Influence of Different Protein Intake on Renal Growth in Young Rats

ABSTRACT. We have examined the effect of high protein intake on kidney growth and function in growing rats. The rats were kept on an isocaloric diet containing 12%, 21% and 50% protein, from weaning (16 days) until the time of investigation (18, 20, 24,40 or 80 days). There was no significant difference between the 12% and 21% protein groups in any of the parameters studied. 50% protein increased body weight (BW) and kidney weight (KW). The increase in kidney weight was already evident after 2 days and exeeded the increase in body weight in all age groups. At 24 days renal cortical DNA and the protein/DNA ratio were significantly increased in the 50% protein group. At 40 days the cortical DNA content, but not the protein/DNA ratio, was significantly increased in the 50% group. The glomerular filtration rate (GFR) was studied at 40 days. Total GFR as well as GFR/BW was significantly higher in the 50% group than in the 21% group. In one protocol the diet was discontinued at age 40 days and the rats were studied at age 80 days. In these rats all parameters of renal size and function were the same as in the rats that had had a normal (21%) protein intake from weaning. We conclude that in young rats high protein intake reversibly increases GFR out of proportion to BW and selectively and reversibly stimulates kidney growth by stimulating cell proliferation.     

Influence of age on compensatory renal growth in rats

Rats were nephrectomized (nx) or sham-operated (s) at the age of 5 days (young) or 55 days (adult). Nx and s rats from the same litters were studied at various times 5-75 days after surgery with determination of kidney weight and of renal cortical DNA and protein content. In some protocols protein and DNA content were determined in a more homogeneous population of proximal tubular cells. In s rats body weight, kidney weight, renal cortical DNA content, and protein/DNA ratio increased until at least 80 days of age. Body growth was the same in nx and s rats. In young nx rats the remnant kidney was significantly enlarged 5 days after surgery. The difference in kidney size between nx and s rats increased continuously at least until the age of 80 days. The remnant kidney was 125 +/- 9% enlarged 3 wk after nx and 175 +/- 18% enlarged 8 wk after nx. Five days after nx there was no increase in cortical DNA content but a significant increase in protein/DNA ratio. From 2 wk after nx on, the DNA content was significantly higher in nx than in s rats but the protein/DNA ratio was the same in nx and s rats. In adult nx rats, the remnant kidney was enlarged to the same extent 3 and 8 wk after surgery (130 +/- 7 and 132 +/- 8%, respectively). The increase in kidney weight 8 wk after nx was significantly smaller in adult than in young rats. The cortical DNA content and protein/DNA ratio were both moderately but significantly increased in adult rats 8 wk after nx. In conclusion this study has established age-dependent differences regarding the degree, the nature and the duration of compensatory renal growth.(ABSTRACT TRUNCATED AT 250 WORDS)     

Body weight and brown fat activity in hyperphagic cafeteria-fed female rats and their offspring

Presenting pregnant rats with a varied choice of human food items (a cafeteria diet) caused a slight reduction in total protein intake and significant increases in energy intake (32%) and weight gain compared to pregnant females fed stock diet (controls). Cafeteria-fed mothers gave birth to the same number and weight of pups as controls, and these grew normally, but were fatter at weaning than control pups. Cafeteria-fed dams lost more weight than controls during lactation, in spite of sustained hyperphagia, and body fat and energy was the same as controls at 21 days post-partum. Brown adipose tissue protein content and thermogenic activity (assessed from mitochondrial purine nucleotide binding) were both elevated in cafeteria-fed mothers when compared to controls at 21 days post-partum, but brown fat activity in their offspring at weaning did not differ between treatments, although tissue protein content was depressed in the pups of cafeteria-fed dams.     

