Placental insufficiency results in temporal alterations in the renin angiotensin system in male hypertensive growth restricted offspring

Abstract

Reduced uterine perfusion initiated in late gestation in the rat results in intrauterine growth restriction (IUGR) and development of hypertension by 4 wk of age. We hypothesize that the renin angiotensin system (RAS), a regulatory system important in the long-term control of blood pressure, may be programmed by placental insufficiency and may contribute to the etiology of IUGR hypertension. We previously reported that RAS blockade abolished hypertension in adult IUGR offspring; however, the mechanisms responsible for the early phase of hypertension are unresolved. Therefore, the purpose of this study was to examine RAS involvement in early programmed hypertension and to determine whether temporal changes in RAS expression are observed in IUGR offspring. Renal renin and angiotensinogen mRNA expression were significantly decreased at birth (80 and 60%, respectively); plasma and renal RAS did not differ in conjunction with hypertension (mean increase of 14 mmHg) in young IUGR offspring; however, hypertension (mean increase of 22 mmHg) in adult IUGR offspring was associated with marked increases in renal angiotensin-converting enzyme (ACE) activity (122%) and renal renin and angiotensinogen mRNA (7-fold and 7.4-fold, respectively), but no change in renal ANG II or angiotensin type 1 receptor. ACE inhibition (enalapril, 10 mg x kg(-1) x day(-1), administered from 2 to 4 wk of age) abolished hypertension in IUGR at 4 wk of age (decrease of 15 mmHg, respectively) with no significant depressor effect in control offspring. Therefore, temporal alterations in renal RAS are observed in IUGR offspring and may play a key role in the etiology of IUGR hypertension.

Figure 1

Inhibition of the renin angiotensin system in intrauterine growth restricted (IUGR) offspring. Mean arterial pressure was measured in conscious chronically instrumented offspring at 4 and 5 weeks of age following treatment with either vehicle or enalapril (treated; 10mg/kg/day by gavage from 2 to 4 weeks of age). 4 week group: control vehicle (n=11), IUGR vehicle (n=7), control treated (n=10), and IUGR treated (n=9). 5 week group: control vehicle (n=8), IUGR vehicle (n=5), control treated (n=7), and IUGR treated (n=6). *P<0.05 vs. untreated control. †P<0.05 vs. untreated IUGR. All data are expressed as mean ± SEM.

Figure 2

Temporal changes in renal renin and angiotensinogen in intrauterine growth restricted (IUGR) offspring. Real time PCR was utilized to assess renal renin mRNA expression in newborn (day 1) (a), 6 weeks of age (b), and 16 weeks of age (c) or renal angiotensinogen mRNA expression of in newborn (day 1) (d), 6 weeks of age (e), and 16 weeks of age (f). Quantitation of renal RAS components was normalized relative to renal β-actin mRNA expression levels. For newborn samples mRNA expression was quantitated from whole kidney homogenates representing a pool of tissues collected from a single litter, n = 8 IUGR litters and 6 control litters; individual cortical sections were analyzed from 8 IUGR and 8 control offspring at 6 weeks of age; 7 IUGR and 8 control offspring at 16 weeks of age. Standard error is calculated from at least 3 determinations from at least three independent experiments. *P<0.05 vs. control. All data are expressed as mean ± SEM.

Figure 3

Renal ACE, AT₁ receptor, and angiotensin II in intrauterine growth restricted (IUGR) offspring at 16 weeks of age. Real time PCR was utilized to assess renal ACE (a) and AT₁ receptor (d) mRNA expression. Quantitation of renal RAS components was normalized relative to renal mRNA β-actin mRNA expression levels. Individual cortical sections were analyzed from 7 IUGR and 8 control offspring at 16 weeks of age. Standard error was calculated from at least 3 determinations from at least three independent experiments. Quantitative binding of renal ACE (b) and AT₁ receptor (e) was determined in 8 IUGR and 8 control offspring. Renal ACE activity (c) and renal ANG II (f) was determined in 6 IUGR and 5 control offspring. All data are expressed as mean ± SEM.

Figure 4

Quantitative autoradiography of angiotensin type 1 (AT₁R) receptors and angiotensin converting enzyme (ACE) in whole kidney from control and IUGR offspring at 16 weeks of age. Representative autoradiographs are shown of ACE (a), AT₁R (b), and non-specific binding (c) of 125 I-SI ANG II.