IVABRADINE INDUCED VASORELAXATION IN A HYPERANDROGENIC RAT MODEL OF POLYCYSTIC OVARIAN SYNDROME, EFFECT OF VITAMIN D SUPPLEMENTATION

Objective: Polycystic ovary syndrome (PCOS) is the most prevalent endocrine disorder of women in fertile age. It is characterized by hyperandrogenism, and Vitamin D hypovitaminosis occurs in 80% of the cases. PCOS often presents an elevated cardiovascular risk. In the thoracic aorta of rats, the presence of all four isotypes of hyperpolarization and cyclic nucleotide regulated channels (HCN) has been detected, and the non-selective HCN inhibitor ivabradine was shown to cause vasorelaxation. In diabetes mellitus changes in HCN 1-4 expression was also observed. Our aim was to detect the potential changes in HCN dependent vascular reactions in a rat model of hyperandrogenism and the possible effect of Vitamin D supplementation. Design and method: 44 female Wistar rats (weighing 70-90 g) were randomly divided to four groups: Controls (C), Vitamin D supplemented (D), transdermal testosterone treated (T) and T+D groups that received both testosterone and Vitamin D for 8 weeks. Isolated thoracic aortic rings were cut into 3-4 mm long segments for wire myography, and after phenylephrine pre-contraction, ivabradine dose-response was recorded; on other segments HCN 1-4 was labelled by immunohistochemistry. Results: Relaxation was defined as percentage of maximal contraction induced by phenylephrine (10-6 M). Testosterone slightly decreased, while Vitamin D supplementation slightly increased ivabradine-induced relaxation (Ivabradin concentration ∗ testosterone and Ivabradin concentration∗ Vitamin D: p<0.05, 3-way RM ANOVA). HCN1 and 4 stainings showed no differences; however, HCN2 was detected in higher level in T+D rats than in the T group (noncalibrated optical density: C: 0.148+/-0.11; D: 0.148+/-0.07; T: 0.104+/-0.06; T+D: 0.223+/-0.01∗p<0.05 vs T, N=2-8) HCN3 staining was elevated in T+D rats compared to controls (noncalibrated optical density: C: 0.08+/-0.001; D: 0.084+/-0.007; T: 0.096+/-0.01; T+D: 0.107+/-0.02∗∗p<0.01 vs C, N=4-8.) When performing two-way ANOVA, testosterone treatment was found contributing to HCN3 staining variance (p<0.01), whereas vitamin D influenced HCN4 density (p<0.05). Conclusions: Ivabradine-induced relaxation was enhanced with vitamin D supplementation, with expression patterns of HCN isoforms altered by vitamin D (HCN2, HCN4) and hyperandrogenism (HCN3). These findings suggest HCN channels may contribute to vascular dysfunction in PCOS, and ivabradine having a potential beneficial cardiovascular effect in PCOS.