Effects of Labetalol and Bisoprolol on Endothelial Nitric Oxide Signalling in the Fetoplacental Circulation

Abstract

Beta-blockers ( β-blockers) are widely prescribed during pregnancy to manage maternal hy-pertension; however, their effects on the fetoplacental circulation, particularly nitric oxide (NO) production and its underlying signalling, remain poorly understood. This thesis inves-tigated: (1) the expression of β-adrenergic receptors (βAR) in placental and maternal ves-sels; (2) the signalling mechanisms regulating β-adrenergic-mediated eNOS activation in endothelial cells; and (3) the impact of hypertension and β-blocker exposure on NO produc-tion in primary fetoplacental endothelial cells. Immunofluorescence and immunohistochemistry were performed on chorionic plate arteries (CPAs) and omental arteries (OAs). Endothelial cells were successfully isolated and charac-terised from normal pregnancies and were stimulated with isoprenaline to assess eNOS Ser1177 phosphorylation by immunofluorescence and ELISA. The involvement of major signalling pathways was examined using specific inhibitors. In parallel, the effects of labetalol and bisoprolol were assessed on total eNOS expression and phospho-eNOS Ser1177 (p-eNOS Ser1177). HPAECs were also isolated from pregnancies with normal blood pres-sure, hypertension without medication, and hypertension treated with labetalol or bisoprolol, and exposed to 5 dynes/cm² shear stress to quantify NO production using the Griess reaction. Both β1 and β2 adrenergic receptors were detected in CPAs and OAs, with significantly higher β2AR expression in OAs (p < 0.05). Normal HPAECs and HOAECs displayed typical cobblestone morphology and expressed CD31, vWF, and UEA-1. Isoprenaline significantly increased eNOS Ser1177 phosphorylation (p < 0.05), with evidence supporting involvement of the ERK1/2 pathway. Labetalol and bisoprolol had no significant effect on total eNOS expression across early and late passages, and their effects on p-eNOS were inconclusive. Across the four HPAEC cohorts, labetalol treatment showed a trend toward restoring NO levels to those of normal pregnancy, particularly at 24 hours, although this did not reach sta-tistical significance. In contrast, bisoprolol consistently showed lower NO levels at all time points (p = 0.24–0.48), suggesting a potential suppressive effect. In conclusion, this thesis provides direct evidence of functional βAR in HPAECs and demonstrates that β-adrenergic stimulation contributes to eNOS Ser1177 phosphorylation, likely via the ERK1/2 pathway. These findings enhance understanding of β-adrenergic sig-nalling in the fetoplacental endothelium and support the consideration of fetal growth and Doppler surveillance when β-blockers, particularly bisoprolol, are used during pregnancy.

Date of Award	6 May 2026
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Paul Brownbill (Main Supervisor) & Jenny Myers (Co Supervisor)