Animal Reproduction Science 64 2000 199–209
Uptake of glucose and cholesterol by the ovary of sheep and cattle and the influence of arterial LH
concentrations
A.R. Rabiee
a,∗
, I.J. Lean
b
a
Department of Veterinary Science, University of Melbourne, Werribee, Vic. 3030, Australia
b
Bovine Research Australasia, PO Box 660, Camden, NSW 2570, Australia Received 4 April 2000; received in revised form 5 September 2000; accepted 5 September 2000
Abstract
Time series analysis methods were used to evaluate the relationships between the uptake of glu- cose and cholesterol, and arterial luteinizing hormone LH concentrations. Classical arterio-venous
difference methods were applied to study ovarian uptake of metabolites. Arterial and venous samples n = 20 were obtained from six cows and nine sheep every 10 min. There were highly significant
positive cross-correlations of 0.5 for cattle and 0.8 for sheep between the uptake of glucose and cholesterol at lag 0. All individual cross-correlations were significant for sheep. Uptake of these
metabolites was not significantly associated with arterial LH concentrations in the cows.
This study suggests that glucose may promote cholesterol uptake into the ovarian cells or vice versa. This study is the first to identify such a relationship. If these findings are repeated, the
possibility exists that control of the oestrous cycle and fertility may be achieved by seeking a common regulator of uptake of these metabolites or by uncoupling the association between glucose
and cholesterol. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Cholesterol; Glucose; Cattle ovary
1. Introduction
Improved knowledge of the metabolic demands of the ovary could lead to the development of new methods of controlling reproduction in animals. There are only a limited number of
studies describing ovarian energy metabolism, and these studies were primarily conducted in vitro. The sources for energy used by the ovary are the subject of conflicting reports. It is
∗
Corresponding author. Tel.: +61-397420484; fax: +61-397420400. E-mail address:
a.rabieevet.unimelb.edu.au A.R. Rabiee. 0378-432000 – see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 4 3 2 0 0 0 0 0 2 0 8 - 6
200 A.R. Rabiee, I.J. Lean Animal Reproduction Science 64 2000 199–209
known that blood cholesterol concentrations and steroid hormones synthesis are positively related to energy intake and health of animals Velhankar, 1973, and lower cholesterol and
glucose concentrations after calving have been associated with an increased number of days from calving to conception Kappel et al., 1984. The demands of reproductive tissue for
energy and cholesterol, and the metabolism of these in reproductive tissues are important aspects of metabolism to understand.
It has been suggested that lipids are the main energy source used by the ovary Flint and Denton, 1970, but more recent Chase et al., 1992 and some older studies Gafvels
et al., 1987 suggest that glucose is a major energy source for the ovary. It was demon- strated that glucose uptake by the corpus luteum CL plays a role in its energy metabolism
in vitro in rats Gafvels et al., 1987. Studies Chase et al., 1992 of glucose metabolism in the bovine CL in vitro also indicated that glucose was a major energy source used by
the ovary, and that physiological state, stage of the oestrous cycle and time after calving significantly alters in vitro rates of uptake and metabolism of glucose by luteal tissue.
The presence of glucose has been found to markedly stimulate the incorporation of car- bon from acetate into sterol and steroid in ovarian tissue in vitro in the rat Flint and
Denton, 1969. In vitro studies also show a positive relationship between ATP and preg- nenolone synthesis in ovarian mitochondria Uzgiris et al., 1970; Robinson and Stevenson,
1971. We reported Rabiee et al., 1997 that glucose was the primary source of energy and that free fatty acids were not a significant source of energy for the bovine ovary in
situ.
There are few reports on the effects of gonadotrophins on aspects of the cellular metabolism other than those involved directly in the steroidogenesis. Armstrong and Greep 1962 re-
ported that administration of luteinizing hormone LH increased uptake of glucose and production of lactic acid by the luteinized rat ovaries in vitro. Investigations regarding
the site in the metabolic pathway stimulated by LH, and the effect of LH on incorpo- ration of cholesterol into steroids have often yielded varied or conflicting results. LH
may influence progesterone synthesis through a pathway that does not involve choles- terol as an intermediate or precursor Savard et al., 1965. The influence of LH on choles-
terol uptake and de novo synthesis of cholesterol in luteal tissue remains controversial. Time series analysis methods allow an evaluation of relationships between the uptake
of metabolites by the ovary and the role of LH in influencing the uptake of metabo- lites. The objective of this study was to examine relationships between the uptake of
glucose and cholesterol and arterial concentrations of LH both in sheep and cattle in vivo.
2. Materials and methods
