Energetic, metabolic and contractile effects of vasopressin in mammalian heart

The effects of arginine vasopressin (VP), 8 mU/ml, on contractility, heat production and glucose metabolism were investigated in isolated, arterially perfused, interventricular rabbit septa. Rest tension linearly increased in the presence of VP with a slope of 0.095 +/- 0.008 g/min. Developed tension (DT), maximal rate of tension development (+dT/dt)max and maximal rate of relaxation (-dT/dt)max showed a biphasic response in the presence of VP. The first phase showed a rapid decline in all three contractile parameters [DT, (+dT/dt)max and (-dT/dt)max] with a half time of 4.4, 3.3 and 4.6 min, respectively. This rapid decline was followed by a recovery period that occurs with an increase in glycolytic flux and on lactic acid production. Along with the effects on contractile parameters, VP increases the ratio heat production over developed tension (40% over control values), indicating that in the presence of VP "muscle efficiency" decreases since it is energetically more costly to generate a given level of isometric tension. This was further confirmed by experiments performed under low Ca conditions (150 microM Ca Cl2) in which, while VP showed no significant changes on contractile parameters, myocardial heat production and heat production over developed tension increased.