^74 



SPERM, OVA, AND PREGNANCY 



hormone varies with the species involved. 

 Still unsolved is the question as to whether 

 the water-soluble extract obtained from the 

 ovary and referred to as relaxin is a single 

 substance or a group of active substances 

 (Friedcn and Hisaw, 1933; Sher and Mar- 

 tin, 1956). 



The concentration of relaxin in the blood 

 increases as pregnancy progresses until a 

 plateau is reached. This has been demon- 

 strated in the rabbit (Marder and Money, 

 1944), guinea pig (Zarrow, 1947), cow 

 (Wada and Yuhara, 1955), and human 

 being (Zarrow, Holmstrom and Salhanick, 

 1955). Relaxin has also been found to in- 

 crease in the ovary of the sow (Hisaw and 

 Zarrow, 1949). In general, the shape of the 

 curve for the concentration of relaxin in 

 the blood as a function of the length of 

 pregnancy has been more or less the same 

 for all species studied. Figure 16.12 indi- 

 cates that the concentration of relaxin in 

 the blood of the pregnant rabbit rises from 

 a level of 0.2 guinea pig unit (G.P.U.) per 

 ml. for the first trimester of pregnancy, i.e.. 

 until day 12, to a level of 10 G.P.U. per ml. 



on day 24. This concentration was then 

 maintained until parturition. After delivery 

 of the young, the concentration of the hor- 

 mone decreased 80 per cent in 6 hours. On 

 the 3rd day postpartum no hormone could 

 be detected. 



As indicated above, the concentration of 

 relaxin in the blood of the pregnant cow 

 and human being showed approximately 

 the same type of curve. In the cow the con- 

 centration rose gradually from a level of 1 

 G.P.U. per ml. to a maximum of approxi- 

 mately 4 G.P.U. at 6 months (Fig. 16.13). 

 Thereafter the level remained unchanged 

 until parturition, wdien the level dropped at 

 a rate comparable to that seen in the rab- 

 bit. The curve for the concentration of re- 

 laxin in the blood serum of the pregnant 

 woman followed the general pattern de- 

 scribed above (Fig. 16.14). The concentra- 

 tion rose from a level of 0.2 G.P.U. per ml. 

 the 6th week of i:)regnancy to a maximum 

 of 2 G.P.U. the 36th week. Thereafter the 

 level remained unchanged until delivery. 

 Again the postpartum fall was precipitous 

 and the hormone was not detectable at 24 



12 15 18 21 24 



DAYS AFTER MATINO 



27 



30 



35 



Fig. 16.12. Concentration of relaxin in the blood of the rabbit during pregnancy. Parturi- 

 tion (P) occurred 32 days after mating. Guinea pig units (G.P.U.) of relaxin are plotted 

 against days pregnant. (From S. N. Marder and W. L. Money, Endocrinology, 34, 115, 

 1944.) 



