The effects of thiamine inhibition on ruminal fermentation: a preliminary study

Inhibition of methanogenesis in ruminal cultures was attempted by hindering thiamine availability through its degradation by ‘polyphenols’ and competition for active sites on enzymes and transporters using thiamine structural analogs. Effects on fermentation were small and not consistently reversed by adding thiamine. Lack of major effects of the compounds evaluated could be due to intracellular synthesis of thiamine covering most requirements.     

Release of arachidonic acid from human endometrial cells in culture mediated by calcium ionophore (A23187) or fluoride.

Primary cultures of endometrial glands and stromal cells were labelled with [14C]-arachidonic acid for 4 h before exposure to either the calcium ionophore, A23187 (which activates phospholipase A2 (PLA2) by increasing intracellular calcium concentrations) or sodium fluoride (which activates a G-protein). Calcium ionophore (0.5-50 mumol/l) stimulated a dose- and time-dependent release of arachidonic acid from endometrial glands. Incubation with ionophore (10 mumol/l) for 1 h released 22% of the incorporated arachidonic acid. There was a corresponding decrease in phospholipids and no loss from triglycerides. Stromal cells were unresponsive to ionophore. Fluoride (10 mmol/l) stimulated a release of arachidonic acid from stromal cells and endometrial glands (6.5% of the total arachidonic acid incorporated). In stromal cells, arachidonic acid was released from triglycerides in Day-1 cultures and from phospholipids in Day-2 cultures. In both Day-1 and Day-2 cultures of endometrial glands, arachidonic acid was released from phospholipids, but not from triglycerides. Among the phospholipids, phosphatidylcholine was always the major source of arachidonic acid. Arachidonic acid release from endometrial glands and stromal cells may be mediated by activation of PLA2 (or phospholipase C) via a G-protein, but in glands calcium ionophore may have a direct effect on PLA2. The response to calcium ionophore may reflect the differences in calcium requirements of the two endometrial PLA2 isoenzymes.