Pregnant mare serum gonadotrophin: ratio of follicle-stimulating hormone and luteinizing hormone activities measured by radioreceptor assay.

This study develops specific radioreceptor assays to measure follicle-stimulating hormone (FSH) and luteinizing hormone (LH) activities in pregnant mare serum gonadotropin (PMSG). The research found that the FSH:LH ratio remains constant throughout a particular stage of gestation and differs when produced by cultured equine trophoblast cells or partially purified serum extracts of PMSG.

Introduction to Radioreceptor Assays for FSH and LH

• The research develops a specific kind of assay— radioreceptor assays— used for the purpose of measuring activity of two hormones: FSH and LH.
• These assays make use of tissue receptors from rat testes and highly purified human FSH and LH samples. These samples serve as standards in the assay measurement.
• These assays are developed to measure the FSH-like and LH-like activities present in pregnant mare serum gonadotropin (PMSG), a hormone produced in the placenta of pregnant mares.

Constant FSH:LH Ratio in Pregnancy

• Upon using their developed assays to measure FSH and LH concentrations in the serum of six pregnant pony mares, the researchers discovered that the ratio of these two hormones did not significantly change between different mares.
• This ratio also remained constant between days 40 and 80 of gestation with an averaged value of 1.45 ± 0.04 (standard error of mean).

FSH:LH Ratio in Different Conditions

• Apart from looking at the FSH:LH ratio during gestation, the researchers also observed this ratio in different conditions.
• When PMSG was produced by cultured equine trophoblast cells— cells forming the outer layer of a blastocyst— the FSH:LH ratio was found to be lower at 0.72 ± 0.03 SEM.
• When observing the ratio in partially purified serum extracts of PMSG, it was noted to be 1.08 with a range from 0.87 to 1.30.

Conclusions and Implications

• The key finding of the study suggests that the FSH:LH ratio remains constant throughout a specific stage of gestation—days 40 to 80.
• However, this ratio can vary based on whether PMSG is produced by cultured equine trophoblast cells or derived from partially purified serum extracts of PMSG. This information provides potential for further research into the role of these hormone variations in horse reproduction and embryo development.