AN EVALUATION OF TRANSOVARIAN UPTAKE OF METABOLITES USING ARTERIOVENOUS DIFFERENCE-METHODS IN DAIRY-CATTLE

Arterio-venous (A-V) difference techniques were used in cattle to exam ine ovarian energy metabolism, cholesterol uptake and steroid hormone outputs. Catheters were inserted into the ovarian vein and facial arte ry, and Transonic flow transducers were placed around the ovarian A-V plexus. Further, in some cows, the effects of a challenge with GnRH we re examined. Glucose uptake and lactate output were significant in mos t individual cows. Nonesterified fatty acids (NEFA) uptake were not si gnificant in any cow in dioestrus. Ovarian uptake of beta-Hydroxybutyr ate (3-OHB) was significant in 4 cows in dioestrus. Cholesterol uptake was significant in only I cow. Oxygen uptake was significant in all c ows at all stages of the oestrous cycle. All cows had significant outp ut of progesterone and oestradiol-17 beta. These data show that the bo vine ovary utilises significant amounts of glucose, and Respiratory qu otient (RQ) estimates demonstrated that glucose was the primary fuel u sed by the ovary. The significant output of lactate suggested that ana erobic pathways were mainly used for glucose oxidation. The observed u ptakes of 3-OHB indicated that the ovary utilises 3-OHB as a source of energy. Cholesterol uptake was nota rate-limiting factor for steroid hormone production in the ovary. Despite the high metabolic rate in th e luteal ovary, the small difference in P-O2 between arterial and ovar ian venous blood indicated that the ovary consumes only a small propor tion of available oxygen. GnRH had no significant effect on the uptake of metabolites and energy metabolism, but it increased OBF and the ou tput of progesterone and oestradiol-17 beta. The use of A-V methods to determine the metabolic needs of the ovary is useful in understanding the means by which nutrition can influence fertility. (C) 1997 Elsevi er Science B.V.