GESTATION 



995 



(glomerular filtration rate divided by the 

 renal plasma flow) remained low in the first 

 2 trimesters and increased in the last tri- 

 mester. This is evidence for an increase in 

 tubular resorption of water and electrolyte. 

 It can only be concluded, therefore, that 

 kidney function is altered during preg- 

 nancy, especially the 1st trimester. Results 

 from investigations involving the 2nd and 

 3rd trimesters are contradictory. De Al- 

 varez concludes that the changes in renal 

 hemodynamics during pregnancy are medi- 

 ated by the endocrine system because the 

 alterations in renal function seem to be 

 related to the sodium and water retention. 

 If the changes are progressive throughout 

 gestation, it would be possible to correlate 

 the phenomenon with a number of hor- 

 mones that increase during pregnancy. On 

 the other hand, if the phenomenon is transi- 

 ent, i.e., only during the 1st trimester, then 

 the phenomenon can only be correlated with 

 HCG. 



X. Enzymes 



A. HISTAMIXASE 



The presence of histaminase or diamine 

 oxidase in tissues of the body has been 

 known for some time. As yet the enzyme 

 lias not been crystallized but is believed to 

 he a flavoprotein (Swedin, 1943). The en- 

 zyme is not specific for histamine because it 

 inactivates other diamines such as cadaver- 

 ine and putrescine. Histaminase determina- 

 tions, in general, are based on incubation of 

 the test material with histamine dihydro- 

 chloride for a fixed period of time and the 

 bioassay of the residual histamine carried 

 out on an isolated strip of guinea pig in- 

 testine. 



Histaminase has been found in the 

 l)lasma of men and women with an increase 

 (luring ])regnancy from a value of between 

 0.003 and 0.008 /^g. per ml. per hr. to a 

 value of between 3.5 and 10 at parturition 

 (Ahlmark, 1944, 1947). This has been con- 

 firmed by Swanberg (1950), who de- 

 termined the histaminolytic activity in pe- 

 i-iplK>ral blood throughout pregnancy (Fig. 

 16.29). A marked rise is observed from 

 the 10th to the 20th week of pregnancy, 

 and thereafter the concentration plateaus 

 until after parturition. 



20 30 40 weeks 



Fif!. 16.29. Tlie histaminase activity of the 

 peripheral blood of the human female during 

 pregnancy (•) and at parturition (®). (From 

 H. Swanberg, Acta scandinav., Suppl. 79, 23, 

 1950.) 



Both the maternal placenta and the 

 decidual tissue have been identified as 

 major sites for formation of the enzyme. 

 Danforth and Gorham (1937) reported the 

 presence of histaminase in the placenta 

 of a series of patients at term. This was 

 confirmed by Swanberg (1950) who, in 

 addition, separated the placenta by a series 

 of slices parallel to the surface of the organ 

 and reported that the layer adjacent to 

 the uterine wall, consisting of practically 

 only the thin decidual membrane, contained 

 a mean value of 614 /xg. per gm. per hr. of 

 histaminase as compared to 38 for the fetal 

 portion of the placenta. Confirmation of the 

 concept that the maternal placenta is the 

 main source of histaminolytic activity can 

 be obtained from the finding of histaminase 

 in decidual tissue of nonpregnant females 

 and in the maternal placentas of animals. 

 In cases in which maternal and fetal 

 placentas can be separated easily, the 

 maternal placenta contained from 14- to 

 100-fold the activity seen in the fetal 

 placenta. Comparison of the histaminolytic 

 activity in the decidual tissue of the sterile 

 horn and the control pregnant horn of the 

 uterus of a rabbit revealed 319 fig. per gm. 

 per hr. and 222 fxg. per gm. per hr., respec- 

 tively. Treatment with progesterone or in- 

 duction of jiseudopregnancy caused a 

 marked rise in the histaminase of the 

 endometrium to upwards of 1000 fig. per 

 gm. per hr. Nonetheless, histaminase was 



