IN-VIVO RESPONSIVENESS OF THYROID-GLANDS TO TSH IN NORMAL AND NOVEL GROWTH-RETARDED MICE - TRANSIENT ELEVATION IN NORMAL MICE AND IMPAIRMENT IN GROWTH-RETARDED MICE
K. Tomita et al., IN-VIVO RESPONSIVENESS OF THYROID-GLANDS TO TSH IN NORMAL AND NOVEL GROWTH-RETARDED MICE - TRANSIENT ELEVATION IN NORMAL MICE AND IMPAIRMENT IN GROWTH-RETARDED MICE, Journal of Endocrinology, 144(2), 1995, pp. 209-214
The in vivo responsiveness of thyroid glands to TSH at various ages in
novel 'growth-retarded' (grt/grt) mice derived from Snell's dwarf (DW
/J) mice and in their normal counterparts were analysed by determining
serum T-4 concentrations before and after the administration of exoge
nous TSH. The serum T-4 concentration in normal mice increased in resp
onse to TSH at 2, 4 and 12 weeks of age but not at 1 week of age. A tr
ansient augmentation of such thyroidal responsiveness to TSH was appar
ent in normal mice at 2 weeks of age, when the serum T-4 level exhibit
s a peak and the pubertal growth of mice starts. In contrast to normal
mice, at any age examined from 2 to 12 weeks after birth, exogenous T
SH did not influence serum T-4 concentrations in the grt/grt mice at a
ll. On the other hand, serum TSH concentrations in young grt/grt mice
were highly elevated compared with those in normal mice and they were
normalized by a 2-3 week's treatment with T-3. Morphological studies d
emonstrated degenerated thyroid glands in the grt/grt mice. These resu
lts suggest that the severe hypothyroidism and consequent growth retar
dation in growth-retarded mice are due to impairment of the thyroid gl
ands of the mutant mice in producing and/or secreting thyroid hormones
in response to TSH.