1. Insulin-like growth factor I is a major mediator of growth-promoting activities. We studied the ventricular insulin-like growth factor I gene expression at mRNA and peptide levels in 24 heart transplant recipients (14 children and 10 adults), using ‘slot blot' hybridization with insulin-like growth factor I cDNA probe and a specific radioimmunoassay.

2. Ventricular insulin-like growth factor I mRNA was detected in all the cardiac transplant children but was below the limit of detection in the cardiac transplant adults. Ventricular insulin-like growth factor I levels were significantly higher in the transplant children [174 ± 15 (SEM; range 39–950) pg/mg soluble protein] than in transplant adults [39 ± 2 (range 14–85) pg/mg soluble protein, P < 0.01, n = 14]. Circulating levels of insulin-like growth factor I in the cardiac transplant children [164 ± 10 (range 105–192) ng/ml] and adults [176 ± 15 (range 126–244) ng/ml] were within normal ranges for children and adults.

3. These results suggest that the human heart is a site for insulin-like growth factor I production and provide support for an autocrine role for insulin-like growth factor I in the ventricle, despite cardiac denervation.

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