Neuroendocrinology

Leptin Prevents Fasting-Mediated Reductions in Pulsatile Secretion of Luteinizing Hormone and Enhances Its Gonadotropin-Releasing Hormone-Mediated Release in Heifers

Abstract
We tested the hypotheses that leptin could prevent fasting-mediated reductions in pulsatile secretion and modify GnRH-mediated release of LH in heifers approaching puberty. Thirteen crossbred, prepubertal heifers (13.5 - 16 mo; 280 - 350 kg) exhibiting frequencies of pulses of LH between 0.67 and 1 pulse/h, were assigned randomly to two groups: 1) Control (n = 6); fasted for 72 h with s.c. injections of saline at 12-h intervals, and 2) Leptin (n = 7); fasted for 72 h with s.c. injections of oleptin (19.2 µg/kg) at 12-h intervals. Blood samples were collected intensively for 6h on Days 0 and 3. This was followed on Day 3 with sequential administration of physiological (0.0011 µg/kg, i.v.) and pharmacological (0.22 µg/kg, i.v.) doses of GnRH and additional blood sampling. Leptin treatment increased (P = 0.0003) plasma concentrations of leptin 5-6 fold compared to controls. Fasting caused a marked decline (P = 0.01) between Day 0 and 3 in the frequency of LH pulses in controls; however, this effect was prevented in the Leptin group, with pulse frequency increasing (P < 0.008) from Day 0 to 3. Leptin treatment increased GnRH-induced release of LH at both low (P = 0.04) and high (P = 0.02) doses. Plasma insulin and IGF-1 were reduced by fasting and unaffected by leptin. Leptin increased mean concentrations of GH. Results indicate, for the first time, that exogenous leptin can prevent fasting-mediated reductions in the frequency of LH pulses and modify GnRH-mediated release of LH in intact, prepubertal heifers.

Key words: Neuroendocrinology • Gonadotropin-releasing hormone • Leptin • Luteinizing hormone • Pituitary hormones

This article has been cited by other articles:

				C. Crane, N. Akhter, B. W. Johnson, M. Iruthayanathan, F. Syed, A. Kudo, Y.-H. Zhou, and G. V. Childs Fasting and Glucose Effects on Pituitary Leptin Expression: Is Leptin a Local Signal for Nutrient Status? J. Histochem. Cytochem., October 1, 2007; 55(10): 1059 - 1073. [Abstract] [Full Text] [PDF]

				C. L. Gasser, G. A. Bridges, M. L. Mussard, D. E. Grum, J. E. Kinder, and M. L. Day Induction of precocious puberty in heifers III: Hastened reduction of estradiol negative feedback on secretion of luteinizing hormone J Anim Sci, August 1, 2006; 84(8): 2050 - 2056. [Abstract] [Full Text] [PDF]

				M. N. Maciel, D. A. Zieba, M. Amstalden, D. H. Keisler, J. P. Neves, and G. L. Williams Chronic administration of recombinant ovine leptin in growing beef heifers: Effects on secretion of LH, metabolic hormones, and timing of puberty J Anim Sci, October 1, 2004; 82(10): 2930 - 2936. [Abstract] [Full Text] [PDF]

				D.A. Zieba, M. Amstalden, S. Morton, M.N. Maciel, D.H. Keisler, and G.L. Williams Regulatory Roles of Leptin at the Hypothalamic-Hypophyseal Axis Before and after Sexual Maturation in Cattle Biol Reprod, September 1, 2004; 71(3): 804 - 812. [Abstract] [Full Text] [PDF]