A sensitive bioassay for luteinizing hormone-like activity applied to systemic plasmas of foetal rats

Abstract

A sensitive bioassay for plasma LH-like activity has been developed by utilization of the testosterone response of foetal rat testes to gonadotrophic stimulation in vitro. The volume of plasma required for the assay and the target organ make the method suitable for bioassays of circulating LH-like activity in foetal rat plasma. When applied to foetal plasmas, the method has shown that castration performed on day 19 of gestation induced 24 h later an increase in the LH-like activity of the plasma and that decapitation under the same conditions led to a decrease in this activity in male foetuses.

Correlative Study on Sex Differences in Pituitary Luteinizing Hormone Content and the Number of Immunoreactive Luteinizing Hormone Cells in Perinatal Rats

“…It has also been reported that in males pituitary LH content is almost unchanged from the late gestational period to birth [7], In accord with their results, the LH synthetic capacity of the male rat pitu itary between day 21.5 of gestation and the day of birth was far lower when compared to that of the female gland (table I). All of these data together with a notable change of pitu itary cells after castration in utero indicate the possibility of testicular negative feedback in male rats during late gestation [20,23], On the other hand, the more pronounced suppression of the male pituitary during the 1st and 4th postnatal days is most likely to result from the postpartum testosterone surge [7], Although pituitary LH content of neona tal rats has been relatively well investigated, that of fetal rats has been reported less fre quently. Nemeskeri et al [21] have detected immunoreactive LH in rat fetuses as early as day 12 of gestation.…”

Attempts for Identification of a Chorionic Gonadotrophin-Like Bioactivity in the Rat Placenta Which Stimulates the Testosterone Secretion of the Fetal Testis in vitro

“…The bioactivities of the placental extracts were measured with the fetal rat testis testosterone (FRTT) bioassay previously described [10,11]. This method is based on the measurement of the increase of the testosterone secreted by the fetal rat testis in vitro, in response to the addition of placental extracts to be assayed.…”

“…Brains from 18.5-dayold fetus were extracted to evaluate the blank value: one brain per ml increased testosterone secretion by 1.16 and 1.40-fold over control. Maximum biological response of the testis to gonadotrophic stimulation corresponds to a 7-to 8-fold increase in testosterone secretion [10].…”

“…Since these discrepancies could be related to the differences in sensitivity and in speci ficity of the biological tests used, we reinves tigated the existence of rCG with the sensitive bioassay that we had previously developed [10,11 ]. It is based on the measurement of the increase in testosterone secretion by the fetal testis in vitro in response to the addition of the solution to be assayed.…”

Pituitary-Gonadal Interactions in Perinatal Rats: Relationships of Plasma Luteinizing Hormone and Testosterone Concentrations, and Pituitary Levels of LH Subunit mRNAs

“…Injection of T to pregnant rats causes a decrease in testicular T of male fetuses from day f 19.5 onwards, as a sign of functional negative feedback [11], Fetal decapitation reduces basal in vitro secretion of testicular T from day f20.5 onwards [12,13], and on day f22.5, but not on day f20.5, plasma T concentration is decreased [13]. Castration on day f 19.5 causes a 2-fold increase within 24 h in the serum LH-like bioactivity, and decapitation at the same time point decreases this activity [ 14], Taken together, the above results suggest that the gonadal negative feedback regulation of pituitary function develops in the male rat during the last 3 days of gestation. However, there is still some uncertainty about the exact timing of these events.…”