Human Reproduction, Vol 13, 3016-3022, Copyright © 1998 by Oxford University Press
CJ de Souza, BK Campbell and DT Baird
In women there is a gradual rise in the basal level of follicle stimulating
hormone (FSH) in the years prior to the menopause (pre- menopause) which is
thought to be due to a relative lack of ovarian factors reflecting the
number of antral follicles present in the ovaries. Experimental animal
models for this phenomenon, particularly in mono-ovulatory species, have
been lacking due to most animals' relatively short life span. We have
available a group of experimental ewes in which the right ovary was removed
and the left ovary was autotransplanted to the neck at least 10 years
previously, which have been maintained in good health until an age of 12-13
years. Two experiments were conducted with these animals to determine the
endocrine and follicular effects of age: a retrospective experiment in the
same Finn-Merino ewes (n = 5) when the animals were 6-7 or 12-13 years of
age; and a cohort experiment in old (12-13 years, n = 6) and young (2
years, n = 5) ewes of the same breed. In both retrospective and cohort
experiments, the concentrations of FSH were significantly higher (P <
0.05) in older animals during the luteal phase when oestradiol secretion
was low. This increase in FSH was associated with a decrease in the
concentration of inhibin A (P < 0.05) in older animals in both the
follicular and luteal stages of the cycle but the concentrations of
oestradiol were similar between ages. Although there were significantly
fewer antral follicles (P < 0.05) available for development in older
ewes during the early luteal phase of the cycle, the ovulation rate was
similar to that observed in younger animals (2.0+/-0 vs 2.0+/-4; P >
0.05) but the interval from luteal regression to the onset of the LH surge
was longer (P < 0.05) in older animals. In conclusion, the endocrine
changes associated with increasing reproductive age in sheep are therefore
similar to those observed in women, suggesting that the sheep could be a
useful animal model to study the effect of age on human fertility.
ARTICLES
Incipient ovarian failure associated with raised levels of follicle stimulating hormone and reduced levels of inhibin A in older sheep
Department of Obstetrics and Gynaecology, University of Edinburgh, Centre for Reproductive Biology, UK.
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