A search for structure in the n-p scattering cross section

Schwartz, R. B.; Schrack, R.A.; Heaton, Henry

doi:10.1016/0370-2693(69)90281-0

Cited by 18 publications

(15 citation statements)

References 3 publications

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“…These serum LH concentrations were similar to those observed in intact rats on proestrus (6,7), indicating that ovariectomy at 10:00 AM did not interfere with the mechanisms controlling LH secretion on proestrus. This finding confirms previous observations that ovariectomy on the morning of proestrus does not prevent the proestrous LH surge (8,9). On the next 2 days, however, no LH surges occurred, LH levels remaining at low basal levels similar to those observed in intact diestrous rats (Fig.…”

Section: Resultssupporting

confidence: 93%

A Daily Signal for the LH Surge in the Rat

1975

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We have demonstrated that a brief step-like increment in circulating estradiol concentrations to approximately 100 pg/ml, achieved by SC insertion of Silastic capsules containing estradiol-17 beta and their withdrawal after 29 1/2 hr, elicited a daily LH surge on 4 consecutive afternoons in rats ovariectomized 2 weeks previously. Since the duration of this stimulus was similar to that of the preovulatory increment in serum estradiol concentrations, it was postulated that the endogenous estrogen signal in intact rats might also trigger repetitive LH surges if ovulation and formation of corpora lutea were prevented. To test this hypothesis, rats were ovariectomized at 10:00 AM on proestrus (day 1) and blood samples were obtained at 12:30 and 5:00 PM on days 1 to 4. Although an LH surge occurred on proestrus, no subsequent LH discharges were observed. The absence of an LH surge on consecutive days could not be attributed to a difference between the endogenous estradiol stimulus and the exogenous stimulus which elicited repetitive LH surges in long-term ovariectomized rats. Rather, it was determined that in recently ovariectomized rats, in contrast to long-term ovariectomized rats, a daily LH surge occurred only if elevated serum estradiol concentrations were maintained. Thus, by leaving implants in place, an LH discharge was elicited on 10 consecutive days. These results support the concept that a neural signal for the LH surge is emitted each day throughout the estrous cycle of the rat, and that prolonged maintenance of elevated circulating estradiol concentrations is essential for the expression of these signals.

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Section: Resultssupporting

confidence: 93%

A Daily Signal for the LH Surge in the Rat

1975

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“…Whether the diminished serum E 2 concentrations following P treatment were produced by inhibition of gonadotropin release via a central action of P is not yet resolved (5,6,25,26). It is noteworthy that despite suppressed E 2 levels in P treated rats we did not observe any diminuition of serum LH.…”

Section: Discussionmentioning

confidence: 77%

“…(Endocrinology 95: 1711,1974) A NUMBER of investigators have detected an increase in peripheral blood levels of estradiol (E 2 ) during the interval between late diestrus and the critical period on proestrus (1)(2)(3)(4). This is in support of the concept that estrogen stimulates ovulation and the release of gonadotropins (5,6). The possible role of progesterone (P) in triggering the release of gonadotropins in the afternoon of proestrus is not yet resolved due to the conflicting data on circulating levels of P in the morning of proestrus (5,(7)(8)(9)(10)(11)(12).…”

mentioning

confidence: 85%

Temporal Interrelationships Among Circulating Levels of Estradiol, Progesterone and LH During the Rat Estrous Cycle: Effects of Exogenous Progesterone¹

Kalra

1974

Endocrinology

182

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Serum progesterone (P) levels display a circadian rhythm of varying amplitude during the estrous cycle. This rhythm is characterized by lowest levels of the day around noon and maximal levels at 1600 or 2300 hr. Amplitude was smallest on estrus and progressively greater on diestrus II, diestrus I and proestrus. Serum estradiol (E 2 ) concentrations declined gradually through estrus till 0800 hr of diestrus I. Thereafter, levels increased rapidly to peak at noon, and returned later to near nadir at 2300 hr of diestrus I. During diestrus II and morning of proestrus serum E 2 concentrations increased in a biphasic pattern; a moderate increase till 1800 hr of diestrus II was followed by relatively rapid rise to peak levels at 0800 hr of proestrus. A reciprocal relationship between circulating levels of E 2 and P during the estrous cycle was also detected. The elevations in serum P levels during estrus, diestrus I and proestrus appeared to coincide with a gradual reduction in serum E 2 levels. In addition to the surge of serum LH in the afternoon of proestrus small increases in serum concentration of LH over the base line value were noted at 0800 hr of diestrus I and at 1600 hr of estrus.The influence of experimentally altering the circulating levels of P on endogenous levels of E 2 was next examined. Administration of P at 0800 hr of diestrus I blocked the afternoon rise in serum E 2 ; the suppressive effects persisted till 1800 hr of diestrus II. Similarly, injection of P at 0800, 1800 or 2300 hr of diestrus II suppressed the rise in E 2 normally observed at proestrus. These observations suggest that circadian variations in peripheral serum P concentrations during the estrous cycle may constitute a regulatory mechanism for the observed daily fluctuations in serum E 2 . (Endocrinology 95: 1711(Endocrinology 95: , 1974

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“…Progesterone may initiate the increase in GnRH receptors during diestrus, and receptor number may be maintained subsequently by the increasing estradiol concentrations secreted from developing ovarian follicles. If estradiol is important in increasing GnRH binding, then this effect clearly precedes the positive feedback of estradiol on LH release,.which is exerted between 2300 on the day of diestrus and 0300 on the day of proestrus (15), and is important in triggering the preovulatory gonadotropin surge (11). Exogenous GnRH can evoke LH and FSH surges on the afternoon of diestrus (5), demonstrating that the GnRH receptors present at this time are functional.…”

mentioning

confidence: 97%

Pituitary Gonadotropin-Releasing Hormone Receptors During the Rat Estrous Cycle

Savoy‐Moore

Schwartz

Duncan

et al. 1980

Science

251

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The binding of [6-alanine]gonadotropin-releasing hormone to pituitary plasma membranes increased threefold between metestrus and early proestrus in female rats. Receptor numbers fell rapidly on the afternoon of proestrus coincident with the preovulatory gonadotropin surge. The numbers of receptors for gonadotropin-releasing hormone were positively correlated with concentrations of estradiol in serum; this pattern may be a necessary component of increased pituitary sensitivty to gonadotropin-releasing hormone observed during proestrus.

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A search for structure in the n-p scattering cross section

Cited by 18 publications

References 3 publications

A Daily Signal for the LH Surge in the Rat

A Daily Signal for the LH Surge in the Rat

Temporal Interrelationships Among Circulating Levels of Estradiol, Progesterone and LH During the Rat Estrous Cycle: Effects of Exogenous Progesterone¹

Pituitary Gonadotropin-Releasing Hormone Receptors During the Rat Estrous Cycle

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A search for structure in the n-p scattering cross section

Cited by 18 publications

References 3 publications

A Daily Signal for the LH Surge in the Rat

A Daily Signal for the LH Surge in the Rat

Temporal Interrelationships Among Circulating Levels of Estradiol, Progesterone and LH During the Rat Estrous Cycle: Effects of Exogenous Progesterone1

Pituitary Gonadotropin-Releasing Hormone Receptors During the Rat Estrous Cycle

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Temporal Interrelationships Among Circulating Levels of Estradiol, Progesterone and LH During the Rat Estrous Cycle: Effects of Exogenous Progesterone¹