Effect of epidermal growth factor on wool fibre morphology and skin histology

Abstract

Jugular infusion of 2.8 mg mouse epidermal growth factor (EGF) into 40 kg merino ewes over a 24 hour period resulted in a sequence of changes in wool fibres, their follicles and accessory structures. An initial increase in wool fibre diameter was followed by a diminution in diameter. Examination of the enlarged region revealed the presence of aberrant scale formation and an uneven profile. A decrease in linear frequency of scales was associated with the diminution in diameter. Marked hypertrophy of sebaceous glands, follicle walls and sudoriferous ducts followed EGF administration. Jugular infusion of 3.0 to 4.8 mg EGF induced shrinkage of the fibre root bulb and its withdrawal from the dermal papilla beginning within eight hours after infusion. Fibre regeneration was evident 12 days after infusion, with complete recovery by 28 days. Strategic administration of 35S-cysteine and subsequent autoradiography of fibres established that fibre volume growth rate was reduced for 12 days following EGF treatment. Cutaneous infusion of 105.0 to 149.5 μg EGF into a caudal branch of the deep circumflex iliac artery over 24 hours induced no apparent changes in the morphology of fibres sampled from the area of skin served by this vessel. This finding was associated with efferent plasma EGF levels which were similar to circulating levels measured during whole body infusion of 2.8 mg EGF. The circulating jugular plasma levels during cutaneous infusion were all less than 0.5 ng/ml. Subsequent cutaneous infusions of 300 to 400 μg EGF were found to have no effect on fibre morphology. It is suggested that concurrent endocrine changes or some peripheral alteration in the EGF molecule may account for the lack of local effects of EGF.