Troponin T expression in normal and pressure-loaded fetal sheep heart.

The effects of cardiac hypertrophy in adult animals on the expression of a number of genes are well established. There is, however, a paucity of information about the effect of pressure overload on the expression of genes coding for the contractile proteins in the prenatal developing heart. The prenatal cardiac muscle can increase cell number in response to stress, whereas the adult heart increases cell mass. Thus, the response of the fetal heart to pressure overload cannot be assumed to be identical to that of adult myocardium. We studied the effect of banding the great vessels of fetal sheep hearts on the expression of troponin T (TNT). In other vertebrates, TNT mRNA is generated by alternative splicing of a primary transcript. Thus, both the levels and patterns of TNT isoforms generated by alternative splicing in the heart could be influenced by pressure overload. The techniques of cDNA library screening and polymerase chain reaction were used to define the influence of in utero banding of the great vessels on TNT expression. The data indicate that there is a single dominant isoform of TNT expressed from mid-gestation to adult life in sheep. The pattern of TNT isoform expression in the sheep heart proved to be unique among all animals studied to date.