Short Communication Decline in Assayable Progesterone in Bovine Serum under Di¡erent Storage Conditions T.deCastro 1 *,L.Valdez 1 ,M.Rodriguez 1 ,N.Benquet 1 andE.Rubianes 2 1 Animal Reproduction Department,Veterinary Faculty, Lasplaces 1550, 11600 Montevideo,Uruguay; 2 Animaland Forage Sciences Department, Facultyof Agriculture, Montevideo, Uruguay *Correspondence: E-mail: tdec@adinet.com.uy de Castro, T., Valdaz, L., Rodriguez, M., Benquet, N. and Rubianes, E., 2004. Decline in assayable progesterone in bovine serum under di¡erent storage conditions. Tropical Animal Health and Production, 36(4),381^384 Keywords: beefcattle,progesterone,storage,RIA Abbreviations: RIA,radioimmunoassay INTRODUCTION The use of radioimmunoassay (RIA) to determine hormone concentrations in domesticated livestock has widely expanded our knowledge of reproductive endocri- nology. However, the treatment and storage of blood or serum samples prior to analysiscanin£uencethevalueobtainedforthehormonelevelmorethantheprecision andaccuracyoftheRIAmethodemployed(OltnerandEdqvist,1982).Itisessential therefore,thatcarefulhandlingandstandardizedproceduresshouldbeusedtoallowa correctdeterminationofhormonelevels. Frozenplasmaorserumsamplescanbestoredforlongperiodswithoutsigni¢cant loss in hormone concentrations, but progesterone concentrations in bovine plasma and serum decrease proportionally with time elapsed between collection and separa- tionfromcellularelements(OltnerandEdqvist,1982;Reimers et al ., 1983; Breuel et al ., 1988; Pulido et al .,1991).Temperaturealsoplaysanimportantroleintherateof progesterone metabolization by red blood cells, since refrigeration delays the proges- terone decline (Oltner and Edqvist, 1982; Reimers et al., 1983; Breuel et al., 1988; Pulido et al ., 1991). Although not as rapid and pronounced as in the cow, a 50% declineinovineprogesteroneconcentrationswasfoundwhenheparinizedovineblood was stored at 228C for 24 h (Wiseman et al ., 1982), while in dogs, pigs, llamas and horsesnochangeshavebeenfoundinprogesteroneconcentrationsafterstoringwhole bloodatdi¡erenttemperatures(OltnerandEdqvist,1982;Aba et al .,1996). TropicalAnimalHealthandProduction,36(2004)381^384 # 2004KluwerAcademicPublishers.PrintedintheNetherlands 381