Alterations in circulatory and renal angiotensin-converting enzyme and angiotensin-converting enzyme 2 in fetal programmed hypertension

Abstract

Antenatal betamethasone treatment is a widely accepted therapy to accelerate lung development and improve survival in preterm infants. However, there are reports that infants who receive antenatal glucocorticoids exhibit higher systolic blood pressure in their early adolescent years. We have developed an experimental model of programming whereby the offspring of pregnant sheep administered clinically relevant doses of betamethasone exhibit elevated blood pressure. We tested the hypothesis as to whether alterations in angiotensin-converting enzyme (ACE), ACE2, and neprilysin in serum, urine, and proximal tubules are associated with this increase in mean arterial pressure. Male sheep were administered betamethasone (2 doses of 0.17 mg/kg, 24 hours apart) or vehicle at the 80th day of gestation and delivered at term. Sheep were instrumented at adulthood (1.8 years) for direct conscious recording of mean arterial pressure. Serum and urine were collected and proximal tubules isolated from the renal cortex. Betamethasone-treated animals had elevated mean arterial pressure (97+/-3 versus 83+/-2 mm Hg; P<0.05) and a 25% increase in serum ACE activity (48.4+/-7.0 versus 36.0+/-2.7 fmol/mL per minute) but a 40% reduction in serum ACE2 activity (18.8+/-1.2 versus 31.4+/-4.4 fmol/mL per minute). In isolated proximal tubules, ACE2 activity and expression were 50% lower in the treated sheep with no significant change in ACE or neprilysin activities. We conclude that antenatal steroid treatment results in the chronic alteration of ACE and ACE2 in the circulatory and tubular compartments, which may contribute to the higher blood pressure in this model of fetal programming-induced hypertension.

Figure 1

Antenatal betamethasone administration significantly increased MAP in adult sheep and was reduced to the control values 45 minutes after candesartan (0.3 mg/kg) bolus injection, Data are means±SEM. *P<0.05 vs control.

Figure 2

Antenatal betamethasone increased ACE activity and reduced ACE2 activity in betamethasone-treated animal serum vs control values. A, MAP was positively correlated with ACE activity in serum. B, MAP was negatively correlated with ACE2 activity. C, The ACE:ACE2 ratio was positively correlated with MAP. D, Data are means±SEM. *P<0.05 vs control.

Figure 3

Antenatal betamethasone reduced ACE2 activity in betamethasone-treated animal isolated proximal tubules vs control values. A, Western blot for ACE2 normalized to annexin 2 showed a 68% reduction in ACE2 protein expression in betamethasone-treated sheep. B, Antenatal betamethasone reduced ACE2 activity in urine from treated vs control. Data are means±SEM. *P<0.05 vs control.