Species Differences in Egg Transport in Response to Exogenous Estrogen GILBERT S . GREENWALD Departments of Obstetrics and Gynecology and Anatomy, University of Kansas Medical CenteT, Kansas City, Kansas The effect of exogenous estrogen on tubal transport of ova was deABSTRACT termined in the guinea pig, hamster, mouse, rabbit and rat. T h e animals were given a single injection of estradiol cyclopentylpropionate ( E C P ) shortly after mating. The dose of ECP required to interrupt pregnancy in 80% or more of the animals was as follows: guinea pig (10 fig); hamster (25 p g ) ; mouse (1 fig); rabbit ( 5 0 pg); rat (10 pg). Acceleration of egg transport through the oviduct occurred after the following doses of ECP: guinea pig (50-100 pg); hamster (100 pg); mouse (1 pg and above); rabbit (25 pg); rat (10 pg and above). Hence, the amount of estrogen which accelerates egg transport in the guinea pig and hamster is considerably higher than the dose which interrupts pregnancy. Retention of ova for longer than the normal period of tubal passage (tube-locking) resulted from the following doses of ECP: guinea pig (250 pg); hamster (250 pg); mouse (1pg); rabbit (100 pg); rat (no dose). In the species i n which ova were tubelocked, the majority of eggs were located a t the ampullary-isthmic junction rather than the utero-tuba1 region of the oviduct. Tube-lockjng of ova was never observed in the rat; ECP always caused premature entry of eggs into the uterus and eventual expulsion per uaginam. For example, eggs passed through the cervix by 12 hours after the administration of 250 fig ECP at day 1 of pregnancy. The effectiveness of estrogens in interrupting pregnancy in the mouse and rat was first shown by Parkes and Bellerby ('26) and Smith ('26). A fruitful period of research occurred during the next decade, culminating in the work of Burdick and associates (Burdick and Pincus, '35; Whitney and Burdick, '36, '38; Pincus and Kirsch, '36). These investigations were mainly concerned with the effect of exogenous estrogen on egg transport in the mouse and rabbit. The major findings were that moderate doses of estrogen retained eggs in the oviduct for longer than the usual period of tubal passage (henceforth referred to as tube-locking) : however, large doses of estrogen accelerated transport so that ova were prematurely expelled from the oviduct into the uterus. There has recently been renewed interest in the effect of estrogen on pregnancy in rodents. Most of these studies have used as an endpoint the number of young delivered at term or the number of embryos present at 8-10 days past coitum. In view of the numerous pre-implantation events affected by estrogen, such studies quite ANAT. REC., 157: 163-172. obviously shed little light on the mechanisms responsible for embryonic mortality. Several studies from this laboratory have considered the effect of exogenous estrogen on egg transport in the rabbit and rat. Contrary to the initial reports, small doses of estrogen in the rabbit expelled ova from the reproductive tract and large doses caused tube-locking (Greenwald, '57,'59, '63). It is of interest that the block to egg transport was located at the level of the ampullary-isthmic junction rather than the utero-tuba1 junction (Greenwald, '61a). In the rat, effective doses of estrogen always caused premature entry of eggs into the uterus; no dose was found which retarded egg transport through the oviduct (Greenwald, '61b). Several authors have postulated that in the rat tube-locking is responsible for the embryonic mortality that follows estrogen treatment. However, the concept of tube-locking is based on the mouse and there is no evidence to substantiate its existence in the rat. The guinea pig is the only other species in which the effect of estrogen on tubal transport has been determined (Deanesly, '61 ) Over the . 