Sex Differences in Autonomic Blood Pressure Regulation: Sex Chromosome Complement and Hormonal Involvement

Round 1

Reviewer 1 Report

Authors did a good review of sex disparities in blood pressure regulation. 

Overall the manuscript is well written with some re-organization and terminology issues.

My specific comments are:

1. In this review authors used gender (men and women) but mentioned as sex (which is technically male and female). I hope authors know the difference between sex (biological component) and gender (social component). This should be cleared in the manuscript.

2. Effect of sex on cardiovascular disease was mentioned in many places. I would suggest to organize all these cardiovascular related discussions in a separate sub-heading.

3. Few simple flow-charts, or schematic diagrams on how sex hormones influence blood pressure and thereby cardiovascular and other diseases will significantly improve the manuscript and helpful for the readers to understand the overall intent of the authors.

4. Authors can also organize all the mechanisms in a separate heading. I see mechanistic discussions in some places.

5. Limitations of the study should also be included.

Author Response

First of all, we would like to thank the Editors and Reviewers for their thorough analysis and suggestions. All the contributions have been included and we believe that they have resulted in a substantial improvement for the manuscript. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The review “Sexual dimorphism in blood pressure regulation: sex chromosome complement and hormone involvement” focuses on some aspects of blood pressure regulation and gender differences in this regulation. The review focuses only on baroreflex blood pressure regulation through autonomic nervous system parasympathetic and sympathetic activity, while the other aspects of blood pressure regulation are completely neglected (and not even mentioned to exist) in this review.

The review has some good points, but there are serious pitfalls:

1.       As already said, the review focuses only on baroreflex blood pressure regulation through autonomic nervous system parasympathetic and sympathetic activity, while the other aspects of blood pressure regulation are completely neglected (and not even mentioned to exist) in this review. Therefore, the title of the article needs to be changed, to convey a clear message that this review examines only parasympathetic and sympathetic blood pressure regulation. The same should be emphasized in the abstract.

2.       The references in the review are outdated: from 87 references only 20 are after 2010 (!), and many are even before 2000. Moreover, many of these old references are review articles, so the original studies are difficult to find and probably are much older. Therefore, the review seems outdated.

3.       There is a lot of repletion of general statements and well-known facts, with a small level of new information and specific studies. The information given from the cited references is quite vague and not specific, without leaving a clear idea of what was found and where.

4.       The number of studies on the effect of sex hormones on blood pressure in males and females is rather limited. There are mentioned some studies on the effect of estrogens and androgens (the effect of progesterone was not even mentioned!), but their number is small, and more studies are needed to be described. Particularly the studies on ovariectomized and orchiectomized animals (or humans), with and without substitution of various sex hormones, or studies with intrauterine injection of sex hormones during intrauterine development. The studies must be distinguished if they were in females and males, because the effect of various sex hormones is very different in males compared to females. There are plenty of such studies, and they need to be presented.

5.       The genes on the X chromosome related to blood pressure regulation are not mentioned at all, and the effect of (incomplete) inactivation of the second X chromosome in females is not mentioned at all.

6.       Epigenetic influences are poorly mentioned and discussed.

The other specific issues are mentioned below:

Line 44: subsection “2. Baroreflex blood pressure regulation and brain-stem pathways involved”: too long, general information, unnecessarily focused on the anatomy of the autonomic nervous system in the brain, which is not relevant to this article (i.e., already known, not relevant to the topic of gender differences).

Line 83: to which animals are referred 15 and 16? Please, add to the main text, because is not clear that it is related to animals, and describe in more detail the findings.

Line 89-91: “Children and adolescents demonstrate significant sex differences on measures of vagal activity, with girls displaying lower resting state cardiac vagal activity and greater mean heart rate than boys [22].”

What was the age of these children? The sentence seems contradictory with the later statements in women, when they have higher vagal activity in earlier age (e.g., “While young women show a main parasympathetic control in cardiovascular regulation, in postmenopausal women sympathetic tone dominates [20,27]”). Are there studies in adolescents?

Line 114: “4. But why do males and females show a sex-specific cardiovascular phenotype?”- the title is improper, since there is only blood pressure analyzed (more specific: sympathetic/ parasympathetic response), but not other aspects of “cardiovascular phenotype”.

Line 116: why the abbreviation SCC is not used for ‘sex chromosome complement”? Can you define and explain much more in detail what was meant by “sex chromosome complement”?

