STUDY OBJECTIVE - The aim of the study was to examine the effect of prior induction of the heat shock response on heat shock protein synthesis and physiological variables relevant to the shock response. DESIGN - Synthesis of heat shock protein (SP71, molecular mass 71,000) was induced in rats by 15 min hyperthermia (42 degrees C). Protein synthesis, heart rate, blood pressure and creatine kinase activity were determined in comparison with controls (no heat shock) and a group receiving two heat shock treatments 24 h apart (prior induction group). SUBJECTS - 24 male Sprague-Dawley rats (125-150 g) were used, divided into three groups: controls (n = 4), heat shock X 1 (HS, n = 11), heat shock X 2 (2 X HS, n = 9). Heat shock was induced under anaesthesia on a heating pad. MEASUREMENTS and RESULTS - Blood pressure and heart rate were measured at the beginning of the hyperthermia period, when body temperature first reached 42 degrees C (t = 0 min) and at the end of the hyperthermia treatment (t = 15 min). At t = 0 min systolic blood pressure and heart rate were increased compared to the control values in both HS and 2 X HS groups. At t = 15 min heart rate in the HS group was increased to 554 (SEM21) beats.min-1 v control 465(19) (p less than 0.05). In the 2 X HS group, heart rate of 494(14) beats.min-1 at t = 15 min was not significantly different from control. At t = 15 min, creatine kinase values in the hyperthermia treatment groups were not different from control. However at 2.5 h after hyperthermic treatment plasma creatine kinase was increased in the HS group to 481(83) mU.ml-1 (n = 6) v 223(20) in controls, but was not increased in the 2 X HS group [178(64), n = 4]. Rats were radiolabelled for 2 h with 1.0 mCi of [35S]-methionine 30 min after hyperthermic treatment in HS group and 30 min after the second hyperthermic treatment in 2 X HS group. Following the 2 X HS treatment, synthesis of SP71, though increased above control values, was lower than in the HS group. CONCLUSIONS - The reduction in heart rate, plasma creatine kinase and synthesis of SP71 following a second hyperthermic exposure could be caused by a protective influence of the first exposure.

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