Reply to “Permissive Role of GPER for Arterial Hypertension”

We appreciate the note by Drs. Barton and Meyer that our study has reported a novel Gper1^−/− strain that could be used as a tool for constructing future tools on different genomic backgrounds for studies on a variety of phenotypes.

Drs. Barton and Meyer state that there is no evidence of Gper1 as a receptor for aldosterone. However, our statement about this was based entirely on the literature. Gros et al. have demonstrated the effects of aldosterone on vascular endothelial cells through activation of Gper1 [1, 2]. Additionally, Briet and Schiffin also documented the role of GPR30 (Gper1) as an aldosterone receptor [3]. These studies provide evidence to support that Gper1 is also recognized as aldosterone receptor, and were the basis for our claim.

Secondly, Barton and Meyer appear to imply that 2% dietary sodium chloride that was used in our study to represent a high salt diet was not indeed high enough to represent a high salt content in the diet. Most standard Lab chow diets contain about 1% dietary salt whereby, 2% is not considered relatively very high for generic laboratory strains of rats and mice, which are not selectively bred models. The S rat model of hypertension is highly salt-sensitive, whereby we maintain their entire colony on a low (0.3%) sodium chloride diet (from Teklad). By this standard, 2% sodium chloride is a truly high salt content in their diet for the S rats. Furthermore, there is a common misconception that S rats show an increase in blood pressure (BP) only upon feeding excess salt. This is not true [4]. Original selection done by Dahl was based on the BP of rats on high salt. Therefore, any gene function to elevate the blood pressure regardless of salt intake would also have been selected along with genes responsible for causing high BP.

Third, Barton and Meyer state that the role of microbiota in this study is still unknown because there were no differences seen in males. This is not the case. We noted clear differences in the bacterial communities of wild-type and Gper1^−/− rats (Figure 5B in [5]). Moreover, after the transplant of wild-type microbiota into Gper1^−/− rats, the BP lowering effect was reversed in both males and females. As seen in Figure 2 [5], with the native microbiota both males and female Gper1^−/− rats had lower BP compared to controls. However, after the transplant, there was no difference in BP of male Gper1^−/− rats compared to wild-type rats, and female Gper1^−/− rats actually had an increased BP compared to wild-type rats (Figure 4 in [5]). Therefore, there is evidence that microbiota do have a role in this BP effect.

Lastly, Barton and Meyer point out the differences in BP between the male and female rats. Although this would have been interesting to compare and contrast, it is not an accurate means to do so for the following two reasons. First, the blood pressures of S rats measured at two different times of the year cannot be compared because the BP varies throughout the year as we have previously documented [6]. Because of this variance in the blood pressure, in every blood pressure study, control S rats are concomitantly raised along with the test strain for the comparison of blood pressure effect. Therefore, any comparisons made can only be within an individual study. Secondly, the males and females in this study were implanted with different BP telemetry transmitters from Data Sciences International (C40 for males, C10 for females), as stated in our supplemental methods. The reason for this variance is because female rats are smaller in size, which cannot be implanted with the C40 transmitters. The two telemetry transmitters, C40 and C10 have different baseline readings for BP, whereby, technically, it is inaccurate to compare BPs from two different telemetry transmitters. For these reasons, it is not possible for conclusions to be drawn from comparisons between males and females.