On Circulating Sex Steroids During the Estrous Cycle and the Early Pseudopregnancy in the Rat with Special Reference to its Luteal Activation

Horikoshi, Hiroyoshi; Suzuki, Yohichi

doi:10.1507/endocrj1954.21.69

Cited by 32 publications

(15 citation statements)

References 13 publications

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“…In our study, using a preinjury treatment, neuroprotection was observed with physiological progesterone levels. Plasma levels of progesterone produced by the administration of the neuroprotective dose of 2 mg/kg were within the ranges previously observed for diestrus and/or estrus rats (Butcher et al, 1974;Horikoshi and Suzuki, 1974;Shaikh and Shaikh, 1975;Belanger et al, 1981;Frye and Bayon, 1999). Similarly, hippocampal levels of progesterone were analogous to those previously reported for behavioral estrus (%10 ng/g) .…”

Section: Discussionsupporting

confidence: 85%

Reduced metabolites mediate neuroprotective effects of progesterone in the adult rat hippocampus. The synthetic progestin medroxyprogesterone acetate (Provera) is not neuroprotective

et al. 2006

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The ovarian hormone progesterone is neuroprotective in different experimental models of neurodegeneration. In the nervous system, progesterone is metabolized to 5alpha-dihydroprogesterone (DHP) by the enzyme 5alpha-reductase. DHP is subsequently reduced to 3alpha,5alpha-tetrahydroprogesterone (THP) by a reversible reaction catalyzed by the enzyme 3alpha-hydroxysteroid dehydrogenase. In this study we have analyzed whether progesterone metabolism is involved in the neuroprotective effect of the hormone in the hilus of the hippocampus of ovariectomized rats injected with kainic acid, an experimental model of excitotoxic cell death. Progesterone increased the levels of DHP and THP in plasma and hippocampus and prevented kainic-acid-induced neuronal loss. In contrast to progesterone, the synthetic progestin medroxyprogesterone acetate (MPA, Provera) did not increase DHP and THP levels and did not prevent kainic-acid-induced neuronal loss. The administration of the 5alpha-reductase inhibitor finasteride prevented the increase in the levels of DHP and THP in plasma and hippocampus as a result of progesterone administration and abolished the neuroprotective effect of progesterone. Both DHP and THP were neuroprotective against kainic acid. However, the administration of indomethacin, a 3alpha-hydroxysteroid dehydrogenase inhibitor, blocked the neuroprotective effect of both DHP and THP, suggesting that both metabolites are necessary for the neuroprotective effect of progesterone. In conclusion, our findings indicate that progesterone is neuroprotective against kainic acid excitotoxicity in vivo while the synthetic progestin MPA is not and suggest that progesterone metabolism to its reduced derivatives DHP and THP is necessary for the neuroprotective effect of the hormone.

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Section: Discussionsupporting

confidence: 85%

Reduced metabolites mediate neuroprotective effects of progesterone in the adult rat hippocampus. The synthetic progestin medroxyprogesterone acetate (Provera) is not neuroprotective

et al. 2006

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“…This may suggest that the hypothala mus of the ovariectomized monkey is more sensitive than that of the intact monkey to the negative feedback effect of estrogen. Serum estradiol values observed 3 or 4 days after the implantation of estradiol-containing silastic tub ing in this study were similar to or slightly exceeded the serum estradiol values of the proestrous rat in our labora tory [27], This level of estrogen totally suppressed the MUA volleys in this study, while the pulsatile release of either GnRH [28] or LH [19] has been demonstrated on proestrus in the rat, suggesting that the hypothalamus is also more sensitive to estrogen in ovariectomized than in intact rats. Nevertheless, the present study clearly showed that estrogen had an inhibitory effect on the excitability of neurons comprising the hypothalamic GnRH pulse gener ator in the rat.…”

Section: Resultssupporting

confidence: 82%

Cessation of the Electrical Activity of Gonadotropin-Releasing Hormone Pulse Generator during the Steroid-Induced Surge of Luteinizing Hormone in the Rat

