title: Plasma LH levels in the mare during the oestrous cycle.
abstract: Plasma levels of LH were determined by heterologous radioimmunoassay utilizing highly purified equine LH as standard. Samples were taken regularly from eleven mares for twenty-six oestrous cycles over a period of 10 weeks. The mean cycle length was 20-5 +/- 3-1 (S.D.) days, and ovulation occurred on average 4-3 +/- 1-6 (S.D.) days from the time heat was first detected. Levels of LH were persistently low from Days 5 to 16 of the cycle (ovulation = Day 0). They then increased slowly over a number of days and continued to rise beyond the levels observed at any time during the immediate preovulatory period or the day of ovulation. A significant decrease from peak levels was not observed until the 3rd day after ovaulation, from which time levels continued to decline toward dioestrous values by an apparent first-order decay process with a half-life of 1-8 days. The pattern of plasma LH in the mare differs from that reported for other species and it is suggested that persistance of high concentrations of LH results from a long half-life of the endogenous LH. This in turn may be responsible for the relatively large number of second ovulations detected in many oestrous cycles.
mesh_terms: D000818:Animals; D004971:Estrus; D005260:Female; D006736:Horses / Q000097:blood*; D007986:Luteinizing Hormone / Q000097:blood*; D010060:Ovulation; D011247:Pregnancy; D011863:Radioimmunoassay; D013997:Time Factors
chemical_list: D007986:Luteinizing Hormone