163 164 GILBERT S. GREENWALD dosages utilized, estrogen induced premature entry of guinea pig eggs into the uterus; higher doses which might have been expected to cause tube-locking were not tested. The present report was designed to compare the effects of estrogen on egg transport in five species: guinea pig, hamster, mouse, rabbit and rat. It was felt that the uniformity resulting from the use of a single estrogenic preparation, administered over the same dosage range to all five species, combined with a standard method to recover ova from the reproductive tracts would considerably enhance the value of such a study. The specific objectives of this investigation were to ( 1 ) determine the dose of estradiol cyclopentylpropionate (ECP) required to interrupt pregnancy, when given as a single injection shortly after mating; ( 2 ) to ascertain whether the embryonic mortality following estrogen treatment was attributable to acceleration of egg transport and/or tubelocking of ova, and ( 3 ) to localize the site in the oviduct at which ova are trapped if tube-locking does occur. MATERIALS AND METHODS Positive smear or vaginal plug) with different doses of ECP; ova were flushed from the reproductive tract during the next 2 to 5 days. Sixty-one guinea pigs of a mixed strain were placed with fertile males on the night of full vaginal cornification. Mating was either observed or confirmed by the presence of sperm in the vagina by the next morning (day 1 of pregnancy). Animals were then injected subcutaneously with 1 to 250 ug ECP. In contrast to the other species in which ova were recovered by flushing via the ostium tubae abdominale, eggs were recovered from the guinea pig by inserting the 30 gauge needle into the oviduct via the uterotubal junction. Tube-locking of ova was observed in the guinea pig, hamster, mouse and rabbit. To determine the region in the fallopian tube at which ova were blocked, the oviduct was divided into three segments : ampullaryisthmic region, isthmus and utero-tuba1 junction. Each segment was then flushed with 0.9% physiologic saline. The ampullary-isthmic region consisted of the ampulla and the contiguous first loop of isthmus; the utero-tuba1 junction contained the tip of the uterus and the adjacent segment of isthmus. All doses of estradiol cyclopentylpropionate were injected in 0.1 ml cottonseed oil. Additional experiments are described in appropriate sections of the text. A total of 45 New Zealand giant white rabbits were used in the experiments. The does were mated twice to males of proven fertility and immediately post coiturn given a single intramuscular injection of 25 to 250 wg estradiol cyclopentylpropionate RESULTS (ECP). During the next five days, rabbits Guinea pigs were given a single injecwere killed by intravenous injection of 5 ml sodium pentobarbitone. The location tion of cottonseed oil or ECP on the mornof tubal ova was determined by a previ- ing of sperm-positive vaginal smears. At ously described method (Greenwald, '61a). laparotomy, 12 to 15 days later, only half Sprague-Dawley rats of the Holtzman of the animals treated with 1 vg ECP were strain (66 animals) were caged with males pregnant whereas five of six pregnancies and on the morning that sperm were found were terminated by 10 vg of the hormone in the vaginal smear (designated as day 1 (table 1). However, regressing avascular of pregnancy) the females were injected corpora lutea were observed in the ovaries subcutaneously with 1 to 500 vg of ECP. of a number of the ECP-treated animals The animals were killed at various inter- SO that it appeared likely that the interrupvals during the preimplantation period by tion of pregnancy was due to a luteolytic an overdose of ether. The oviducts and action of ECP rather than to its effects on cornua were flushed separately with physi- egg transport. The former explanation was apparently ologic saline by a 30 gauge needle attached to a 0.5 ml tuberculin syringe. confirmed when the location of ova was Similarly, 69 golden hamsters and 70 determined following ECP treatment. In white swiss mice were mated and injected control animals (injected with cottonseed subcutaneously on day 1 (day of sperm oil) ova were present in the oviduct on 165 ESTROGEN AND EGG TRANSPORT TABLE 1 Effect of ECP on pregnancy in the guinea pig Mean no. embryos (+- SE) Trealment at day 1 No. of animals 0.1 ml cottonseed oil 7 6 3.5 f0.86 - 1 p g ECP 8 4 3.0f0.58 3 animals with regressing corporalutea (C.L.) 10 p g ECP 6 1 3.0 4 animals with regressing C.L. 1 Laparotomy No. pregnant 1 Remarks at 12 to 15 days P.C. TABLE 2 Effect of ECP Time examined (days p.c.1 OR ova distribution in the guinea pig No. of Location of ova 3 4 3 5 oviduct ( 3 ) oviduct (3)[ uterus ( 2 ) J 2-4 celled ova; x’ no. eggs = 2.7 3 1 4 1 oviduct uterus - 3 4 2 1 oviduct uterus .- 50 pg ECP 3 4 3 2 oviduct missing E no. eggs = 2.0 100 p g ECP 3 4 1 7 oviduct missing - 250 pg ECP 4 7 oviduct ( 5 ) missing (2) - oviduct ( 3 ) missing ( 1 ) - Treatment at day 1 Controls 1 pg ECP 10 p g ECP 5 1 4 Remarks 12-16 celled ova no eggs in tract no eggs in tract ._ - No. in parentheses = no. of animals in thls category. day 3 p.c. (table 2). By the morning of day 4, eggs began to enter the uterus although in some animals they were still present in the oviduct. Following the injection of 1 to 50 Vg ECP ova were still located in the oviduct by day 3. However, with 50 or 100 vg ECP, ova were absent from both the uterine tubes and horns by day 4. These doses presumably accelerated egg transport to the extent that ova were expelled from the reproductive tract. Tubelocking of guinea pig ova occurred after the injection of 250 vg ECP at day 1, although in a few instances no eggs were found in any portion of the tract (table 2). The oviduct was sectioned at day 5 in three animals which received 250 pg ECP. Normal morulae were recovered from all animals ( 2 , 3 , 3 eggs) from the ampullaryisthmic region of the tube, which lies approximately 4 cm above the utero-tuba1 junction. Effectsof ECP on pregnancy in the hamster The hamster was much more resistant to the deleterious effects of ECP than the other species that were investigated. Neither 1 nor 10 pg ECP interrupted pregnancy (table 3) but 25 to 100 pg of the hormone terminated pregnancy in every animal. Treatment with 25 vg or more of ECP led to the regression of the corpora lutea of pregnancy; they were represented 166 GILBERT S. GREENWALD TABLE 3 Effect of ECP on pregnancy in the hamster Treatment at d a y 1 No. of No. animals pregnant 1 Mean no. embryos Remarks (._ + SE) ~~I 1pg ECP 10 Fg ECP 25 pg ECP 50 p.g ECP 100 gg ECP 4 4 4 4 0 4 4 0 0 4 1 Hamsters killed 10.0-+0.71 11.0* 1.08 -0-0- -0- - 2/4 with corpora albicantia (CA) 4/4 with CA 4/4 with CA at eight days p.c. TABLE 4 Effect of ECP on ova distTibution in the hamster Treatment at day 1 Controls Time examined No. of (days P.c.) Location of ova Remarks 2 3 4 3 3 3 oviduct ( 3 ) oviduct ( 3 ) uterus ( 3 ) 2 celled eggs 4-8 celled eggs beginning of nidation 25 gg ECP 5 3 oviduct and uterus ( 3 ) 4-8 celled eggs 50 pg ECP 3 3 4 3 oviduct and uterus (3)( no eggs recovered J 14 eggs - oviduct 116 eggs - uterus 100 pg ECP 2 3 3 oviduct ( 3 ) no eggs in tract (3) j ; no. eggs 250 fig ECP 2 2 3 4 38 4 3 5 oviduct (2 ) oviduct (3) missing ( 1) oviduct ( 3 ) oviduct (4) missing ( 1) 3 - = 10.7 - eggs = 10.0 -xx no. no. eggs = 2.3; 4celledeggs --xx no. no. eggs = 9.3 eggs = 3.3; blastocysts and degenerating ova 5 3 oviduct ( 3 ) NO.in parentheses = no. of animals inthis category. Cornua ligated at day 1. - ;no. eggs = 3.3; ova degenerating in the ovary on day 8 by small, avascular locking of ova. However, from day 3 on very few ova were retained in the falcorpora albicantia. The normal rate of egg transport was lopian tubes and it seemed plausible that determined in a series of uninjected ham- the missing ova had already entered the sters. Ova were present in the oviduct on uterus before being expelled from the tract. day 2 and the morning of day 3, but they To test this possibility, the oviducts of entered the uterus by the afternoon of three ECP-treated animals were ligated at day 3 (table 4). Blastocysts could no the utero-tuba1 junction on day 1. When longer be flushed from the uterus by day 4 killed two days later, the normal compleindicating that nidation had begun. A ment of ova were found in the ligated single injection of 50 vg of ECP accel- tubes (table 4). The specific site at which hamster ova erated the rate of transport; healthy blastocysts in normal numbers