Changes in the hypothalamic-hypophyseal axis of mares in relation to the winter solstice.

The research explored the changes within the hypothalamic-hypophyseal axis of mares, specifically focusing on the Gonadotrophin-releasing hormone (GnRH) concentrations around the winter solstice in relation to the seasonal anoestrus period.

Study Design and Methodology

• Researchers conducted an in-depth analysis of the fluctuations in GnRH concentrations in the hypothalamic tissue of mares, around the time of the winter solstice (22 December 1986).
• Six groups of mares were studied, each group containing 6 to 12 mares. Biopsies were taken from these mares 1 week before the winter solstice and at 1, 2, 3, and 12 weeks after the solstice.
• Pituitary gland, ovaries, hypothalamic tissues and blood samples were examined.

Findings

• The study did not find significant changes in weights of the anterior pituitary gland or concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) within the anterior pituitary gland.
• There was no remarkable change in the number or the mean diameter of the largest follicle, or in the serum concentrations of LH and FSH, from 1 week before to 3 weeks after the winter solstice. However, they found a notable increase by the 12th week.
• GnRH content and concentration in the median eminence were low 1 week before the winter solstice, gradually increased to a peak 1 week after the solstice, and then subsided to low levels again by the 12th week.
• The mean GnRH measurements for the weeks before, one week after, and 12 weeks after the winter solstice were 33.5, 117.7, and 29.8 ng GnRH, respectively.
• The study found a reciprocal pattern of change in the concentration of GnRH in the preoptic area of the hypothalamus.

This research sheds light on the role of the winter solstice in potentially impacting hormonal changes within the hypothalamic-hypophyseal axis in mares during their seasonal anoestrus period. The exact implications and potential for practical applications would require further research.