Androgen and progesterone effects on follicle-stimulating hormone and luteinizing hormone secretion in anestrous mares.

The research investigates the impact of certain hormones on how anestrous (non-ovulating) mares (female horses) secrete two other hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), following treatment with gonadotropin-releasing hormone (GnRH). The results suggest that certain treatments can influence the FSH response but not the LH response to GnRH administration.

Research Methodology and Treatment Groups

• The experiment involved anestrous lighthorse mares which were put into different groups and treated with various hormones (DHT, P, DHT+P, T) or a vehicle control-substance. There were 4 mares in each group.
• Every day from Day 1, blood samples were collected from the mares.
• On Day 4, all the mares were given a pre-treatment injection of GnRH. Blood was drawn regularly to examine the changes in FSH and LH concentrations.
• On Day 18, all mares were again administered GnRH and blood samples were collected frequently.

Observations from the Experiment

• After treatment, the mares who received DHT, P, or T had increased plasma concentrations of those hormones, approximately to 1.5 ng/ml, during the last 10 days of treatment.
• There were no significant effects seen from the treatment on LH or FSH concentrations in daily blood samples.

FSH and LH Responses after Gonadotropin-Releasing Hormone (GnRH) Injection

• Those mares that were treated with T or DHT+P secreted about 65% more FSH in response to the post-treatment GnRH injection, as compared to their response to the pre-treatment GnRH injection.
• The FSH response to the second GnRH injection was not altered significantly in mares treated with DHT or P, or the control group.
• No effect was observed on LH secretion, regardless of the steroid treatment given, following administration of GnRH.
• Averaged out for all mares, around 94 times more FSH than LH was secreted in response to an injection of GnRH.