Temperature-dependence of maturation of chronotropic and inotropic responses to isoproterenol

Effects of varying temperature (26, 32, 38°C) on age-related differences in inotropic and chronotropic sensitivities were investigated on electrically stimulated left atria and spontaneously beating right atria isolated from newborn and adult rabbits. Adult tissue had significantly greater sensitivity (low ED₅₀) than newborn tissues to isoproterenol-induced inotropic responses at 26 and 32°C (p < 0.01), but not at 38°C. The chronotropic sensitivity of adult tissues was significantly greater than the newborn at 26°C (p < 0.01), but not different at 32 or 38°C. It is concluded that age-related differences in inotropic and chronotropic responses in vitro are more pronounced at low temperatures and tend to disappear at physiological temperatures.