Renal prostaglandin E2 synthesis and degradation in the developing rat

Postnatal development of glomerular filtration rate (GFR) and renal blood flow is associated with a fall in renal vascular resistance that may be mediated by vasoactive substances. We examined differences in the regulation of one such substance, prostaglandin E2 (PGE2). The present studies examined renal cortical and medullary PGE2 synthesis and degradation in rats aged 20 days (30.7 g), 31 days (101 g), and 120 days (413 g). PGE2 synthesis in cortical microsomes was highest in 20-day-old rats compared to 31- and 120-day-old rats. In contrast, medullary PGE2 synthesis was lowest in 20-day-old rats compared to 31- and 120-day-old rats. Both cortical and medullary PGE2 degradation were highest in 20-day-old rats and decreased with age. Despite demonstrating significant age-dependent differences in cortical and medullary PGE2 synthesis, 11 days of aspirin given between age 20-31 days blocked PGE2 synthesis in cortex and medulla by 60 and 76%, respectively, but GFR was similar to control 31-day-old rats (0.78 +/- 0.04 ml/min/g kidney weight, aspirin-treated, versus 0.85 +/- 0.03 ml/min/g kidney weight, control), suggesting that observed age-dependent differences in renal PGE2 synthesis is not a major determinant of development of GFR. A more important determinant of GFR may be age- related differences in renal cortical prostaglandin turnover.     

Effect of early weaning and prolonged nursing on development of the rat pancreas

Pancreatic development was studied in rats 17-28 days of age. Control pups, weaned naturally at 21-24 days showed a gradual increase in body weight, pancreatic weight, total DNA and protein content with age. Pups weaned at 17 days showed a transient increase in pancreatic weight and protein content only at day 22; at no time did they show a difference in either DNA content or body weight. Pups nursed up to 25 days of age had a smaller body weight, but had DNA and protein content similar to control rats. Control pups showed gradual increases in lipase and trypsinogen with a sharp increase in amylase between days 22 and 25. Pups weaned at 17 days showed a precocious increase in trypsinogen and a sharp increase in amylase between days 19-22, but an immediate decrease in lipase which eventually returned to the control level at day 28. Pups nursed beyond the weaning stage showed an increase in lipase and trypsinogen but no sharp increase in amylase. A significant increase in all pancreatic enzymes, pancreatic mass, pancreatic DNA and protein content was seen in all groups of rats irrespective of their diet. The results suggest an inherent biological program as a basic control of pancreatic ontogeny with diet playing a modifying role.     

Role of dietary protein adaptation at weaning in the development of the rat gastrointestinal tract

To evaluate the role of the quantitative adaptation in dietary protein at weaning in the growth and maturation of the rat gastrointestinal tract, we studied parameters of tissue mass, DNA synthesis, and enzyme activities in suckling pups weaned by day 17 to a semipurified synthetic, isocaloric diet that contained either 8 or 27% casein (controls). Rats of both groups were studied on days 21, 28, and 35 postpartum. On day 21, protein restriction had little effect on mean body weight, wet stomach and liver weight, gut length and colonic, jejunal or ileal mucosal weights per centimeter, whereas on day 35, all these tissue mass parameters were significantly (p less than 0.01 versus controls) depressed in the 8% protein group. DNA and protein content expressed per intestinal segment or per total organ and the protein/DNA ratio paralleled the changes in tissue mass, except that total DNA of the small intestine was decreased by 33% (p less than 0.01 versus controls) in 21-day-old rats with protein restriction. In the same age group, DNA synthesis rate, measured by the incorporation rate of [3H]-thymidine per milligram tissue DNA, was markedly depressed in the small intestine (4-fold decrease; p less than 0.001 versus controls) and in the liver (2-fold decrease; p less than 0.05 versus controls) while in the colon the effect of protein restriction occurred later (day 35).(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth hormone secretion in the stunted head-irradiated rat