Lines 115-133. Much more on genes on the X chromosome involved in blood pressure regulation and (incomplete) inactivation of the second X chromosome in females needs to be said. Are there other genes apart from the Sry gene on the Y chromosome involved in blood pressure regulation?

Lines 136-141: Pretty repetition of lines 88-104.

Lines 143-145: “”... While the use of oral contraceptives abolishes the cardiac vagal differences observed during the menstrual cycle [41].” How? Give more details on these findings, because it is quite unclear what was meant by this. Which OC were used there? Is this contradictory with the further lines in this paragraph (148-150)?

Line 150: “..while it also stimulates noradrenaline uptake [38].” – Where? What is the meaning/significance of this?

Line 167: ” Testosterone, meanwhile, has been shown to enhance the synthesis of noradrenaline, inducing an increase in sympathetic drive [38].”- Where does it increase synthesis in the body? In which models it was studied?

Lines 168- 169: Furthermore, the administration of androgen reduces cardiac vagal activity, and this effect is reversed with the administration of an androgen antagonist [58].” – To whom? Which model was used?

Line 180-181: “Previous studies in patients and spontaneously hypertensive rats demonstrated an association of the Y chromosome with high blood pressure [59,60].”- What is meant by that? Please, give more details and clarifications how and what was studied there and compared. Describe these studies

182-184: “The Syr gene present on the Y chromosome not only initiates gonad determination during 182 early development in males but can also modulate norepinephrine synthesis in males, [61,62,63]. “ – how it can modulate norepinephrine synthesis in males? What happened? Give more details on the findings, do not give only general statements.

Please, eliminate “...the major neurotransmitter of the peripheral sympathetic nervous system””- it is an unnecessary well-known fact.

Lines 187-191”: What was meant by: “However, Shi et al.’s study used transcriptomic and proteomic analyses to demonstrate that some cardiac sex disparities in mice occur at the earliest stages of heart formation (before gonad formation), and that thus demonstrated that cardiac sex differences are determined not only by sex hormones but also by sex-dependent chromosome mechanisms [64].” - can you give more details of this study and the specific findings?

Line 217-218: ‘Angiotensin II (Ang II) exerts differential effects on cardiovascular parameters in males and females [66], increasing sympathetic activity while decreasing parasympathetic drive, “ – how is differential in males and females? Which effects on cardiovascular parameters? Give more details

Lines 221-227: Pease, give more details. Were those ovariectomized and orchiectomized animals?

Lines 230-233: Quite unclear. What is XX-SCC, XY-SCC? Please, use XX-Sry or XY-Sry where necessary. Define more which animals (i.e., which genotype) it was.

Lines 248-267: The same as above.

Lines 234-235: Please, explain in more detail: ”experimental studies also revealed an interaction of organizational hormone and SCC factors on the dimorphic bradycardic response due to phenylephrine infusion [69].” – what is meant by that?

Is it meant “organizational hormonal”?

Author Response

First of all, we would like to thank the Editors and Reviewers for their thorough analysis and suggestions. All the contributions have been included and we believe that they have resulted in a substantial improvement for the manuscript. Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

There is a significant improvement in the manuscript, and I would like to thank the authors.

However, small additional changes are still needed (including giving some more information on specific topics).

Abstract, line 26: Please, reframe “This review explores the fundamental physiology of the autonomic system,” to more specific “This review explores the sex disparities in the autonomic nervous system regulation of blood pressure (particularly baroreceptor function)”,

Line 49: “in particular analyzing sex chromosome complement (SCC) and sex hormonal effects.”, please, reformulate to “in particular analyzing the effects of sex chromosome complement (SCC) and sex hormones.”. (more clear)

Line 59: “which would be the first age- and sex-dependent switch during life in..”, please, rephrase into: “suggesting the age- and sex-dependent switch during life in…”(more clear and scientific sound)

62-63: “thus showing a stronger association than men between early decline in baroreflex sensitivity and age”, please, rephrase into:” “thus showing an earlier decline in baroreflex sensitivity with age than in men”. more clear and scientific sound)

Lines 68-74: please, move this paragraph to the beginning of chapter 2. (to line 53)

73-74: “Factors influencing baroreflex function may have an important bearing on cardiovascular disease, and sex factor is not an exception.”, better reformulate to “Factors influencing baroreflex function, including sex,  may have an important bearing on cardiovascular disease, and sex factor is not an exception.” (more scientific sound)

Line 77-76: please, eliminate: “which has been found to be not only sex- but also age-dependent.” (already said in lines 53-67).

