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Unilateral ovariectomy results in compensatory follicular growth and doubling of the number of ovulations in the remaining ovary. It has been suggested that this is (at least partly) due to the increased availability of circulating gonadotrophins to the remaining ovary (McLaren, 1966). If this view is correct, it could be expected that in hypophysectomized rats treated with fixed regimens of pregnant mare serum gonadotrophin (PMS), follicular development in one ovary would be stimulated by removal of the other ovary.
Wistar rats (180–200 g) which had had at least three consecutive 5-day cycles were used. In a first experiment (Table 1) the effect of unilateral ovariectomy on follicular growth in rats with an intact hypophysis was determined. The animals were unilaterally ovariectomized during oestrus or 2 days later (dioestrus 2). They were killed 1, 2, 3 or 4 days thereafter. In these rats a significant increase of follicular growth in the
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Detection of ovulation or processes resembling ovulation in ovarian grafts is regularly used to demonstrate ovulatory discharge of gonadotrophins. However, corpora lutea atretica (CLA), i.e. corpora lutea with entrapped ova, are often found (Noyes, Yamate & Clewe, 1958; Moll & Zeilmaker, 1966; Quinn, 1966). Since CLA occur not only in grafts (Deanesley, 1956; Jones & Krohn, 1960) but also in ovaries in situ (Jones & Krohn, 1961), especially after an inadequate ovulatory stimulus (Rowlands, 1944), they may reflect both abnormal responsiveness of the tissue after grafting and abnormal discharge of gonadotrophins. Therefore, the occurrence of CLA in ovarian grafts functioning under normal hormonal control was studied.
In a first experiment neonatal rats were ovariectomized unilaterally (15 rats) or bilaterally (12 rats) and received one ovarian autograft under the left kidney capsule. Normal (19) and unilaterally ovariectomized rats (16) served as controls. The rats were killed during the first, fifth or
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SUMMARY
Cyclic rats received at 13.00 h on the day of pro-oestrus a single i.v. injection of one of the following antiserum preparations: AOLH (raised in rabbits against NIH-LH-S17); AOFSH (raised against NIH-FSH-S9) or pAOFSH (AOFSH preincubated with 195 μg NIH-LH-S16/ml). Rats were killed at day 1, 3 or 5 after injection, and the ovaries prepared for histological study of the antral follicles.
After AOLH, ovulation and resumption of meiosis in oocytes in pre-ovulatory follicles were prevented but follicular development during the following cycle appeared undisturbed. After either AOFSH or pAOFSH, blockade of ovulation was never observed but the formation of antral follicles normally occurring between mid-pro-oestrus and mid-oestrus was postponed by about one day. The later development of antral follicles might reflect a supranormal compensatory secretion of endogenous gonadotrophin because the development does not occur in AOFSH- or pAOFSH-treated rats hypophysectomized 24 h after injection and subsequently treated with pregnant mare serum gonadotrophin in dosage approximating the amount of gonadotrophin secreted endogenously during dioestrus.
The results imply (1) that the pre-ovulatory surge of LH release is not essential for follicular development during the oncoming cycle whereas (2) a surge of FSH release is required for the formation of the new cohort of antral follicles that is normally seen at the start of a new cycle.
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Department of Anatomy, Medical Faculty, Erasmus University, Rotterdam, The Netherlands
(Revised manuscript received 28 June 1974)
In the rat, unilateral ovariectomy (ULO) performed at dioestrus 2 results in compensatory follicular growth within 24 h (Welschen, 1972). Furthermore, compensatory follicular growth seems to require increased gonadotrophin levels (Greenwald, 1968; Welschen, 1972). Benson, Sorrentino & Evans (1969) and Peppler (1972), using bioassay methods, detected changes in serum gonadotrophin levels 1–4 days after ULO. However, on the basis of the follicular response, more acute changes might be expected. Therefore, it seemed of interest to measure gonadotrophin levels at short intervals after ULO.
