Hormonal changes in the immature rat after administration of pregnant mare serum gonadotrophin: influence of body weight.
Abstract: 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.
Publication Date: 1983-10-01 PubMed ID: 6313840DOI: 10.1677/joe.0.0990063Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research studies the impact of body weight on hormonal reactions in immature rats after administration of pregnant mare serum gonadotrophin (PMSG). Key findings include differences in hormonal reactions based on body weight and the identification of a potentially inactive form of LH in rats under 60g that do not ovulate.
Background and Research Motivation
- The researchers had previously observed that pregnant mare serum gonadotrophin (PMSG) induces ovulation only in rats weighing over 60 g. This study aims to further understand the hormonal changes that occur in the rats.
Research Approach
- The research compared plasma hormone concentrations in rats treated with PMSG that weighed over and under 60 g. The samples for the measurements were taken on the day of the expected preovulatory LH surge, between 13:00 and 22:00.
Hormonal Changes Based on Weight
- Prolactin and corticosterone levels were found to be lower in the lighter (under 60g) group compared to the heavier (over 60g) group.
- The midday pulse of GH, which was detected in the over-60 g animals, did not occur in the under-60 g group.
- Rats under 60g showed slightly higher levels of ACTH and lower corticosterone concentrations, indicating adrenal insensitivity.
- However, the levels of oestradiol, progesterone, and TSH were the same in both groups.
Focus on LH and FSH
- The research also reveals that the under-60 g rats that do not ovulate secrete a pleiomorphic form of LH, which they suspect might be inactive.
- Since progesterone secretion is under LH control, the researchers hypothesize that this ‘inactive’ pleiomorphic form of LH must have steroidogenic activity.
- There was also an indication that the under-60 g rats secreted a pleiomorphic form of FSH.
Hormones and Puberty
- The research explored the connections between hormones and puberty, given that prolactin, corticosterone, and GH have been reported to influence natural puberty.
- In the under-60 g rats that were unresponsive, plasma levels of these three hormones were found to be low, indicating that they may also influence precocious puberty induced by PMSG.
- The release of these hormones may depend on the physical maturity of the animal as represented by body weight.
Cite This Article
APA
Wilson CA, ter Haar MB, Bonney RC, Buckingham J, Dixson AF, Yeo T.
(1983).
Hormonal changes in the immature rat after administration of pregnant mare serum gonadotrophin: influence of body weight.
J Endocrinol, 99(1), 63-76.
https://doi.org/10.1677/joe.0.0990063 Publication
Researcher Affiliations
MeSH Terms
- Adrenocorticotropic Hormone / metabolism
- Animals
- Body Weight
- Corticosterone / metabolism
- Female
- Gonadotropins, Equine / pharmacology
- Growth Hormone / metabolism
- Prolactin / metabolism
- Rats
- Rats, Inbred Strains
- Sexual Maturation
Citations
This article has been cited 2 times.- Andreu CV, Buscaglia CA, Parborell F, Stein P, Tesone M. Regulation of ovarian follicle differentiation in gonadotrophin-stimulated rats. Endocrine 1997 Apr;6(2):145-51.
- Rivest RW. Sexual maturation in female rats: hereditary, developmental and environmental aspects. Experientia 1991 Oct 15;47(10):1027-38.
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