FEEDBACK EFFECT OF OESTROGEN ON LUTEINIZING HORMONE SECRETION BY THE RAT PITUITARY GLAND

1982 ◽  
Vol 92 (3) ◽  
pp. 389-395 ◽  
Author(s):  
TAKASHI HIGUCHI ◽  
MASAZUMI KAWAKAMI
Keyword(s):  
Pituitary Gland ◽  
Hormone Secretion ◽  
Feedback Effect ◽  
Ovariectomized Rats ◽  
Luteinizing Hormone Secretion ◽  
Hypothalamic Area ◽  
Serum Lh ◽  
Lh Rh ◽  
Lh Releasing Hormone ◽  
Lh Secretion

Ovariectomized rats with neural deafferentation at the level of the posterior border of the anterior hypothalamic area (AC rats) were used to re-evaluate the direct feedback effect of oestrogen on the regulation of LH secretion by the pituitary gland. Synthetic LH releasing hormone (LH-RH; 300 ng/kg), injected at 30-min intervals into AC rats with undetectable basal LH, induced pulsatile increase of serum LH concentrations. Oestradiol-17β (5 μg), administered i.v. just before the first LH-RH injection, significantly decreased the LH response to a second injection of LH-RH given 30 min later and to subsequent injections. Maximal inhibition was 58%. Oestradiol-17β (5 μg) given i.v. to control ovariectomized rats decreased serum LH concentrations 40 min after administration; the maximum reduction being 52%. An s.c. injection of oestradiol benzoate (5 μg) increased pituitary responsiveness to LH-RH by the next day in AC rats but decreased serum LH levels in control ovariectomized rats. These results indicate that acute inhibitory and chronic facilitatory effects of oestrogen on LH secretion are exerted at the pituitary gland, without a change in LH-RH secretion. The prolonged inhibitory effect of oestrogen is at the level of the hypothalamus and causes a reduction in LH-RH secretion.

CIRCADIAN RHYTHM OF LUTEINIZING HORMONE SECRETION IN THE OVARIECTOMIZED RAT IMPLANTED WITH OESTRADIOL

1977 ◽  
Vol 75 (2) ◽  
pp. 251-260 ◽  
Author(s):  
G. CHAZAL ◽  
M. FAUDON ◽  
F. GOGAN ◽  
M. HERY ◽  
C. KORDON ◽  
...  
Keyword(s):  
Circadian Rhythm ◽  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Ovariectomized Rats ◽  
Luteinizing Hormone Secretion ◽  
Implantation Time ◽  
Light Darkness ◽  
Lh Rh ◽  
Lh Releasing Hormone ◽  
Afternoon Peak

Implantation of a solid source of oestradiol into ovariectomized rats produced constant plasma concentrations of the hormone over a long period of time. Under these conditions, LH is released in a circadian pattern with a very marked peak in the afternoon. This circadian rhythm is synchronized to the light–darkness cycle, since it follows exactly a shift in the nycthemeral cycle. The first peak appeared on day 3 after placement of the oestrogen implant; its amplitude was constant from days 3 to 9 after implantation, and decreased gradually during prolonged implantation. The afternoon peak was not correlated with changes in the pituitary sensitivity to exogenous LH releasing hormone (LH-RH), since the LH response to increasing doses of the peptide could be superimposed in the morning and in the afternoon. However, the decreased amplitude of the rhythm observed after more than 9 days of implantation seemed to depend upon a progressive desensitization of the pituitary gland to LH-RH. Pituitary LH content also decreased as a function of implantation time. It is concluded that, under conditions of constant plasma oestradiol concentrations and of constant pituitary sensitivity to LH-RH, a daily activation of the neural trigger releasing pituitary gonadotrophins occurs.

