title: Hyperthyroidism is associated with preserved preconditioning capacity but intensified and accelerated ischaemic contracture in rat heart.
abstract: BACKGROUND
  The present study was undertaken to define the effects of thyroxine administration on ischaemic preconditioning (PC) and the ischaemic contracture.
  
  
  METHODS
  Hyperthyroidism was induced by administration of L-thyroxine in rats (THYR) while normal animals served as controls (NORMa). Isolated rat hearts were perfused in a Langendorff preparation. NORMa control (n = 16) and THYR control (n = 9) hearts underwent 20 min of ischaemia and 45 min reperfusion while NORMa PC (n = 16) and THYR PC (n = 14) were subjected to PC before ischaemia. Additional normal hearts were subjected to 30 min of ischaemia with and without PC, NORMb control, n = 8 and NORMb PC, n = 6. Postischaemic recoveries of left ventricular (LV) developed pressure were expressed as % of the initial value (LVDP%). Severity of contracture was measured by the time (Tmax) and magnitude (Cmax) of peak contracture.
  
  
  RESULTS
  LVDP% was significantly higher after PC, both in NORMa and THYR rats. In NORMa control hearts, ischaemic contracture had not yet reached a plateau at 20 min of ischaemia. Contracture appeared earlier in THYR control and PC than in NORMa control and PC groups. Tmax was 22.1 (0.9) vs 16.8 (1.4) min for NORMb control and PC, p < 0.05 and 12.5 (1.0) vs 9.3 (1.1) min for THYR control and PC hearts, p < 0.05. Tmax was earlier in both THYR groups compared to NORMb groups, p < 0.05. Cmax was significantly higher in both THYR groups compared to both NORMb groups.
  
  
  CONCLUSIONS
  Ischaemic contracture is both accelerated and accentuated in thyroxine treated hearts while preconditioning capacity is preserved. Preconditioning and thyroxine administration shorten Tmax in an additive way, whereas Cmax in hyperthyroid hearts did not further increase by preconditioning.
authors.affiliation: Department of Pharmacology, University of Athens, Greece.
authors.forename: C I
authors.initials: CI
authors.lastname: Pantos
authors.forename: D D
authors.initials: DD
authors.lastname: Cokkinos
authors.forename: S M
authors.initials: SM
authors.lastname: Tzeis
authors.forename: V
authors.initials: V
authors.lastname: Malliopoulou
authors.forename: I S
authors.initials: IS
authors.lastname: Mourouzis
authors.forename: H C
authors.initials: HC
authors.lastname: Carageorgiou
authors.forename: C
authors.initials: C
authors.lastname: Limas
authors.forename: D V
authors.initials: DV
authors.lastname: Varonos
authors.forename: D V
authors.initials: DV
authors.lastname: Cokkinos
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001835:Body Weight; D006980:Hyperthyroidism / Q000503:physiopathology*; D019194:Ischemic Preconditioning; D008297:Male; D009200:Myocardial Contraction; D051381:Rats; D017208:Rats, Wistar; D016277:Ventricular Function, Left
chemical_list: D000255:Adenosine Triphosphate