Search Results

You are looking at 1 - 5 of 5 items for

  • Author: B Karels x
  • Refine by access: All content x
Clear All Modify Search
J. E. Sánchez-Criado
Search for other papers by J. E. Sánchez-Criado in
Google Scholar
PubMed
Close
,
J. Th. J. Uilenbroek
Search for other papers by J. Th. J. Uilenbroek in
Google Scholar
PubMed
Close
, and
B. Karels
Search for other papers by B. Karels in
Google Scholar
PubMed
Close

ABSTRACT

Administration of the antiprogesterone RU486 (2 mg/day) for 14 days to rats with a 5-day reproductive cycle resulted in an increase in both ovarian and pituitary weight in contrast with rats with a 4-day oestrous cycle. Luteal progesterone production decreased earlier in 4-day than in 5-day cyclic rats. Treatment of 5-day cyclic rats with antiprogesterone from the day of metoestrus onwards resulted in the advancement of the preovulatory prolactin surge by 24 h. Progesterone production by the corpus luteum was, however, not affected, indicating that in 5-day cyclic rats the corpora lutea are still functionally active at the time of the preovulatory surge of prolactin. They become, therefore, stimulated both in size and progesterone production. In contrast, the corpora lutea in 4-day cyclic rats are functionally inactive at the time of the preovulatory surge of prolactin, and prolactin acts luteolytically. In conclusion, the advancement of the preovulatory surge of prolactin by 24 h accounts, at least in part, for the increase in ovarian weight in 5-day cyclic rats after treatment with antiprogesterone. The results of these experiments do not agree with a direct effect of the antiprogesterone RU486 on progesterone secretion by the corpus luteum.

Journal of Endocrinology (1992) 132, 115–122

Restricted access
W. J. de Greef
Search for other papers by W. J. de Greef in
Google Scholar
PubMed
Close
,
W. Klootwijk
Search for other papers by W. Klootwijk in
Google Scholar
PubMed
Close
,
B. Karels
Search for other papers by B. Karels in
Google Scholar
PubMed
Close
, and
T. J. Visser
Search for other papers by T. J. Visser in
Google Scholar
PubMed
Close

ABSTRACT

The changes in hypothalamic release of dopamine and thyrotrophin-releasing hormone (TRH) into the hypophysial portal vascular system during an oestrogen-stimulated surge of prolactin in ovariectomized rats were investigated.

A single injection of 5 μg oestradiol benzoate resulted in a reliable increase in the plasma levels of prolactin during the afternoon 3 days later. Anaesthesia did not block this afternoon surge of prolactin, although its magnitude was only half of that of unanaesthetized rats. Before and during this surge, hypophysial stalk blood was collected into methanol to analyse the hypothalamic release of dopamine and TRH. Immunoreactive TRH in these methanolic extracts eluted as a single peak with the same retention time as authentic TRH on reverse-phase high performance liquid chromatography. In comparison to the morning values, levels of dopamine decreased and those of TRH increased in hypophysial stalk blood by 50 and 240% respectively. These data indicate that hypothalamic dopamine and TRH may be involved in the afternoon surge of prolactin.

Daily treatment with parachlorophenylalanine, an inhibitor of serotonin synthesis, reduced the hypothalamic release of TRH by 50%, but did not prevent the afternoon surge of prolactin and TRH induced by oestradiol benzoate.

J. Endocr. (1985) 105, 107–112

Restricted access
W. J. de Greef
Search for other papers by W. J. de Greef in
Google Scholar
PubMed
Close
,
J. de Koning
Search for other papers by J. de Koning in
Google Scholar
PubMed
Close
,
A. M. I. Tijssen
Search for other papers by A. M. I. Tijssen in
Google Scholar
PubMed
Close
, and
B. Karels
Search for other papers by B. Karels in
Google Scholar
PubMed
Close

ABSTRACT

Treatment of ovariectomized rats with 50 μg oestradiol benzoate, followed by 20 μg oestradiol benzoate 3 days later, induced surges of LH and FSH on the day following the second injection with oestradiol benzoate. During this surge of gonadotrophins, which was not blocked by the anaesthetic required to collect hypophysial stalk blood, increased hypophysial stalk plasma levels of immunoreactive LHRH were noted. Furthermore, the levels of LHRH in hypophysial portal blood were found to fluctuate. Measurement of LHRH in a pool of portal plasma revealed similar results when determined by radioimmunoassay and by a sensitive in-vitro bioassay.

To mimic the observed release of LHRH during the surge of gonadotrophins, LHRH was infused, either systemically or directly into a long portal vessel, into oestrogen-treated, ovariectomized rats which had their endogenous release of LHRH blocked by pentobarbitone. An infusion of LHRH into the jugular vein, resulting in peripheral levels of LHRH which were somewhat lower than those measured in hypophysial stalk plasma, caused a surge of FSH similar to that found in rats used for collection of hypophysial stalk blood. When compared with the values in the latter animals, however, the levels of LH became two to four times higher by this infusion of LHRH. When LHRH was infused directly into a long portal vessel to mimic the observed secretion rate of LHRH during the oestrogen-stimulated surge of gonadotrophins, then the surges of LH and FSH were lower than those observed in the rats used for collection of stalk blood.

