1018 



SPERM, OVA, AND PREGNANCY 



cervical end. As evacuation of the lowest 

 implantation site starts, changes occur in 

 the periods of contractions of segments of 

 uterine artery near its entrance into the 

 uterine wall (Knisely, 1934; Keiffer, 1919). 

 Gradually the constriction phase becomes 

 proportionately longer than the dilation 

 phase until the arterial lumen is obliterated. 

 The myometrium in the area of the con- 

 stricting segments becofes more active and, 

 after long intense local contractions of the 

 uterine muscle, the fetuses and the placen- 

 tas separate and are discharged through the 

 dilated cervix. After evacuation, a relaxa- 

 tion of the contracted segment of uterus 

 occurs and the process is repeated at the 

 next implantation site. 



Recently, Cross (1958) re-examined the 

 problem of labor in the rabbit. He concluded 

 that (1) oxytocin in physiologic amounts 

 can induce labor that is comparable to the 

 events normally seen, (2) oxytocin is re- 

 leased during a normal labor, and (3) oxy- 

 tocin can induce delivery without sup- 

 plementary mechanisms. He noted that 

 straining movements involving reflex ab- 

 dominal contractions initiated by distention 

 of the vagina and cervix aided in expulsion 

 of the fetus. It is also possible that this 

 might cause reflexly an increased secretion 

 of oxytocin. Other reflex mechanisms have 

 been suggested, but evidence is inadequate. 

 Cross cites a report by Kurdinowski pub- 

 lished in 1904 in which the entire process of 

 labor and delivery in an isolated full-term 

 rabbit uterus perfused with Locke's solution 

 is described. In these experiments orderly 

 delivery of the viable fetuses was affected 

 by the contractile efforts of the uterus and 

 vagina in absence of any hormonal or nerv- 

 ous stimuli. 



XIV. Conclusion 



Although we have garnered much infor- 

 mation, no major conclusions can be drawn 

 at this time concerning gestation in the 

 mammal. This is probably true because of 

 the vastness of the subject and the lack of 

 sufficient data, especially that of a com- 

 parative nature. It is probably fitting to 

 close this chapter with the final statement 

 written by Newton in the second edition of 

 Sex and Internal Secretion, "It seems rather 



that the investigation of endocrine rela- 

 tionships during pregnancy is still in the 

 exploratory stage and that the time is not 

 ripe for systematization." 



It is true that many data have been ac- 

 cumulated in the last two decades since the 

 publication of the second edition of this 

 book. It is also probably true that some sys- 

 tematization can now be started. But above 

 all we need more data on different species 

 in order to systematize fully the role of the 

 various hormones and glands in pregnancy 

 and to evaluate the metabolic and other 

 changes that occur at this time. 



XV. References 



Adams, J. Q. 1954. Cardiovascular physiology in 

 normal pregnancy: studies with the dye dilu- 

 tion technique. Am. J. Obst. & Gynec, 67, 

 741. 



Ahl.mark, a. 1944. Studies on the histaminolytic 

 jiower of i)lasma with special reference to 

 pregnancy. Acta physiol. scandinav., 9, suppl. 

 28. 



Ahlmark, a. 1947. The histaminolytic power of 

 ]ilasma with special reference to pregnancy. 

 In 17th International Physiological Congress, p. 

 127. Oxford. 



AiTKKX, E. H., AND Preedy, J. R. K. 1957. The 

 determination of plasma estiogen levels in late 

 pregnancy. Ciba Foundation Colloquia Endo- 

 crinol., 11, 331. 



Albp:rt, a. 1949. Evaluation of the hypermia test 

 for ])regnancy as a routine clinical laboratory 

 procedvu'e : comparison of results with those of 

 1000 consecutive Friedman tests. Proc. Staff 

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Alexander, D. A., Fr.«er, J. F. D., and Lee, J. 

 1955. The effect of steroids on the mainte- 

 nance of pregnancy in the spayed rat. J. Phys- 

 iol., 130, 148. 



Allan, H., and Wile-s, P. 1932. The role of the 

 pituitary gland in pregnancy and parturition, 

 hypophysectomy in the cat. J. Physiol., 75, 23. 



Allen, E., Hisaw, F. L., .\nd Gardner. W. U. 1939. 

 The endocrine function of the ovaries. In Sex 

 and Internal Secretions, 1st ed., E. Allen, Ed. 

 Baltimore : The Wilhams & Wilkins Company. 



Allen, W. M. 1937. Some effects of estrin and 

 progestin in the rabbit. Cold Spring Harbor 

 Symposia Quant. Biol., 5, 104. 



Allen, W. M., Butenandt, A., Corner, G. W., and 

 Slotta, K. H. 1935. Nomenclature of corpus 

 luteum hormone. Science, 82, 153. 



Allen, W. M., and Corner, G. \V. 1929. Physi- 

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