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Hemipituitary glands of immature female rats, aged 10, 15, 20, 25, 30 and 35 days and either ovariectomized or sham-operated 5 days earlier, were incubated for 2 h in vitro with or without LH releasing hormone. Concentrations of LH and FSH were determined at the end of the incubations in the incubation media and in the hemipituitary glands, and also in the sera collected at the beginning of the incubation experiments.
Results showed that in many instances gonadotrophin release was higher after incubation of glands of ovariectomized rats than with glands of control animals. However, these effects of ovariectomy were much smaller than those observed in vivo and were generally absent in rats of less than 20 days of age. It was concluded that ovariectomy may change the secretory characteristics of the gonadotrophic cells of immature rats but that such changes were largely restricted to immature rats older than 20 days.
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SUMMARY
Pituitary glands from immature female and male rats aged between 5 and 30 days were incubated in vitro and the effect of LH releasing hormone (RH) on the release of LH and FSH was studied. Pituitary gonadotrophin contents were also measured.
Gonadotrophin release showed changes with age as well as sex differences: after LH-RH stimulation the female pattern of release of LH and FSH (expressed per mg pituitary tissue) showed a peak at day 15; the male pattern of LH release was characterized by a steady increase with age, whereas FSH release stayed more or less constant from day 10 onwards. In both sexes the LH:FSH ratio increased with age, both in pituitary gonadotrophin content and in the mixture of gonadotrophins released. It is discussed, that the prepubertal development of pituitary gonadotrophic function might be determined on the one hand by rather autonomous growth processes (more or less similar in female and male hypophyses) and on the other hand by modulating influences of sex steroid hormones, which are different in female and male animals.
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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
Serum LH, FSH, prolactin and progesterone concentrations and follicular size were measured in rats during pseudopregnancy after unilateral ovariectomy (ULO) on day 1. This operation did not affect the duration of pseudopregnancy. Following pseudopregnancy compensatory ovulation occurred.
After ULO progesterone concentrations remained low as compared with control values but the progesterone secretion per ovary was increased slightly. After ULO, LH concentrations were significantly increased on days 3 and 4 of pseudopregnancy. FSH concentrations were increased 5 h after the operation and again on days 4–7 of pseudopregnancy when compared with sham-operated control animals. During pseudopregnancy prolactin secretion increased each night. Increased prolactin levels were observed 18 and 36 h after ULO. The number of medium-sized follicles had increased 24 h after ULO.
From the present study it is concluded that progesterone secretion by the corpora lutea can be increased to a limited degree by the increased release of gonadotrophins. Furthermore, it is concluded that a rapid increase in FSH concentrations after ULO is responsible for the initiation of the compensatory follicular growth.
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SUMMARY
Pseudopregnant rats were treated early in pseudopregnancy with 1 or 10 mg medroxyprogesterone acetate (MPA). Serum FSH, LH and progesterone concentrations were determined on days 2–20 of pseudopregnancy in treated and control rats.
The mean duration of pseudopregnancy was 13·5 days in the control animals, but when animals were treated with 1 mg MPA a dioestrous period of 21·4 days was observed. A period with leucocytic vaginal smears of at least 2 months was observed after treatment with 10 mg MPA.
Injection with MPA on day 3 of pseudopregnancy did not affect the serum FSH concentrations during the subsequent days. The progesterone pattern was alike in the three groups of animals, i.e. the duration of the activity of the corpora lutea was similar in all groups. However, 10 mg MPA slightly lowered progesterone concentrations on days 4–8 of pseudopregnancy. In the saline-treated rats, LH concentrations decreased from days 2–5, and remained low until they increased after day 11 of pseudopregnancy. This increase was delayed until day 20 in the animals treated with 1 mg MPA, and was not observed in the animals treated with 10 mg MPA.
It is argued that the increase of LH concentration at the end of pseudopregnancy is not instrumental in the decrease of peripheral progesterone concentration but rather that the decrease in the progesterone concentration leads to the increase in the LH concentration.
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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.
