抄録
X-box binding protein 1 (XBP1) is the transcription factor activated in response to ER stress. The XBP1 gene expression in the rat liver is sexually dimorphic and increased by growth hormone (GH). We have examined whether the sexual dimorphism is due to sex steroids or GH secretory pattern.The XBP1 mRNA level of the liver in the normal male rat was higher than that in the normal female. It decreased to the female level after hypophysectomy (HPX) or orchidectomy (OCX). The mRNA level was not influenced by HPX or ovariectomy (OVX) in female rats. To determine the role of sex steroids, rat GH was infused continuously with Alzet miniosmolar pump and estradiol (E2) or dihydrotestosterone (DHT) was given for 7 days to the rat with HPX and OCX. The XBP1 mRNA levels were sustained at the female level after these treatments. To examine the effect of GH secretory pattern, GH was administered every 3-h-bolus (male like) or continuously (female like) for 24-h to the rat with HPX and OCX. XBP1 mRNA level increased 1- and 2-h after the last bolus of GH, and reached to the normal male level. It did not change with continuous infusion. It has been shown that GH secretory pattern changes to male like pattern, when the OVX rat is treated with DHT. The XBP1 mRNA level increased in the OVX female rats treated with DHT, but did not reach to the normal male level.These results indicate that the sexually dimorphic expression of the XBP1 mRNA in the rat liver depends on the GH secretory pattern, but not on the sex steroids. [J Physiol Sci. 2008;58 Suppl:S139]
