RADIOIMMUNOASSAY OF A NEWT SEX-PHEROMONE, SODEFRIN, AND THE INFLUENCEOF HORMONES ON ITS LEVEL IN THE ABDOMINAL GLAND

A specific and sensitive radioimmunoassay (RIA) was developed for the measurement of sodefrin, a female-attracting decapeptide pheromone of the red-bellied newt, Cynops pyrrhogaster. Sodefrin synthesized accord ing to the amino acid sequence of native sodefrin, isolated from the a bdominal glands of the cloaca of the male newt, was used as a referenc e standard. An antiserum to sodefrin was produced by immunizing a rabb it with synthetic sodefrin that was extended on its C-terminus with Cy s coupled to hemocyanin. For the radioligand, sodefrin N-terminally ex tended with Tyr was used. An aqueous extract of the abdominal glands o f C. pyrrhogaster produced a displacement curve parallel to the sodefr in standard, whereas that from the sword-tailed newt (Cynops ensicauda ) showed no inhibition of binding in this RIA. The sensitivity of the RIA was 30.5 +/- 3.4 pg/100 mu l assay buffer. Intraassay and interass ay coefficients of variation were 1.6 and 4.5%, respectively. The RIA was used to determine sodefrin levels in the abdominal gland of the ma le newt. Hypophysectomy and castration greatly reduced the sodefrin co ntent. Administration of testosterone propionate (TP) to the hypophyse ctomized and castrated newt increased the pheromone content in the abd ominal gland. A combination of prolactin (PRL) and TP elevated the sod efrin content markedly, while PRL alone scarcely affected it. Immunore active sodefrin was observed in the epithelial cells of the abdominal gland of both hormone-treated and saline-injected newts. Among them, g roups treated with PRL plus TP and TP alone exhibited strong immunorea ctivity in their abdominal gland compared with PRL-treated and saline- injected groups. (C) 1996 Academic Press, Inc.