GESTATION 



975. 



6 7 8 9 



• — Pregnancy (in months) 



2 6 10 15 



After parturition (in days) — * 



Fig. 16.13. Concentration of I'elaxin in the blood of the cow during pregnancy. Partiui- 

 tion is indicated by P. (From H. Wada and M. Yuhara, Jap. J. Zootech. Sc, 26, 12, 1955.) 



6 12 18 24 30 36 



LENGTH OF PREGNANCY - WEZKS 



HOURS POST- 

 PARTURITON 



Fig. 16.14. The concentration of relaxin in the blood serum of normal pregnant women. 

 (From M. X. Zarrow, E. G. Holmstrom and H. A. Salhanick, Endocrinology. 15, 22. 1955.) 



hours postpartum. Studies in the guinea pig 

 revealed a marked rise in relaxin on day 

 21 of gestation to a maximal concentration 

 of 0.5 G.P.U. per ml. serum on day 28 

 (Zarrow, 1948). Thereafter the level re- 

 mained unchanged for approximately 4 

 weeks. Contrary to the results obtained in 

 the rabbit, cow, and human being a drop in 

 the concentration of the hormone in the 

 pregnant guinea pig was noted before par- 

 turition. The concentration of relaxin fell 



to 0.33 G.P.U. per ml. on the 63rd day of 

 gestation and then dropped to nondetect- 

 able levels within 48 hours postpartum. 



Although no studies have been carried 

 out on the blood levels of relaxin in the sow 

 as a function of the length of pregnancy, 

 analysis of the ovary for relaxin has re- 

 vealed a situation comparable to that re- 

 ported for the blood in other species. The 

 concentration rose from 5 G.P.U. per gm. 

 ovarian tissue during the luteal phase of 



