Alterations in Circulatory and Renal Angiotensin-Converting Enzyme and Angiotensin-Converting Enzyme 2 in Fetal Programmed Hypertension

Abstract

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 (97Ϯ3 versus 83Ϯ2 mm Hg; PϽ0.05) and a 25% increase in serum ACE activity (48.4Ϯ7.0 versus 36.0Ϯ2.7 fmol/mL per minute) but a 40% reduction in serum ACE2 activity (18.8Ϯ1.2 versus 31.4Ϯ4.4 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. Key Words: fetal programming Ⅲ hypertension Ⅲ renin-angiotensin system Ⅲ sheep Ⅲ angiotensin-converting enzyme 2 Ⅲ proximal tubules and serum I n a landmark article, Liggins and Howie 1 demonstrated that antenatal glucocorticoid therapy administered to women at risk for preterm delivery reduced the incidence of respiratory distress syndrome and mortality in their offspring. The efficacy of antenatal glucocorticoid therapy has been confirmed subsequently by many randomized, controlled trials. 2,3 The reduction in the severity and incidence of respiratory distress syndrome has resulted in decreased requirements for surfactant therapy, lower concentrations of supplemental oxygen, and a decreased need for prolonged mechanical ventilation in the neonatal period. 4 Indeed, various organizations, including the National Institutes of Health 4 and the American College of Obstetricians and Gynecologists, have recommended antenatal glucocorticoid treatment for women at risk for preterm delivery before 34 weeks of gestation. However, a recent report showed that, at 14 years of age, blood pressure was higher in a group of children born preterm whose mothers received betamethasone before preterm delivery compared with a similar group who were not exposed to corticosteroids. 5 The mechanism for this increase in blood pressure is not fully known, but severa...

Differential regulation of circulating and renal ACE2 and ACE in hypertensive mRen2.Lewis rats with early-onset diabetes

“…We employed a sensitive HPLC-based method to measure the conversion of the endogenous substrates Ang I and ANG II to the enzymatic products ANG II and Ang-(1-7) for the determination of ACE and ACE2 activities (34,35,44,45). Early-onset diabetes increased ACE2 activity ninefold in female and threefold in male mRen2.Lewis rats, the greater magnitude of change in ACE2 likely due to the lower circulating activity in control females.…”

“…ACE, ACE2, and neprilysin activities in serum and purified cortical membranes were performed using an HPLCbased assay with 125 I-labeled Ang I or 125 I-ANG II as substrates in the presence of various peptidase inhibitors (33,44,45). Non-ACEdependent generation was performed with all inhibitors except the chymase inhibitor chymostatin (44).…”

“…Non-ACEdependent generation was performed with all inhibitors except the chymase inhibitor chymostatin (44). Kinetic analysis of ACE2 activity was performed on pooled serum from control and diabetic females as described (45).…”

“…Although ACE2 was originally characterized for its ability to hydrolyze ANG I to Ang-(1-9), subsequent studies revealed a very high catalytic activity to convert ANG II to Ang-(1-7) (41,44,45,56,58). Indeed, ACE2 inhibition or genetic knockout studies reveal a heightened sensitivity to ANG II-induced increases in blood pressure, as well as an exacerbation of end-organ damage in these experimental models (31,32,46,48,52,60).…”

Review:Novel roles of nuclear angiotensin receptors and signaling mechanisms

“…Betamethasone exposure in pregnant sheep that parallels the gestational age for premature infant administration of glucocorticoids results in a "fetal programming phenotype," in which the offspring exhibit reduced nephron number, glucose insensitivity, attenuated baroreflex sensitivity, and elevated blood pressure (16,42,86,87). Altered renal mechanisms that favor increased sodium retention with an enhanced response to ANG II and a reduced natriuretic effect of ANG-(1-7) are evident in this model (16,97).…”