Male-female differences in upregulation of vasoconstrictor responses in human cerebral arteries

Abstract

Background and purpose: Male-female differences may significantly impact stroke prevention and treatment in men and women, however underlying mechanisms for sexual dimorphism in stroke are not understood. We previously found in males that cerebral ischemia upregulates contractile receptors in cerebral arteries, which is associated with lower blood flow. The present study investigates if cerebral arteries from men and women differ in cerebrovascular receptor upregulation.

Experimental approach: Freshly obtained human cerebral arteries were placed in organ culture, an established model for studying receptor upregulation. 5-hydroxtryptamine type 1B (5-HT1B), angiotensin II type 1 (AT1) and endothelin-1 type A and B (ETA and ETB) receptors were evaluated using wire myograph for contractile responses, real-time PCR for mRNA and immunohistochemistry for receptor expression.

Key results: Vascular sensitivity to angiotensin II and endothelin-1 was markedly lower in cultured cerebral arteries from women as compared to men. ETB receptor-mediated contraction occurred in male but not female arteries. Interestingly, there were similar upregulation in mRNA and expression of 5-HT1B, AT1, and ETB receptors and in local expression of Ang II after organ culture.

Conclusions and implications: In spite of receptor upregulation after organ culture in both sexes, cerebral arteries from women were significantly less responsive to vasoconstrictors angiotensin II and endothelin-1 as compared to arteries from men. This suggests receptor coupling and/or signal transduction mechanisms involved in cerebrovascular contractility may be suppressed in females. This is the first study to demonstrate sex differences in the vascular function of human brain arteries.

Figure 1. Male-female differences in contractile responses of human cerebral arteries subjected to 48 h organ culture.

Concentration-response curves to (A) 5-CT, (B) Ang II and (C) ET-1 are illustrated. Data are expressed as % of the contraction to K⁺ (63.5 mM) in the same tissue. Each point represents mean ± SEM; females, n = 6 and males n = 8 to 9. The concentration-response curves for each agonist were analyzed with extra sum-of-squares F test to determine if the curves were statistically different between male and female arteries (P-values are presented above the curves). Exact values and statistical significance for individual parameters such as E_MAX and pEC₅₀ are found in Table 1.

Figure 2. Effect of organ culture on mRNA levels of cerebrovascular receptors in human cerebral arteries.

mRNA expression for (A) 5-HT_1B receptors, (B) AT₁ receptors and (C) ET_B receptors before (0 h OC) and after organ culture (48 h OC) are illustrated. Each bar represents mean ± SEM; females, n = 4 and males n = 8; *P<0.05.

Figure 3. Upregulation of contractile receptors and Ang II in human cerebral arteries after organ culture (OC).

The smooth muscle layers (ML, medial layer) show a dramatic increase in immunofluorescent staining of (A, B) 5-HT_1B receptors, (C, D) AT₁ receptors, (E, F) ET_B receptors and (G, H) Ang II after 48 h of culture (48 h OC) as compared to non-incubated arteries (0 h OC). Fluorescent intensity measurements (arbitrary units, AU) were performed in the medial layer (ML), and are represented as mean ± SEM (right panel). Ang II, 5-HT_1B and ET_B immunofluorescence can also be seen in endothelial cells (when they are present, arrowheads). Autofluorescence in the internal lamina elastica is indicated by the asterisk.

Figure 4. Phosphorylated ERK1/2 (p-ERK1/2) expression in male and female cerebral arteries after organ culture (OC).

(A) Representative images of p-ERK1/2 in the medial layer (ML) of human cerebral arteries before (0 h OC) and after organ culture (48 h OC). Similar expression of p-ERK1/2 was observed in male arteries, while an increased immunoreactivity was observed in female arteries after organ culture. (B) Fluorescence intensity measurement (arbitrary units, AU) of p-ERK1/2 immunohistochemical staining in the ML.