Changes in the endocrine system controlling reproduction in mature female rats neonatally exposed to a low dose of gamma irradiation.
Female rats which were exposed to a single low dose of gamma irradiation (6R or 15R) at the age of 8 days produce smaller litters when mature than untreated controls. The possibility that such an impaired reproductive performance could result from changes in the endocrine system was investigated. Plasma levels and hypophyseal contents of LH and FSH, plasma levels of testosterone and hypothalamic content of GnRH were determined. The responsiveness of the pituitary to a single injection of GnRH (50 ng/rat) given on day of proestrus was evaluated. The results indicated that plasma levels of FSH but not of LH were lower in the irradiated rats. This was accompanied by changes in the hypothalamic content of GnRH. The possibility that the pituitary was sensitive to gamma irradiation was excluded. Twenty five minutes after a single injection of GnRH a 2-5 fold increase in LH plasma levels was noticed in all the groups, thus indicating that the reduced fertility could not be attributed to hypophyseal malfunction but rather to an impaired hypothalamic stimulus. Moreover, the lower levels of FSH might result from the significantly elevated levels of testosterone which were observed in the irradiated rats. Apparently, neonatal exposure to a single low dose of gamma irradiation resulted in a new hormonal equilibrium which was responsible for the reduced fertility in such rats.
Freud
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Department of Radiochemistry, Nuclear Research Center-Negev, Beer-Sheva, Israel.
Sod-Moriah
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UA
D000818:Animals; D000831:Animals, Newborn; D004971:Estrus; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism*; D005720:Gamma Rays; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D011359:Proestrus; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D012098:Reproduction / Q000187:drug effects*; D013739:Testosterone / Q000097:blood / Q000378:metabolism*
D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone