Anterior Pituitary Leptin Expression Changes in Different Reproductive States: Stimulation, In Vitro, by Gonadotropin Releasing Hormone (GnRH)

Noor Akhter ^1*, Brandy W. Johnson ¹, Christopher Crane ¹, Mary Iruthayanathan ¹, Yi-Hong Zhou ¹, Akihiko Kudo ¹ and Gwen V. Childs ¹

¹ Department of Neurobiology and Developmental Sciences, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, Arkansas (NA,BWJ,CC,GVC); Division of Endocrinology, Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, The University of Iowa, Iowa City, Iowa (MI); Department of Neurological Surgery, University of California Irvine, Orange, California (Y-HZ); and Department of Anatomy, Kyorin University School of Medicine, Tokyo, Japan (AK)

^* To whom correspondence should be addressed. E-mail: akhternoor{at}uams.edu.

Submitted on August 7, 2006
Accepted on 28 September 2006

	Abstract

This study was designed to learn more about the changes in expression of rat anterior pituitary (AP) leptin during the estrous cycle. QRT-PCR assays of cycling rat AP leptin mRNA showed 2--fold increases from metestrus to diestrus followed by an 86% decrease on the morning of proestrus. Percentages of leptin cells increased in proestrus and pregnancy to 55-60% of AP cells. Dual labeling for leptin proteins and growth hormone (GH) or gonadotropins, showed that the rise in leptin protein-bearing cells from diestrus to proestrus was mainly in GH cells. Only 10-20% of leptin cells in male or cycling female rats coexpress gonadotropins. In contrast, 50-73% of leptin cells from pregnant or lactating females coexpress gonadotropins and only 19% coexpress GH, indicating plasticity in the distribution of leptin. Leptin cells expressed GnRH receptors; and estrogen and GnRH together increased the coexpression of leptin mRNA and gonadotropins. GnRH increased cellular leptin proteins 3-4x and mRNA 9.8x in proestrous rats and stimulated leptin secretion in cultures from diestrous, proestrous and pregnant rats. These regulatory influences, and the high expression of AP leptin during proestrus and pregnancy, suggest a supportive role for leptin during key events involved with reproduction.

Key Words: leptin, anterior pituitary, gonadotropes, somatotropes, gonadotropin-releasing hormone, estrous cycle, pregnancy, lactation, males, rat, QRT-PCR, in situ hybridization, immunolabeling

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