GESTATION 



981 



stance in the blood by cross transfusion be- 

 tween a normal and hypophysectomized rat 

 united in parabiosis. Gemzell, Heijkenskjold 

 and Strom (1955), using the technique of 

 adding exogenous growth hormone to the 

 sample of blood, failed to find any growth- 

 jiromoting substance in 23-ml. equivalents 

 of blood. However, retroplacental blood from 

 human beings gave a positive response at a 

 level of 7- to 15-ml. equivalents of plasma 

 without the addition of exogenous STH. In- 

 crease in the width of the proximal tibial 

 epiphysis of the rat was used as an end 

 l)oint. A comparable concentration of 650 

 fxg. eciuivalent of the standard STH per 100 

 ml. plasma was also found in the blood from 

 the umbilical cord. 



Contopoulos and Simpson (1956, 1957) 

 measured the STH of the plasma in the 

 pregnant rat, using the tibial cartilage, tail 

 length, and body weight increase. No sig- 

 nificant increase in plasma STH was noted 

 on the 5th day of pregnancy, however, a sig- 

 nificant rise was observed by the 9th day. 

 An estimated 3-fold increase in plasma STH 

 during pregnancy was reported from calcu- 



lations on both the tibial cartilage and the 

 tail length tests. No changes were reported 

 in the STH activity of the pituitary gland 

 throughout pregnancy. Recently, the per- 

 sistence of greater than normal amounts of 

 growth-promoting activity was reported in 

 the plasma of pregnant rats after hypophy- 

 sectomy. Since the fetal pituitary probably 

 does not contribute to the STH pool of the 

 mother, at least in early pregnancy, it is 

 likely that the placenta may be a source of 

 the hormone. 



I. PROLACTIN 



Few data are available on the concentra- 

 tion of prolactin during gestation. This has 

 been due, in part, to the minute amounts of 

 the hormone present in the urine and blood 

 and to the inadequacy of the available as- 

 says. Although Hoffmann ( 1936 ) failed to 

 find any prolactin in the urine of women 

 before parturition, Coppedge and Segaloff 

 (1951) and Fujii and Schimizu (1958) re- 

 ported measurable amounts of prolactin in 

 the urine of pregnant women. Coppedge and 

 Segaloff reported a gradual rise in the excre- 



FiG. 16.18. The level of protein-bound iodine in the pregnant woman. (From J. P. 

 Peters, E. B. Man and M. Heinemann, in The Normal and Pathologic Physiology oj 

 Pregnancy, The Williams & Wilkins Co., 1948.) 



