Pituitary and Plasma Levels of Luteinizing Hormone and Prolactin in the Immature Female Rat Following Administration of Pregnant Mares’ Serum

Johnson, Linda Y; Reíter, Russel J.; Blask, David E.

doi:10.1159/000122426

Cited by 3 publications

(2 citation statements)

References 14 publications

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“…After PMSG treatment prolactin release was stimulated and significantly higher concentrations were seen at all times (except 15.00 h) between 14.00 and 21.00 h in the over-60 g rats. There was, however, no obvious preovulatory peak as has been noted by others (Johnson et al 1975). In the under-60 g rats prolactin levels were only slightly (and never significantly) higher than those in the untreated animals.…”

Section: Prolactin (Fig 2)supporting

confidence: 68%

“…This is followed by an increase in hypo¬ thalamic gonadotrophin releasing hormone concentration (Sorrentino & Sundberg, 1975) and stimulation of the release of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin from the pituitary gland (Johnson, Reiter & Blask, 1975;Sasamoto & Johke, 1975), and various gonadal and adrenal steroids, including progesterone and testosterone, at 52-56 h after PMSG (Wilson et al 1974;). Ovulation occurs 12h after the release of gonadotrophin.…”

Section: Introductionmentioning

confidence: 99%

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Hormonal changes in the immature rat after administration of pregnant mare serum gonadotrophin: influence of body weight

Wilson¹,

Haar²,

Bonney³

et al. 1983

Journal of Endocrinology

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We have shown previously that pregnant mare serum gonadotrophin (PMSG) induces ovulation only in rats weighing over 60 g on the day of injection. The under-60 g rats do not ovulate although they secrete a preovulatory surge of a pleiomorphic form of LH. Presumably this pleiomorph is inactive. Comparisons were made of plasma hormone concentrations in rats treated with PMSG that weighed over and under 60 g. The measurements were made on samples taken between 13.00 and 22.00 h on the day of the expected preovulatory LH surge. Prolactin and corticosterone levels were lower in the lighter group compared with the heavier group. A midday pulse of GH detected in the over-60 g animals did not occur in the under-60 g group. Levels of ACTH were slightly higher in the under-60 g rats and together with the low corticosterone concentrations indicate adrenal insensitivity. Oestradiol, progesterone and TSH concentrations were the same in the two groups. Since progesterone secretion is under LH control, the 'inactive' pleiomorphic form of LH must have steroidogenic activity. There was an indication that the under-60 g rats also secreted a pleiomorphic form of FSH. Reports in the literature indicate that prolactin, corticosterone and GH have a positive modulatory influence on natural puberty. They may also influence precocious puberty induced by PMSG, since in the unresponsive under-60 g rat plasma levels of these three hormones were low. Perhaps the release of one or more of these hormones is dependent upon the physical maturity of the animal as represented by body weight.

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Section: Prolactin (Fig 2)supporting

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Hormonal changes in the immature rat after administration of pregnant mare serum gonadotrophin: influence of body weight

Wilson¹,

Haar²,

Bonney³

et al. 1983

Journal of Endocrinology

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The Preovulatory Prolactin Surge: An Evaluation of the Role of Dopamine*

