Lori L. Woods

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 ± 0.16 106 μm3, LP versus 1.11 ± 0.10 106 μm3, 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.

Perinatal ANG II programs adult blood pressure, glomerular number, and renal function in rats

ANG II is known to be important in normal renal development, but the long-term consequences of a suppressed renin-angiotensin system (RAS) during the developmental period are not completely understood. This study tested the hypothesis that the RAS in the developing animal is important in long-term regulation of renal function and arterial pressure. Newborn Sprague-Dawley rat pups were given the ANG II AT1 receptor antagonist losartan (25 mg . kg-1 . day-1 sc) for the first 12 days of postnatal life (Los). Body weights at weaning (22 days) were significantly reduced in Los (53.4 +/- 3.2 vs. 64.5 +/- 3.6 g in controls); however, at the time of study (approximately 22 wk), body weights and the kidney-to-body weight ratios were not different. In chronically instrumented conscious animals, glomerular filtration rate and effective renal plasma flow were reduced by 27 and 20%, respectively, in Los; the filtration fraction was not different. Maximal urine concentrating ability was also reduced in Los (1,351 +/- 45 vs. 2,393 +/- 52 mosmol/kg in controls). Mean arterial pressure was significantly higher in Los (134 +/- 3 vs. 120 +/- 1 mmHg). The number of glomeruli per kidney was reduced by 42% in Los, but the total glomerular volume was unchanged. Thus perinatal blockade of ANG II AT1 receptors results in fewer but enlarged glomeruli, reduced renal function, and an increased arterial pressure in adulthood. These data indicate that perinatal ANG II, acting via AT1 receptors, plays an important role in renal development and long-term control of renal function and arterial pressure. Physiological conditions that cause suppression of the RAS in the developing animal may have long-term consequences for renal function and blood pressure.ANG II is known to be important in normal renal development, but the long-term consequences of a suppressed renin-angiotensin system (RAS) during the developmental period are not completely understood. This study tested the hypothesis that the RAS in the developing animal is important in long-term regulation of renal function and arterial pressure. Newborn Sprague-Dawley rat pups were given the ANG II AT1 receptor antagonist losartan (25 mg ⋅ kg-1 ⋅ day-1sc) for the first 12 days of postnatal life (Los). Body weights at weaning (22 days) were significantly reduced in Los (53.4 ± 3.2 vs. 64.5 ± 3.6 g in controls); however, at the time of study (∼22 wk), body weights and the kidney-to-body weight ratios were not different. In chronically instrumented conscious animals, glomerular filtration rate and effective renal plasma flow were reduced by 27 and 20%, respectively, in Los; the filtration fraction was not different. Maximal urine concentrating ability was also reduced in Los (1,351 ± 45 vs. 2,393 ± 52 mosmol/kg in controls). Mean arterial pressure was significantly higher in Los (134 ± 3 vs. 120 ± 1 mmHg). The number of glomeruli per kidney was reduced by 42% in Los, but the total glomerular volume was unchanged. Thus perinatal blockade of ANG II AT1 receptors results in fewer but enlarged glomeruli, reduced renal function, and an increased arterial pressure in adulthood. These data indicate that perinatal ANG II, acting via AT1 receptors, plays an important role in renal development and long-term control of renal function and arterial pressure. Physiological conditions that cause suppression of the RAS in the developing animal may have long-term consequences for renal function and blood pressure.

