968 



SPERM, OVA, AND PREGNANCY 



E 6 



M 



o 



a- 5 



u 

 u 



UJ 



a. 3 

 2 

 I 



lii i fV^» 15 « ? i f 



T 



12 3 4 5 6 



Day* afl«r finding vaginal plug 



Fig. 16.6. Concentration of free and bound gestagen in the plasma of the pregnant 

 mouse. Gestagen levels were determined by the Hooker-Forbes test. (From T. R. Forbes 

 and C. W. Hooker, Endocrinology, 61, 281, 1957.) 



15 



17 



Ttrm 



on the part of the corpora lutea, an ex- 

 planation of the second peak and the drop 

 between the two peaks offers more diffi- 

 culty. The latter may reflect a diminished 

 luteal activity. This could be assumed on 

 the grounds that the corpus luteum is the 

 only source of gestagen during this period 

 of gestation and that the luteal cells show 

 cytologic signs of regressive changes, al- 

 though the drop in serum progestogen anti- 

 dates the cytologic changes by several 

 days. An explanation for the second peak 

 would probably involve increased secretory 

 activity !)y the placenta. Progestational 

 activity has l)een found in i:)lacental ex- 

 tracts and progesterone has been isolated 

 from the placentae of human beings and 

 mares (Salhanick, Noall, Zarrow^ and 

 Samuels, 1952; Pearlman and Cerceo, 

 1952; Zander, 1954; Short, 1956). Thus, the 

 drop in serum gestagen seen on day 10 

 could be due to loss in the activity of the 

 corpora lutea and the second rise as a con- 

 tribution from the placentas. It is of interest 

 that the low levels on days 10 to 13 and be- 

 tween day 16 to term appear to have no 

 counterpart in other species. The physiologic 

 significance of this is still unknown and will 

 require further work on additional spe- 

 cies and on the mouse before an explana- 

 tion is forthcoming. It is of interest that the 

 concentration of gestagen in the blood dur- 



ing the first 12 days of pregnancy corre- 

 sponds with the intensity of the response to 

 progesterone exhibited by the endometrium 

 during the same period (Atkinson and 

 Hooker, 1945). This w^ould suggest that 

 the serum gestagen levels reflect the phys- 

 iologic state of the animal. 



Serum gestagen levels in the rabbit re- 

 veal a curve of increasing concentration 

 throughout pregnancy (Zarrow and Neher, 

 1955). Initial values of 0.3 to 1 yug. per 

 ml. serum were noted at the time of mating, 

 with a sharp rise beginning on the 4th day 

 of gestation. The concentration rose to a 

 level of 6 to 8 /xg. per ml. by the 12th day 

 and thereafter showed only a slight rise to 

 a maximal concentration of 8 to 10 /xg. per 

 ml. serum at parturition (Fig. 16.7). No 

 drop in serum hormone level was observ- 

 able at parturition or 1 hour later. The 

 first significant drop occurred at 6 to 12 

 hours postpartum when the gestagen level 

 had decreased 50 per cent. It is of interest 

 that the serum progestagen levels did not 

 fall until after the conceptus had been ex- 

 pelled. 



castrated the 12th, 

 of gestation aborted 

 following removal of 

 the ovaries (Zarrow and Neher, 1955). In 

 all instances the serum gestagen levels fell 

 before the abortion. Figure 16.8 shows the 



Pregnant rabbits 

 19th, or 24th day 

 within 1 to 3 days 