were present in were retained was determined by sectionthe uterus on day 3. Following treatment ing the oviduct into three segments (table with 100 pg ECP, two-celled eggs were in 5 ) . The results indicate that the majority the oviduct on day 2 but ova were missing of eggs were trapped at the ampullaryfrom the tract by day 3. A single injection isthmic junction and not in the proximity of 250 pg of the hormone caused tube- of the utero-tuba1 junction. By day 4, some 167 ESTROGEN AND EGG TRANSPORT of the tube-locked ova were still normal but all eggs had degenerated by the next day. TABLE 5 Site of tube-locking of ova i n hamster' Day oviduct sectioned: Day4 Day5 No. of hamsters: 4 4 No. with tube-lockedova: 4 4 122 4 2 0 0 Location of ova: 1. Ampullary-isthmicjunction (MS) 2. Isthmus 3. Utero-tubal junction ( UTJ 1 1 a 92 Hamsters injected with 250 pg ECP at day 1. No. of ova recovered from each segment. Effect of ECP on mouse pregnancy A single injection at day 1 of 0.1 pg ECP had no more effect on pregnancy in the mouse than the injection of cottonseed oil; the percentage of pregnant animals and mean number of embryos did not differ between the two groups (table 6). Pregnancy was interrupted in every instance on increasing the dose of ECP to 1 wg. In control mice, ova were present in the oviduct on the morning of day 3 but all o n pregnancy i n the mouse eggs migrated into the uterus by the next morning (table 7). After the injection of Mean no. No. of No. 0.1 vg ECP, ova were retained in the ovianimals pregnant 1 Tybg~ duct at day 4 in over half the animals (table 7) and an average of 5.6 normal 6 4 9.3& 0.85 appearing blastocysts were recovered. 6 4 11.0f0.41 Treatment with 1 pg ECP resulted in tubal retention of ova in five mice, with an aver6 0 age of five blastocysts per animal. However, in four additional animals, no eggs days p.c. TABLE 6 Effect of ECP Treatment at day 1 ~~ 0.1 ml cottonseed oil 0.1 pg ECP 1 pg ECP 1 Mice killed 9-12 TABLE 7 Effect of ECP on ova distribution in mice Treatment at day 1 Cottonseedoil 0.1 fig ECP 1 pg ECP Time examined (days P.c.) N?. Location of ova Of 3 4 5 2 3 4 1 7 3 2 4 10 Remarks oviduct ( 2 ) uterus ( 3 ) l uterus (2)J 4-8-celled eggs blastocysts uterus oviduct ( 4 ) uterus (2) no eggs (1) oviduct (5) uterus (1) missing ( 4 ) - - - - - no eggs in tract 10 pg ECP 4 5 missing ( 5 ) no eggs in tract 100 fig ECP 4 4 missing ( 4 ) no eggs in tract 1 No. of animals in this category. TABLE 8 Location of tubal ova in mice at day 4 after ECP treatment Dose of ECP at day 1 No: of mice No. with tubal ova Tuba1 ova/ animal Location of tubal ova 1 AIJ Isthmus UTJ 0.1 fig 5 2 1.5 0 0 3 1.0fig 16 11 4.2 27 10 9 Actual number of eggs recovered from each segment. 168 GILBERT S. GREENWALD were recovered from either the oviduct or uterus. With 10 or 100 vg ECP, no ova were found in the reproductive tracts by day 4. Attention was next directed to the specific site in the oviduct at which ova were tube-locked on day 4 p.c. (table 8). The results indicate that a single injection of 0.1 clg ECP at day 1 was relatively ineffective in retaining ova in the tubes; the few ova present were clustered at the uterotubal junction. However, following the administration of 1 ug ECP, considerably more ova were tube-locked, with the majority recovered at the ampullary-isthmic junction. For the 1 ug ECP group, the average number of eggs found on sectioning the oviduct into three portions was similar to the number recovered following flushing of the tube in toto. On the other hand, there was a discrepancy between the number of eggs collected by the two methods in mice receiving only 0.1 vg ECP. The fewer ova recovered from these mice could be attributed either to the small number of animals sampled or to possible loss of ova at the time that the oviduct was divided. Vigorous contractions of the muscular isthmic and utero-tuba1 areas might expel ova from the divided oviduct. This phenomenon apparently also occurs in the rabbit since there is a discrepancy in the number of ova recovered from the lower isthmus when eggs are flushed from the intact or divided tube (Greenwald, '61a). TABLE 9 Effect of ECP on pregnancy in the rabbit' Dose 1Pg 10 ag 25 /a 50 ag 100 Pg 250 pg No. No. of animals pregnant 6 6 6 6 6 6 6 3 3 1 0 0 Mean no. of embryos I + SE', 8.332 1.02 3.17% 1.45 1.50-tO.80 0.33t0.33 0.0 0.0 Modified from Greenwald ('63). mating, resulted in a marked disparity between the number of corpora lutea and embryos by eight days post coitum (table 9). Of 18 rabbits given from 50 to 250 vg of ECP, only one animal remained pregnant; 25 clg was almost as effective in interrupting pregnancy. The oviduct was flushed during the first five days after ovulation to ascertain whether disturbances in the rate of egg transport could account for the embryonic loss. Ova normally remain in the oviduct for 72-75 hours p.c. before entering the uterus (Boving, '56). By 48 hours after mating, most of the eggs passed through the oviducts of rabbits given 25 ug of ECP (table 10). On the other hand, treatment with 100 or 250 vg of the hormone leads to retention of ova in the fallopian tube, primarily at the ampullary-isthmic region of the tube. All eggs had degenerated by day 5 . Effect of ECP on pregnancy in the rat Effect of ECP on pregnancy in the rabbit The effect of a single injection of ECP A single intramuscular injection of 10 on rat pregnancy is summarized in table ug ECP, administered immediately after 11. The administration at day 1 p.c. of 5 TABLE 10 Location of ova in the rabbit after ECP treatment Location of ova in oviduct 62 12 AIJ (9) Isthmus ( 3 ) 4 31 23 AIJ (21) Isthmus (2) 4 37 28 AIJ (20) Isthmus (8) Day killed No. of animals 25 fig 3 7 100 Pg 5 250 cLg 5 1 Day 1 = day of mating. Total no. of Total no. eggs recovered Dose of EqP at day 1 * No. of ova recovered from each segment. lutea 169 ESTROGEN AND EGG TRANSPORT uterine eggs were recovered from only one of five rats. With higher doses of ECP, ova were missing from both the oviducts and No. cornua at day 5. Thus, ECP in the doses Treatment ~ o . o f pregnant ys:g at day 1 animals (9-11 utilized, never produced tube-locking of days P.c.) (*SE) ova. 0.1 ml cottonThe results suggested that, if anything, 4 4 10.5 k2.9 seed oil exogenous estrogen in the rat caused pre4 4 11.3 42.8 1 pg ECP mature entry of ova into the uterus and thence their expulsion per vaginum. To 4 3.9 C 1.7 8 5 fig ECP test this possibility, rats given a single in1 0.4 f0.37 8 10 p g ECP jection of 250 pg ECP were killed at progressively earlier times and the reproduc1 Modified from Greenwald (’61). tive tract examined for ova. The results TABLE 12 (table 13) indicate that ova disappeared Location of ova in the rat after ECP treatment by day 2 P.c.; i.e. 24 hours after the injecTime No. of tion of 250 pg ECP. Ova still embedded in Treatment examined No’ Of animals (days P.c.) with ova granulosa cells were recovered from the oviduct, five hours after the administration Controls 2 1 1 oviduct of ECP but by 12 hours, most of the eggs 4 3 3 oviduct were no longer in the tract. An additional 5 6 6 uterus 5 0.1pgECP 5 5 uterus group of three mated rats were injected 5 5 1pgECP 4 uterus with 250 pg ECP and the cornua then 10mECP 5 5 1 uterus ligated at the cervical end (table 13). When killed 12 hours later, eggs were recovered from the uterus, a site normally not reached until days 4 to 5 p.c. The obor 10 pg ECP interrupted pregnancy in al- vious conclusion is that egg transport in most every animal. The rats were pseudo- the rat is extremely sensitive to estrogen pregnant on the basis of persistent vaginal with considerable acceleration in the rate diestrus. of migration of ova. The location of ova in the reproductive DISCUSSION tract is recorded in table 12. In normal pregnant rats, ova were still present in the A comparison of the effects of a single oviduct on the morning of day 4 but mi- injection of ECP on egg transport in the grated into the uterus by the next day. five species amply justifies the inclusion Following the injection of 0.1 or 1.0 crg of the phrase “species-differences” in the ECP, normal blastocysts were found in the title of this paper. In the mouse, a relauterus on day 5 but with 10 pg ECP, tively small dose of ECP caused tubeTABLE 11 Effect of ECP on pregnancy i n th.e rat Lzfc:toa’]. TABLE 13 Effect of 250 pg ECP on e g g transport in the rat Time examined Day 5 Location and no. of ova 5 0/5 - Day 3 2 0/2 - Day 2 2 0/2 - Dayl- 1 animals NO. of animals with ova No. of 5hours 2 2/2 oviduct (13,13) Day 1 - 12 hours 2 1/2 oviduct ( 5 ) Day 1 - 12 hours 3 3/3 oviduct (O,O,2) uterus ( 6 , 9 , 4 ) Uterus ligated immediately after ECP injection. 