Hypertension After Neonatal Uninephrectomy in Rats Precedes Glomerular Damage

The present study was designed to determine whether adult hypertension caused by a reduced number of nephrons from birth is due to preceding glomerular damage. Newborn male Sprague-Dawley rat pups were uninephrectomized during the first 24 hours after birth (UNX rats). At 20 weeks of age, chronically instrumented UNX animals were hypertensive on a normal-sodium (0.20%) diet compared with sham-operated controls (142±2 versus 124±2 mm Hg in controls). Body weights and the total kidney-to–body weight ratio were not significantly different in adult UNX animals compared with controls. Glomerular filtration rate (GFR) was reduced by 49% in UNX rats (1.85±0.24 versus 3.65±0.22 mL/min). Urine protein excretions were higher in UNX rats (20±2 versus 7±1 mg/d in controls). On a high-sodium (3.15%) diet, arterial pressure increased more in UNX than in controls (28±9 versus 3±1 mm Hg). In contrast, in animals studied at 8 weeks of age, GFR was only reduced by 26% in UNX animals (2.02±0.06 versus 2.73±0.07 mL/min). Their hypertension (125±2 versus 117±2 mm Hg) was also salt sensitive (increase on high-sodium diet of 35±11 versus 8±2 mm Hg in controls) but was not associated with proteinuria or histological signs of glomerular disease. Number of glomeruli per kidney in UNX animals was not different from controls, but individual glomerular volume increased by 41%. Thus, surgical removal of 50% of the nephrons, when done during development, causes reduced renal function and salt-sensitive hypertension in adulthood. Hypertension is present earlier in life than signs of glomerular disease, which suggests that hypertension is a major contributor to rather than primarily resulting from onset of renal disease.

Neonatal uninephrectomy causes hypertension in adult rats

This study was designed to test the hypothesis that a reduced number of nephrons from birth leads to increased arterial pressure in adulthood. Newborn Sprague-Dawley rat pups were uninephrectomized during the first 24 h after birth. In chronically instrumented adult animals (approximately 22 wk), mean arterial pressure on a normal (0.20%)-Na+ diet was higher in uninephrectomized rats (133 +/- 2 mmHg vs. 121 +/- 2 mmHg in controls, P < 0.0001). Body weights were not significantly different, but the total kidney-to-body weight ratio was significantly reduced by 14% in adult uninephrectomized animals (P < 0.05). Glomerular filtration rate was reduced by approximately 30% in uninephrectomized rats (1.84 +/- 0.09 vs. 2.63 +/- 0.14 ml/min, P < 0.0002), and effective renal plasma flow was reduced to a lesser degree (6.37 +/- 0.38 vs. 7.87 +/- 0.51 ml/min, P < 0.03), such that the filtration fraction was also reduced (0.291 +/- 0.007 vs. 0.338 +/- 0.014, P < 0.01). After 7-10 days on a high (3.15%)-Na+ diet, arterial pressure increased more in uninephrectomized animals than in controls (20 +/- 3 vs. 1 +/- 1 mmHg, P < 0.003). Thus surgical removal of 50% of the nephrons, when done during development, caused reduced renal function and a salt-sensitive hypertension in adulthood. These data suggest that a reduced nephron endowment from birth, caused by genetic and/or perinatal environmental factors, could contribute to essential hypertension in adulthood.This study was designed to test the hypothesis that a reduced number of nephrons from birth leads to increased arterial pressure in adulthood. Newborn Sprague-Dawley rat pups were uninephrectomized during the first 24 h after birth. In chronically instrumented adult animals (∼22 wk), mean arterial pressure on a normal (0.20%)-Na+ diet was higher in uninephrectomized rats (133 ± 2 mmHg vs. 121 ± 2 mmHg in controls, P < 0.0001). Body weights were not significantly different, but the total kidney-to-body weight ratio was significantly reduced by 14% in adult uninephrectomized animals ( P < 0.05). Glomerular filtration rate was reduced by ∼30% in uninephrectomized rats (1.84 ± 0.09 vs. 2.63 ± 0.14 ml/min, P < 0.0002), and effective renal plasma flow was reduced to a lesser degree (6.37 ± 0.38 vs. 7.87 ± 0.51 ml/min, P < 0.03), such that the filtration fraction was also reduced (0.291 ± 0.007 vs. 0.338 ± 0.014, P < 0.01). After 7-10 days on a high (3.15%)-Na+ diet, arterial pressure increased more in uninephrectomized animals than in controls (20 ± 3 vs. 1 ± 1 mmHg, P < 0.003). Thus surgical removal of 50% of the nephrons, when done during development, caused reduced renal function and a salt-sensitive hypertension in adulthood. These data suggest that a reduced nephron endowment from birth, caused by genetic and/or perinatal environmental factors, could contribute to essential hypertension in adulthood.