Nishihara

Sano²,

Kimura³

1994

Neuroendocrinology

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Neuronal activity in the mediobasal hypothalamus was recorded during the steroid-induced surge of luteinizing hormone (LH) in ovariectomized female rats by means of multiunit activity (MUA) recording techniques. The day of subcutaneous implantation of estradiol-containing silastic tubing, which was done at 12.00 h, was designated as day 1, and progesterone (1 mg) dissolved in sesame oil was injected at 12.00 h on day 5. The hypothalamic MUA and serum LH level were monitored between 10.00 and 20.00 h on days 1, 4 and 5. All 5 animals examined showed characteristic increases (volleys) in MUA associated with pulsatile LH secretion. After implantation of estradiol on day 1 gradual and significant decreases in the serum LH level and in MUA volley frequency were observed. In the afternoon of both days 4 and 5, an LH surge occurred, though it was much greater on day 5 than day 4 due to progesterone injection on day 5. However, neither MUA volleys nor considerable changes in baseline MUA were discernible throughout the recording period on days 4 and 5. More than 5 days after the removal of estradiol-containing tubing, MUA volleys were found to reappear in all the animals. These results suggest that estradiol has an inhibitory effect on gonadotropin-releasing hormone (GnRH) pulse generator activity, and that the GnRH pulse generator is not involved in inducing the LH surge in the rat.

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“…There has been no report concerning the diurnal rhythm of serum estrone levels in the immature rat, but for the adult cycling females an afternoon increase has been found [8,11]. The mecha nism for the lack of diurnal rhythm in estrone concentra tions in serum of peripuberal rats remains to be analyzed.…”

Section: Discussionmentioning

confidence: 99%

Development of Orcadian Rhythms in Serum Hormone Levels in the Immature Female Rat

Kimura¹,

Okano²,

Kawakami³

1981

Neuroendocrinology

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Diurnal variations in concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), corticosterone, estradiol-17β and estrone in serum were investigated in 27- to 35-day-old female rats maintained on a 14-hour light and 10-hour dark schedule. Groups of 6–8 rats were decapitated at 3-hour intervals during a 24-hour period. Hormones were measured by radioimmunoassay. LH levels were highly variable over a 24-hour period in rats younger than 32–33 days of age, while in 34- to 35-day-old animals the levels were less variable and a moderate LH peak was seen at 24.00 h. A distinct FSH diurnal rhythm with the peak at 15.00 h was demonstrated in rats older than 32 days of age. The 27- to 28-day-old rat had a diurnal TSH rhythm with the peak at 12.00 h, but older rats had a rhythm with two peaks at 24.00 and 9.00 h. The diurnal corticosterone rhythm analogous to the adult’s was established at 32 days of age, although a significant variation having a peak during the dark period appeared earlier. Similarly, a distinct estradiol rhythm appeared at 29 days of age with the peak at 12.00 h, followed by a change in the peak phase afterwards. Serum estrone levels showed a manifest variation in the 27- to 28-day-old rat, but no variation was observed in the older rats. These results not only confirm the previous reports on the existence of pulsatile LH secretion, and corticosterone and estradiol diurnal rhythms, but also demonstrate the existence of diurnal rhythms in FSH, TSH and estrone levels in the immature female rat. Furthermore, it is possible that the rhythm once developed may change in phase, or even disappear as puberty approaches.

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On Circulating Sex Steroids During the Estrous Cycle and the Early Pseudopregnancy in the Rat with Special Reference to its Luteal Activation

Cited by 32 publications

References 13 publications

Reduced metabolites mediate neuroprotective effects of progesterone in the adult rat hippocampus. The synthetic progestin medroxyprogesterone acetate (Provera) is not neuroprotective

Reduced metabolites mediate neuroprotective effects of progesterone in the adult rat hippocampus. The synthetic progestin medroxyprogesterone acetate (Provera) is not neuroprotective

Cessation of the Electrical Activity of Gonadotropin-Releasing Hormone Pulse Generator during the Steroid-Induced Surge of Luteinizing Hormone in the Rat

Development of Orcadian Rhythms in Serum Hormone Levels in the Immature Female Rat

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