I t >( 12 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



Sturgis (229) found that anything which alters 

 uterine blood flow in the monkey may affect the rate 

 of fluid formation in the uterine lumen (glandular 

 secretion?). This lead has never been followed up, 

 or studied in relation to endometrial physiology or 

 cytology. 



In the absence of large amounts of estrogen, but 

 not in ovariectomized rabbits or guinea pigs, the 

 capillaries of the endometrium exhibit a rather rapid 

 rhythmic blanching and blushing [Markee (141, 

 142)]. This phenomenon is unrelated to myometrial 

 activity. Since capillaries lack contractile elements, 

 it must be, therefore, a manifestation of arteriolar 

 activity. 



UTERINE INNERVATION 



There is a rich sympathetic innervation to the uterus 

 [Reynolds (198), Krantz (130)]. The parasympathetic 

 innervation is limited, so far as is known, to the region 

 of the cervix. Despite the nerve supply, a uterus which 

 is denervated by transplantation to the ventral peri- 

 toneal wall possesses all the normal nongravid re- 

 activity of the uterus in situ [Reynolds & Kaminester 

 (209)]. This is not to say that the innervation is with- 

 out effect upon the vasculature [Reynolds & Kami- 

 nester (210)]. Rather, the hormones are independent 

 of the innervation in their action on the uterus. Cer- 

 tainly, fright causes vasoconstriction, but it is possible 

 that this is a hormonal effect of blood-borne epineph- 

 rine [Markee (142)]. Few data exist which suggest, 

 much less show, what the normal role of the vasomotor 

 innervation to the uterus is. The existence of vaso- 

 motor nerves, however, as entities separate from the 

 nerves which supply the myometrial smooth muscle 

 has been amply shown [Medowar (149)]. Vasodilator 

 fibers may exist since cholinergic sympathetic fibers 

 to the uterus seem to have been demonstrated, as 

 well as adrenergic ones [Burn (46)]. Moreover, 

 atropine has been seen to reduce the hyperemic effect 

 of estrogen on the uterus in situ [Pompen (176)] but 

 not in denervated endometrial transplants in the eye 

 [Kaiser (125)]. 



PREGNANCY AND THE UTERINE CIRCULATION 



Pregnancy imposes an array of special requirements 

 upon the uterine circulation. These are, as mentioned 

 above, responses to growth of the conceptus and 

 spatial adjustments that are of great magnitude. 



At the outset of pregnancy, the uterine hyperemia 

 of estrus gives way to a quality in the circulation in 

 the uterus prior to implantation and for a time after 

 which renders the uterus bluish in appearance as if 

 the circulation were turgid. This is seen with the 

 uterus in situ [Barcroft & Rothschild (21)] and in 

 ocular grafts [Neumann (160)]. Aside from the 

 generalized uterine hyperemia referred to above, 

 localized hyperemia, more marked in some parts of 

 the endometrium than in others, has long been known 

 and suspected to be related to implantation. This was 

 reported in the human by His (108), Ilitschmann & 

 Adler (109), Strahl & Beneke (227), Delporte (65), 

 Teacher (231), Falkiner & Fleming (76), and Wilkin 

 (242). More refined examination of this in controlled 

 experiments on animals awaited the work of Bacsich 

 & Wyburn (15-17) in the guinea pig and more re- 

 cently in the rat [Williams (246), Holmes & Davis 

 (112)] and hamster [Orsini (164)]. Perhaps the most 

 remarkable instance of localized implantation is found 

 in the South African shrew, Elephantulus myurus 

 jamesoni, which has a uterus duplex. This species 

 sheds dozens of ova at each ovulation; all become 

 fertilized but only two become implanted, one in 

 each uterus in a region of remarkable vascular de- 

 velopment [van der Hoist & Gillman (115)]. 



The meaning of the above relationships is being 

 studied by Boving (36, 37). Implantation occurs in 

 the vicinity of a single capillary loop lying beneath 

 the endometrial epithelium. Attachment (in the 

 rabbit) takes place when the abembryonic pole of the 

 blastocyst develops a sticky substance that is lacking 

 over the embryonic pole. This substance is related to a 

 gradient of alkalinity occurring within the blastocyst 

 and is associated with the differential in production of 

 metabolites between the embryonic pole and the 

 abembryonic pole of the blastocyst. The concept is 

 that the blood flowing through the capillary loop 

 removes C0 2 about as fast as it is produced, leaving 

 behind on the surface of the blastocyst a calcium- 

 proteinate residue that is sticky. Carbonic anhydrase 

 is present in high concentration in the endometrium 

 [Lutwack-Mann & Laser (138)]. The epithelium of 

 the endometrium breaks down when attachment 

 occurs [Boving (37)]- In intraocular transplants in 

 rats, trophoblast causes a breakdown of capillaries 

 [Grobstein (86)] as it does in the endometrium 

 [Mossman (158)]. 



From this time until the period of uterine conver- 

 sion (see above), when the pregnant uterus changes 

 from spheroidal to an elongating form, the uterine 

 vasculature undergoes enlargement and its blood 