Perinatal programming, renal development, and adult renal function☆

Substantial data indicate that maternal diet during gestation, as well as perinatal events, affect organogenesis and, furthermore, may affect organ function at maturity, thus determining whether an individual is prone or resistant to a variety of health problems such as hypertension, cardiovascular disease, or renal dysfunction. This concept is called perinatal programming, or the fetal origins of adult disease (FOAD), a concept that arose after the publication of epidemiologic observations by Barker and colleagues that birth weight among apparently normal individuals studied in midlife was inversely associated with the presence of cardiovascular disease and hypertension. We now review evidence from studies in experimental animal models that have used nutritional and pharmacologic manipulation to extend epidemiologic observations.

Naturally occurring intrauterine growth retardation and adult blood pressure in rats.

In humans, infants who are born small have been reported to have higher blood pressure in adulthood than do larger infants. This suggests that factors in the intrauterine environment that affect fetal growth can program the individual for hypertension later in life. The present study determined whether there is a similar, naturally occurring relationship between birth weight and adult blood pressure in rats. Female Sprague-Dawley rats bred in our colony were fed a normal diet during pregnancy. On the day of delivery, any pups that weighed <90% of the mean pup weight for the litter were identified as runts. For each runt, a sex-matched littermate of normal weight was also identified and assigned to this study. These pairs were chronically instrumented at ∼20 wk of age. Mean arterial pressure was significantly higher in runt male and female offspring compared with their normal birth weight littermates (males: 149 ± 7, runts versus 129 ± 4 mm Hg, controls; females: 128 ± 1, runts versus 119 ± 2 mm Hg, controls). Although the runts had smaller body weights at study than did their littermate controls, the kidney-to-body weight ratio and renal function normalized to kidney or body weight were not different. These studies indicate that adult blood pressure is related to birth weight in rats, as it is in humans. The relative hypertension in runt animals is not due to gross differences in renal function but may be related to more subtle renal structural and/or functional differences.

Castration fails to prevent prenatally programmed hypertension in male rats

Male offspring of rats that were modestly protein restricted during pregnancy become hypertensive as adults, whereas their female littermates remain normotensive. The purpose of this study was to determine the role of testosterone in promoting this sexual dimorphism of prenatally programmed hypertension. Rats were fed either a normal (19% protein, NP) or modestly protein-restricted (8.5% protein, LP) diet throughout pregnancy. Male offspring either remained intact or were castrated (CAS) at 30 days of age. Female offspring remained intact. At approximately 22 wk of age, the offspring were chronically instrumented for measurement of mean arterial pressure and renal function. Intact male LP offspring were hypertensive compared with male NP offspring (138 +/- 2 vs. 130 +/- 2 mmHg, P < 0.007), whereas female LP offspring were normotensive (123 +/- 1 vs. 122 +/- 2 mmHg in NP females). In CAS males, blood pressure in both diet groups was not different from that in intact males of the same group (138 +/- 3 mmHg in LP CAS males, and 131 +/- 2 mmHg in NP CAS males). Glomerular filtration rate and effective renal plasma flow were also not significantly affected by castration. However, castration significantly reduced protein excretion in LP males to levels not different from those in NP CAS and intact males. Renal histopathology scores showed a similar pattern. Thus removal of androgens by castration failed to provide any protective effect against the hypertension programmed by maternal protein restriction. Castration also failed to abolish the sex difference in blood pressure in both diet groups. These findings suggest that the lifelong presence of normal levels of testicular hormones does not play a major role either in maintaining baseline blood pressure higher in males than in females, or in promoting further elevations in blood pressure in males due to prenatal undernutrition. However, androgens such as testosterone may promote renal injury in LP males.

