title: Substance P effects on developing thymocytes in hindlimb unloaded rats.
abstract: BACKGROUND
  The purpose of this study was to examine the effects of substance P (SP) on the immune system in a condition similar to microgravity. We analyzed immune disturbances caused by subjecting Fischer 344 rats to a 45 degrees antiorthostatic suspension technique, otherwise known as the hindlimb unloading (HU) model.
  
  
  METHODS
  Four groups of rats were assigned to either the prone control non-substance P group (P-NSP), prone control substance P group (P-SP), hindlimb unloaded non-substance P (HU-NSP) or the hindlimb unloaded substance P group (HU-SP). SP was administered at 10 ml of a 1 micromol x L(-1) concentration for 15 min x d(-1). HU and SP exposure for all groups lasted 16 d. After 16 d, 500 microl of blood was obtained to assay for both T-cell phenotype and corticosterone (CS) levels. Thymus lobes were excised in order to examine T-cell phenotype. Thymocytes were counted and stained for lymphocyte markers (CD4, CD8, and CD3). An analysis of variance (ANOVA) test was used to determine significance between groups (p < or = 0.05).
  
  
  RESULTS
  HU-NSP rats showed a decrease in thymic CD4+CD8 +/- cells from 85.51 +/- 1.9% to 62.06 +/- 1.9% when compared with P-NSP rats. SP reversed these effects and returned CD4+CD8+ cells to control levels (76.60 +/- 1.9%).
  
  
  CONCLUSIONS
  Daily SP treatment was found to reverse the deleterious effects caused by HU and corticosterone in rat thymic immune cells. SP could prove to be an effective means for keeping the immune system functioning at normal levels in microgravity, allowing astronauts to stay in space longer and maintain a more productive immune system.
authors.affiliation: University of Arizona College of Medicine, Department of Microbiology and Immunology, Tucson, AZ 85724, USA.
authors.forename: Ty W
authors.initials: TW
authors.lastname: Lebsack
authors.forename: Chris
authors.initials: C
authors.lastname: Kreulen
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Deever
authors.forename: David T
authors.initials: DT
authors.lastname: Harris
authors.forename: Mark L
authors.initials: ML
authors.lastname: Witten
mesh_terms: D000818:Animals; D017252:CD3 Complex / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000378:metabolism; D003345:Corticosterone / Q000097:blood; D019417:Hindlimb Suspension; D051381:Rats; D011916:Rats, Inbred F344; D013373:Substance P / Q000494:pharmacology*; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology
chemical_list: D017252:CD3 Complex; D013373:Substance P; D003345:Corticosterone