OLFACTORY TRANSDUCTION MECHANISMS IN SHEEP

The enzyme adenylyl cyclase from sheep olfactory epithelium is dually regulated by GTP and is highly sensitive to the nucleotide analogues G TP gamma S and GppNHp, as well as to fluoride ions and forskolin. Many , but not all, odorants tested are able to stimulate adenylyl cyclase in a dose-dependent manner and with different potencies. Such an effec t is detectable only in the presence of GTP. The odorants belonging to the putrid class are the least effective in stimulating adenylyl cycl ase activity, and only furfuryl mercaptan significantly increases cAMP biosynthesis. Mixtures of two odorants, chosen among those able to ac tivate adenylyl cyclase, induce additive or supraadditive effects, sug gesting the presence of many different receptor types. The presence of an alternative olfactory signal transduction process, i.e. the inosit ol phospholipid second messenger system, has been evaluated. Triethyla mine, a putrid odorant completely ineffective on cAMP levels, is able to significantly increase inositol phosphate accumulation, indicating the coexistence of both cAMP- and InsP(3)-mediated signalling pathways in sheep olfactory epithelium.