Sex dependent compensatory mechanisms to preserve blood pressure homeostasis in PGI2receptor deficient mice

Inhibitors of microsomal prostaglandin E synthase-1 (mPges-1) are in the early phase of clinical development. Deletion of mPges-1 confers analgesia, restrains atherogenesis and fails to accelerate thrombogenesis, while suppressing prostaglandin (PG) E 2 , but increasing biosynthesis of prostacyclin (PGI 2 ). In hyperlipidemic mice, this last effect represents the dominant mechanism by which mPges-1 deletion restrains thrombogenesis, while suppression of PGE 2 accounts for its anti-atherogenic effect. However, the impact of mPges-1 depletion on blood pressure (BP) in this setting remains unknown. To address how differential effects on PGE 2 and PGI 2 might modulate salt-evoked BP responses in the absence of mPges-1, we generated mice lacking the I prostanoid (Ipr) receptor or mPges-1 on a hyperlipidemic background caused by deletion of the low density lipoprotein receptor (Ldlr KOs). Here, mPges-1 depletion significantly increased the BP response to salt loading in male Ldlr KO mice, whereas, despite the direct vasodilator properties of PGI 2 , Ipr deletion suppressed it. Furthermore, combined deletion of the Ipr abrogated the exaggerated BP response in male mPges-1 KO mice. Suppression of PGE 2 biosynthesis was enough to explain the exaggerated BP response to salt loading by either mPges-1/Ldlr depletion or by an MPGES-1 inhibitor in mice expressing human mPGES-1. However, the lack of a hypertensive response to salt in Ipr-deficient mice was attributable to reactive activation of the atrial natriuretic peptide pathway. Interestingly, these unexpected BP phenotypes were not observed in female mice fed a high salt diet. This is attributable to the protective effect of estrogen in Ldlr KO mice and in Ipr /Ldlr DKOs. Thus, estrogen compensates for a deficiency in PGI 2 to maintain BP homeostasis in response to high salt in hyperlipidemic female mice. In males, by contrast, augmented formation of ANP plays a similar compensatory role, restraining hypertension and oxidant stress in the setting of Ipr depletion. Hyperlipidemic males on a high salt diet might be at risk of a hypertensive response to mPGES-1 inhibitors.