[Changes in circadian rhythms of urinary catecholamine excretion in cold-stressed spontaneously hypertensive rats]

Investigations of the changes in ambulation and water drinking behavior of SHR were carried out and an attempt was made to determine the influence of cold exposure on the systolic blood pressure (SBP) and urinary catecholamines excretion (UCA) in SHR. Twenty week old male SHR-Okamoto strain (approximately 350 g) were used. The automatic Ambulo-Drinkometer was used to determine ambulatory activity and water drinking in SHR. UCA was determined by the trihydroxyindole method using high performance liquid chromatography. Cold exposure was performed for a period of 24 hours in a room maintained between 0--3 degrees C. It was observed that ambulatory activity and water drinking of SHR in dark phase were higher than those in the light phase (P less than 0.001). Significant increases in urinary norepinephrine (UNE), urinary epinephrine (UE), and urinary dopamine (UDA) contents as well as in urine volume were observed in the dark phase as compared with those in the light phase. SBP was significantly elevated after cold exposure. It was also demonstrated that cold exposure produced a significant increase in UNE and UE both in light and dark phases. Significant increase in UDA in cold stressed SHR was observed in dark phase. Although at room temperature (20 +/- 2 degrees C) significant difference in UCA between light and dark phases was observed, during cold exposure no significant difference was apparent. These findings suggest that temperature modulation induces changes in circadian rhythms of urinary CA excretion in SHR.