Endocrine responses in the llama to copulation

Nine adult female llamas were used to determine the time course for secretion of luteinizing hormone (LH) and estradiol-17β (E 2) following a single copulation (average 18 min), and progesterone (P 4) during the development of the subsequent luteal phase. Heparinized blood samples were obtained through an indwelling jugular cannula at 15-min intervals for up to 24 h following copulation and then once daily for up to 10 d. Luteinizing hormone, assayed by radioimmunoassay (RIA) using a monoclonal antibody 518B7 against the β subunit of bovine LH, was determined at 15 min intervals for 24 h following copulation. Estradiol-17β was determined by RIA at 4-h intervals following copulation, then daily, while P 4 values were determined daily by enzyme immunoassay. A significant increase in LH concentration was observed by 15 min after the onset of copulation, with the peak of the preovulatory surge of LH occurring at 2 h; values were basal by 7 h after copulation. Estradiol-17β values, unchanged through 18 h after copulation, tended to decline at 22 h (24 h, P