Effect of maternal treatment with altrenogest on pituitary response to exogenous GnRH in pubertal stallions.

This study investigates the impact of the drug altrenogest on the pituitary response to an external hormone (GnRH) in young male horses (colts). The research suggests that the levels of two vital hormones (LH and FSH) fluctuate over time in response to the drug, but it is not significantly disrupted.

Overview of the Experiment

• The researchers conducted an experiment involving 8 quarter horse colts, monitoring them from 32 weeks to 96 weeks of age.
• The colts were divided into two groups based on whether they were born from dams (female horses) that were given daily doses of either neobee oil (the control substance) or altrenogest, a synthetic hormone used to manage reproductive cycles in mares.
• The dosages were administered based on body weight – 2 ml of the respective substance per 50 kg of weight.

Gonadotropin-Releasing Hormone (GnRH) Challenges

• The GnRH challenges involved administering 5 micrograms of GnRH per kilogram of body weight at eight-week intervals.
• This was done to estimate the pituitary content of luteinizing hormone (LH), a hormone that triggers the release of eggs from a female’s ovaries and aids the production of sperm in males.

Data Collection

• Blood samples were taken several times before and after administering GnRH, and the concentration levels of both LH and follicle-stimulating hormone (FSH) were determined.
• Baseline levels were taken to be the average of the two pre-GnRH samples.

Results of the Study

• The study found that altrenogest did not significantly affect the baseline concentration levels of LH and FSH.
• The serum concentration of LH reported a decline from 40 to 56 weeks, followed by an increase between 72 and 80 weeks.
• The base level concentration of FSH also decreased from 32 to 56 weeks and subsequently fluctuated widely after that.
• In both groups, the maximum LH response to GnRH declined steadily from 48 to 64 weeks but remained relatively consistent afterwards.
• In a similar manner, the highest FSH response to GnRH decreased from 32 to 64 weeks then maintained a steady level.
• Despite the occasional increase at 72 weeks, the GnRH-induced release of the gonadotropic hormones (LH and FSH) remained low in general.