Submission Number: JIU-4-4-32

Abstract Number: 91

PREVIOUS FEED RESTRICTION AND INSULIN TREATMENT AFFECT LUTEAL FUNCTION IN THE IMMEDIATE POST-OVULATORY PERIOD IN GILTS: PROGESTERONE PRODUCTION IN VITRO AND mRNA EXPRESSION FOR KEY STEROIDOGENIC ENZYMES.

J Mao, FRCL Almeida, Susan Novak, BK Treacy, Walter T Dixon and George R Foxcroft*

Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada T6G 2P5. ¹

Abstract:
Subnormal luteal function in the pig has been suggested as one cause for nutritionally-induced infertility. Luteal tissue recovered 12-20 h after ovulation from previously feed-restricted and insulin-treated gilts (n=44) was used to determine progesterone production in vitro (PP) and mRNA expression for key enzymes. Time of feed restriction (first or second week of the estrous cycle) did not affect PP, or mRNA expression. However, luteal tissue from gilts restricted in the first but not the second week responded to LH stimulation by increasing PP (P<0.05). Insulin treatment during the second week of restriction increased PP, restored responsiveness to LH stimulation, up-regulated StAR protein, P450scc, and 3beta-HSD mRNA expression and down-regulated TIMP-1 mRNA expression in luteal tissue (P<0.01). PP and mRNA expression for steroidogenic enzymes increased in non-insulin-treated animals as ovulation-to-surgery time interval increased (P<0.001). mRNA expression was strongly correlated with PP (r = 0.64~0.74; P<0.001), and PP was strongly correlated with oviductal and peripheral plasma progesterone concentrations (r=0.72~0.77; P<0.001). Our results demonstrate that differences in circulating progesterone in the critical post-ovulatory period are likely determined by inherent differences in luteal function established by treatment imposed in the late luteal phase. .

Keywords: Feed restriction; Insulin; Progesterone; mRNA expression

This abstract is being presented at: 8:00 AM in session:
Corpus Luteum