PARENT SESSION
NUTRITION AND REPRODUCTION

Monday, August 2, 2004
10:30 AM–12:30 PM
Buchanan Courtyard

(61) EXPRESSION OF LEPTIN RECEPTOR AND SUPPRESSOR OF CYTOKINE SIGNALING-3 IN ADENOHYPOPHYSIS OF NORMAL-FED AND FASTED COWS.

Amstalden, Marcel^{1, 2, 3}, Spencer, Thomas^{2, 3}, Harms, Paul², Keisler, Duane⁴, Williams, Gary^{1, 2, 3}, ¹ Animal Reproduction Laboratory, Beeville, TX² Department of Animal Science, College Station, TX³ Center for Animal Biotechnology and Genomics, College Station, TX⁴ Department of Animal Science, Columbia, MO

ABSTRACT- Leptin has been shown to communicate nutritional status to the central nervous system, including centers that control reproduction. Central or peripheral administration of leptin increases mean circulating concentrations of LH in fasted, but not in normal-fed cows (Amstalden et al. 2002; Zieba et al. 2003). This effect is mediated, in part, by direct actions on the adenohypophysis, because leptin increased basal release of LH from adenohypophyseal explants collected from fasted but not normal-fed cows (Amstalden et al. 2003). Expression of leptin receptor (LR) is increased in hypothalamus of nutritionally-restricted sheep, supporting the hypothesis that increased responsiveness to leptin might be attributed to an increased number of receptors. In contrast, resistance to leptin was associated with excessive expression of suppressor of cytokine signaling (SOCS)-3, an intracellular factor that inhibits LR signaling. In these studies, we investigated whether changes in LR and SOCS-3 in the adenohypophysis could account for the increased responsiveness of the hypothalamic-adenohypophyseal axis to leptin observed in fasted cows. Ten ovariectomized, estradiol-implanted cows were assigned to one of two groups: Normal-fed (n=5); or Fasted (fasted for 72 h; n=5). At the end of the dietary treatments, the adenohypophyses were collected. Real-time PCR was used to quantify the amount of LR and SOCS-3 mRNA, and in situ hybridization was used to localize LR mRNA in adenohypophysis of normal-fed and fasted cows. Expression of LR in adenohypophysis did not differ (P > 0.1) between normal-fed and fasted cows. In situ hybridization analysis for LR mRNA indicated expression throughout the adenohypophysis with no differences observed in normal-fed and fasted cows. Contrary to our hypothesis, SOCS-3 mRNA was increased (P < 0.05) in adenohypophysis of fasted cows. These results suggest that changes in LR and SOCS-3 mRNA do not account for the increased responsiveness of the hypothalamic-adenohypophyseal axis of fasted cows to leptin. (Supported by USDA-NRI 03-35203-13542)

KEY WORDS: Leptin receptor, Fasting, Adenohypophysis, SOCS-3