Mechanical responses of chromium-deficient developing rat heart

Mechanical responses were compared between controls, developing Sprague-Dawley rat papillary muscle and age-matched weanlings fed with Torula yeast, a food source deficient in chromium. At 8 weeks postnatal, deficient rats differed in significant ways from their normal counterparts. Deficient rats in contrast to controls weighed less, their interval-force (I-F) relationship was more negative and their inotropic response to high calcium concentrations was greater. At this time, however, deficient and control rats responded equally to alpha (phenylephrine) and beta (isoproterenol) agonists. At 10 weeks of age, the controls exhibited a less negative I-F and a negative inotropic response to high calcium concentrations while the response to alpha and beta agonists was unchanged. In contrast, at 10 weeks of age, the chromium-deficient rats exhibited a highly negative I-F response and significant inotropic response to high calcium concentrations. The response of the deficient hearts to beta-agonists diminished. At 13 weeks postnatal, control hearts showed only a 10-15% negative I-F response, a persistent response to catecholamines and negative inotropic responses to high calcium concentrations. In deficient hearts, the negative I-F response was reduced and the response to beta-agonists was further diminished but a positive inotropic response to phenylephrine and high calcium concentrations persisted. These observations in deficient animals are explained in terms of a retarded development of the calcium handling elements in the heart and a lack of an insulin-like growth factor.