IMPORTANCE OF THE EPISODIC NATURE OF LUTEINIZING HORMONE SECRETION FOR NORMAL DEVELOPMENT OF THE BOVINE TESTIS DURING PUBERTY: INTERFERENCE WITH OESTRADIOL-17β

1981 ◽  
Vol 88 (3) ◽  
pp. 393-400 ◽  
Author(s):  
B. D. SCHANBACHER
Keyword(s):  
Normal Development ◽  
Pubertal Development ◽  
Hormone Secretion ◽  
Serum Testosterone ◽  
Luteinizing Hormone Secretion ◽  
Testicular Growth ◽  
Serum Lh ◽  
Beef Bulls ◽  
Lh Releasing Hormone ◽  
Lh Secretion

An experiment was conducted to determine the importance of episodic LH secretion during pubertal development in beef bulls. Testicular growth, LH secretory patterns and serum testosterone concentrations were monitored in control bulls, and bulls implanted with one or two oestradiol-filled capsules from 26 to 38 weeks of age. Control but not oestradiol-treated bulls showed normal testicular growth and episodic LH secretory patterns. Serum LH and testosterone responses of 38-week-old control and oestradiol-treated bulls to an intravenous challenge of 5 μg LH releasing hormone indicated normal pituitary responsiveness, but steroidogenic responsiveness had not yet developed in oestradiol-treated bulls. Removal of the capsules at 38 weeks of age resulted in a normal episodic release pattern for LH, with concomitant growth of the underdeveloped testes up to 44 weeks of age. Serum concentrations of LH and testosterone were within the range of normal, adult values by 42 weeks of age. These results suggest that oestradiol can interfere with episodic LH secretion and normal pubertal development in beef bulls, and furthermore that episodic LH secretion is commensurate with the establishment of normal development of the bovine testis during puberty.

EFFECT OF 20α-HYDROXYY-4-PREGNEN-3-ONE ON LUTEINIZING HORMONE SECRETION IN THE FEMALE RABBIT

1977 ◽  
Vol 84 (1) ◽  
pp. 45-50 ◽  
Author(s):  
E. V. YoungLai
Keyword(s):  
Luteinizing Hormone ◽  
Hormone Secretion ◽  
Luteinizing Hormone Secretion ◽  
Releasing Hormone ◽  
Female Rabbit ◽  
Oestradiol Benzoate ◽  
Lh Rh ◽  
Lh Releasing Hormone ◽  
Lh Secretion

ABSTRACT Experiments were performed in the rabbit to determine whether 20α-hydroxy-4-pregnen-3-one (20-OHP) can maintain luteinizing hormone (LH) secretion after injections of LH-releasing hormone (LH-RH). Female rabbits were castrated at least 2 weeks prior to investigation. On the day before LH-RH injection they were cannulated and a dose of oestradiol benzoate (OeB), 100 μg/kg, given intramuscularly. LH-RH, 500 ng/kg, was injected as a bolus via the cannula and 20-OHP, 100 μg/kg and 2.5 mg/kg, injected intramuscularly immediately after. Blood was withdrawn at intervals for up to 5½ h after LH-RH injection. LH secretion dropped to pre-stimulation levels within 3 h after LH-RH alone or in combination with 20-OHP. Administration of LH-RH to oestrogen primed intact females also gave a peak of LH which returned to pre-stimulation levels within 3 h. However, mating seemed to maintain LH levels for a greater period of time.

Changes in the characteristics of pulsatile luteinizing hormone secretion during the oestrous cycle and after ovariectomy and oestrogen treatment in female rats

1982 ◽  
Vol 94 (2) ◽  
pp. 177-182 ◽  
Author(s):  
Takashi Higuchi ◽  
Masazumi Kawakami
Keyword(s):  
Hormone Secretion ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Oestrous Cycle ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Luteinizing Hormone Secretion ◽  
Oestrogen Treatment ◽  
Serum Lh ◽  
Lh Release

