Epidermal growth factor measurements in mouse plasma: method, ontogeny, and sex difference

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Abstract
A highly sensitive mouse plasma (serum) epidermal growth factor (EGF) radioimmunoassay was utilized to determine EGF levels in mouse plasma and submandibular gland (SMG) at different ages. Plasma and serum levels were not different. Inferior vena caval blood was used because even at the age of 12 days EGF levels were markedly higher in neck blood. At 2 wk serum EGF levels were 60% of adult female levels. After a temporary decrease, mean EGF concentrations reached adult values at 31 and 60 days in the female but not yet in the male. In adults male serum EGF levels were twofold higher than female levels. This difference is parallel to but much smaller than the sex difference in SMG-EGF. SMG-EGF showed a very different ontogeny. Moreover, no correlation was present in the adults between the SMG and serum EGF concentrations. Testosterone treatment of adult females doubled their serum EGF levels, but the stimulated values were still below the mean of the male levels. The present observed plasma (serum) EGF levels in the mouse are 20-40% of previously reported values, probably because of the absence of EGF contamination from hair (urine) and milk.