Induction of Ovulation in Hypophysectomized Rats by Progesterone*

Takahashi, Michio; Ford, J. J.; Yoshinaga, Koji; Greep, Roy O.

doi:10.1210/endo-95-5-1322

Cited by 43 publications

(18 citation statements)

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“…The s.c. P 4 injection to rats hypophysectomized just after a proestrous rise in LH release could still induce ovulation as an LH substitute [39]. Subsequent reports demonstrated that additional P 4 can also enhance the E 2 -induced surge [17,18].…”

Section: Discussionmentioning

confidence: 99%

Temporal Changes Occur in the Neuroendocrine Control of Gonadotropin Secretion in Aging Female Rats: Role of Progesterone1

Tsai

LaPolt

Olcott

et al. 2004

Biology of Reproduction

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The present study examined the gonadotropin surge-inducing actions of estradiol (E(2)), both alone and with progesterone (P(4)), in middle-aged, early persistent-estrous (PE) female rats that had become PE within 35 days. In addition, we also assessed the effect of P(4) on the mating-induced gonadotropin surges in these acyclic animals. Early PE rats were ovariectomized and received E(2) implants (Day 0). On Day 4, an s.c. injection of P(4) (0.5 mg/ 100 g body weight) at 1200 h markedly increased plasma P(4) and elicited both LH and FSH surges, whereas vehicle-treated controls displayed no rise in P(4) or gonadotropins. This observation confirms that at middle age, female rats no longer respond to the positive-feedback stimulation of E(2) on gonadotropin surges whenever the estrous cyclicity ceases. As PE continued, such a surge-inducing action of E(2) plus P(4) became diminished after 75 days of PE and disappeared thereafter. When caged with males, vehicle-treated early PE rats display a mating-induced increase in P(4) from the adrenal along with small gonadotropin surges. The amplitude of these mating-induced gonadotropin surges was enhanced by supplementation with exogenous P(4) in early PE rats. Our findings indicate that during the early phase of PE, the surge-inducing action of E(2) and P(4) remains intact but deteriorates as PE continues. Thus, a deficiency in P(4) secretion during aging may contribute to the diminished gonadotropin surge response in the hypothalamic-pituitary axis and the subsequent cessation of estrous cyclicity.

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Section: Discussionmentioning

confidence: 99%

Temporal Changes Occur in the Neuroendocrine Control of Gonadotropin Secretion in Aging Female Rats: Role of Progesterone1

Tsai

LaPolt

Olcott

et al. 2004

Biology of Reproduction

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“…Progesterone is reported to decrease the output of LHRH into stalk blood in female rats (Sarker and Fink, 1979) and is said to act in the brain to decrease the frequency of LHRH pulses in sheep (Karsch et al, 1980). The end of LHRH secretion in this study can possibly be correlated with the time when plasma LH attained a plateau level, since LH at a level comparable to preovulatory surge can temporarily stimulate the secretion of progesterone from the preovulatory follicles (Takahashi et al, 1974) and therefore, may terminate LHRH secretion.…”

Section: Discussionmentioning

confidence: 54%

Preovulatory changes in luteinizing hormone releasing hormone concentrations in peripheral plasma in constant estrous rats at induced ovulation.

et al. 1982

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Cervical stimulation was used to induce synchronous ovulation in rats that were induced into constant estrus by exposure to continuous lighting. Anti-LHRH or anti-LH serum completely blocked the induced ovulation when administered iv within 5 or 40min after cervical stimulation. Peripheral concentrations of LH and LHRH hypothalamic content of LHRH were quantified before and at various intervals (0.5-70min) after cervical stimulation. The radioimmunoassay for LHRH employed a specific antiserum, OAL-513, with high affinity and specificity and highly purified 125I-LHRH.Measurement of LHRH in extracts of 3-5ml of plasma gave values that were readable in the middle portion of the standard curve.A two-fold increase in the LHRH concentration in peripheral plasma was observed 30sec after the start of cervical stimulation. The elevated LHRH level was sustained for 15min, though associated with large fluctuations. Serum LH levels started to rise 4 to 10 min and returned to the basal level 70min after cervical stimulation. The hypothalamic LHRH content continued to increase throughout the entire experimental period and attained 140% of the initial level. No significant deflection due to LHRH release was observed in the hypothalamic LHRH content. Changes in the peripheral hormone level after cervical stimulation were competent for chronologically reasoning the effectiveness of the antihormone treatment for blockage of the induced ovulation.From these results it is concluded that LHRH release before the preovulatory LH surge in light-estrous rats was brief in duration and erratic in mode.