170 GILBERT S. GREENWALD locking of ova; larger doses accelerated the rate of transport through the oviduct. These results confirm the findings of Burdick and Pincus ('35) which to my knowledge have never been repeated since the original observations. ECP in a dose range of 1 to 500 pg failed to induce tube-locking of ova in the rat. On the contrary, estrogen treatment above the 1 clg dose consistently accelerated egg transport. Following the injection of 250 vg of ECP, ova were normally expelled from the reproductive tract within 12 hours. The acceleratory effects of estrogen on egg transport in the rat confirm preliminary observations (Greenwald, '61b) and the work of Banik and Pincus ('64). The latter authors found that doses of 20 clg or higher of estrone caused a premature expulsion of eggs into the uterus in about 20-24 hours. The marked sensitivity to estrogen of the reproductive tract of the female rat is of interest for two reasons. Firstly, a number of authors have postulated that tubelocking of rat ova accounts for the preimplantation mortality that follows estrogen administration. This represents an unfounded extrapolation from the effects of estrogen in the mouse. Secondly, the rat has been used extensively to determine the mode of action of various nonsteroidal compounds which interrupt pregnancy (for references, see Walpole, '65). The failure to recover ova from rats treated with these compounds has been interpreted as indicating that they exert a direct anti-zygotic action, leading to rapid degeneration of ova. However, these compounds have estrogenic as well as antiestrogenic activity and the disappearance of ova could result from acceleration of egg transport rather than the dissolution of ova in utero. This has already been shown to be the case with a diphenylindene derivative-U-11 lOOA (Greenwald, '65a). The simple procedure of ligating the cornua at the cervical end would permit a distinction between the direct or indirect effect on ova of these non-steroidal agents. With the exception of the mouse and rat, increasing doses of ECP first accelerated egg transport and then at still higher levels caused retention of eggs in the oviduct. The results in the rabbit are consistent with previous investigations from this laboratory (Greenwald, '61a, '63). My findings contradict the previous studies of Pincus and Kirsch ('35) who reported that low doses of estrogen induced tube-locking of ova in the rabbit whereas high doses invariably accelerated egg transport. No explanation can be offered for the different results. In both the hamster and guinea pig the dose of ECP which disrupted egg transport was considerably higher than the minimal amount required to terminate pregnancy. Hence, other mechanisms sensitive to estrogen are responsible for the interruption of pregnancy by the hormone. It has already been well established for the hamster that estrogen has a luteolytic action on the corpora lutea of pregnancy (Greenwald, '65b). This is accomplished by a single injection of 25 ug ECP compared to the 100 pg dose necessary to expel ova from the reproductive tract. The hamster was by far the most resistant species to ECP, requiring a minimum of 25 clg of the hormone to interrupt pregnancy. This may account for the fact that massive amounts of U-11100A are unable to interfere with pregnancy in the hamster (Duncan et al., '63) unlike the situation in the rat. The effective dose of ECP which interrupted pregnancy in the guinea pig was also less than the amount required to alter tuba1 transport. The lower dose level appears to also act on the maintenance of the corpus Iuteum since regressing corpora albicanita were observed in a number of