| Research Abstract |
In this study, as in the followings, we determined the characteristics and the age associated change of the endocrine system of the mutant strain of mouse, the "growth retarded" (gr) mouse, which was newly derived from DW/J strain mouse with special attention to the pituitary-thyroid axis and other anterior pituitary hormones.
1) gr mice suffer a severe deficiency in thyroid hormone from neonate due to primary hypothyroidism as in the human cretinism. The character inherits in an autosomal recessive manner and the gene responsible was named as grt.
2) The serum concentration of thyroxine in gr mice slightly increases after three months of age but remains subnormal through their lives.
3) The lack of thyroid hormones results in the extraordinary stimulation of both hormone synthesis and secretion, and finally exhaustion, in the thyrotrophs of gr mice and, on the other hand, in the delayd proliferation and/or maturation of somatotrophs and lactotrophs. The pituitary contents of growth hormo
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ne and prolactin in gr mice increased at a same extent of delay as the growth retardation compared to normal mice and remained subnormal until old ages.
In order to see the effects of such as endocrine status of gr mice on the life span of mice, we attempted to determine the longevity of gr mice under a SPF (specific pathogen free) condition and compare with that of normal mice. The study is still in progress and, however, the days of 50 % survival calculated for a group of 7 male gr mice and a group of 14 normal counterparts with similar birth dates were found to be about 600 and 700 days, respectively. As previously reported, the pituitary glands of gr mice enlarge with age and, in most of the gr mice examined at death, the pituitary glands enlarged so much that they looked as if tumors.
Taking into consideration of these facts, the results of present study indicate that thyroid hormones and growth hormone are essential for the growth and maturation of mice but not for the maintenance of life of adult mice, at least, under a comfortable condition. The analyzes of the age associated changes of certain physiological functions, such as energy metabolism, that should serve a suitable measure of ageing process in gr mice remain as interesting future subjects. Less
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