Arbogast

Ben‐Jonathan

1988

Endocrinology

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This study examined the contribution of dopamine (DA) to the control of PRL secretion during the preovulatory PRL surge. Immature female rats were injected with PMSG on day 28. At selected times during the periovulatory period, rats were injected with different pharmacological agents, and jugular blood was collected at frequent intervals. Blood PRL levels in vehicle-treated rats were low on the morning of day 30, rose 15- to 20-fold to peak levels from 1400-1500 h, were maintained at a plateau from 1900-2300 h, and were reduced to basal levels on the morning of day 31. Haloperidol, a DA antagonist, induced a 20-fold rise in PRL before the surge, a 2-fold rise above peak PRL levels at 1500 h, and a 50-fold rise on the morning of day 31. In contrast, haloperidol failed to alter PRL release during the plateau phase. Apomorphine, a DA agonist, reduced PRL levels when injected during either the peak or the plateau phase. Injection of 5-hydroxytryptophan, a serotonin precursor, increased PRL levels at all times examined. Anterior pituitary PRL content was reduced to 30% and 10% of the presurge level during the peak and plateau phases, respectively, but increased on the morning of day 31. Basal PRL release by hemipituitaries incubated in vitro paralleled the anterior pituitary PRL content, with markedly less PRL secreted during the peak and plateau phases compared to the presurge period. However, the percent inhibition of PRL release by hemipituitaries incubated with 50 nM DA was similar at all times tested. These data indicate that the peak PRL surge occurs in spite of DA input to the anterior pituitary, a continued responsiveness to DA inhibition, and a diminishing pituitary PRL content. We conclude that a nondopaminergic mechanism, possibly involving a PRL-releasing factor, is responsible for the peak. The plateau phase probably results from an absence of DA input to the anterior pituitary together with a reduction in the releasable pool of PRL. The termination of the PRL surge is caused by the restoration of DA input.

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The Preovulatory Prolactin Surge Is Prolonged by a Progesterone-Dependent Dopaminergic Mechanism*

Arbogast

Ben‐Jonathan

1990

Endocrinology

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The preovulatory PRL surge consists of a sharp peak, a prolonged plateau, and a termination phase. This study examined the role of progesterone in maintaining elevated PRL release during the plateau phase and its effect on dopaminergic (DA) neuronal activity. Immature rats were injected with PMSG on day 28, and blood was collected during the periovulatory period. Plasma estradiol levels were elevated before and during the PRL peak and declined during the plateau. Plasma progesterone levels were low before and during the peak, rose 4- to 5-fold during the plateau, and decreased to basal levels at the termination phase. In a second experiment rats were subjected to acute ovariectomy (OVEX) or sham surgery (SHAM) just before the onset of the PRL surge. Some OVEX rats were either immediately implanted with an estradiol-containing capsule or given three injections of progesterone during the time of the plateau phase. Blood PRL levels in SHAM rats showed the typical peak, plateau, and termination phases. The PRL peak was evident, but the plateau was missing in OVEX rats with or without estradiol treatment. Replacement with progesterone restored the plateau. In a third experiment, the stalk-median eminence, posterior pituitary, and striatum were removed during the time of the midplateau phase. Tyrosine hydroxylase activity was determined in tissue homogenates by a coupled hydroxylation-decarboxylation assay. Tyrosine hydroxylase activity in the stalk-median eminence of SHAM and progesterone-treated OVEX rats was similar, but was significantly lower than that in OVEX rats with or without estradiol. Tyrosine hydroxylase activity in the posterior pituitary and striatum was unchanged. To assess the functional DA input to the anterior pituitary, haloperidol, a DA antagonist, was injected during the midplateau phase. It induced a 12- to 17-fold rise in plasma PRL in both untreated and estradiol-treated OVEX rats, but failed to increase PRL above the plateau levels in SHAM and progesterone-treated OVEX rats. We conclude that the plateau phase of the preovulatory PRL surge is dependent on the concomitant rise in progesterone. Progesterone probably acts by reducing the DA neuronal activity in the SME, resulting in an absence of functional DA input to anterior pituitary lactotrophs.

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Pituitary and Plasma Levels of Luteinizing Hormone and Prolactin in the Immature Female Rat Following Administration of Pregnant Mares’ Serum

Cited by 3 publications

References 14 publications

Hormonal changes in the immature rat after administration of pregnant mare serum gonadotrophin: influence of body weight

Hormonal changes in the immature rat after administration of pregnant mare serum gonadotrophin: influence of body weight

The Preovulatory Prolactin Surge: An Evaluation of the Role of Dopamine*

The Preovulatory Prolactin Surge Is Prolonged by a Progesterone-Dependent Dopaminergic Mechanism*

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