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M. J. PEDDIE
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A method for making statistical comparisons between populations and types of antral follicles within the ovary of the immature guinea-pig is described. This was used to demonstrate that atresia in the antral follicles first appeared at around 14 days of age, but that the population of healthy antral follicles remained remarkably consistent throughout the second half of the prepubertal period, since neither the total number of healthy antral follicles nor the proportion of atretic follicles changed significantly. However, the maximum diameter of the antral follicles gradually increased with age, from 400 μm at 7 days to 1000 μm at 28 days, 4 days before the vagina first opened. Because the percentage distribution of all types of follicles was so consistent at any age, although individuals showed substantial differences in the numbers of follicles within each ovary, it is suggested that mechanisms operate which regulate the total population of antral follicles within the ovary.

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M. J. PEDDIE
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SUMMARY

The development of antral follicles and of atretic follicles throughout the cycle of adult guinea-pigs is a continuous process, but there are two stages when atresia is most pronounced: immediately after oestrus and in the late luteal phase. New atretic antral follicles were not found in the ovaries until around day 10 of the cycle, when an injection of HCG caused atresia of the medium-sized antral follicles within the ovary and luteinization of the largest follicles but spared the smallest antral follicles. Following the induced atresia, cycle lengths were prolonged, but the population of antral follicles could be restored to normal within 10 days of gonadotrophin treatment.

It is suggested that the growth rate of antral follicles is flexible and proceeds most rapidly at the end of the luteal phase. It is not clear whether ovarian steroids play an integral part in regulating follicular growth and atresia.

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O M Onagbesan
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I Woolveridge
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M J Peddie
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Abstract

The presence of epidermal growth factor receptors (EGF-R) and the ligands epidermal growth factor/transforming growth factor-α (EGF/TGFα) have been reported in mammalian ovaries where they are implicated in folliculogenesis and steroidogenesis. Evidence is presented to show that authentic EGF/TGFα receptors are expressed by the avian granulosa cells. The TGFα receptors (TGFα-R) from chicken granulosa cells were characterized by specific binding of 125I-human TGFα. In this study, competition with human EGF, human TGFα, human IGF-I, human basic fibroblast growth factor (bFGF) and insulin for 125I-human TGFα binding demonstrated that the avian granulosa cell TGFα-R binds human EGF with 300-fold lower affinity than human TGFα. IGF-I, bFGF and insulin did not displace bound 125I-TGFα. Scatchard analysis showed that a single class of high-affinity binding sites is present on the granulosa cells (K d 0·23 ± 0·009 nm). However, the number of binding sites altered during follicular maturation with a significant decline in the most mature follicle. These results go some way to explaining the basis for the changing sensitivity of avian granulosa cells to EGF/TGFα stimulation as they mature. In addition, the gonadotrophins, LH and FSH, increased the number of receptors in cultured granulosa cells and may therefore partially influence folliculogenesis and steroidogenesis through this route.

Journal of Endocrinology (1996) 149, 171–179

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B. T. DONOVAN
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M. B. TER HAAR
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A. N. LOCKHART
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M. J. PEDDIE
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SUMMARY

The concentration of FSH in the plasma of guinea-pigs from day 50 of gestation to day 45 of postnatal life was assayed by a radioimmunological procedure utilizing a cross-reaction with the NIAMDD S6 antiserum to rat FSH.

At 68 days of gestation the mean plasma FSH concentration of female foetuses was greater than that of the males, although the concentrations in the two sexes were similar on day 50 of gestation. Maternal levels remained consistently low throughout gestation. Postnatally there were no marked changes in plasma FSH levels through to maturity, although a transient rise in the male occurred over the first 3 days after birth.

Gonadectomy on days 0, 5, 10, 15, 25 or 35 of postnatal life, or when adult, resulted in a significant increase in plasma levels of FSH within 10 days. The rise in plasma FSH concentration was greater in males than in females at all ages, although a larger increase was observed in females spayed at 5 or 10 days of age than at other times.

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B. T. DONOVAN
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M. B. TER HAAR
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A. N. LOCKHART
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P. C. B. MACKINNON
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J. M. MATTOCK
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M. J. PEDDIE
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SUMMARY

The concentration of LH in the plasma of guinea-pigs from day 50 of gestation to day 45 of postnatal life was assayed by radioimmunoassay utilizing a cross-reaction with anti-ovine LH antiserum. The effect of gonadectomy in infancy and in the adult upon the plasma concentration of LH was also studied.

The LH concentration in the plasma of male or female foetuses was high immediately prenatally and fell at birth. High levels of LH were again detected in male, with a lesser increase in female, guinea-pigs over the first 10 days postnatally. Maternal plasma concentrations of LH remained consistently low. Removal of the gonads on days 0, 5, 10, 15, 25 or 35 of postnatal life, followed by blood collection at autopsy 10 days later, caused a significant rise in plasma LH content at all ages. The rise in plasma LH after gonadectomy in adults was less marked in male than in female guinea-pigs.

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