Mechanical responses of chromium-deficient developing rat heart

Abstract

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 α (phenylephrine) and β (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 α and β 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 β-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 β-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.