title: Seasonal fluctuation in diurnal rhythms of luteinizing hormone secretion in ewes during the mid-luteal phase of the oestrous cycle.
abstract: Diurnal and seasonal fluctuations were detected in luteinizing hormone (LH) interpulse interval, but not amplitude, in ewes examined during the mid-luteal phase of an oestrous cycle at five stages of the breeding season. Daytime and night-time LH interpulse intervals were greater in the early and late than in the mid-breeding season (P < 0.05). During the early and late breeding season, LH interpulse interval was less during daylight than during darkness (P < 0.05). Toward the mid-breeding season, interpulse interval decreased during daytime earlier in the season than the night-time decrease. It was concluded that the diurnal fluctuations observed are a component of a circannual rhythm in LH secretion resulting from gradual seasonal transitions in photoperiodic drive to, or an endogenous rhythm in, the hypothalamic-pituitary axis in ewes.
authors: Veterinary Physiological Sciences, University of Saskatchewan, Saskatoon, Canada.
authors: W D
authors: WD
authors: Currie
authors: R J
authors: RJ
authors: Medhamurthy
authors: S J
authors: SJ
authors: Cook
authors: N C
authors: NC
authors: Rawlings
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D005260:Female; D008183:Luteal Phase / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D012621:Seasons; D012636:Secretory Rate / Q000502:physiology; D012756:Sheep / Q000502:physiology*
chemical_list: D007986:Luteinizing Hormone