N OCIETY' - the Society for Reproductive Biology

Ovarian Uptake of Leptin and Glucose and the Role of Glucose in the Regulation of Leptin Levels inSheepJim McFarlane, Kathleen Kauter, Broce Campbell), David Baird 2 , Amande Leigh 2 and Rex Scaramuzzi 2Animal Physiology, University of New England, Armidale NSW 2351; IDepartment of Obstetrics &Gynaecology, University of Nottingham, Nottingham UK; 2Royal Veterinary College, Royal College Street,London NWl OTU, UK.IntroductionIt has been known for some time that the nutritional status of a ewe during the oestrous cycle caninfluence the number of ovulations (1), however the mechanism for this remains unknown. Leptin is arecently reported hormone released predominately by adipose tissue (2) and was originally proposed as aregulator of satiety and energy expenditure. Recent studies have shown that it is likely to play an importantrole in many other systems including the reproductive system. In this study we have examined the uptake ofglucose and leptin by the sheep ovary and examined the role of glucose as a regulator of blood plasma leptinlevels.Materials and MethodsTwelve ewes with an ovarian autotranplants were treated with a GnRH antagonist to make themhypogonadotrophic and then follicular development was induced using a combination of pulsatile LHtreatment and continuous FSH infusion (3). Samples (5ml) of58706050~ 30::I 20c;10Carotid Ovarian JugUlarCarotid Ovarian JugUlarFigure 1: Uptake ofglucoseand leptin by the ovary andbrain.ovarian/carotid arterial blood, jugular venous blood and ovarian venousblood were collected over a 3 minute periods 48 hours after the start ofcombination LHIFSH treatment and stored frozen at -20°C until assayed.In another group of 6 ewes, oestrus was synchronised usingprogestagen sponges inserted for 12 days. At sponge removal the eweswere mated with entire rams. On day 12 of pregnancy bilateral jugularcannulae were inserted under local anaesthesia. The next day (day 13)groups of ewes (n = 3) were infused with either saline or glucose(50mMlh) until day 18. Pregnancy was confirmed by ultrasound on day22. Blood was collected by jugular venepuncture once a day from day 8after mating until day 25.The concentration of glucose was determined in triplicate using afluorimetric glucose oxidase based assay. Plasma leptin levels weredetermined in duplicate using a discontinuous indirect competitiveELISA, which uses an antiserum raised against bovine recombinantleptin (br-Ieptin).Results & DiscussionA significant (P< 0.05) uptake of glucose was observed by theovary as shown in figure 1. This would suggest that the ovary like thebrain utilizes glucose rather than fatty acids as its primary source ofenergy. A significant (P