Changes in the characteristics of LH secretory pulses in female rats were determined in different hormonal conditions; during the oestrous cycle and after ovariectomy and oestrogen treatment. The frequency and amplitude of the LH pulses were stable during the oestrous cycle except at oestrus when a pattern could not be discerned because of low LH concentrations. These were significantly lower than those measured during other stages of the cycle. Mean LH concentrations and LH pulse amplitudes increased with time up to 30 days after ovariectomy. The frequency of the LH pulse was unchanged 4 days after ovariectomy when mean LH levels had already increased. The frequency increased 10 days after ovariectomy and then remained stable in spite of a further increase in mean serum LH concentrations. Oestradiol-17β injected into ovariectomized rats caused a decrease in LH pulse amplitude but no change in pulse frequency. One day after treatment with oestradiol benzoate no LH pulse was detectable, probably because the amplitude was too small. A generator of pulsatile LH release is postulated and an oestrogen effect on its function is discussed.

Serotonin-reinstatement of luteinizing hormone surges after loss of positive feedback in ovariectomized rats bearing subcutaneous capsules containing oestrogen

1983 ◽  
Vol 98 (1) ◽  
pp. 7-17 ◽  
Author(s):  
R. F. Walker
Keyword(s):  
Positive Feedback ◽  
Ovariectomized Rats ◽  
Facilitatory Effect ◽  
Serum Progesterone ◽  
Serotonin Content ◽  
Serum Lh ◽  
Serotonin Turnover ◽  
Lh Rh ◽  
Lh Releasing Hormone ◽  
Feedback Responses

In ovariectomized rats treated chronically with oestrogen there is a loss of positive feedback effects on LH secretion. This was not due to depletion of pituitary LH since injection of LH releasing hormone (LH-RH; 50 ng/100 g body wt) caused a significant (P < 0·01) rise in serum LH even after the loss of spontaneous LH surges. However, the magnitude of the increase in serum LH in response to LH-RH was greater (412 ± 41 μg/l) before than after (291 ± 29 μg/l) loss of the LH surges. Excessive blood sampling was also not responsible, since positive feedback responses declined comparably in rats bled daily or once every 3–4 days. Progesterone (0·5 mg s.c.), administered for 5 consecutive days, failed to restore LH surges indicating that deficiency of this steroid after ovariectomy does not cause positive feedback responses to disappear in rats exposed chronically to oestrogen. Moreover regular daily fluctuations in serum progesterone, probably of adrenal origin, occurred before as well as after daily LH surges were lost. Serotonin content and turnover were depressed (P < 0·05) when ovariectomized rats first received the subcutaneous capsules containing oestrogen. This change correlated temporally with the onset of daily LH surges and was eventually lost. After 30 days exposure to oestrogen, serotonin turnover increased (P < 0·01) and positive feedback responses were absent. Catecholamine levels and turnover did not show differential responses to oestrogen and were depressed after acute as well as chronic steroid treatment. p-Chlorophenylalanine (pCPA; 250 mg/kg)+ l-dihydroxyphenylalanine (l-DOPA; 200 mg/kg), which depress serotonin and enhance catecholamine synthesis respectively, failed to reinstate LH surges, but these were restored in 22% of the rats receiving l-DOPA alone. pCPA, followed 2 days later by 5-hydroxytryptophan (5-HTP) at 11.00 h, reinstated LH surges in 88% of rats, and a dose–response curve showed that as little as 4 mg 5-HTP/kg stimulated repetitive LH surges when given with pCPA according to this schedule. However, the administration of α-methyl-p-tyrosine + l-DOPA, an analogous treatment involving catecholamines, was only marginally effective (15%). These findings suggest that perturbations of monoamine metabolism occurring in ovariectomized rats exposed to oestrogen for several weeks contribute to loss of daily LH surges. Since pCPA + 5-HTP restored LH surges most effectively, then positive feedback may disappear as the facilitatory effect of serotonin is lost after chronic oestrogen administration.

