Antenatal betamethasone has a sex-dependent effect on the in vivo response to endothelin in adult sheep

Abstract

Antenatal steroid administration is associated with multiple cardiometabolic alterations, including hypertension; however, the mechanisms underlying this phenomenon are unclear. The aim of the present study was to ascertain, in vivo, the contribution of the endothelin system to the development of hypertension in the adult offspring and the signaling pathway involved. Pregnant sheep were treated with two doses of betamethasone (n = 23) or vehicle (n = 22) at 80 days (~0.55) gestation and allowed to deliver at term. Adult sheep were chronically instrumented under general anesthesia to place vascular catheters and a femoral artery flow probe. Blood pressure and flow were recorded continuously, and femoral artery vascular resistance was calculated before and during administration of endothelin 1 (ET-1). Selective blockers (dantrolene, BQ123, niacinamide) or saline were administered simultaneously. Betamethasone-exposed animals exhibited a significant elevation in mean blood pressure (female: 98 ± 1.8 vs. 92 ± 2.1; males: 97 ± 3.4 vs. 90 ± 2.3; mmHg; P < 0.05). ET-1 elicited a significant increase in blood pressure (F = 56.4; P < 0.001) and in vascular resistance (F = 44.3; P < 0.001) in all groups. A betamethasone effect in the vascular resistance response to ET-1 (F = 25.7; P < 0.001) was present in females only, and the effect was partially blunted by niacinamide (F = 6.6; P < 0.01). Combined administration of niacinamide and BQ123, as well as of dantrolene abolished the betamethasone effect on vascular resistance. No significant differences in mRNA expression of ET(A) or ET(B) in endothelial or smooth muscle cells of resistance-size arteries were observed. We conclude that the betamethasone effect on vascular resistance is mediated by an enhanced response to ET-1 through ET(A) receptor via the cyclic ADPR/ryanodine pathway.

Fig. 1.

Effects of 1-h continuous infusion of either saline (baseline), niacinamide (6 mg·kg⁻¹·min⁻¹), BQ 123 (300 nmol/min), or niacinamide plus BQ123 on mean femoral artery vascular resistance in female sheep-treated antenatally with either vehicle (n = 5) or betamethasone (n = 5). ^a,bColumns with different letter superscripts are statistically significantly different by ANOVA. *P < 0.05, beta vs. vehicle.

Fig. 2.

Dose-response effects of intra-arterial endothelin-1 (ET-1) on mean arterial pressure in sheep exposed antenatally to betamethasone or vehicle. A: males [vehicle: n = 5; betamethasone (beta): n = 9]. B: females (vehicle: n = 12; beta: n = 9) *P < 0.05 for ET-1dose effect. †P < 0.05 for betamethasone treatment effect by ANOVA.

Fig. 3.

Dose-response effects of intra-arterial ET-1 on femoral artery vascular resistance in sheep exposed antenatally to betamethasone or vehicle. A: males (vehicle: n = 5; beta: n = 9), B: females (vehicle: n = 12; beta: n = 9) *P < 0.05 for ET-1 dose effect. †P < 0.05 for betamethasone treatment effect by ANOVA.

Fig. 4.

Dose-response effects of intra-arterial endothelin on femoral artery vascular resistance in female sheep exposed antenatally to betamethasone or vehicle. A: endothelin alone. B: endothelin plus niacinamide. C: endothelin plus dantrolene. Niacinamide and dantrolene were administered for 1 h prior and during the eight doses of ET-1. *P < 0.05 for ET-1 dose effect. †P < 0.05 for betamethasone treatment effect by ANOVA.

Fig. 5.

Dose-response effects of intra-arterial endothelin on femoral artery vascular resistance in female sheep exposed antenatally to vehicle (top) or betamethasone (bottom). In each panel, the effects of ET-1 are shown along side endothelin plus niacinamide and ET-1 plus dantrolene. The dantrolene and niacinamide infusions were administered for 1 h prior and during the eight doses of ET-1. Statistical significance for each plot in each panel is indicated by *P < 0.05 for ET-1 dose effect. †P < 0.05 for betamethasone treatment effect. ‡P < 0.01 for drug treatment effect by ANOVA.

Fig. 6.

Dose-response effects of intra-arterial endothelin on femoral artery vascular resistance in male sheep exposed antenatally to betamethasone or vehicle. In each panel, the effects of ET-1 are shown along side endothelin plus niacinamide and ET-1 plus dantrolene. The dantrolene and niacinamide infusions were administered for 1 h prior and during the 8 doses of ET-1. Statistical significance for each plot in each panel is indicated by *P < 0.05 for ET-1 dose effect by ANOVA. No significant effects of either niacinamide or dantrolene were observed in either group.

Fig. 7.

Dose-response effects of intra-arterial endothelin on femoral artery vascular resistance in female sheep exposed antenatally to vehicle (top) or betamethasone (bottom). In each panel, the effects of ET-1 are shown along side endothelin plus dantrolene and ET-1 plus BQ-123 and niacinamide. The dantrolene and BQ123 plus niacinamide infusions were administered for 1 h prior and during the eight doses of ET-1. Statistical significance for each plot in each panel is indicated by *P < 0.05 for ET-1 dose effect. †P < 0.05 for betamethasone treatment effect. ‡P < 0.01 for drug treatment effect by ANOVA.

Fig. 8.

Endothelin receptor mRNA expression in resistance arteries of female (A) and male (B) adult sheep treated antenatally with either vehicle or betamethasone. The denuded to intact expression ratio for either ET_A or ET_B mRNA was not statistically different either by sex or by antenatal treatment.