860 



SPERM, OVA, AND PREGNANCY 



blastocyst fluid is increased by the ioniza- 

 tion of the inherent calcium carbonate re- 

 serve. Deficient respiration of the free blas- 

 tocyst may perhaps lead to the production 

 of acids which react with the calcium car- 

 bonate reserve. At the time of uterine at- 

 tachment, there is improved gas exchange 

 due to the embryo's close proximity to sub- 

 epithelial blood vessels. Thus the bound 

 alkali is liberated, the ionic concentration 

 of the fluid is decreased, and blastocyst 

 turgidity is lessened. 



In measuring the bicarbonate of the rab- 

 bit blastocyst cavity fluid, Lutwak-Mann 

 and Laser (1954) found a remarkably high 

 content in 6- and 7-day-old embryos. There- 

 after, the level of bicarbonate fell rapidly 

 so that on the 8th day, when implantation 

 is completed, the level was somewhat below 

 that for maternal blood. The occurrence of 

 high concentrations of bicarbonate in the 

 unattached blastocysts led to assays of 

 carbonic anhydrase activity in extracts of 

 pregnant and nonpregnant rabbit uterine 

 mucosa. It was found that carbonic an- 

 hydrase activity was very low in the uteri 

 from nonpregnant animals but very high 

 in the uteri from pregnant individuals. The 

 oviducts, endometrium, and placental tis- 

 sues are the main loci of carbonic anhydrase 

 activity in the female reproductive tract. 

 There are, however, species differences in 

 the extent and the time at w^hich the enzyme 

 can be demonstrated. The endometria of 

 pregnant or nonpregnant hamsters, rats, 

 and guinea pigs do not contain measurable 

 quantities of carbonic anhydrase. However, 

 significant enzyme activity has been found 

 in the maternal portions of the placenta of 

 these animals (Lutwak-Mann, 1955). 



It has been clearly established for the 

 rabbit that the enzyme is hormone-de- 

 pendent. Progesterone and progesterone-like 

 compounds greatly increase the amounts of 

 the enzyme measured in the endometrium 

 and this increase is proportional to the 

 dosage of the hormone injected. There is 

 no concomitant increase of carbonic an- 

 hydrase in the blood (Lutwak-IVIann and 

 Adams, 1957a, b). 



There is a 10- to 30-fold increase in the 

 weight of the blastocyst between the 5th 

 and 6th days. Dry weight measurements 

 have shown that this increase is due pri- 



marily to water. The enzyme system re- 

 sponsible for the active transport of water 

 is as yet unknown, but is being actively 

 sought. Concentrations of Na, K, and CI 

 ions in the yolk sac fluid approach or, in the 

 case of K, exceed that of the maternal 

 serum. Glucose, on the other hand, is present 

 in less than half the amount found in mater- 

 nal blood on the 7th day and two-thirds the 

 amount on the 8th day. Data are also 

 available on total nitrogen, phosphorus, bi- 

 carbonate, and various vitamins, particu- 

 larly the components of the B complex, 

 in the unimplanted blastocyst (Kodicek 

 and Lutwak-Mann, 1957; Lutwak-Mann, 

 1959). Obviously the opportunities for uti- 

 hzing isotopes for transfer studies in the 

 fresh and implanting blastocysts are many 

 indeed, and one may confidently expect a 

 rapid unravelling of the manifold functional 

 aspects of implantation if these techniques 

 are employed by competent investigators. 



p. EMBRYO-ENDOMETRIAL RELATIONSHIPS 



The interrelationship between the blasto- 

 cyst and the endometrium at the time of at- 

 tachment and implantation is not only 

 exceedingly comjilex but also highly vari- 

 able in different species. Irrespective of 

 the complexity of the attachment, each 

 type has as its purpose the apposition 

 or intimate fusion of the fetal mem- 

 branes to the maternal endometrial epi- 

 thelium or stroma so that adequate phys- 

 iologic exchange can take place. 



Earlier studies on the experimental pro- 

 duction of deciduomas by mechanical stim- 

 ulation of the sensitized endometrium, and 

 the dependence of implantation on the proper 

 hormonal stimulation of the uterine mucosa, 

 had the effect of swinging the pendulum of 

 opinion toward the endometrium as being 

 the most active agent in the process of nida- 

 tion (Huber, 1915; Kirkham, 1916; Selye 

 and McKeown, 1935; Krehbiel, 1937; Ross- 

 man, 1940). More recently, however, the ob- 

 servations ( 1 ) on the development of the 

 attachment cone in some specific area of the 

 trophoblastic wall just before attachment, 

 (2) the changes in the viscosity and ad- 

 hesiveness of the egg envelopes at the 

 time of attachment, and on the develop- 

 mental potentialities of ova transplanted 

 to the anterior chamber of the eye and 