Effects of valproate-induced alteration of the GABAergic system on pulsatile luteinizing hormone secretion in ovariectomized women

1996 ◽  
Vol 135 (3) ◽  
pp. 293-298 ◽  
Author(s):  
Joaquin Lado-Abeal ◽  
Jose L Liz ◽  
Carlos Rey ◽  
Manuel Febrero ◽  
Jose Cabezas-Cerrato
Keyword(s):  
Luteinizing Hormone ◽  
Sodium Valproate ◽  
Pulse Generator ◽  
Hormone Secretion ◽  
Gabaergic System ◽  
Luteinizing Hormone Secretion ◽  
Serum Lh ◽  
Nutrition Service ◽  
Significant Difference ◽  
Lh Secretion

Lado-Abeal J, Liz JL, Rey C, Febrero M, Cabezas-Cerrato J. Effects of valproate-induced alteration of the GABAergic system on pulsatile luteinizing hormone secretion in ovariectomized women. Eur J Endocrinol 1996;135:293–8. ISSN 0804–4643 It is well established that valproate increases hypothalamic concentrations of γ-aminobutyric acid (GABA). Although little research has been done on the role of GABA in the control of pulsatile luteinizing hormone (LH) secretion in humans, our group recently found that administration of valproate had no significant effect on pulsatile LH secretion in late follicular and mid-late luteal phase normal women. However, the results of several studies of rats suggest that GABAergic regulation of LH secretion may depend on steroid levels. The objective of this work was to determine whether regular administration of sodium valproate inhibits pulsatile LH secretion in ovariectomized women. Twelve women who had undergone ovariectomy for causes other than malignant tumors were each studied in two 8 h sessions, in each of which blood samples were taken every 5 min. The first session was the control; for the second, 400 mg of sodium valproate was administered every 8 h during the seven preceding days and at 08.00 h and 14.00 h on the day of the study session. Serum valproate was determined by repolarization fluorescence spectrophotometry, and LH, estradiol and progesterone by radioimmunoassay. The serum LH series were subjected to a deconvolution procedure to reconstruct the pattern of pituitary LH secretion. Luteinizing hormone pulses were identified by the authors' nonparametric method. Control and post-valproate results were compared with regard to number of pulses, pulse duration, the quantity of LH secreted in each pulse, interpulse interval and mean serum LH level. There was no statistically significant difference between control and post-valproate results for any of the variables considered. It is concluded that sustained serum valproate levels do not alter pulsatile secretion of LH in ovariectomized women. This implies that, in humans, GABA is probably not a decisive factor in the regulation of the GnRH pulse generator. J Cabezas-Cerrato, Endocrinology and Nutrition Service, General Hospital of Galicia, c/Galeras s/n 15705, Santiago de Compostela, La Coruña, Spain

LUTEINIZING HORMONE RELEASING HORMONE-INDUCED RELEASE OF LUTEINIZING HORMONE FROM PITUITARY EXPLANTS OF COWS KILLED BEFORE OR AFTER OESTRADIOL TREATMENT

1981 ◽  
Vol 88 (1) ◽  
pp. 17-25 ◽  
Author(s):  
E. M. CONVEY ◽  
J. S. KESNER ◽  
V. PADMANABHAN ◽  
T. D. CARRUTHERS ◽  
T. W. BECK
Keyword(s):  
Luteinizing Hormone ◽  
Pituitary Gland ◽  
Lh Surge ◽  
Releasing Hormone ◽  
Oestradiol Treatment ◽  
Readily Releasable Pool ◽  
Serum Lh ◽  
Pituitary Glands ◽  
Lh Rh ◽  
Lh Releasing Hormone

