Impaired cardiovascular responsiveness to an acute cold wind stress in streptozotocin-diabetic rats

In vivo cardiovascular responses were measured using modified impedance cardiographic techniques in urethane-anesthetized (1.5 g/kg) streptozotocin-diabetic (STZ; 65 mg/kg) rats during acute (30 min) cold wind (0 degree C, 1 m/s) exposure. Both control (CON) and diabetic (STZ) groups experienced significant decreases (P < 0.05) in colonic temperature (Tcol) over time with the STZ rats exhibiting greater decrements (P < 0.05) throughout the later stages of cooling. Similar increases (P < 0.05) in cardiac output (Q) and mean arterial pressure (MAP) were observed in both groups during the initial 10 min of cold exposure. Heart rate (HR) accounted for the major portion of the rise in Q since stroke volume remained relatively constant throughout the experimental period. During the later stages of cold wind exposure, Q and MAP were significantly lower (P < 0.05) in STZ compared to CON. In fact, Q and MAP continued to rise during the entire cold period in CON whereas the STZ group failed to respond to the continued decline in Tcol. The results indicate that STZ rats are more vulnerable to cold wind stress as evidenced by the impaired responsiveness of the cardiovascular system to hypothermia. The pattern of responses for both the thermoregulatory and cardiovascular systems could be partially explained by beta-receptor insensitivity to catecholamine stimulation.