Ka. Ribbons et al., SUBCUTANEOUS BUT NOT INTRALUMINAL EPIDERMAL GROWTH-FACTOR STIMULATES COLONIC GROWTH IN NORMAL ADULT-RATS, Growth factors, 10(3), 1994, pp. 153-162
Epidermal growth factor (EGF) was administered by chronic subcutaneous
or intracolonic infusion into normal adult rats to determine the effe
ct on colonic growth. Subcutaneous infusion of 200 mu g EGF/kg/day for
7 days increased the cross-sectional mass and protein content of the
muscularis and mucosal layers of the proximal colon, with the distal c
olon showing less response. In the mucosa, subcutaneous EGF induced pr
oportional increments in the number of cells per crypt, and in the num
ber of cells positively labelled for PCNA, while maintaining a normal
crypt growth fraction. In contrast, an 8-fold higher dose of EGF admin
istered intraluminally had no effect on colonic mucosal or muscularis
growth. This lack of bioactivity was unlikely to reflect rapid luminal
degradation as radiolabelled EGF remained stable in the colonic lumen
for at least 4 h. The results demonstrate that the normal adult colon
is responsive to subcutaneously delivered EGF, particularly the proxi
mal colon, whereas EGF may not be active on the normal colon when pres
ented from the luminal direction.