|
(593) THE OVARIAN RESPONSE TO GONADOTROPINS IS NOT DIMINISHED IN EARLY REPRODUCTIVE AGING. Wu, Julie1, Abdelnabi, Mahmoud1, Hazelton, Julie1, Ottinger, Mary Ann1, 1 Dept of Animal and Avian Sciences, College Park, MD ABSTRACT- Japanese quail are an excellent model for studying ovarian aging due to early reproductive aging and utility of monitoring ovulation by egg production. Our objective was to evaluate ovarian responsiveness in hens at peak and with declining reproduction. Hens from two age groups were monitored to determine % daily egg production. Laying hens (L) were 4 months (90% egg production). Irregularly laying hens (IL) were 17 months (less than 50% egg production). Non-laying hens (NL) were 17 months (0% egg production). Six hours after the estimated LH surge, 1 mL of blood was collected. 150mg ovine luteinizing hormone (oLH; NHPP) in 50 mL 0.7% saline (0.1% BSA), was immediately injected into the contra-lateral jugular vein. In experiment I, L birds were injected with oLH and euthanized after 20 min (n=2) and 40 min (n=2) by cervical dislocation and blood was collected. Post-mortem examination confirmed ovulation and gross ovarian abnormalities were noted. Ovary weight (OW) and number of hierarchical follicles (# HF) were recorded. Plasma was either extracted and analyzed for progesterone (P4) and estradiol (E2) by RIA (DPC; Endocrine Sciences). E2 was unchanged at both times; P4 was elevated at 40 mins. Experiment II compared the ovarian response to oLH stimulus in L, IL and NL birds by measuring change in P4 after 40 minutes. Basal P4 (L, 0.363±0.193 ng/mL; IL, 0.705±0.356 ng/mL; NL, 0.244±0.039 ng/mL) was highest in IL and lowest in NL. Birds from all age groups responded to ovarian stimulation; a change in P4 was documented at all ages (L, 0.791±0.200 ng/mL; IL, 0.587±0.113 ng/mL; NL, 1.005±0.379 ng/mL). Despite a lack of egg production, NL ovaries appeared normal and maintained follicular hierarchy. Non-ovulation was associated with increased P4 in laying birds, presumably due to the presence of the F1 follicle, which has shown to be the primary source of P4 in chickens. Conversely, NL birds had high OW and #HF with low basal P4 levels, regardless of ovulation. Therefore, despite low levels of basal P4 the ovary remained responsive to exogenous hormone, suggesting that reduced hormone levels may be due to a diminished endogenous ovarian stimulation, and not of reduced functionality. This suggests that the process of reproductive aging in hens is a process that involves the multiple systems, and not solely ovarian in origin. KEY WORDS: ovary, Japanese quail, progesterone, aging |
