomerular and tubular level, although it did not promote a reduction in urinary flow.

Effects of parathyroid hormone on urinary acidification in the rat.

To evaluate the effects of parathyroid hormone (PTH) on urinary acidification parameters, thyroparathyroidectomy was performed in normal (TPTX) and in calcium-supplemented rats (TPTX + Ca2+). Both groups were supplemented with thyroxin. Glomerular filtration rate (GFR) fell from 7.79 +/- 0.33 in the control group (C) to 4.88 +/- 0.26 ml min-1 kg-1 in TPTX, while net acid excretion fell from 5.65 +/- 0.22 in C to 3.76 +/- 0.25 mumol min-1 kg-1 in TPTX. Kinetic data of urinary acidification obtained by microperfusion techniques in proximal tubules showed that the half-time of acidification (t/2) rose from 4.75 +/- 0.24 s in C to 8.97 +/- 0.64 s in TPTX and persisted elevated in TPTX + Ca2+ (7.40 +/- 0.43 s); in the latter group, stationary pH was not significantly different from that of the control group. Bicarbonate reabsorption (JHCO3) fell from 2.18 +/- 0.15 in C to 0.823 +/- 0.082 in TPTX and was 1.53 +/- 0.073 nmol s-1 cm-2 in TPTX + CA2+. These data suggest that normal pH gradients depend on normal calcium levels, but acidification half-times are dependent on PTH, which also contributes to keeping glomerular hemodynamics and acidification rates at normal levels.

Function and morphometric evaluation of intrauterine undernutrition on kidney development of the progeny.

Renal function and renal morphometry of the progeny of rats submitted to 50% dietary restriction (pair-fed with control group) throughout pregnancy (RT group), during the first half of pregnancy (R1 group) or during the second half of pregnancy (R2 group) were studied 3 months after birth. Glomerular filtration rate (GFR) and renal plasma flow (RPF) decreased significantly in all groups when compared to control (C) (GFR, 4.44 +/- 0.12, 4.04 +/- 0.18, and 4.00 +/- 0.16 vs 6.87 +/- 0.17, and RPF, 19.06 +/- 0.57, 17.00 +/- 1.14, and 13.31 +/- 0.50 vs 22.57 +/- 0.67, respectively). Urinary osmolality tended to be lower in the R2 and RT groups (877.1 +/- 42.36 and 868.0 +/- 42.36 vs 975.1 +/- 38.31 in C), and the net acid excretion calculated per ml of GFR was either maintained or stimulated (R1 group). A significant decline in the number of glomeruli occurred in R1, R2 and RT rats (79.84 +/- 2.08, 62.30 +/- 2.07, and 58.16 +/- 2.31 vs 99.77 +/- 2.28 in C respectively). The results show that intrauterine undernutrition actually caused a deleterious effect on the number of functional nephrons.

Effects of parathyroid hormone on urinary acidification in the rat

To evaluate the effects of parathyroid hormone (PTH) on urinary acidification parameters, thyroparathyroidectomy was performed in normal (TPTX) and in calcium-supplemented rats (TPTX+Ca2**). Both groups were supplemented with thyroxin. Glomerular filtration rate (GFR) fell from 7.79 ñ 0.33 in the control group (C) to 4.88 ñ 0.26 ml min**-1Kg**-1 in TPTX, while net acid excretion fell from 5.65 ñ 0.22 in C to 3.76 ñ 0.26 µmol min**1Kg in TPTX. Kinetic dat of urinary acidification obtained by microperfusion techniques in proximal tubules showed that the half-time of acidification (t/2) rose from 4.75 ñ 0.24 s in C to 8.97 ñ 0.64s in TPTX and persisted elevated in TPTx +Ca**2+ (7.40 ñ 0.43s); in the latter group, stationary pH was not significantly different from that of the control group. Bicarbonate reabsorption (J**HCO3) fell from 2.18 ñ 0.15 in C to 0.823 ñ 0.082 in TPTX and was 1.53 ñ 0.073 nmol s**-1 cm**-2 in TPTX+Ca**2+. These suggest that normal pH gradients depend on normal calcium levels, but acidification half-times are dependent on PTH, which also contributes keeping glomerular hemodynamics and acidification rates at normal levels

Effects of intrauterine undernutrition on the renal function of the progeny.