In ovariectomized heifers, oestradiol decreases concentrations of LH in serum for approximately 12 h after which LH is released in a surge comparable in size and duration to the preovulatory surge. Using this model, we measured LH release induced by LH releasing hormone (LH-RH) from pituitary explants taken from ovariectomized heifers before or after an oestradiol-induced LH surge. These changes were related to changes in LH concentrations in serum and pituitary glands and hypothalamic LH-RH content. Twenty Holstein heifers were randomly assigned to one of four treatment groups to be killed 0, 6, 12, or 24 h after the injection of 500 μg oestradiol-17β. Jugular blood was collected at −2, −1 and 0 h then at intervals of 2 h until slaughter. Pituitary glands were collected and ≃2 mm3 explants were exposed to 4 ng LH-RH/ml medium for 30 min (superfusion) or 4 ng LH-RH/ml medium for 2 h in Erlenmeyer flasks. Levels of LH were measured in the medium. Hypothalami, collected at autopsy, were assayed for LH-RH content. To determine pituitary LH content, an additional 15 ovariectomized heifers were killed, five each at 0, 12 and 24 h after the injection of 500 μg oestradiol. In both groups of heifers, oestradiol reduced serum LH concentrations to ≃ 1 ng/ml, a level which persisted for 12 h, when LH was released in a surge. Pituitary sensitivity to LH-RH was increased at 6 and 12 h after the injection of oestradiol, but was markedly decreased at 24 h, i.e. after the LH surge. Despite this twofold increase in capacity of the pituitary gland to release LH in response to LH-RH, pituitary LH content did not change during 12 h after oestradiol treatment. However, LH content decreased after the LH surge and this decrease was associated with a decrease in pituitary responsiveness to LH-RH. Hypothalamic LH-RH content was not altered by these treatments. We have interpreted our results as evidence that oestradiol exerts a positive feedback effect on the pituitary gland of ovariectomized heifers such that pituitary sensitivity to LH-RH is increased twofold by the time the LH surge is initiated. In addition, oestradiol causes a transitory inhibition of LH-RH release as shown by the fact that serum LH concentrations remained low during the interval from injection of oestradiol until the beginning of the LH surge despite the fact that pituitary sensitivity to LH-RH is increased at this time. Depletion of a readily releasable pool of pituitary LH may be the mechanism by which the LH surge is terminated.

Control of follicle-stimulating hormone secretion by steroid-free bovine follicular fluid in the ovariectomized rat

1983 ◽  
Vol 99 (1) ◽  
pp. 1-8 ◽  
Author(s):  
T. R. Koiter ◽  
G. C. J. van der Schaaf-Verdonk ◽  
H. Kuiper ◽  
N. Pols-Valkhof ◽  
G. A. Schuiling
Keyword(s):  
Luteinizing Hormone ◽  
Follicular Fluid ◽  
Hormone Secretion ◽  
Ovariectomized Rats ◽  
Ovariectomized Rat ◽  
Releasing Hormone ◽  
Basal Release ◽  
Lh Release ◽  
Lh Releasing Hormone ◽  
Lh Secretion

The effects of steroid-free bovine follicular fluid (bFF) and sodium phenobarbitone on spontaneous LH releasing hormone (LHRH)-induced secretion of FSH and LH were studied in ovariectomized rats. Luteinizing hormone releasing hormone was administered by infusion to rats anaesthetized with phenobarbitone. Bovine follicular fluid reduced FSH release and synthesis. Luteinizing hormone release remained unaffected after bFF treatment. Phenobarbitone reduced both FSH and LH release. The observed suppressive effects of bFF and phenobarbitone on FSH secretion were additive, suggesting that the basal release of FSH has an LHRH-dependent and an LHRH-independent component. Furthermore, bFF did not affect pituitary responsiveness of LH secretion to LHRH and reduced the responsiveness of FSH secretion only when administered some time before the LHRH challenge. The present observations support the view that in the ovariectomized rat the pituitary gland is the only site of action of inhibin-like activity as present in bFF.

scholarly journals Alcohol Alters Luteinizing Hormone Secretion in Immature Female Rhesus Monkeys by a Hypothalamic Action

Endocrinology ◽  
2004 ◽  
Vol 145 (10) ◽  
pp. 4558-4564 ◽  
Author(s):  
Gregory A. Dissen ◽  
Robert K. Dearth ◽  
H. Morgan Scott ◽  
Sergio R. Ojeda ◽  
W. Les Dees
Keyword(s):  
Rhesus Monkeys ◽  
Sucrose Solution ◽  
Hormone Secretion ◽  
Luteinizing Hormone Secretion ◽  
Immature Female ◽  
Blood Samples ◽  
Female Rhesus ◽  
Lh Release ◽  
Lh Releasing Hormone ◽  
Lh Secretion