Wistar rats (180–200 g), which had had at least three consecutive 5-day cycles, were used. ULO or sham-operation was performed under ether anaesthesia at oestrus (12.00 h) or at dioestrus 2 (12.00 h). The rats were bled and killed after a postoperative period of 0-96 h. Blood was obtained under ether
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SUMMARY
Oestradiol-17β (E2) was measured by radioimmunoassay in the plasma of immature female rats. Maximal E2 levels of 55–60 pg/ml were found at 10–15 days of age; from day 25 to day 35 E2 levels were low to undetectable. The E2 measured appeared to be of ovarian origin: ovariectomy performed on day 13 resulted in a decreased E2 level 2 days later (13 pg/ml) as compared with the value from the control litter mates (46 pg/ml); after adrenalectomy the level of circulating E2 remained normal (54 pg/ml). The effects of ovariectomy and adrenalectomy on uterine weights followed a similar pattern: ovariectomy resulted in a decrease and adrenalectomy in no change in uterine weight.
In the strain of rat used, levels of follicle-stimulating hormone (FSH) in the serum (measured by radioimmunoassay) were high from day 10 to day 20 and showed a steep decrease on day 21. After ovariectomy on day 15 this decrease in serum FSH was not observed.
The influence of circulating E2 on serum levels of FSH was studied after ovariectomy followed by treatment with varying doses of oestradiol benzoate. Ovariectomy on day 13 resulted in a significantly increased FSH level 2 days later (1770 ng NIAMD-rat-FSH RP-1/ml) as compared with the value obtained from control animals (1033 ng/ml). This increase was not observed after daily injections of 0·1 μg oestradiol benzoate/100 g body weight.
The results indicate that E2 and FSH concentrations show a similar pattern between 5 and 35 days of age. Furthermore, an inhibitory feedback mechanism between oestrogens and FSH concentrations was found to be operative. The implications of these findings are discussed.
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SUMMARY
Throughout a period of pseudopregnancy the peripheral blood levels of progesterone, oestradiol-17β, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), as well as the size-distribution of ovarian antral follicles were estimated in the rat. The progesterone concentrations, as measured by a competitive protein-binding technique, exceeded metoestrous values (25 ng/ml plasma) from day 3 of pseudopregnancy onwards. The highest levels were found on days 6 and 8 (91 ng/ml). From day 8 onwards the levels decreased gradually but were still above metoestrous values on the day of pro-oestrus after pseudopregnancy. Concentrations of oestradiol-17β, as measured by radioimmunoassay, were within the range of those at metoestrus (about 5 pg/ml plasma) until day 10. Thereafter levels increased to a value of 57 pg/ml.
Concentrations of FSH, measured by radioimmunoassay, were within the range of metoestrous values until day 10 (about 100 ng NIAMD-rat-FSH RP-1/ml serum), but declined to a level of 33 ng/ml on day 12. Concentrations of LH, measured by radioimmunoassay, were generally within the wide range of metoestrous values (9–60 ng NIAMD-rat-LH RP-1/ml serum), but concentrations found on days 4, 8 and 10 were significantly lower than those found on preceding or subsequent days.
Histological determination of the number of follicles present in various volume-classes, showed an increase in antral follicles on days 1 and 2, comparable to the increase observed during metoestrus and dioestrus 1 of the normal cycle. There was no change in the follicles between days 3 and 10 and they resembled those of early dioestrus. Preovulatory growth had occurred by day 12. Injection of human chorionic gonadotrophin (HCG) on days 2, 4 or 6 showed that ovulation could be induced only in some of the larger follicles.
On the basis of these results it is suggested that during pseudopregnancy the high progesterone levels present result in a decreased plasma LH level which is insufficient to cause full maturation of the follicles and to stimulate oestrogen secretion to the levels required for induction of an ovulatory surge of LH release.
