P-009. Growth hormone receptor and its binding protein gene expressions during pregnancy and lactation in rat tissues: Relationship to serum GH levels

It is reported that the growth hormone (GH) level is kept high in the pregnant mouse and rat, but the physiological functions of this GH have not been detailed. In this study, we have investigated the relation between expression of GH receptor (GH-R) and GH binding protein (GH-BP) mRNAs in rat tissues and serum GH level during pregnancy and lactation. Total RNA was extracted from liver, kidney, mammary gland, heart, intestine, adrenal, uterus, ovary and cerebrum of pregnant and lactating rats, respectively. The expression level of GH-R and GH-BP mRNAs were analyzed by solution hybridization with the RNA probe which can detect both RNAs. In addition, the serum GH level was measured by RIA. The serum concentration of GH continuously increased in pregnancy, and reached over 20 times higher than that of the control, and immediately decreased after parturition. Both GH-R and GH-BP mRNA expressions in liver, kidney, intestine and ovary raised during pregnancy and then gradually decreased after delivery, corresponding to serum GH level. In mammary gland and uterus, these expressions were high at early pregnancy decreasing then after gradually. In cerebrum, heart and adrenal, expressions for these two mRNA species were relatively unchanged. These results suggest that the mRNA expressions for GH-R and GH-BP in rat tissues are differentially regulated during pregnancy and lactation.