Morphological changes in the skin and wool fibres of Merino sheep infused with mouse epidermal growth factor.

Intravenous infusion of 4.5-4.7 mg of mouse epidermal growth factor (mEGF) into nine castrated male Merino sheep for 26 h resulted in complete casting of the fleeces 6-8 days later. The morphological changes which occurred in the skin were studied in skin samples taken before infusion and at intervals between 1 h and 42 days after the infusion had begun. Wool fibres from the shed fleeces were examined with the scanning electron microscope. Increased cell proliferation occurred in the epidermis and sebaceous glands, whereas the wool follicles regressed. Transient dermal haemorrhages occurred during the first 3 h of infusion. The fibre and inner root sheath in the keratogenous zone of 30-40% of the follicles were partially disrupted within the first 6 h of mEGF infusion; catagen began in all follicle bulbs within 24 h. Fibre and inner root sheath production, although markedly reduced, continued in about 60% of follicles which had partially regressed, but production ceased in the remainder in which tapered ends formed on the fibres prior to shedding. Follicles began to regenerate asynchronously 4-8 days after the beginning of infusion and completed their development during the next 3 weeks. The follicle regression and fleece casting induced by mEGF infusion, and subsequent follicle regeneration were completed more rapidly than observed previously with other depilatory agents, and, except for prolonged epidermal thickening, there was no lasting cutaneous abnormality.