Juvenile growth reduces the influence of epithelial sodium channels on myogenic tone in skeletal muscle arterioles

Response Gene to Complement 32 Maintains Blood Pressure Homeostasis by Regulating α-Adrenergic Receptor Expression

RATIONALE

Hypertension prevalence is much higher among children and adolescents with low birth weight and greater postnatal weight gain than in individuals with normal birth weight. However, the cause and molecular mechanisms underlying this complication remain largely unknown. Our previous studies have shown that RGC-32 (response gene to complement 32)-deficient (RGC-32^-/-) mice are born significantly smaller but grow faster than their WT (wild type) controls, which allows adult RGC-32^-/- mice to attain body weights similar to those of control mice.

OBJECTIVE

The objective of this study is to determine whether RGC-32^-/- mice develop hypertension, and if so, to elucidate the underlying mechanisms.

METHODS AND RESULTS

By using a radiotelemetry system, we found that RGC-32^-/- mice exhibit higher mean arterial pressure than WT mice (101±4 versus 119±5 mm Hg), which enabled us to use RGC-32^-/- mice to study the mechanisms underlying low birth weight-related hypertension. The increased blood pressure in RGC-32^-/- mice was associated with increased vascular tone and decreased distensibility of small resistance arteries. The increased vascular tone was because of an increase in the relative contribution of sympathetic versus parasympathetic activity and was linked to increased expression of AT1R (angiotensin II type I receptor) and α1-AdR (α1-adrenergic receptor) in arterial smooth muscles. Mechanistically, RGC-32 regulated AT1R gene transcription by interacting with Sp1 (specificity protein 1) transcription factor and further blocking its binding to the AT1R promoter, leading to suppression of AT1R expression. The attenuation of AT1R leads to reduction in α1-AdR expression, which was critical for the balance of sympathetic versus parasympathetic control of vascular tone. Of importance, downregulation of RGC-32 in arterial smooth muscles was also associated with low birth weight and hypertension in humans.

CONCLUSIONS

Our results indicate that RGC-32 is a novel protein factor vital for maintaining blood pressure homeostasis, especially in individuals with low birth weight.

In utero exposure to alcohol alters reactivity of cerebral arterioles

Our goal was to examine whether in utero exposure to alcohol impaired reactivity of cerebral arterioles during development. We fed Sprague-Dawley dams a liquid diet with or without alcohol (3% ethanol) for the duration of pregnancy (21-23 days). Around 4-6 weeks after birth, we examined reactivity of cerebral arterioles to eNOS- (ADP) and nNOS-dependent (NMDA) agonists in the offspring. We found that in utero exposure to alcohol attenuated responses of cerebral arterioles to ADP and NMDA, but not to nitroglycerin in rats exposed to alcohol in utero. L-NMMA reduced responses to agonists in control rats, but not in rats exposed to alcohol in utero. Treatment of dams with apocynin for the duration of pregnancy rescued the impairment in reactivity to ADP and NMDA in the offspring. Protein expression of NOX-2 and NOX-4 was increased in alcohol rats compared to control rats. We also found an increase in superoxide levels in the cortex of rats exposed to alcohol in utero. Our findings suggest that in utero exposure to alcohol impairs eNOS and nNOS reactivity of cerebral arterioles via a chronic increase in oxidative stress.