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“…Interestingly, superovulation in AIS-treated rats occurred despite the attenuated proestrous afternoon LH secretion. This could be because only about 50% of the LH surge is needed for full ovulation [34,35,36]. FSH-dependent increased concentration of E2 is not the cause of the reduction in LH surge magnitude since during the proestrous morning E2 acts in its positive feedback mode [2,7,37,38].…”

Section: Discussionmentioning

confidence: 99%

Immunoneutralization of Inhibin in Cycling Rats Increases Follicle-Stimulating Hormone Secretion, Stimulates the Ovary and Attenuates Progesterone Receptor-Dependent Preovulatory Luteinizing Hormone Secretion

Gordon

Aguilar²,

Garrido‐Gracia³

et al. 2010

Neuroendocrinology

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Passive immunization against inhibin with an anti-inhibin serum (AIS) during the diestrous phase in cycling rats increased follicle-stimulating hormone secretion, stimulated the ovaries and reduced the magnitude of the luteinizing hormone (LH) surge in the afternoon of proestrus. The involvement of gonadotrope progesterone receptor (PR) expression/action in the inhibitory effects of the follicle-stimulating hormone-dependent putative ovarian factor gonadotropin surge-attenuating factor on preovulatory LH secretion was studied in the absence of circulating free inhibin. Proestrous pituitaries from rats injected with AIS or a non-immune serum (NIS) were studied for determination of PR-AB and PR-B mRNAs by RT-PCR and PR-B and PR-A isoform proteins by Western blot. In addition, pituitaries from AIS- and NIS-injected rats were incubated and studied for PR-dependent LH secretion parameters: LH-releasing hormone (LHRH)-stimulated LH secretion, progesterone-potentiated LHRH-stimulated LH secretion and LHRH self-priming. Also, the effects of the antiprogestagen RU486 on these LH secretion parameters were evaluated and compared with those of AIS. Finally, gonadotrope PR phosphorylation was evaluated by immunohistochemistry. Results showed that the hyperstimulated ovaries of AIS-injected rats produce a factor, different from inhibin, that blocked LHRH self-priming and P-potentiation of LHRH-stimulated LH secretion. These effects were not due to decreased pituitary PR mRNAs, PR protein expression or PR protein B/A ratio. The inhibitory effect of AIS on PR-dependent LH secretion seemed to be due to gonadotrope PR dephosphorylation. Taken together, the findings indicated that the putative gonadotropin surge-attenuating factor affected LH surge through an inhibition of PR phosphorylation/action but not PR expression.

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Induction of Ovulation in Hypophysectomized Rats by Progesterone*

Cited by 43 publications

References 0 publications

Temporal Changes Occur in the Neuroendocrine Control of Gonadotropin Secretion in Aging Female Rats: Role of Progesterone1

Temporal Changes Occur in the Neuroendocrine Control of Gonadotropin Secretion in Aging Female Rats: Role of Progesterone1

Preovulatory changes in luteinizing hormone releasing hormone concentrations in peripheral plasma in constant estrous rats at induced ovulation.

Immunoneutralization of Inhibin in Cycling Rats Increases Follicle-Stimulating Hormone Secretion, Stimulates the Ovary and Attenuates Progesterone Receptor-Dependent Preovulatory Luteinizing Hormone Secretion

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