| Summary: | The function and morphometry of human chorionic gonadotropin (hCG)-induced corpora lutea (CL) were examined. In experiment 1, ultrasonography and progesterone (P4) were used to characterize the development and function of induced corpora lutea (CL). Between d 5 and 14, spontaneous CL were larger (P < 0.01) than induced CL. Among cows with induced CL only,P4 concentration increased to reach peak concentrations on d 18 but was lower (P < 0.01)
throughout the study period than for the spontaneous CL. Intrauterine infusion with Indomethacin, a prostaglandin synthase inhibitor, were examined in experiment 2. There were no differences P > 0.05) in 13,14-dihydro-15-keto-prostaglandin F2 (PGFM) concentrations. However, pulsatile PGFM secretion was abolished in one indomethacin treated cow sampled at 6 h intervals. Plasma P4 and CL diameter were not different between indomethacin treated and control cows. In experiment 3, the morphometry and functional characteristics were compared. Weight of induced and spontaneous CL were not different (P > 0.05). Basal P4 production was higher (P < 0.01) among induced than spontaneous CL. Human CG increased (P < 0.01) P4 production at low but not at high concentrations. A higher (P < 0.02) number of large luteal cells (LLC) and a concomitant reduction in the number of small luteal cells (SLC) was observed among induced
CL.
The effects of hCG on the morphometry and P4 production ability of spontaneous CL
exposed to hCG were investigated in experiment 4. Basal P4 production was lower (P < 0.01) in
hCG-exposed CL removed on d 12, than in the control CL. However, hCG-exposed CL removed
on d 15 secreted more (P < 0.01) P4 than d 12 hCG-exposed and control CL. Treatment with
hCG was also associated with an increase (P < 0.01) in the number of LLC and a concomitant
reduction in the number of SLC in hCG-exposed CL. Administration of hCG on day 7 of the cycle was associated with alterations in follicular dynamics but did not affect cycle length
(experiment 5). In conclusion, in vivo studies show that the induced CL are inherently subnormal
in function. In vitro studies showed that P4 production is significantly higher among hCG-induced
and d 15 hCG-exposed spontaneous CL. Such increases in P4 are associated with an increased
differentiation of small into large luteal cells.
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