Oxytocin synthesis and secretion from bovine corpora lutea exposed in vitro to cycloheximide and colchicine

Abstract

Two experiments were conducted to study the effects of cycloheximide and colchicine on prostaglandin F 2α (PGF 2α)-induced secretion and synthesis of oxytocin in bovine luteal tissue in vitro. Corpora lutea were collected from beef heifers on Day 8 of the estrous cycle. In Experiment 1, incorporation of [ 14C]-leucine into oxytocin synthesized and secreted by luteal slices after exposure to PGF 2α, cycloheximide and cycloheximide plus PGF 2α was examined. In Experiment 2, synthesis and secretion of oxytocin were evaluated in luteal slices incubated with colchicine and PGF 2α alone and in combination. Cycloheximide inhibited incorporation of labeled leucine into luteal proteins by more than 90% and no labeled oxytocin was detected in the media or tissue. Prostaglandin F 2α induced significant secretion of oxytocin that was not inhibited by cycloheximide. Tissue levels of oxytocin after incubation with cycloheximide and/or PGF 2α did not differ and were similar to those of the incubated control. Colchicine alone did not suppress oxytocin secretion and did not alter the ability of PGF 2α to induce significant secretion of this nonapeptide. Tissue concentrations of oxytocin after incubation with colchicine and/or PGF 2α did not differ. These studies indicate that secretion and replenishment of luteal oxytocin in vitro is not contingent upon de novo protein synthesis. Inability of colchicine to suppress oxytocin secretion and synthesis may have been due to the short duration of exposure of luteal tissue to the drug.