534 



PHYSIOLOGY OF GONADS 



luteuni. and changes in the smusoidal pat- 

 tern suggesting reduced circulation. Such 

 changes are first observed in the guinea pig 

 corpora lutea on about the 13th day of the 

 cycle. One has the choice of taking this date 

 as the end of the pseudopregnant phase or, 

 alternatively, the date on which the first 

 indications of estrus are noted. Either choice 

 is arbitrary, but the former seems preferable 

 as it suggests that progesterone secretion is 

 diminishing and probably is no longer suf- 

 ficient to maintain progestational changes 

 in the uterus. In fact, regression of the endo- 

 metrium sets in about a day earlier than 

 frank degenerative changes in the corpora 

 lutea. In the cat, according to van Dyke and 

 l.i (1938) the corpora lutea 20 days after 

 ovulation no longer secrete enough pro- 

 gesterone to cause motor effects of epineph- 

 rine in the myometrium, the so-called "epi- 

 nephrine-reversal" effect, yet by histologic 

 criteria corpus luteum regression is not ap- 

 parent until 28 days or later (Liche, 1939; 

 Foster and Hisaw, 1935). In the bitch the 

 uterus begins regression 20 to 30 days after 

 heat, l)ut the corpora lutea are said to re- 

 main in good condition for a longer time 

 (see Asdell, 1946, for references). Regres- 

 sion is so gradual that anestrum is not 

 reached until about 85 days. In the primates 

 the beginning of menstruation offers a means 

 of delimiting the luteal phase, inasmuch as 

 menstruation in the ovulatory cycle reflects 

 a marked reduction in corpus luteum func- 

 tion. Nevertheless, this reduction probably 

 occurs a few days before bleeding begins. 

 The i^eak of pregnanediol excretion in 

 women (Venning and Browne, 1937) and of 

 plasma progesterone concentration in 

 women and monkeys (Forbes, 1950; Bryans. 

 1951 ) is passed about midway between ovu- 

 hition and menstruation. 



2. Xciivdl Factors in Pseudoprciindiicji 



The importance of the nervous system 

 in control of pseudopregnancy is well recog- 

 nized in only the few species re])resented 

 by the rat. .\ neural effect in the mink and 

 similar Mustelidae is implied by the rela- 

 tion of hiteal function to daily illumination, 

 as mentioned earlier. Beyond that fact, how- 

 ever, no information is available. Att(>ntion 

 will therefore be directed largely to the rat. 



Not only sterile mating, but se\'eral other 



procedures involving neural stimulation will 

 cause rats to become pseudopregnant. Stim- 

 ulation of the cervix by mechanical means 

 (Long and Evans, 1922) or electric shock 

 (Shelesnyak, 1931) have become standard 

 methods. In fact, Greep and Hisaw (1938) 

 obtained pseudopregnancies after electrical 

 stimulation during early diestrum, several 

 days before ovulation. Pseudopregnancy is 

 also invoked by continuous stimulation of 

 the nipples for several days (Selye and Mc- 

 Keown, 1934). According to Harris (1936) 

 electric shock through the head is effective. 

 His negative results with "spinal shock" 

 are difficult to explain. From the description 

 of position of the electrode it seems doubt- 

 ful that the current passed through the cord 

 itself, yet the sacral plexus must have been 

 stimulated. 



Al)dominal sympathectomy or superior 

 cervical ganglionectomy are said to diminish 

 the numbers of animals responding to elec- 

 trical or mechanical stimulation of the cer- 

 vix (Vogt, 1931; Haterius, 1933; Friedgood 

 and Bevin, 1941). On the other hand, there 

 is no diminution of response to sterile copu- 

 lation, which shows that the sympathetic 

 chains are not essential. Ball (1934) em- 

 phasized the quantitative aspects of the 

 problem, noting that partial resection of the 

 uterus or excision of the cervix diminished 

 the response to sterile copulation, but only 

 when "single-plug" matings were allowed. 

 Multiple plugs gave pseudopregnancy in 100 

 per cent of the animals. It may be assumed 

 that Vogt's (1933) negative results after 

 hysterectomy resulted from single-jilug cop- 

 ulations. Kollar (1953) re-opened the cjues- 

 tion and found that pelvic nerve resection 

 usually pi-evented the response to mating. It 

 is not clear, howevei', whether multiple cop- 

 ulations wnv the rule, although it seems that 

 the I'outiiie procedure was to leave the male 

 with the female overnight. His contention 

 was that cervicectomy fails to abolish the 

 resjionse completely because the vagina re- 

 mains sensitive. 



Anesthesia with ether, nitrous oxide, or 

 ethylene ( Mcyei', Leonard and Hisaw, 1929) 

 diniiiiished the ficciuency of response to 

 inecliaiiical stimulation of tlu> (•er\-ix. The 

 statement was made, although without v\\- 

 (len(c, that spinal anesthesia |)re\-ents pseu- 

 dopreiinanev. Aeeoi'ding to A'ogt (1933), 