The progeny of rats submitted to 50% food restriction during a) the first 11 days of pregnancy (R1 group) and b) the entire period of pregnancy (RT group) was studied for renal function. After birth, the litter was left with the mother for 28 days and allowed free access to food and water until the experimental time, which occurred 3 months after birth. Glomerular filtration rate (GFR), renal plasma flow (RPF) and urinary flow (V) decreased significantly in both the Rl and RT groups when compared to control rats (C) (GFR = 4.44 +/- 0.12 and 4.26 +/- 0.17 vs 6.95 +/- 0.25, and RPF = 19.06 +/- 0.57 and 12.59 +/- 0.60 vs 24.64 +/- 1.18). However, net acid excretion calculated per ml GFR was maintained or even stimulated (AB = 12.63 +/- 0.44 and 8.31 +/- 0.29 vs 7.9 +/- 0.85). The results show that a definite impairment of glomerular hemodynamics is demonstrable 3 months after birth in the progeny of mothers submitted to severe food restriction during pregnancy, even when the progeny have been on a normal diet for 2 months after suckling.

The renal effects of kainic acid.

The effect of kainic acid (KA), a potent neurotoxic agent, on the renal function of rats was investigated. Intrahippocampal and intraperitoneal KA injections (2.5 micrograms and 8 mg/kg, respectively) led to a decrease in glomerular filtration rate and U/P inulin ratio with a concomitant increase in the amount of excreted Na+. However, acid excretion was maintained. These findings support the idea of a straight connection between neurohormonal secretion and renal function and may provide an interesting model to study renal hemodynamic changes induced by neurological disturbances.

Evaluation of distal tubular function in aminoglycoside-induced nephropathy.

Acute metabolic acidosis potentiates the nephrotoxicity of aminoglycosides by impairing the adequate excretion of ammonium and titratable acidity. The present study assesses distal tubular function after aminoglycoside administration in the rat. Two aminoglycosides, gentamicin and netilmycin were given to rats either in low doses equivalent to those used clinically (BG4 and BN5 groups) or in doses ten times higher (BG40 and BN50). The rats were subjected to acute metabolic alkalosis and the pCO2 of urine was continuously evaluated. The regression lines obtained by plotting the differences between urine and blood pCO2 as a function of urinary HCO3- in low dose models were similar to those obtained for the control group. However, the slopes obtained for BG40 and BN50 were significantly different from the control, suggesting an impairment of H+ secretion.

Aminoglycosides and renal acid excretion.

The effect of three aminoglycosides, gentamicin, netilmicin and amikacin, on renal acid excretion was studied in rats treated with doses equivalent to 10 times those used clinically. The gentamicin and amikacin groups showed a marked decrease (P less than 0.05), in glomerular filtration rate (GFR), U/P inulin ratio and renal plasma flow (RPF), while in the normal acid-base state. Under acidotic conditions, only gentamicin promoted significant alterations in GFR and RPF. Net acid excretion as measured by the acid balance (BH) was calculated as the sum of ammonium excretion (NH4+) and titratable acidity (AT) minus the amount of excreted bicarbonate (CHCO3-). Under normal conditions, netilmicin promoted a considerable fall in both NH4+ and AT, which led to a significant decrease in BH, whereas no changes were observed in these parameters with the other two drugs. In contrast, during acute metabolic acidosis, all tested antibiotics promoted a marked fall in BH, particularly due to a significant decrease in NH4+ and AT. These data suggest that the effects of aminoglycoside treatment during acute metabolic acidosis in clinical practice deserve further study in view of possible deleterious effects on the clinical state.

Role of luminal buffers in renal tubular acidification.

The acidification of kinetics of artificial solutions containing buffers of different permeancy were studied in rat proximal tubules by means of stationary microperfusion techniques. Luminal pH changes were measured by antimony microelectrodes and used to calculate net rates of acidification and the approach to steady-state pH levels. For most buffer species, tracer efflux out of the lumen was compared with changes in buffer concentration as derived from calculations based on the Henderson Hasselbalch equation. Steady-state luminal pH was similar for most buffer systems studied. However, secretory hydrogen ion fluxes into the lumen were significantly higher for permeant than for less permeant buffers. The most likely explanation is that permeant buffers behave as "open" systems maintaining constant low diffusible acid levels in the lumen, whereas impermeant buffers behave as "closed" systems in which non-ionized acid levels are maintained at higher levels. A behavior consistent with this thesis was directly demonstrated for glycodiazine and, to a lesser degree, for DMO. In contrast, phosphate and creatinine behave like buffers in a "closed" system. Characteristics of proximal tubular acidification, of buffer reabsorption, and the effect thereupon of carbonic anhydrase inhibitors are satisfactorily explained by an essential role of (1) hydrogen ion secretion, (2) pK differences, and (3) different permeance of the non-ionized buffer species. However, specific transport mechanisms may, in addition, also contribute to differences in transepithelial buffer movement.