Age-related differences in the cutaneous vascular response to exogenous angiotensin II

Angiotensin II type 2 receptor-mediated dilation is greater in the cutaneous microvasculature of premenopausal women compared with men

Differential activation of the renin-angiotensin system (RAS) likely contributes to sex differences in cardiovascular outcomes in premenopausal women compared with age-matched men. Women demonstrate reduced activation of the vasoconstrictor angiotensin II type 1 receptors (AT1R) compared with men, and evidence suggests that women also likely have increased sensitivity of the vasodilatory angiotensin II type 2 receptors (AT2R). However, few in vivo studies have directly examined sex differences in AT2R-mediated dilation, or the balance between AT1R- and AT2R-mediated vascular responses in humans. Using the cutaneous microcirculation as a model, we hypothesized that AT2R-mediated dilation would be greater in premenopausal women compared with men, and that AT1R-blockade would augment AT2R-mediated dilation to a greater extent in men than in women. Twelve healthy women (22 ± 3 yr) and 12 men (23 ± 5 yr) had two intradermal microdialysis fibers placed in the ventral forearm for graded infusions of compound 21 (AT2R agonist; 10-12 to 10-8 M) in a control fiber site and a site treated with 43 µM losartan (AT1R antagonist). Red blood cell flux was measured continuously by laser-Doppler flowmetry, and cutaneous vascular conductance [CVC = flux/mean arterial pressure (MAP)] was normalized to maximum [%max; 28 mM sodium nitroprusside (SNP) + 43 °C]. Women had greater AT2R-mediated dilation compared with men (women: 25 ± 4 vs. men: 15 ± 2%max, P = 0.03). Local AT1R inhibition increased AT2R-mediated dilation in men (losartan: 26 ± 4 vs. control: 15 ± 2%max, P < 0.001) but had no effect in women (losartan: 27 ± 6 vs. control: 25 ± 4%max, P > 0.05). These data suggest that premenopausal women have a greater AT2R-mediated vasodilation response than men, and that AT1R activation inhibits AT2R-mediated dilation in men, but not in women.NEW & NOTEWORTHY Premenopausal women have greater protection against cardiovascular disease than age-matched men. However, the role of vasoconstrictor angiotensin II type 1 receptors (AT1R) and vasodilatory angiotensin II type 2 receptors (AT2R) in mediating these sex differences is unclear. Here, we demonstrate that women have greater AT2R-mediated vasodilation than men and that AT1R negates AT2R-mediated dilation in men, but not in women.

A phase 2 trial investigating the effects of the angiotensin II type 2 receptor agonist C21 in systemic sclerosis-related Raynaud's

OBJECTIVE

Our main aim was to investigate the effect of a single oral dose of C21, a selective angiotensin II type 2 receptor agonist, on cold-induced vasoconstriction in SSc-related RP.

METHODS

This was a phase IIa, randomized, double-blind, cross-over, single-dose, placebo-controlled, single-centre study. Twelve female patients with SSc (median age 58.5 years, median duration of RP 19.0 years) attended on four occasions: screening, treatment visits 1 and 2 (separated by 3-7 days) and follow-up. At the first treatment visit, patients were randomized to receive either a single oral dose of C21 (200 mg) or placebo, then the opposite treatment on the second visit. Forty min after each treatment, each patient underwent a standard hand cold challenge. The primary end point was the area under the curve (AUC) for rewarming for each finger (eight fingers) over 15 min. Secondary end points included the maximum finger temperature after rewarming (MAX). Statistical analyses were performed by multiplicative ANCOVA models.

RESULTS

For all eight fingers combined, mean AUC for rewarming was higher after treatment with C21 than after placebo (geometric mean 20 046°C*s vs 19 558°C*s), but not significantly (P = 0.380) and MAX (at 15 min) was also higher (geometric mean 23.5°C vs 22.5°C; P = 0.036). C21 was well tolerated.

CONCLUSION

Despite the small trial size, a signal emerged suggesting that even in patients with established SSc, C21 may confer benefit for RP and deserves further investigation.

TRIAL REGISTRATION

ClinicalTrials.gov, https://clinicaltrials.gov, NCT04388176.

Ageing and the Autonomic Nervous System

The vertebrate nervous system is divided into central (CNS) and peripheral (PNS) components. In turn, the PNS is divided into the autonomic (ANS) and enteric (ENS) nervous systems. Ageing implicates time-related changes to anatomy and physiology in reducing organismal fitness. In the case of the CNS, there exists substantial experimental evidence of the effects of age on individual neuronal and glial function. Although many such changes have yet to be experimentally observed in the PNS, there is considerable evidence of the role of ageing in the decline of ANS function over time. As such, this chapter will argue that the ANS constitutes a paradigm for the physiological consequences of ageing, as well as for their clinical implications.

Pernio (Chilblains), SARS-CoV-2, and COVID Toes Unified Through Cutaneous and Systemic Mechanisms

Pernio or chilblains is characterized by erythema and swelling at acral sites (eg, toes and fingers), typically triggered by cold exposure. Clinical and histopathologic features of pernio are well described, but the pathogenesis is not entirely understood; vasospasm and a type I interferon (IFN-I) immune response are likely involved. During the coronavirus disease 2019 (COVID-19) pandemic, dermatologists have observed an increase in pernio-like acral eruptions. Direct causality of pernio due to COVID-19 has not been established in many cases because of inconsistent testing methods (often negative results) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, a form of COVID-19‒associated pernio (also called COVID toes) is probable because of increased occurrence, frequently in young patients with no cold exposure or a history of pernio, and reports of skin biopsies with positive SARS-CoV-2 immunohistochemistry. PubMed was searched between January 1, 2020, and December 31, 2020 for publications using the following keywords: pernio, chilblain, and acral COVID-19. On the basis of our review of the published literature, we speculate that several unifying cutaneous and systemic mechanisms may explain COVID-19‒associated pernio: (1) SARS-CoV-2 cell infection occurs through the cellular receptor angiotensin-converting enzyme 2 mediated by transmembrane protease serine 2, subsequently affecting the renin-angiotensin-aldosterone system with an increase in the vasoconstricting, pro-inflammatory, and prothrombotic angiotensin II pathway. (2) Severe acute respiratory syndrome coronavirus 2 cell infection triggers an immune response with robust IFN-I release in patients predisposed to COVID-19‒associated pernio. (3) Age and sex discrepancies correlated with COVID-19 severity and manifestations, including pernio as a sign of mild disease, are likely explained by age-related immune and vascular differences influenced by sex hormones and genetics, which affect susceptibility to viral cellular infection, the renin-angiotensin-aldosterone system balance, and the IFN-I response.