Estrogen protects against increased blood pressure in postpubertal female growth restricted offspring

Abstract

Placental insufficiency in the rat results in intrauterine growth restriction and development of hypertension in prepubertal male and female growth-restricted offspring. However, after puberty, only male growth-restricted offspring remain hypertensive, whereas female growth-restricted offspring stabilize their blood pressure to levels comparable to adult female controls. Because female rats reach their maximum levels of estrogen at puberty, we hypothesize that estrogen may be a factor involved in the stabilization of blood pressure in adult female growth-restricted offspring. At 10 weeks of age, female control and growth-restricted offspring underwent ovariectomy or sham surgery and insertion of a telemetry probe. Mean arterial pressure was similar at 16 weeks of age between control (123+/-4 mm Hg) and growth-restricted offspring (122+/-2 mm Hg); however, ovariectomy led to a significant increase in blood pressure in growth-restricted offspring (140+/-2 mm Hg; P<0.05 versus intact counterpart) with no significant effect in controls (124+/-1 mm Hg). Estrogen replacement by subcutaneous minipellet initiated at 14 weeks of age in a subset of ovariectomized control and growth-restricted offspring reversed the effect of ovariectomy on blood pressure in growth-restricted offspring at 16 weeks of age (111+/-3 mm Hg; P<0.05 versus ovariectomized counterpart); renin angiotensin system blockade also abolished ovariectomy-induced hypertension in female growth-restricted offspring (106+/-2 mm Hg; P<0.05 versus ovariectomized counterpart). Therefore, sex differences are observed in this model of fetal programmed hypertension, and results from this study suggest that estrogen contributes to normalization of blood pressure in adult female growth-restricted offspring.

Figure 1. Ovariectomy and blood pressure in IUGR offspring

Mean arterial pressure was measured by radio telemetry from 12 to 16 weeks of age in animals that underwent either sham (intact) or ovariectomy (OVX) at 10 weeks of age. Control intact (n=7), control OVX (n=7), IUGR intact (n=7), and IUGR OVX (n=8). *P<0.01 vs. IUGR intact. All data are expressed as mean ± SEM.

Figure 2. The effect of E2 replacement on hypertension induced by ovariectomy in adult female IUGR offspring

Mean arterial pressure was measured by radio telemetry from 12 to 16 weeks of age. E2 replacement (17β estradiol valerate minipellets, SC) was administered from 14 to 16 weeks of age. Control-OVX-untreated (n=7), IUGR-OVX-untreated (n=8), Control-OVX + E2 (n=6) and IUGR-OVX + E2 (n=8). * P<0.05 vs. control; † P<0.05 vs. untreated counterpart All data are expressed as mean ± SEM.

Figure 3. The effect of ACE inhibition on hypertension induced by ovariectomy in adult female IUGR offspring

Mean arterial pressure was measured by radio telemetry from 12 to 16 weeks of age. ACE inhibitor (enalapril, 250mg/L by drinking water) or vehicle was administered from 14 to 16 weeks of age. Control-intact-vehicle (n=7), IUGR-intact-vehicle (n=8,) Control-intact-enalapril (n=7), IUGR-intact-enalapril (n=8), Control-OVX-untreated (n=7), IUGR-OVX-untreated (n=8), Control-OVX-Enalapril (7) IUGR-OVX-Enalapril (n=7). * P<0.05 vs. control; † P<0.05 vs. untreated counterpart All data are expressed as mean ± SEM.

Figure 4. Estrogen levels in control and IUGR offspring

a) Time line of estrogen levels. Estrogens levels were measured at 4, 6, 8, 10, 12 and 16 weeks of age. N = 6-8 per age group. *P<0.05 vs. 4 and 6 weeks of age younger counterpart. b) Estrogens levels in intact, ovariectomized, and ovariectomized plus estrogen replacement. Estrogens levels were measured at 16 weeks of age. N = 6-8 per group. * P<0.05 vs. intact counterparts † P<0.05 vs. ovariectomized counterparts. All data are expressed as mean ± SEM.

Figure 5. Renal ACE and ACE2 mRNA expression in intact and ovariectomized control and IUGR offspring

Renal ACE and ACE2 mRNA expression were assessed using a Real Time PCR. Results were calculated using the 2^−ΔΔCT method and expressed in folds increase/decrease of the gene of interest. Control-intact (n=7), IUGR-intact (n=7), Control-OVX d (n=7), and IUGR-OVX (n=8) * P<0.05 vs. control-intact ACE2. † P<0.05 vs. IUGR-intact ACE2. All data are expressed as mean ± SEM.