Mechanism of Stimulatory Feedback Effect of Estradiol Benzoate on the Pituitary

Weick, Richard F.; Smith, E. R.; Domı́nguez, Roberto; Dhariwal, A. P. S.; Davidson, Julian M.

doi:10.1210/endo-88-2-293

Cited by 34 publications

(17 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The result showing that, in ovariectomized estradiol-treated rats, the LH surge could be completely blocked by even 125 µg/day, a dose at which estradiol-induced uterine growth and lactotrope proliferation were only partially inhibited, indicates that the LH surge is the most sensitive to the peripheral action of ICI amongst the three events that are totally dependent upon the peripheral estradiol action. The results of the previous two studies [5, 45]and ours do not invalidate the results of the numerous studies that have shown central sites of estradiol action on gonadotropin surges in intracerebral implantation and lesion experiments [for review, see 7, 8]and are also consistent with those of other studies using estrogen implants into the pituitary [46, 47]. …”

Section: Discussionsupporting

confidence: 90%

Direct Actions of Estradiol on the Anterior Pituitary Gland Are Required for Hypothalamus-Dependent Lactotrope Proliferation and Secretory Surges of Luteinizing Hormone but Not of Prolactin in Female Rats

Yin

Kawashima

2002

Neuroendocrinology

View full text Add to dashboard Cite

Estradiol induces surges of prolactin (PRL) and luteinizing hormone (LH) secretion as well as lactotrope proliferation in female rats. We examined whether these hypothalamus-dependent events require the direct action of estradiol on the anterior pituitary gland by selective blockade of its peripheral actions, using ICI182,780 (ICI), an antiestrogen that cannot cross the blood-brain barrier. Injection of ICI into ovariectomized rats, at a dose of 250 µg/day for 4 days, almost completely inhibited estradiol-induced growth of the uterus, proliferation of lactotropes as determined by bromodeoxyuridine incorporation, and afternoon surges of LH secretion. However, ICI only partially inhibited estradiol-induced surges of PRL secretion and had no effect on estradiol-induced tonic inhibition of LH secretion even at the highest dose of 1,000 µg/day. The inhibitory effects of ICI found at 250 µg/day were attributable to its selective peripheral, but not central actions since ICI did not alter hypothalamic expression of progesterone receptors, an estradiol-dependent brain process. Estradiol-induced increases in the number of progesterone receptor-immunoreactive cells in the hypothalamic ventromedial nucleus and the medial preoptic area were not inhibited by this dose of ICI but were inhibited by 500 µg/day tamoxifen, an antiestrogen that can cross the blood-brain barrier. Treatment of cycling female rats with 250 µg/day ICI beginning from diestrus day 2 was also effective in blocking estrous lactotrope proliferation and preovulatory surges of LH secretion but not PRL secretion. Finally, in ovariectomized estradiol-treated pup-deprived lactating rats, ICI did not affect suckling-induced PRL secretion but completely blocked lactotrope proliferation. These results suggest that a direct estradiol action on the anterior pituitary gland is required for lactotrope proliferation and the positive feedback action on LH secretion but not for the secretory surges of PRL or for negative feedback.

show abstract

Section: Discussionsupporting

confidence: 90%

Direct Actions of Estradiol on the Anterior Pituitary Gland Are Required for Hypothalamus-Dependent Lactotrope Proliferation and Secretory Surges of Luteinizing Hormone but Not of Prolactin in Female Rats

Yin

Kawashima

2002

Neuroendocrinology

View full text Add to dashboard Cite

show abstract

“…The site where the needle was introduced was assessed histologically with a stereoscopic microscope by noting the end of the needle tracts in 100-m brain slices. The injection into the pituitary was corroborated following protocols described by Weick et al [30] . Only data from animals where the injection into the hypothalamus or pituitary was confi rmed were used in the analysis.…”

Section: Autopsy Proceduresmentioning

confidence: 99%

Effects of Injecting Thymulin into the Anterior or Medial Hypothalamus or the Pituitary on Induced Ovulation in Prepubertal Mice