Abstract We determined whether the effect of alcohol (ALC) to suppress LH secretion in immature female monkeys is due to a hypothalamic or pituitary site of action. Beginning at 20 months of age, four monkeys received a single intragastric dose of ALC (2.4 g/kg), and four monkeys received an equal volume of a saline/sucrose solution daily until they were 36 months old. For the hypothalamic response test, two basal samples (3.5 ml) were collected at 15-min intervals via the saphenous vein, and then N-methyl-d-l-aspartic acid (NMA; 20 mg/kg) was given iv and four more blood samples collected. Three weeks later, this protocol was repeated except LH-releasing hormone (LHRH) (5 μg/kg) was used to test pituitary responsiveness. NMA or LHRH was administered 3 h after the ALC. After the pituitary challenge, each monkey was ovariectomized and 6 wk later, implanted with an indwelling subclavian vein catheter. Blood samples were drawn every 10 min for 8 h to assess effects of ALC on post-ovariectomy LH levels and the profile of LH pulsatile secretion. The hypothalamic challenge showed NMA stimulated LH release in control monkeys, an action that was blocked by ALC. The pituitary challenge revealed that LHRH stimulated LH release equally well in control and ALC-treated monkeys. A post-ovariectomy rise in LH was observed in both groups, but levels were 45% lower in ALC-treated monkeys. This reduction was attributed to an ALC-induced suppression of both baseline and amplitude of pulses. Results demonstrate that the ALC-induced suppression of LH in immature female rhesus monkeys is due to an inhibitory action of the drug at the hypothalamic level.

EFFECT OF SYNTHETIC THYROTROPHIN RELEASING FACTOR ON PROLACTIN AND LUTEINIZING HORMONE SECRETION IN MALE AND FEMALE RATS DURING VARIOUS REPRODUCTIVE STATES

1975 ◽  
Vol 67 (3) ◽  
pp. 425-430 ◽  
Author(s):  
R. P. DEIS ◽  
NIA ALONSO
Keyword(s):  
Hormone Secretion ◽  
Female Rats ◽  
Male Rats ◽  
Serum Prolactin ◽  
Serum Prolactin Level ◽  
Luteinizing Hormone Secretion ◽  
Male And Female Rats ◽  
Serum Lh ◽  
The Mean ◽  
Lh Secretion

SUMMARY The effect of synthetic thyrotrophin releasing factor (TRF) on serum prolactin and LH concentrations was determined by radioimmunoassay in male, cyclic and pseudopregnant female rats. A solution of TRF (0·1, 0·25, 0·5 and 1 μg/rat) was injected i.v. at 17.00 h into rats pretreated with sodium pentobarbitone at 13.00 h. A group of male rats was also treated with TRF at 11.00 h after pretreatment with sodium pentobarbitone at 07.00 h. Fifteen minutes after TRF administration, blood samples were obtained by heart puncture. Doses of 0·25, 0·5 and 1 μg TRF significantly increased the serum prolactin concentration in pro-oestrous rats. The mean serum prolactin level after the injection of 0·5 and 1 μg into oestrous rats and 0·5 μg TRF into dioestrous day 2 rats, was significantly greater than the control values. Injection of TRF on day 1 of dioestrus had no effect. Serum LH concentration was not significantly modified by the various doses of TRF administered. On day 3 of pseudopregnancy a significant increase of serum prolactin values was obtained with 0·5 and 1 μg TRF. On day 7 of pseudopregnancy a dose of 0·5 μg produced the same effect, but on day 10 of pseudopregnancy only 1 μg TRF significantly increased serum prolactin levels when compared with the control rats. In male rats serum prolactin concentration was significantly greater than the control values after TRF treatment either in the morning or the afternoon. The response was similar to that obtained in pro-oestrous rats. The results suggest that the ability of synthetic TRF to stimulate prolactin release exists in both female and male rats and that TRF does not affect LH secretion.

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