Graduate Thesis Or Dissertation
 

Oxytocin synthesis and release by the bovine corpus luteum

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  • Four experiments were conducted to determine oxytocin concen tration of bovine luteal tissue at different stages of the estrous cycle and to study the effects of prostaglandins F₂α (PGF₂α), E₂ (PGE₂), luteinizing hormone (LH), cycloheximide, colchicine and cytochalasin B on oxytocin synthesis and release in vitro. In experiment 1, luteal oxytocin concentrations (ng/g) in beef heifers increased from 414 ± 84 on day 4 to 2019 ± 330 on day 8 and then declined to 589 ± 101 on day 12 and 81 ± 5 on day 16 of the cycle. Prostaglandin F₂α induced a significant in vitro release of luteal oxytocin on day 8 but not on days 12 or 16, while PGE₂ and LH had no effect on oxytocin release at any stage of the cycle studied. Total oxytocin concentration (incubation medium + tissue) increased twofold after 2 h of incubation. In experiment 2, six beef heifers were used to investigate in vitro effects of 10, 20 and 40 ng PGF₂α /ml of medium on oxytocin release from day 8 luteal tissue. A significant linear doseresponse relationship was observed indicating oxytocin release was dosedependent. In experiment 3, the effects of cycloheximide on oxytocin synthesis as well as PGF₂α-induced oxytocin release from day 8 bovine luteal tissue was investigated. Although, cycloheximide inhibited incorporation of labeled leucine into protein by more than 90%, it did not affect processing of prohormone or prostaglandin F₂α -induced release of this nonapeptide from luteal tissue. No incorporation of labeled leucine was detected in oxytocin. In experiment 4, the effects of cytochalasin B and colchicine on oxytocin synthesis and release from day 8 bovine luteal tissue were investigated. Neither colchicine nor cytochalasin B inhibited oxytocin synthesis or release while PGF₂α caused a significant release of oxytocin that was not inhibited by colchicine. These studies indicate that maximal oxytocin concentrations in bovine luteal tissue occur during the early luteal phase of the cycle. Luteal oxytocin secretion in vitro can be induced by PGF₂α whereas PGE₂ and LH have no effect on oxytocin secretion. Increased oxytocin concentration due to short term incubation represents a post- translational processing of an oxytocin prohormone because it occurred in the absence of incorporation of labeled leucine and during inhibition of de novo protein synthesis.
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file details AbdelgadirSalaheldinEltigani1988.pdf 2017-08-04 公开 下载