MELATONIN AND PROLACTIN SECRETION PROFILE IN NATURALLY-OCCURRING SCRAPIE IN EWE

The 24 hr pattern of melatonin secretion was determined in scrapie-aff ected ewes during the clinical course of the disease. The melatonin re sponse to a night interruption by a 1 hr period of illumination was al so measured. Fourteen ewes (seven control and seven scrapie-affected e wes) were subjected to artificial short days (9L:15D). Four 24 hr bloo d sampling sessions separated by about 10 days were performed. Ewes we re sacrificed when clinical signs had progressed to irreversible recum bency and the scrapie diagnosis was confirmed by histopathology. Plasm a melatonin was assayed in all samples and prolactin was analysed in s amples obtained during the second sampling session using RIA methods, The instantaneous amplitude of elevation of plasma melatonin concentra tions was calculated for each ewe and each sampling session and the wi thin-ewe repeatability of this parameter was evaluated. The within-ewe repeatability of instantaneous amplitude of melatonin secretion was a pparently greater in control than in scrapie-affected ewes (72% vs. 39 %). The light stimulus induced an abrupt decrease of night melatonin c oncentrations in all ewes. Prolactin secretion was not affected by the disease. It was concluded that the 24 hr pattern of melatonin secreti on was maintained in scrapie-affected ewes. The retinohypothalamic tra ct transducing light information remained functional in diseased ewes despite some evidence of histopathological changes of the pineal gland . The instability of melatonin secretion during the clinical course of scrapie could reflect a disturbance of pineal function. However, whet her this effect exists or not, it could not be used to discriminate sc rapie-affected ewes from control ones.