J. Endocr. (1987) 112, 351–359

Restricted access
W. J. de Greef
Search for other papers by W. J. de Greef in
Google Scholar
PubMed
Close
,
G. A. M. Eilers
Search for other papers by G. A. M. Eilers in
Google Scholar
PubMed
Close
,
J. de Koning
Search for other papers by J. de Koning in
Google Scholar
PubMed
Close
,
B. Karels
Search for other papers by B. Karels in
Google Scholar
PubMed
Close
, and
F. H. de Jong
Search for other papers by F. H. de Jong in
Google Scholar
PubMed
Close

ABSTRACT

Intraperitoneal administration of bovine follicular fluid (bFF) decreased plasma concentrations of FSH in ovariectomized rats after 2–3 h, while plasma LH and prolactin were unaffected. In untreated ovariectomized animals the concentrations of these hormones were found to show pulsatile variations. Concomitant occurrence of peak values of LH and FSH was found in about 40% of the pulses. No pulses of FSH were observed after i.p. treatment with bFF or partly purified preparations of inhibin from bFF, but the pulsatile release of LH and prolactin remained similar. Infusion of bFF into the lateral ventricle of the brain did not alter the concentrations of FSH, whereas administration of bFF into the pituitary gland diminished the plasma concentrations of FSH.

Anaesthesia (urethane plus xylazine) did not prevent the occurrence of the pulses of FSH and LH, but it reduced the pulse amplitude and clearance. During this anaesthesia, the concentrations of LHRH in the hypophysial stalk plasma decreased by 30% after administration of bFF, but did not alter after treatment with partly purified preparations of inhibin. It is concluded that the inhibin-like activity in bFF suppresses pulsatile FSH secretion in ovariectomized rats by an action on the pituitary gland, but has no effect on the pulsatile release of LH and prolactin.

J. Endocr. (1987) 113, 449–455

Restricted access
J Th J Uilenbroek
Search for other papers by J Th J Uilenbroek in
Google Scholar
PubMed
Close
,
P Kramer
Search for other papers by P Kramer in
Google Scholar
PubMed
Close
,
E C M van Leeuwen
Search for other papers by E C M van Leeuwen in
Google Scholar
PubMed
Close
,
B Karels
Search for other papers by B Karels in
Google Scholar
PubMed
Close
,
M A Timmerman
Search for other papers by M A Timmerman in
Google Scholar
PubMed
Close
,
F H de Jong
Search for other papers by F H de Jong in
Google Scholar
PubMed
Close
, and
R de Leeuw
Search for other papers by R de Leeuw in
Google Scholar
PubMed
Close

Abstract

To investigate whether the progesterone antagonist RU486 has a direct effect on ovarian function, it was administered to immature female rats rendered hypogonadotrophic by administration of an LHRH antagonist and in which follicle development was stimulated by recombinant human FSH (recFSH).

In the first experiments the effects of LHRH antagonist and recFSH on follicle growth were evaluated. Female rats of 22 days of age were injected with an LHRH antagonist (Org 30276; 500 μg/100 g body weight) every other day. This treatment resulted in a tenfold decrease in serum LH concentrations and a twofold decrease in serum FSH concentrations at day 30 and caused a reduction in the number and size of antral follicles. Treatment with recFSH (Org 32489) twice daily from day 26 for 4 days in a total dose ranging from 5 to 20 IU/animal increased the number and size of antral follicles in a dose-related manner and resulted after 20 IU recFSH in a tenfold increase in the concentration of inhibin in serum and ovaries at day 30. Once it was established that LHRH antagonist treatment in immature rats could be used to study the effects of gonadotrophins or steroids on follicle function, this animal model was used to study the effects of RU486 on the ovary. RU486 was administered (twice daily for 4 days, 1 mg/injection) to LHRH antagonist-treated rats in which follicular growth and differentation were stimulated by 10 IU recFSH or by 10 IU recFSH plus 0·5 IU human chorionic gonadotrophin (hCG). RU486 had no effect on circulating levels of LH and FSH, but stimulated follicular atresia both in rats treated with recFSH alone and in rats treated with recFSH and hCG. Inhibin concentrations both in serum and ovaries were significantly increased after hCG treatment. RU486, however, did not increase inhibin in the rats treated with recFSH and in those treated with recFSH and hCG.

In summary, the present study has demonstrated that (1) immature rats treated with an LHRH antagonist can be used to study the effects of gonadotrophins and steroids on follicular function and (2) RU486 has a direct stimulatory effect on follicular atresia.

Journal of Endocrinology (1996) 150, 85–92

Restricted access