The effect of equine Chorionic Gonadotrophin (eCG) on luteal vascularity in the mare

Abstract

Although progesterone is required to maintain the pregnant state, oestrogen is also a feature of early equine pregnancy. As early as day 40 a marked increase in serum oestrogen concentrations originates from the primary and any secondary corpora lutea (CL) in response to the gonadotrophic actions of eCG. Oestrogen is a known stimulator of the vascular endothelial growth factor (VEGF) which promotes vasculogenesis and angiogenesis. This study assessed changes in luteal vascularity between days 14 to 50 of gestation. Fifteen pregnant mares in a clinical setting were examined at three time points (days 14–16, 20–30 and 40–50 after ovulation). At each examination pregnancy was confirmed and jugular venous blood samples assayed for progestagen and eCG concentrations. Ultrasonographic and Doppler examinations were performed using a SonoSite Micromaxx (SonoSite Ltd, Hitchin, UK) with a linear probe (5.0 10.0 MHz). Images were obtained in colour flow mode with the medium flow sensitivity pre-set. All images had a standard depth of 7.7 cm with a frequency of 3.92 MHz and pulse repetition frequency of 2.1 MHz. The colour image was frozen at peak systolic flow and recorded; acquisition was repeated 3 to 5 times for each CL. Images were analysed using ImageJ software (National Institutes of Health, Bathesda, USA).