27 THYROXIN (T4) EFFECTS ON GROWTH AND HEPATIC EPIDERMAL GROWTH FACTOR RECEPTOR (EGF) ONTOGENY IN MICE WITH CONGENITAL HYPOTHYROIDISM (CH)

摘要

The effects of thyroid hormones on growth and development are probably mediated by specific growth factors as EGF. We have studied the effects of thyroxine on growth and hepatic EGF receptor ontogeny in a mouse strain with an inherited form of CH.Hypothyroid mice (h/h) were treated with T4 between day 20 and day 40 postnatally, h/h nontreated mice and euthyroid (+/+) mice served as controls. Animals were killed at day 20 or day 40 postnatally. Serum thyroxine was measured by RIA and EGF receptor binding in a liver plasma-membrane homogenate. Up to 20 days of age all mice showed the same weight gain and EGF hepatic receptor binding were low and not significantly different between h/h and +/+ mice. From day 20 h/h mice had a significantly lower growth rate than +/+ mice, a growth retardation that were normalised by T4 treatment.Early postnatal growth (day 0-20) in mice is thyroid hormone independent and resembles in that respect late prenatal growth in humans. In contrast, between day 20 and 40 postnatally thyroid hormone is necessary for normal growth and for the increase in hepatic EGF binding observed in mice. Our results indicate that an altered ontogeny of Epidermal Growth Factor receptors might be involved in the growth and developmental retardation found in CH.