Submitted to: American Society of Animal Science Southern Section Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2007
Publication Date: 9/20/2008
Citation: Aad, P.Y., Echternkamp, S.E., Spicer, L.J. 2008. Evidence for possible involvement of IGF type II receptors (IGF2R) in regulating growth of two concomitant dominant follicles in cattle [abstract]. Journal of Animal Science. 86 (E-Supplement 3):10 (Abstract #38).
Technical Abstract: Regulation of multiple ovulations in monotocous species such as cattle is not well understood. Gene expression of the FSH receptor (FSHR) in granulosa (GC), and LH receptor (LHR) and IGF2R in GC and theca (TC) cells, as well as estradiol (E2) and progesterone (P4) levels in follicular fluid (FF) were quantified in cows selected (Twinner) and unselected (Control) for multiple ovulations. Cows were slaughtered at days 3 and 6 of an estrous cycle, and ovaries from each cow were snap frozen in liquid nitrogen; FF, GC and TC were separated and collected. Total RNA from GC and TC was extracted, and target gene mRNA levels were quantified using multiplex real-time RT-PCR. Follicles were ranked F1 through F3 based on their diameter and E2 level in FF; F1 and F2 had greater diameters and FF E2 levels than F3, but no differences in FF P4 levels were observed among F1, F2 and F3. Twinner cows had on average larger (P < 0.01) F1 and F2 with greater (P < 0.01) FF E2 levels than Control cows. FSHR and LHR mRNA in GC were greater (P < 0.05) in F1 and F2 vs F3, with Control cows having greater (P < 0.05) FSHR mRNA than Twinner cows. Abundance of IGF2R mRNA in TC of F1, F2 and F3 of Twinner cows was less (P < 0.05) than Control cows mainly on day 3. In GC, IGF2R mRNA abundance was less (P < 0.05) in F2 of Twinner than Control cows. Abundance of IGF2R in GC but not TC negatively correlated with size and estradiol (r = -0.33, P < 0.01), Further, in GC, IGF2R mRNA was correlated with only FSH mRNA (r = 0.3, P < 0.05), whereas in TC, IGF2R mRNA was correlated with both GC and TC LHR mRNA (r = -0.27 and 0.67 respectively, P < 0.05). In conclusion, our data support the hypothesis that reduced theca and granulosa cell IGF2R levels in early developing cohort antral follicles of Twinner cows, induced by increased IGF-I, may increase the amount of free or bioavailable IGF-II which in turn may act in an autocrine or paracrine fashion to regulate follicular development such that two cohort follicles are selected and become dominant.