Line 136: please, define the abbreviation “LF/HF” and describe what it means, what represents, and how is measured.

Line 141: what was the age of those women? Were they young?

Section 4: please, as already suggested in my previous report, add a chapter on the effect of progesterone, not only estrogens and testosterone. Progesterone, as the female sex hormone in luteal phasis and pregnancy, is especially important for baroreceptor regulation. Here are some references:

https://pubmed.ncbi.nlm.nih.gov/9087656/

https://pubmed.ncbi.nlm.nih.gov/11458692/

https://pubmed.ncbi.nlm.nih.gov/22483197/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2928618/

https://jps.biomedcentral.com/articles/10.1007/s12576-019-00727-z

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1440-1681.1995.tb01970.x

https://link.springer.com/article/10.1007/BF02332974

https://www.internationaljournalofcardiology.com/article/S0167-5273(05)00884-3/fulltext

https://pubmed.ncbi.nlm.nih.gov/31838497/ (also for the chapter on HRT in menopause in section 5, lines 219-240, add this reference using both estrogens and progestins in HRT)

For estradiol (section 4) and contraceptive treatment (section 5):

https://pubmed.ncbi.nlm.nih.gov/23401618/ , The discussion of this paper is very interesting (gives more mechanisms and explains the differences in the results “We suspect that differences in hormone exposure between the menstrual phase studies and the studies using oral contraceptive contribute to the different findings with regard to baroreflex sensitivity across previous studies. Oestrogen and progestin exposures are much higher with oral contraceptives relative to menstrual phases, and the placebo phase has limitations as a ‘low hormone’ period”)

Line 212. Please, eliminate “(2009)” (year of publication)

Line 248: [52,72] – add also reference 71 there: [52,71,72]

Line 249. Please, eliminate “(2000)” (year of publication)

Line 255. Please, eliminate “(1990)” (year of publication)

Lines 329-330 and 342: Please, define abbreviations AT1, AT2, and Agtr1a/Agtr2

Line 364: Please, define the abbreviation HRV; it should be “described”, not “describe”

Section 8. lines 378-392:

Please, add some lines on the XYY men.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3331829/

https://pubmed.ncbi.nlm.nih.gov/7468595/

https://pubmed.ncbi.nlm.nih.gov/7995613/

https://pubmed.ncbi.nlm.nih.gov/32506668/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7413625/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1684878/

(https://pubmed.ncbi.nlm.nih.gov/22687844/ - warning: there is a mistake in the abstract, it is XXY, not XYY)

Also, give some data on men with hypogonadism (hypoandrogenism), women with polycystic ovaries (PCOS, hyperandrogenism), and genetic abnormality of androgen receptor (AR) and estrogen receptors (ERs: ER alpha and ER beta). Do they have a higher prevalence of hypertension?  

Also, give data on AR, ERs, and progesterone receptor (PR) knock-out animals (ARKO, ERKO: AERKO, BERKO, and PRKO mice). Do they have hypertension? Is there a difference between males and females?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3331829/

https://pubmed.ncbi.nlm.nih.gov/11518735/

https://pubmed.ncbi.nlm.nih.gov/17159084/

Please, (as already suggested in my previous report), say a bit more on intrauterine and early life programming and imprinting of sex hormones, leading to permanent epigenetic changes and the function of numerous genes.

Give some data, e.g., on intrauterine administration of (i.e., exposure to) testosterone to male and female fetuses (sheep, primates, humans). Do they have increased testosterone levels later in life and an increased prevalence of hypertension?

Below are some references:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3364920/

https://www.ahajournals.org/doi/10.1161/HYPERTENSIONAHA.120.16256

https://academic.oup.com/biolreprod/article/91/1/6,%201-7/2433982

https://www.hindawi.com/journals/ijpedi/2012/584831/

https://www.jstage.jst.go.jp/article/internalmedicine/51/11/51_51.7097/_pdf/-char/en

https://pubmed.ncbi.nlm.nih.gov/18971349/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3331829/

https://www.cell.com/trends/genetics/fulltext/S0168-9525(11)00170-3?code=cell-site

https://journals.physiology.org/doi/full/10.1152/ajpregu.90724.2008

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3365381/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7235388/

Finally, the list of abbreviations should be extended as indicated above.

The English language requires small improvements (as indicated above), to increase clarity.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf