Circadian, circhoral and seasonal variation in patterns of gonadotrophin secretion in geldings.

The study investigates patterns of hormone secretion in geldings (castrated male horses) to understand circadian (daily), circhoral (hourly) and seasonal variations. The research found that these horses experience regular fluctuations in hormone levels and that the secretion patterns are not affected by the absence of gonadal steroids, a result of castration.

Horse Selection and Blood Sample Collection

• The research involved 5 mixed-breed geldings who had been castrated for a long time.
• Blood samples were gathered from these horses during five different 24-hour periods spread from May 1984 to April 1985.
• Each sampling period started at 09:00, with samples collected every 15 minutes for the first 8 hours. Thereafter, samples were collected every hour for the remaining 16 hours.

Hormone Analysis

• The researchers examined plasma levels of LH (luteinizing hormone) and FSH (follicle-stimulating hormone) using a method called radioimmunoassay (RIA).
• They assessed seasonal changes in hormone concentrations as well as the frequency and intensity of hormone secretory pulses.
• Neither LH nor FSH secretion showed any daily variation, but hourly changes in the secretion of these hormones were observed.

Comparison to Intact Stallions

• The average LH and FSH concentrations in these long-term castrated geldings were found to be similar to those measured in stallions that had not been castrated.
• Fluctuations in LH concentration over a year varied significantly, reaching its peak value in late April and its lowest in November.
• FSH pulse frequency also showed seasonal variance, with a peak in August and a trough in May.
• However, the intensity (amplitude) of LH and FSH secretion episodes did not change with the season.

Conclusion of the Study

• The study concluded that long-term castrated geldings do exhibit pulsatile (regular fluctuating) secretion of gonadotrophins.
• Furthermore, the researchers found that this hormone secretion experiences seasonal variation even in the absence of gonadal steroids, normally present in intact males but not in geldings due to castration.