Radioimmunoassay and in-vitro bioassay of serum LH throughout the equine oestrous cycle.
Mares were bled once daily throughout a cycle, or 3 times daily from the first day of oestrus to the 2nd day after ovulation. LH was measured by heterologous radioimmunoassay and by an in-vitro bioassay based on LH-stimulated testosterone production by mouse Leydig cells. The patterns of bio- and immuno-active LH during the oestrous cycle were similar but not identical, so that in both groups of mares the ratio of biological: immunological (B:I) activity during the LH surge was significantly higher before than after ovulation (P less than 0 . 001). Considerable individual variation in cycle mean B:I ratio, and extent and duration of the peri-ovulatory change in ratio was observed. While the similarity between bio- and immuno-assay LH profiles indicates that the RIA system used can provide useful measurements of LH in the normal cycle, the significant differences between the two profiles suggest that there are circumstances in which RIA alone may not give adequate information on the level of LH stimulation at target tissues. These changes in B:I ratio during the LH surge suggest qualitative differences in the circulating molecule which may be physiologically important in the control of ovulation. The in-vitro bioassay appears to be a useful method to study the biological role of LH in the mare and investigate the roles of the various forms of this polymorphic hormone.
D000818:Animals; D001681:Biological Assay; D004971:Estrus; D005260:Female; D006736:Horses / Q000502:physiology*; D007985:Leydig Cells / Q000187:drug effects / Q000378:metabolism; D007986:Luteinizing Hormone / Q000097:blood*; D008297:Male; D051379:Mice; D011247:Pregnancy; D011863:Radioimmunoassay; D013739:Testosterone / Q000096:biosynthesis
D013739:Testosterone; D007986:Luteinizing Hormone