Endogenous oestrogens do not regulate endothelial nitric oxide production in early postnatal rats

Area of Science:

• Cardiovascular Physiology
• Endocrinology
• Developmental Biology

Background:

• Young rats exhibit an endothelium-dependent anticontractile effect mediated by nitric oxide (NO) and higher endothelial nitric oxide synthase (eNOS) expression compared to adults.
• Oestrogens are known regulators of eNOS expression and activity in the arterial endothelium.

Purpose of the Study:

• To investigate the hypothesis that endogenous oestrogens regulate the endothelium-dependent anticontractile effect observed in young rats.
• To determine the role of oestrogen signaling in modulating NO production and vascular function during early postnatal development.

Main Methods:

• Wistar rats were treated with ICI 182,780 (oestrogen receptor antagonist) or letrozole (aromatase inhibitor) from postnatal day 2.
• Wire myography was used to assess saphenous artery contractility in 10-12-day-old male rats.
• ELISA and qPCR were employed to measure serum sex steroid levels and arterial mRNA expression of oestrogen receptors and eNOS.

Main Results:

• Male rats aged 10-12 days showed higher serum 17β-oestradiol and increased mRNA for oestrogen receptors (ERα, GPER1) compared to adults.
• Treatment with ICI 182,780 or letrozole did not alter arterial sensitivity to methoxamine or the effects of nitric oxide synthase blockade.
• Endothelium-denuded artery sensitivity to a NO-donor (DEA/NO) and eNOS expression levels remained unchanged by the treatments.

Conclusions:

• Endogenous oestrogens do not appear to play a significant role in regulating the anticontractile effect of NO in the early postnatal development of rat saphenous arteries.
• The study suggests that other factors may be responsible for the observed NO-mediated anticontractile effect in young rats.