The negative inotropic effect of secobarbital on the heart of reserpinised newborn and adult guinea pigs.

The negative inotropic effect of different concentrations of secobarbital was studied on isolated hearts of reserpinised newborn and adult guinea pigs. This effect was expressed as the percentage reduction of contraction height, from which the sensitivity of the heart was obtained as the reciprocal of the secobarbital concentration X1/2 needed to yield a 50% reduction (i.e. 1/X1/2). It was found that in adults depletion of catecholamines increased this sensitivity, but not in newborns. Possible interpretations are discussed and it is concluded that the age effects are not due to an effect of reserpine on contractility.