title: Cold stress effects on cardiomyocytes nuclear size in rats: light microscopic evaluation.
abstract: BACKGROUND
  Total body induced hypothermia and myocardial cooling are effective methods regarding myocardial protection during heart surgery and ischemia. It is described in previous studies that extreme low temperature exposure causes mitochondrial cristae and myofilament disarrangement in cardiomyocytes, however, no investigation has analyzed the effects of cold stress on nuclear size of cardiomyocytes.
  
  
  OBJECTIVE
  To evaluate the effects of acute cold stress exposure on the nuclear size of cardiomyocytes in rats.
  
  
  METHODS
  The experimental study procedures were performed on 300-310 g adult male Wistar rats. Rats (n=20) were divided into two groups: 1) Control (CON) and; 2) Induced hypothermic (IH) group. Animals of IH group were exposed during 4 hours once at a controlled temperature of - 8 degrees C. It was performed histological analysis of liver and adrenal gland to examine the stress condition of animals. Cardiomyocytes nucleus size were examined by three independent investigators with the same and standardized criteria and analyzed by Bartko's intra-class correlation coefficient (R>0.75 = positive concordance). Student's t test was applied. The significance level was set at P<0.05.
  
  
  RESULTS
  The induced hypothermic group presented higher lipid depletion in adrenal gland cells (P<0.05) and higher glycogen depletion in liver glycogen (P<0.05). The experimental group showed lower cardiomyocytes nuclear volume (108 + 1.7 microm(3); P<0.05), it decreased in 76% compared to the control group (142 + 2.3 microm(3)). Bartko's correlation: CON=0.44; IH=0.96, variation analysis between group's means differences was significant.
  
  
  CONCLUSIONS
  These data suggest that acute cold stress exposure induces cardiomyocytes nucleus size reduction in rats.
authors.affiliation: Disciplina de Cardiologia, Faculdade de Medicina do ABC, São Paulo, SP, Brazil.
authors.forename: Adriano
authors.initials: A
authors.lastname: Meneghini
authors.forename: Celso
authors.initials: C
authors.lastname: Ferreira
authors.forename: Luiz Carlos de
authors.initials: LC
authors.lastname: Abreu
authors.forename: Marcelo
authors.initials: M
authors.lastname: Ferreira
authors.forename: Celso
authors.initials: C
authors.lastname: Ferreira Filho
authors.forename: Vitor Engrácia
authors.initials: VE
authors.lastname: Valenti
authors.forename: Neif
authors.initials: N
authors.lastname: Murad
mesh_terms: D000311:Adrenal Glands / Q000378:metabolism / Q000473:pathology; D000818:Animals; D053145:Cell Nucleus Size; D003080:Cold Temperature / Q000009:adverse effects*; D006003:Glycogen / Q000378:metabolism; D006352:Heart Ventricles; D007036:Hypothermia, Induced / Q000009:adverse effects; D008099:Liver / Q000378:metabolism / Q000473:pathology; D008297:Male; D032383:Myocytes, Cardiac / Q000648:ultrastructure*; D051381:Rats; D017208:Rats, Wistar; D013312:Stress, Physiological / Q000502:physiology
chemical_list: D006003:Glycogen