Radioimmunoassay and in-vitro bioassay of serum LH throughout the equine oestrous cycle.

This research explored levels of Luteinizing Hormone (LH) in horses during their estrous cycle using two testing methods: radioimmunoassay and in-vitro bioassay. The study found differences in LH levels before and after ovulation, though measurements were not always consistent, suggesting the hormone’s role in ovulation may be more complex than thought.

Methods of the Research

• This study involved mares being bled once daily throughout a cycle. In some cases, the mares were bled three times daily from the first day of estrus to the second day after ovulation. The blood samples were then used to measure the LH hormone levels.
• The researchers used two different testing methods to measure LH levels – a heterologous radioimmunoassay and an in-vitro bioassay. The in-vitro bioassay was based on LH-stimulated testosterone production by mouse Leydig cells. These two methods allowed researchers to examine the bio-active and immuno-active LH during the estrous cycle.

Findings of the Research

• The research found that patterns of bio- and immuno-active LH during the estrous cycle were similar, but not identical. This suggests that there were variations in the levels and activity of this hormone during the cycle.
• The study also found that the ratio of biological to immunological activity during the LH surge was significantly higher before than after ovulation.
• However, there was also significant individual variation in the mean ratio of biological to immunological activity, as well as in the extent and duration of the peri-ovulatory change in this ratio.

Implications of the Research

• This research indicates that the radioimmunoassay system can be useful for measuring LH levels in the normal cycle, but there can be circumstances in which this method alone may not provide adequate information about LH stimulation levels at target tissues.
• The changes in the ratio of biological to immunological activity during the LH surge suggest differences in the circulating molecule, which could be important for understanding the control of ovulation.
• The in-vitro bioassay may be a useful method for studying the biological role of LH in mares and the effects of different forms of this polymorphic hormone.