Smooth muscle alpha actin and myosin heavy chain expression in the vascular smooth muscle cells surrounding human endometrial arterioles

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Abstract
Endometrial spiral arterioles are believed to play a major role in controlling menstruation. These arterioles coil and grow through the secretory stages of the cycle, unlike the `straight' endometrial arterioles that remain uncoiled. We postulate that alterations in the growth and development of spiral arterioles, in particular the vascular smooth muscle cells (VSMC), may contribute to menorrhagia. We examined smooth muscle alpha actin (αSMA) and myosin heavy chains (MHC), two VSMC differentiation markers, in the endometrial arterioles of 64 women, comparing them in controls, menorrhagic tissues and across the menstrual cycle. αSMA and MHC expression were determined immunohistochemically then evaluated using computer-aided image analysis. αSMA expression in the straight arterioles of menorrhagic women was reduced in the early secretory stage of the cycle and significantly decreased at the mid-secretory stage of the cycle (0.67 ± 0.03 versus 0.55 ± 0.04, P ≤ 0.05). No other significant differences were observed in αSMA and MHC expression in straight arterioles. MHC expression was significantly reduced in the spiral arterioles of menorrhagic tissues at the early secretory stage (0.57 ± 0.01 versus 0.38 ± 0.04, P ≤ 0.05). Our results demonstrate differences in the VSMC of menorrhagic women compared with controls, with delayed MHC expression in the spiral arterioles and reduced αSMA expression in straight arterioles during the mid-secretory stage of the cycle.