Graduate Thesis Or Dissertation
 

Bovine luteal oxytocin synthesis and secretion in vitro : effects of phorbol ester, calcium ionophore and indomethacin

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  • Experiments were conducted to examine the effects of a tumor-promoting phorbol ester, a calcium ionophore and indomethacin on bovine luteal oxytocin (OT) synthesis and secretion and progesterone secretion. Six 18-month-old crossbred beef heifers in Exp. 1 and five similar heifers in Exp. 2 were observed twice daily for estrus using vasectomized bulls. After at least two consecutive estrous cycles of normal duration (18-23 days), corpora lutea surgically removed on day 8 of the estrous cycle (day of estrus = day 0 of the cycle) were sliced and incubated for 2 h with 0.81nM 12-0-tetradecanoylphorbol 13-acetate (TPA), 1.62 nM TPA, 100p,M indomethacin, 1.62 nM TPA and 1001.1M indomethacin or 0.3 ptM calcium ionophore A23187. Both levels of TPA increased OT secretion (ng g⁻¹ 2h⁻¹; control, 407.1; 0.81 nM TPA, 494.7; 1.62 nM TPA, 528.1; common SE = 21.2; P<0.01) and synthesis (control, 368.5; 0.81 nM TPA, 427.6; 1.62 nM TPA, 492.1; common SE = 25.7; P<0.02). Although indomethacin alone did not alter basal OT release significantly, it inhibited TPA-induced OT secretion (TPA x indomethacin interaction, P<0.005) and synthesis (P<0.10). Calcium ionophore increased OT secretion (ng g⁻¹ 2h⁻¹; control, 248.9; A23187, 327.4; common SE = 16.0; P<0.01) and synthesis (control, 129.4; A23187, 165.6; common SE = 16.4; P=0.09). The phorbol ester TPA also induced progesterone secretion (ng g⁻¹ 2h⁻¹; control, 1056.2; 0.81 nM TPA, 1333.3; common SE = 86.4; P<0.025). Because TPA can activate protein kinase C and A23187 increases intracellular calcium, it is concluded that these intracellular constituents may be involved in OT synthesis and release, as well as progesterone secretion.
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