PHOTOSTIMULATION CHANGES THE PATTERN OF LUTEINIZING-HORMONE SECRETIONIN TURKEY HENS

Changes in the secretory pattern of luteinizing hormone (LH) were dete rmined in turkey hens during initiation of reproduction. Photosensitiv e hens were switched from a short day photoschedule of 6L:18D (light:d ark) to 14L:10D and serially bled six times during the next 6 weeks of photostimulation and early after ovulatory cycles had begun. The patt ern of LH secretion at 0-1 day of photostimulation was characterized b y a low baseline concentration of LH with numerous low frequency, high amplitude pulses. This pattern changed at Days 4-5 and 11-12 of photo stimulation (hens photostimulated but not yet laying) to a pattern cha racterized by a high baseline with few ill defined pulses of very shor t duration. Once the hens had initiated egg production, ovulatory surg es of LH (duration of 358 +/- 104 min) were superimposed on the basic pattern seen during photostimulation. The ascending limb of the ovulat ory surge was much shorter in duration than the descending limb. No di urnal variation was detected in baseline concentration before or durin g photostimulation or after egg production had begun. It was concluded that photosensitive turkey hens secrete LH in low frequency; high amp litude pulses superimposed on a low baseline. During photostimulation, this pattern changes to one characterized by a high baseline with few pulses of low amplitude and short duration. This pattern of secretion is stimulatory to the ovary and continues until egg laying begins whe n it is modified by ovulatory surges of LH, characterized by short dur ation ascending limbs and longer duration descending limbs, which are superimposed on the high baseline pattern noted during photostimulatio n. (C) 1994 Academic Press, Inc.