Pulsatile secretion profiles of pituitary growth hormone (GH) and size and number of cells of brain, heart ventricles, liver, kidney, and gastrocnemius muscle were determined in male Long-Evans rats which received 600 rad x-irradiation to the head only at 2 days of age. Controls consisted of sham-irradiated littermates. The irradiated rats showed significant stunting of body weight and tail length beginning prior to weaning and lasting throughout the period (64 days) of observation. In irradiated rats at 20-21 days of age, just prior to weaning, organ weight was significantly reduced in all organs studied. Brain showed a decrease in organ/body ratio (p less than 0.0005) and in total DNA content (p less than 0.0005), but these values were not significantly changed in the other organs. DNA/organ ratio was increased significantly in heart (p less than 0.025) and gastrocnemius muscle (p less than 0.025); brain, liver, and kidney had nonsignificant increases. Protein/DNA ratios were decreased significantly in brain (p less than 0.005), heart (p less than 0.01), and gastrocnemius muscle (p less than 0.05); liver and kidney had nonsignificant decreases. Blood samples were removed for GH determination from cannulated undisturbed irradiated and control rats at 15-min intervals for 18-h periods (9 h light and 9 h dark) at 47-64 days of age. Irradiated rats had normal periodicity of bursts of GH secretion. The area under the curve of GH concentration versus time of the irradiated rat was decreased in light (p less than 0.025) and in dark (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Maturation of glomerular filtration in preterm and mature babies

Glomerular filtration rate (GFR) was measured in 39 healthy infants (gestation 27-40 weeks, birthweight 0.68-3.71 kg) by prolonged inulin infusion between 2 and 63 days of age. Absolute GFR showed a logarithmic rise with conceptional age (gestational plus postnatal age) which was independent of postnatal age. GFR per kilogram showed a slow rise with gestational age, and a rapid rise with increasing postnatal age which was shown to be due to a temporary cessation of growth rather than a true acceleration in renal maturation. GFR per unit surface area showed similar, but steeper rises. Formulae were constructed to predict GFR in the first month of life from postnatal age (PA), weight and birthweight (BW); (GFR = (0.24 BW + 0.18 PA + 0.45) X weight), or from conceptional age (CA); (GFR = 100.0618 CA-1.859). 95% of the predictions fell within 66 and 151%, and 58 and 172% of the measured values, respectively. Data from 14 studies were expressed in the same format where possible. The agreement between the reported data and this study was close. Apparent contradictions between these studies had been largely due to their different forms of presentation.     

Studies in Renal Response to Various Protein Intakes in Preterm Infants

ABSTRACT. The renal effects of two diets—breast-milk and breast-milk with extra human protein (7 g/l breast-milk)—were compared in very low birth weight infants with a gestational age of 26 to 30 weeks. When the infants were given the high protein diet for one week the glomerular filtration rate (GFR) increased significantly more than when breast-milk alone was given. Sodium clearance showed a similar increase in proportion to the GFR during the two diets. The high protein diet raised the urine osmolality moderately in all individuals, while the diuresis remained unchanged. The data in the present study indicate that the function of the immature kidney is influenced by the amount of protein in the diet. However, the long-term renal effects in preterm infants maintained on a high protein intake remain unknown.     

Studies in renal response to various protein intakes in preterm infants

The renal effects of two diets--breast-milk and breast-milk with extra human protein (7 g/l breast-milk)--were compared in very low birth weight infants with a gestational age of 26 to 30 weeks. When the infants were given the high protein diet for one week the glomerular filtration rate (GFR) increased significantly more than when breast-milk alone was given. Sodium clearance showed a similar increase in proportion to the GFR during the two diets. The high protein diet raised the urine osmolality moderately in all individuals, while the diuresis remained unchanged. The data in the present study indicate that the function of the immature kidney is influenced by the amount of protein in the diet. However, the long-term renal effects in preterm infants maintained on a high protein intake remain unknown.     

Chronic caffeine intake by rat dams during gestation and lactation affects various parts of the neonatal brain

Timed-pregnant rats were randomly divided into 2 groups on day 13 of gestation. Group 1 received a 20% protein diet. Group 2 was pair-fed to group 1 with a 20% protein diet containing caffeine (1 mg/100 g body weight). At parturition, the dams of each group were continued on their respective diets until day 22 postpartum. At the time of weaning (day 22), only male rats were continued in the study. At this time, rats from both groups were fed the control diet containing 20% protein. On day 57 and 58, rats were killed, the brains divided into six areas, and DNA, RNA and protein contents were measured. In certain areas of the brain, weight, cholesterol, DNA, RNA and protein contents were different even long after returning to the caffeine-free control diet. The present study demonstrates that even if a relatively small amount of caffeine is taken during gestation and lactation, a time during which the growth rate is greater than in any other period of life, certain areas of the brain may be affected. These findings suggest that future central nervous system impairment may be expressed later in life in these offspring.     

Role of aldosterone for control of colonic NaKATPase activity in weanling rats

Experiments were performed to examine how aldosterone modulates colonic NaKATPase activity during the weaning period. NaKATPase activity was determined in proximal and distal colon in control rats aged 16, 20, and 40 days, in rats aged 20 and 40 days fed low sodium diet for 4 days and in 20-day-old rats adrenalectomized on day 16. In some protocols net sodium and water transport was determined with in vivo perfusion technique. In control rats colonic NaKATPase activity increased significantly between day 16 and 20. This increase was abolished by adrenalectomy but restored by aldosterone substitution, 5 micrograms/100 g body weight/12 h. No significant increase in NaKATPase activity occurred between day 20 and 40. Serum levels of both aldosterone and of corticosterone were low until day 14 and increased to peak level at day 18-20. In 20- and 40-day-old rats fed a low sodium diet, NaKATPase activity increased significantly in proximal and distal colon in both age groups but the increases were significantly greater in the 20- than the 40-day-old animals. A low sodium diet increased serum aldosterone, but not serum corticosterone levels in both age groups: also the low sodium diet significantly increased net sodium and water transport in 20- but not in 40-day-old rats. Aldosterone is of physiological importance for the regulation of NaKATPase activity in the colon at the time of weaning. The immature colon may have an enhanced sensitivity to aldosterone.     

Maternal protein restriction that does not have an influence on the birthweight of the offspring induces morphological changes in kidneys reminiscent of phenotypes exhibited by intrauterine growth retardation rats

Severe restriction of maternal protein intake to 6–8% protein diet results in intrauterine growth retardation (IUGR), low birthweight and high risk of metabolic syndrome in the adult life of the offspring. However, little information is available on the effects of maternal protein restriction on offspring under the conditions that does not have an influence on their birthweight of the offspring,. In the present study, pregnant rats were kept on a diet consisting of either 9% (low‐protein, Lp rats) or 18% (normal‐protein, Np rats) protein by weight/volume/etc. After birth, both Lp and Np rats were kept on a diet containing 18% protein. Neonatal body weight was significantly lower in Lp rats compared to Np rats from 4 days to 5weeks after birth. While glomerular number per unit volume (1 mm³) of the kidney (Nv) was comparable between Lp and Np rats 4 weeks after birth, the Nv was significantly decreased in Lp rats at 20 weeks after birth. Four and 20 weeks after birth, glomerular sclerosis index, interstitial fibrosis score, and ratio of ED1‐positive cell ratio were all significantly higher in Lp compared to Np rats. Transforming growth factor‐β1‐positive cells were observed in the distal tubules in the kidney of 4‐ and 20‐week‐old Lp rats kidneys, but not in those of age‐matched Np rats. Altogether, these findings revealed that maternal protein restriction that does not have an influence on the birthweight of the offspring, induces similar changes as those seen in the kidneys of IUGR neonates.     

Maternal protein restriction suppresses the newborn renin-angiotensin system and programs adult hypertension in rats

Restriction of maternal protein intake during rat pregnancy produces offspring that are hypertensive in adulthood, but the mechanisms are not well understood. Our purpose was to determine whether this adult hypertension could be programmed during development by suppression of the fetal/newborn renin-angiotensin system (RAS) and a consequent reduction in nephron number. Pregnant rats were fed a normal protein (19%, NP) or low-protein (8.5%, LP) diet throughout gestation. Birth weight was reduced by 13% (p < 0.0005), and the kidney/body weight ratio was reduced in LP pups. Renal renin mRNA levels were significantly reduced in newborn LP pups; renal renin concentration and renin immunostaining were suppressed. Renal tissue angiotensin II levels were also suppressed in newborn LP (0.079 +/- 0.002 ng/mg, LP versus 0.146 +/- 0.016 ng/mg, NP, p < 0.01). Mean arterial pressure in conscious, chronically instrumented adult offspring (21 wk) was higher in LP (135 +/- 1 mm Hg, LP versus 126 +/- 1 mm Hg, NP, p < 0.00007), and GFR normalized to kidney weight was reduced in LP (p < 0.04). The number of glomeruli per kidney was lower in adult LP offspring (21,567 +/- 1,694, LP versus 28,917 +/- 2,342, NP, p < 0.03), and individual glomerular volume was higher (1.81 +/- 0.16 10(6) microm(3), LP versus 1.11 +/- 0.10 10(6) microm(3), NP, p < 0.005); the total volume of all glomeruli per kidney was not significantly different. Thus, perinatal protein restriction in the rat suppresses the newborn intrarenal RAS and leads to a reduced number of glomeruli, glomerular enlargement, and hypertension in the adult.     

Long-lasting Effect of Maternal Hyperphenylalaninemia during Pregnancy on Postnatal Brain Development of Mice: Biochemical and Morphological Studies

Abstract The effect of maternal hyperphenylalaninemia on postnatal brain development was examined. Maternal hyperphenylalaninemia was induced by giving chow supplemented with 6% phenylalanine (Phe.) and 0.12% p-chlorophenylalanine (PCPA) for at least one month before coupling and then throughout pregnancy. Offspring from hyperphenylalaninemic mothers were given a normal diet from the first day after birth.
Infant mice were killed on the 21st, 28th and 56th day after birth. The protein, RNA and DNA in the brain were measured to determine the biochemical changes. Maturation of the dendrite of pyramidal cells was also examined by the Golgi method. The body weight of the offspring born to mothers, which had been treated with Phe. and PCPA during pregnancy, was significantly less than that of the control. The gain of cerebral weight showed a similar pattern with that to the body weight.
The total protein, RNA and DNA contents in the cerebrum of the treated group were also reduced significantly on 21st, 28th and 56th days after birth. The dendritic arborization of the cortical pyramidal neurons in the layer V showed significant reductions in the offspring born to hyperphenylalaninemic mothers compared with the age-matched control at 21, 28 and 56 days after birth.
These findings suggest that maternal hyperphenylalaninemia during pregnancy causes an irreversible retardation of the neuronal maturation both biochemically and morphologically, and subsequently gives rise to disorders of the higher cortical functions.     

Kidney functional reserve. An experimental study

The renal functional reserve (RFR), the increase in glomerular filtration rate (GFR) induced by a protein load, seems to be diminished or even lost in renal failure. Our experimental study was undertaken to determine whether the RFR is lost beyond a given level of nephron reduction, using different protein loads. In the first two studies, RFRs were evaluated during an oral protein load consisting in a high-protein diet (30% casein) compared to a low-protein diet (7% casein). Each diet was given to SD rats (200 g) either for three weeks immediately after nephrectomy (Nx) or for four days one month after Nx. Nx was subtotal and consisted in removal of 65 to 85% of the mass of the renal parenchyma. The GFR evaluated by inulin clearance measurements increased considerably after a prolonged (+188%) or short-lived (+35%) oral protein load if less than 70% of the renal mass had been removed. Beyond this threshold of nephron amputation, the high-protein diet had no effect on the GFR, despite an increase in the residual renal mass (+200% in moderate and severe Nxs). In a third study, the GFR was measured one month after Nx and the effects of an infusion of amino acids (vamine) or of a placebo were compared, each rat serving as his own control. Extent of Nx was 0%, 50%, 65-70%, and 80%. Regardless of the extent of nephron reduction, the GFR increased under vamine, but interindividual variations in each group were marked (+5 to +70%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of protein malnutrition and maternal caffeine intake on the growth of fetal rat brain

Pregnant dams were divided into two subgroups on day 10 of gestation. Half were fed a 20% protein diet and the other half an 8% protein diet. A second group also subdivided was pair-fed with rats of the first group. Their diet was supplemented with caffeine in amount calculated to provide daily doses of 2 mg/100 g body weight. On days 18, 20, and 22 randomly selected dams were injected with 3H-thymidine intraperitoneally and 1.5 h later their fetuses were delivered surgically in order to determine the rate of DNA synthesis along the gestation. The rest of the fetuses were delivered surgically on day 22. Pups' brains were rapidly removed and DNA, RNA, protein and 3H-thymidine uptake were studied. Average body weights of the fetuses in the caffeine-supplemented control group were smaller than those of the noncaffeine group. Effects of caffeine that were similar in both diet groups included a decrease in brain DNA content and concentration and an increase in brain protein content and concentration. However, the percent decrease and increase, respectively, was different depending on the nutritional status. DNA synthesis was not affected by malnutrition or caffeine supplementation on day 18 of gestation. Caffeine's effect on the rate of DNA synthesis was different on day 20 of gestation depending on nutritional status. Caffeine supplementation resulted in a decrease in DNA synthesis in both groups on day 22 of gestation. These data indicate that caffeine intake during pregnancy produces differential effects on fetal rat brain depending on dietary protein content.     

Effect of intrauterine ethanol exposure on fetal lung growth

Lung weight, DNA, RNA, protein, and total body weight were analyzed in fetuses from 14 pregnant Sprague-Dawley rats fed a nutritionally complete liquid diet containing v/v 6% ethanol (ethanol group). Each ethanol rat was matched with an isocalorically pair-fed animal (control group) who received the same liquid diet with carbohydrate substituted for ethanol. The rats were killed on day 20 of gestation. The mean maternal blood ethanol concentration at 0700 h on day 20 was 170 +/- 22 (SE) mg/dl. Compared to controls, ethanol fetuses had reduced body weight (21%), lung dry weight (39%), lung wet weight/body weight ratio (10%), DNA (21%), RNA (25%), protein (28%), and protein/DNA ratio (8%) (p less than 0.05). The results indicate that prenatal ethanol exposure inhibits cellular growth in the fetal lung, resulting in hypoplastic lungs which have fewer and smaller cells. The effect on the lung appears to be greater than on the body as a whole. These hypoplastic lungs may be predisposed to the development of pulmonary disease and may explain observations of more frequent and severe lower respiratory infections in children with prenatal ethanol exposure.     

Phosphorus intake in preterm babies and variation of tubular reabsorption for phosphate per liter glomerular filtrate.

Inadequate low intake of phosphorus can induce a hypophosphatemic depletion syndrome resulting in hypercalcemia, hypercalciuria, hypophosphatemia, and rickets. Tubular reabsorption for phosphate per liter glomerular filtration rate (TP/GFR) has been proposed as a reliable index of renal phosphate handling for all age groups. In the present study, carried out in 12 healthy premature babies fed unmodified pooled human milk and then a preterm formula for two periods of 10 days, we demonstrated clearly that TP/GFR as well as calciuria can reflect the poor phosphorus intake and that the kidney of preterm babies is able to rapidly adapt itself to an increase in phosphorus diet content.     

Protein deprivation from the neonatal period impairs lung development in the rat

The effects of early protein-deficiency on lung development were studied in the rat. Newborn male rats were nursed in groups of eight. Control dams and pups received a 15% protein diet during the whole experiment. Test mothers only received 12 and 8% proteins from the 7th and the 14th day of lactation. Test rats fed a diet of 8% protein were weaned at 21 days and maintained on the low protein diet for 1 month. This caused a marked decrease in body weight gain, but lung/body weight ratio was not affected. Lung DNA and protein content, lung protein concentration, but not lung DNA concentration were decreased, suggesting the presence of fewer and smaller cells than in control lungs. Volume-pressure curves were performed on excised lungs. With air-filling, the curve obtained in rats fed a diet with 8% proteins was shifted downward and to the right, even when expressed as percent of maximal volume. Its exponential analysis assessed a decrease in lung compliance. In contrast, with saline-filling, the recoil pressure was decreased in rats fed a diet with 8% proteins. Both with air and saline-filling, the pressure at lung rupture was increased in malnourished rats. It is concluded that protein-deficiency from the neonatal period increases surface forces, decreases tissue elastic forces, and augments resistance of the lung to rupture.