García¹,

Hinojosa²,

Domı́nguez³

et al. 2005

Neuroimmunomodulation

View full text Add to dashboard Cite

In prepubertal mice, subcutaneous thymulin injection before equine chorionic gonadotrophin (eCG) treatment simulates ovulation; seemingly, the thymulin could be acting at the hypothalamus-pituitary axis level. Objective: This study was designed to analyze the effects of injecting thymulin into the hypothalamus or pituitary on induced ovulation of prepubertal mice. Method: Female mice, 19 days old, were anesthetized with ether and injected with saline solution or thymulin into the anterior or medial hypothalamus or the pituitary and treated with eCG when 20 days old. The ova shed were counted and serum concentrations of 17β-estradiol were measured. In the ovaries, the morphometrical analysis was performed and the atresia evaluated. Results: Ether anesthesia treatment blocked eCG-induced ovulation in almost all animals. Mice anesthetized and treated with eCG and gonadotrophin-releasing hormone (GnRH) or human chorionic gonadotrophin (hCG) ovulated a full quota of ova. Injecting saline solution into the anterior or medial hypothalamus or the pituitary did not reduce the blocking effects of ether anesthesia on induced ovulation, but the incidence of atretic follicles was higher. Injecting thymulin directly into the anterior hypothalamus did not restore ovulation, nor diminish the number of atretic follicles. In contrast, injecting thymulin into the medial hypothalamus restored the ovulation ratio and decreased the percentage of atretic follicles. Similar results were obtained by injecting thymulin into the pituitary, though thymulin treatment in the pituitary resulted in a higher number of ova shed and lower follicular atresia. Conclusion: The present results suggest that thymulin acts at the medial hypothalamus level, facilitating the release of GnRH and at the pituitary level regulating gonadotrophin release.

show abstract

“…Weick et al [1971] reported that the estrogen-induced advancement of ovulation could be blocked by pentobarbital administered at the time of estrogen treatm ent (on the day following metestrus). This suggested that neural activation of the pituitary at times other than proestrus could be im portant in determining the events leading to ovulation.…”

mentioning

confidence: 99%

Barbiturate Blockade of Ovulation on Days Other Than Proestrus in the Rat

Domı́nguez¹,

Smith²

1974

Neuroendocrinology

Self Cite

View full text Add to dashboard Cite

Sodium pentobarbital (50 mg/kg) was administered oneach day of the estrous cycle to 4- and 5-day cyclic Long-Evans rats. In rats with 4-day cycles, the incidence of ovulation was significantly decreased when barbiturate was administered as a single injection at various times from 12.45 h on estrus to 12.45 h on diestrus-2. A delay in vaginal cornification and uterine ballooning measured on estrus, as well as decreased sexual receptivity on proestrus, was also found to result from barbiturate injections on diestrus-1, indicating a suppression of estrogen secretion. The deleterious effects of barbiturate treatment could be reversed by the simultaneous administration of gonadotropin. A generally similar pattern of blockade by barbiturate during this time period was found in 5-day cyclic rats, although the inhibitory effects were less than in 4-day cyclic rats. Furthermore, no inhibition of ovulation was found following drug administration on diestrus-3. The pattern of ovulatory blockade by barbiturate on the afternoon of proestrus was also generally similar in the 4- and 5-day cyclic rats. Again, however, more complete suppression was found in the 4-day cycle, and the duration of the inhibitory effects was more prolonged. It was concluded that the inhibitory effects of barbiturate administered early in the estrous cycle (estrus, diestrus-1 and diestrus-2) probably reflect a daily pattern of neural activity which is causally related to gonadotropin and estrogen secretion necessary for the final occurrence of ovulation.

show abstract

Mechanism of Stimulatory Feedback Effect of Estradiol Benzoate on the Pituitary

Cited by 34 publications

References 1 publication

Direct Actions of Estradiol on the Anterior Pituitary Gland Are Required for Hypothalamus-Dependent Lactotrope Proliferation and Secretory Surges of Luteinizing Hormone but Not of Prolactin in Female Rats

Direct Actions of Estradiol on the Anterior Pituitary Gland Are Required for Hypothalamus-Dependent Lactotrope Proliferation and Secretory Surges of Luteinizing Hormone but Not of Prolactin in Female Rats

Effects of Injecting Thymulin into the Anterior or Medial Hypothalamus or the Pituitary on Induced Ovulation in Prepubertal Mice

Barbiturate Blockade of Ovulation on Days Other Than Proestrus in the Rat

Contact Info

Product

Resources

About