Sex-Specific Characteristics of the Microcirculation, Huxley and Kemp, 2018

Sex-Specific Characteristics of the Microcirculation
Virginia Huxley and Scott Kemp
Advances in Experimental Medine and Biology
DOI
Chapter full text link (PDF)

The requirements of metabolizing tissue are both continuous and variable; accordingly, the microvasculature serving that tissue must be similarly dynamic. Just as it is recognized that males and females of the same species have differing metabolic requirements, is it not likely that the microvasculature serving these tissues will differ by sex?

This section focusing on the constituents of the microcirculation identifies what is known presently about the role sex plays in matching metabolic demand with microvascular function and areas requiring additional study.

Many of the identified sex differences are subtle and easily ignored. In the aggregate, though, they can profoundly alter phenotype, especially under stressful conditions including pregnancy, exercise, and disease states ranging from diabetes to heart failure. Although the features presently identified to “have sex” range from differences in growth, morphology, protein expression, and intracellular signaling, males and females alike achieve homeostasis, likely by different means. Studies of microvascular sexual dimorphism are also identifying age as an independent but interacting factor requiring additional attention.

Overall, attempting to ignore either sex and/or age is inappropriate and will prevent the design and implementation of appropriate interventions to present, ameliorate, or correct microvascular dysfunction.

 

Posted in relation to the microclot / capillary dysfunction theory of Long Covid. Any potential theory of ME aetiology needs to account for sex differences, favouring females.

Some example points

• sexual dimorphism exists with respect to the mediators of microvascular tone
• alpha-adrenergic vasoconstriction is lower in young females than males
• nitric oxide synthase blockade induces an increase in blood-brain barrier(BBB) permeability, in females, not in males
  
• when sex differences in MAP and vascular architecture are considered along with the differences in responses to hypercapnia, cerebral blood flow in young women is actually lower than age-matched men
• Female astronauts during space flight experience a greater shift of fluid out of the plasma space than men and following return to gravity experience greater orthostatic intolerance. In response to orthostatic stress, males compensate by changing vascular resistance (microvascular), while females change heart rate.

Conclusion (exert)
Obviously healthy males and females are in fluid homeostasis but how they achieve this state differs by sex. The major implication is that for a given stressor, the responses in males and females, and the resulting pathology should the stressor not be removed, are likely to differ.

 

Note that muscular or brain microvascular regulation is locally controlled (to maintain blood flow), rather than central (which regulates a balance between flow and blood pressure), so things like sympathetic tone (alpha-adrenergic vasoconstriction) isn't as relevant, or only relevant as a secondary factor.