Role of Endogenous Atrial Natriuretic Peptide in Chronic Anemia in the Ovine Fetus: Effects of a Non-Peptide Antagonist for Atrial Natriuretic Peptide Receptor

ABSTRACT: Chronic fetal anemia causes polyhydramnios and fetal hydrops and is associated with increased fetal diuresis and natriuresis. To determine the role of atrial natriuretic peptide (ANP) in the renal adaptation to chronic fetal anemia we studied the effects of HS-142–1 (HS), a specific inhibitor of the guanylate cyclase-linked ANP receptor (ANP-GC), in two groups of chronically instrumented unanesthetized sheep fetuses. Seven fetuses were made anemic by serial isovolemic hemorrhage over 1 wk, and five fetuses served as nonanemic controls. Over the 7 d of hemorrhage ANP concentrations increased (45 ± 7 to 234 ± 15 fmol/mL). Hematocrit and arterial blood oxygen content were significantly lower in the anemic compared with the nonanemic fetuses (13.8 ± 0.7 versus 34.6 ± 2.3% and 0.7 ± 0.1 versus 2.6 ± 0.2 mmol/L). Before HS urine flow rate, urinary sodium excretion, fractional excretion of sodium, and renal blood flow were increased in the anemic fetuses, and the extracellular fluid volume (inulin space) was increased (674 ± 94 versus 497 ± 71 mL/kg). However, GFR was not different between the groups. HS caused a significant increase in the central venous pressure of the anemic fetuses (0.49 ± 0.03 to 0.70 ± 0.05 kPa). Urinary excretion of cGMP was considered to be a marker of endogenous ANP renal effect and was measured before and after a single bolus of HS (5.2 ± 0.30 mg/kg). HS decreased urinary cGMP excretion to 50 and 37% of baseline levels in anemic and nonanemic fetuses, respectively. Urine flow decreased in both nonanemic and anemic fetuses (0.48 ± 0.13 to 0.25 ± 0.06 and 1.30 ± 0.66 ± 0.06 mL/min). Sodium excretion decreased in both groups after HS (19 ± 5 to 9 ± 2 and 83 ± 16 to 39 ± 5 μ mol/min). GFR decreased after HS (3.0 ± 0.8 to 2.4 ± 0.5 and 3.6 ± 0.3 to 2.6 ± 0.2 ML/min. Fraction excretion of sodium also decreased in both groups after HS (4.6 ± 2.7 to 2.7 ± 0.5 and 16.1 ± 2.4 to 11 ± 1.6). Percent decreases in urine flow, sodium excretion, GFR, and fractional excretion of sodium observed in the anemic fetuses were not statistically different from the non-anemic fetuses. Urine flow and sodium excretion did not decrease to control levels after HS, suggesting that factors in addition to ANP contribute to the natriuresis seen with chronic anemia. After HS a transient increase in renal blood flow was observed in the nonanemic fetuses. An immediate and sustained further increase in renal blood flow was observed in the anemic fetuses (336 ± 37 to 436 ± 58 mL/min/100 g of kidney). Decreasing GFR and increasing renal blood flow suggests HS may alter the renal microcirculation by reversing ANP-induced constriction of the glomerular efferent arteriole. We conclude that sustained increases of the central venous pressure suggest that ANP inhibition results in decreased fluid movement into perivascular tissue. Endogenous ANP may help to maintain basal renal function in the normal fetal kidney and participates in the renal adaptation to chronic fetal anemia. ANP may promote urine flow and sodium excretion by its effects on both the renal microcirculation and the sodium reabsorptive capacity of the nephron.

Maternal Low Protein or High Salt Diet in The Perinatal Period Suppresses Newborn Intrarenal Renin-Angiotensin System (RAS) and Programs for Hypertension in Adult Offspring • 1814

Maternal Low Protein or High Salt Diet in The Perinatal Period Suppresses Newborn Intrarenal Renin-Angiotensin System (RAS) and Programs for Hypertension in Adult Offspring • 1814