Dynamic changes in insulin-like growth factor I immunoreactivity correlate to repair events in rat ear after freeze-thaw injury.

The distribution of the trophic peptide insulin-like growth factor I (IGF-I) in the rat ear was mapped after freeze-thaw injury. Immunocytochemical methods and antisera specific to human IGF-I were used. In the ear of normal adult rats scattered basal epidermal cells and a few cells in the underlying connective tissue and elastic cartilage expressed IGF-I immunoreactivity. Within 1 day after injury and reaching maximum in 3 days, all epidermal cells became stained as did invading macrophages and some of the other inflammatory cells. Concomitantly, there were hypertrophic changes. The staining leveled off after 1-2 weeks. Perichondrial cells became IGF-I immunoreactive in increasing frequency during the first week, reached maximal intensity and frequency in 2 weeks, and remained stained for at least 4 weeks. New cartilage was formed concomitantly on both sides of the old one. It is proposed that IGF-I is a substance of general importance for cell maintenance and tissue repair.