Osmoregulation of the Cane Toad, Bufo Marinus, in Salt Water

1. Adult cane toads, B. marinus, survived in salinities up to 40% sea-water (SW). 2. Pre-exposure to 30, then 40% SW, increased the survival time of toads in 50% SW. 3. Plasma from toads acclimated to salt water is hyperosmotic to the environment - a result of increased plasma sodium, chloride and urea concentrations. 4. When toads were placed in tap-water and 20% SW, all significant changes to plasma sodium, chloride, urea and osmotic pressure occurred within the first 2 days of exposure. 5. When toads were placed in 30 and 40% SW environments, the increases in plasma sodium and chloride concentrations occurred within the first 2 days of exposure while urea and total osmotic pressure continued to rise until some time between 2 and 7 days exposure

Initiation of Labour

Since arachidonic acid is the obligatory substrate for the synthesis of prostaglandins, the regulation of arachidonic acid from phospholipid stores is likely to be pivotal in the release of prostaglandins and the initiation of labour. The hydrolysis of phospholipids to yield arachidonic acid is catalysed by phospholipases of which there are two of particular importance. Phospholipase C mediates the action of certain agonists including oxytocin and acts specifically on phosphatidyl-inositol resulting in the release of inositol phosphates. Phospholipase A2 is activated by a variety of physical and chemical agents (e.g. infection, trauma) that increase calcium concentrations in the cell; it releases arachidonic acid from phosphatidyl-choline and phosphatidyl-ethanolamine in particular. Factors influencing phospholipase activity are important in the mechanism initiating labour whether preterm or term. A specific chorionic protein (gravidin) that inhibits activity of phospholipase A&lt;sub&gt;2&lt;/sub&gt; during pregnancy but loses its activity at the onset of labour has been identified and characterised.</jats:p