Biology of Reproduction, Vol 33, 324-334, Copyright © 1985 by Society for the Study of Reproduction

ARTICLES

Seasonal changes in pulsatile luteinizing hormone (LH) secretion in the ewe: relationship of frequency of LH pulses to day length and response to estradiol negative feedback

JE Robinson, HM Radford and FJ Karsch

Seasonal changes in pulsatile luteinizing hormone (LH) secretion in ovariectomized ewes were examined over the course of 2 yr in relation to annual changes in environmental photoperiod, shifts in response to estradiol negative feedback control of LH secretion, and timing of the breeding season. Under natural environmental conditions, the frequency of LH pulses in individual ovariectomized ewes changed gradually and in close association with the annual cycle of day length. As days became shorter in late summer and autumn, LH pulse frequency increased; conversely, as day length increased in late winter and spring, frequency declined. Under artificial conditions in which ovariectomized ewes were exposed to different photoperiods, a similar inverse relationship was observed between day length and LH pulse frequency. The seasonal changes in frequency of LH pulses in ovariectomized ewes, although symmetric with the annual photoperiodic cycle, were not temporally coupled to the dramatic shifts in response to estradiol feedback inhibition of LH secretion at the transitions between breeding season and anestrus. The feedback shifts occurred abruptly and at times when LH pulse frequency in ovariectomized ewes was at, or near, the annual maximum or minimum. The tight coupling between LH pulse frequency and photoperiod leads to the conclusion that there is a photoperiodic drive to the LH pulse-generating system of the ewe. The temporal dissociation between changes in this photoperiodic drive and the seasonal shifts in response to estradiol negative feedback support the hypothesis that the neuroendocrine basis for these two phenomena is not one and the same.

This article has been cited by other articles:

				J. T. Smith, L. M. Coolen, L. J. Kriegsfeld, I. P. Sari, M. R. Jaafarzadehshirazi, M. Maltby, K. Bateman, R. L. Goodman, A. J. Tilbrook, T. Ubuka, et al. Variation in Kisspeptin and RFamide-Related Peptide (RFRP) Expression and Terminal Connections to Gonadotropin-Releasing Hormone Neurons in the Brain: A Novel Medium for Seasonal Breeding in the Sheep Endocrinology, November 1, 2008; 149(11): 5770 - 5782. [Abstract] [Full Text] [PDF]

				A. L. Bogusz, S. L. Hardy, M. N. Lehman, J. M. Connors, S. M. Hileman, J. H. Sliwowska, H. J. Billings, C. J. McManus, M. Valent, S. R. Singh, et al. Evidence that {gamma}-Aminobutyric Acid Is Part of the Neural Circuit Mediating Estradiol Negative Feedback in Anestrous Ewes Endocrinology, June 1, 2008; 149(6): 2762 - 2772. [Abstract] [Full Text] [PDF]

				K. M. Breen, A. E. Oakley, A. V. Pytiak, A. J. Tilbrook, E. R. Wagenmaker, and F. J. Karsch Does Cortisol Acting Via the Type II Glucocorticoid Receptor Mediate Suppression of Pulsatile Luteinizing Hormone Secretion in Response to Psychosocial Stress? Endocrinology, April 1, 2007; 148(4): 1882 - 1890. [Abstract] [Full Text] [PDF]

				J. T. Smith, C. M. Clay, A. Caraty, and I. J. Clarke KiSS-1 Messenger Ribonucleic Acid Expression in the Hypothalamus of the Ewe Is Regulated by Sex Steroids and Season Endocrinology, March 1, 2007; 148(3): 1150 - 1157. [Abstract] [Full Text] [PDF]

				K. M. Breen and F. J. Karsch Does Season Alter Responsiveness of the Reproductive Neuroendocrine Axis to the Suppressive Actions of Cortisol in Ovariectomized Ewes? Biol Reprod, January 1, 2006; 74(1): 41 - 45. [Abstract] [Full Text] [PDF]

				N. Debus, K. M. Breen, G. K. Barrell, H. J. Billings, M. Brown, E. A. Young, and F. J. Karsch Does Cortisol Mediate Endotoxin-Induced Inhibition of Pulsatile Luteinizing Hormone and Gonadotropin-Releasing Hormone Secretion? Endocrinology, October 1, 2002; 143(10): 3748 - 3758. [Abstract] [Full Text] [PDF]

				G. M. Anderson, J. M. Connors, S. L. Hardy, M. Valent, and R. L. Goodman Thyroid Hormones Mediate Steroid-Independent Seasonal Changes in Luteinizing Hormone Pulsatility in the Ewe Biol Reprod, March 1, 2002; 66(3): 701 - 706. [Abstract] [Full Text] [PDF]

				M. Baratta, L.A. West, A.M. Turzillo, and T.M. Nett Activin Modulates Differential Effects of Estradiol on Synthesis and Secretion of Follicle-Stimulating Hormone in Ovine Pituitary Cells Biol Reprod, February 1, 2001; 64(2): 714 - 719. [Abstract] [Full Text]

				J. E. Robinson, R. A. Forsdike, and J. A. Taylor In Utero Exposure of Female Lambs to Testosterone Reduces the Sensitivity of the GnRH Neuronal Network to Inhibition by Progesterone Endocrinology, December 1, 1999; 140(12): 5797 - 5805. [Abstract] [Full Text]

				G. M. Anderson and G. K. Barrell Pulsatile Luteinizing Hormone Secretion in the Ovariectomized, Thyroidectomized Red Deer Hind Following Treatment with Dopaminergic and Opioidergic Agonists and Antagonists Biol Reprod, October 1, 1998; 59(4): 960 - 968. [Abstract] [Full Text]

				J.A. Clapper, J.L. Snyder, A.J. Roberts, D.L. Hamernik, and G.E. Moss Estradiol Increases Relative Amounts of Insulin-Like Growth Factor Binding Protein (IGFBP)-3 in Serum and Expression of IGFBP-2 in Anterior Pituitaries of Ewes Biol Reprod, July 1, 1998; 59(1): 124 - 130. [Abstract] [Full Text]

				D. C. Skinner and A. E. Herbison Effects of Photoperiod on Estrogen Receptor, Tyrosine Hydroxylase, Neuropeptide Y, and {beta}-Endorphin Immunoreactivity in the Ewe Hypothalamus Endocrinology, June 1, 1997; 138(6): 2585 - 2595. [Abstract] [Full Text] [PDF]