guinea pigs killed 12 to 14 days post coitum. However, it is possible that other preimplantation phenomena are affected by the hormone. Deanesly ('61) found that treatment with less than 10 clg of estradiol benzoate did not accelerate oviducal transport of eggs in the guinea pig and there was no evidence that tube-locking of ova occurred at any dose tested. In the present study ova were tube-locked at day 5 after a single injection of 250 clg ECP, a dose considerably higher than any that were used by Deanesly. In the current investigation, the specific site at which ova were tube-locked was of considerable interest. It has previously been shown that ova are retained in the oviduct of the rabbit at the ampullary- ESTROGEN AND EGG TRANSPORT 171 isthmic junction (Greenwald, ’61a). The BGgli, B. 1959 Das tuba-uterine ventil beim goldhamster. Rev. Suisse de Zool., 66: 14-227. present experiments demonstrate that the BGving, B. G. 1956 Rabbit blastocyst distribuprincipal blocking mechanism for egg tion. Am. J. Anat., 98: 403-434. transport also exists at this site in the Burdick, H. O., and G. Pincus 1935 The effect of oestrin injections upon the developing ova mouse, hamster and guinea pig. Burdick, of mice and rabbits. Am. J. Physiol., 111: 201Emerson and Whitney (’40) noted that in 208. the androgen-treated mouse more ova were Burdick, H. O., B. E. Emerson and R. Whitney recovered from the “ovarian” third of the 1940 Effects of testosterone propionate on fallopian tube than the remaining portion. pregnancy and on passage of ova through the The utero-tuba1 junction (UTJ) has long oviducts of mice. Endocrinology, 26: 10811086. been thought to be the major barrier to egg transport and its anatomy has been Deanesly, R. 1961 The effects of oestrogen on tubal transport and ovo-implantation in the the subject of several papers (Lee, ’28; guinea-pig. Proc. IVth Inter. Cong. on Animal Kelly, ’28; Anderson, ’28; Bogli, ’59). It Reprod., 371-374. appears that the ampullary-isthmic junc- Duncan, G. S., S. C. Lyster, J. J. Clark and D. Lednicer 1963 Antifertility activities of two tion (AIJ) may be of greater significance diphenyl-dihydronaphthalene derivatives. Proc. in egg transport than the UTJ. The nature Soc. Exp. Biol. & Med., 112: 43-42. of the blocking mechanism at the AIJ has Greenwald, G. S. 1957 Interruption of pregnot been definitely determined. However, nancy in the rabbit by the administration of estrogen. J. Exp. Zool., 135: 461-481. the AIJ represents the junction between 1959 The comparative effectiveness of the thick muscular isthmus and the less estrogens in interrupting pregnancy in the muscular ampulla. Hence, a sphincteric rabbit. Fertil. & Steril., 10: 155-161. block at the AIJ appears to be a strong 1961a A study of the transport of ova possibility for the tube-locking activity of through the rabbit oviduct. Fertil. & Steril. 12: 80-95. estrogen. 1961b The anti-fertility effects in pregAlthough tube-locking of ova occurred n a n t rats of a single injection of estradiol in all species examined (except for the cyclopentylpropionate. E n d o c r i n o l o g y , 69: rat), massive amounts of estrogen were 1068-1 073. required in the hamster, guinea pig and 1963 Interruption of early pregnancy in the rabbit by a single injection of oestrarabbit. These doses certainly represent diol cyclopentylpropionate. J. Endocrin., 26: pharmacologic amounts, rarely, if ever, 133-138. duplicated by endogenous hormone levels. 1965a Effects of a dihydronaphthalene The usual effect of smaller quantities of derivative (U-11100A) on pregnancy in the rat. Fertil. & Steril., 16: 185-194. exogenous estrogen is acceleration of egg 196513 Luteolytic effect of estrogen on transport through the oviduct and eventual the corpora lutea of pregnancy of the hamexpulsion of ova per vaginam. Hence, egg ster. Endocrinology, 76: 1213-1219. transport is a very vulnerable stage in the Kelly, G. L. 1928 The utero-tuba1 junction in the guinea pig. Am. J. Anat., 40: 373-318. reproductive cycle and one, which for several reasons, would be suitable for various Lee, F. L. 1928 The tubo-uterine junction in various mammals. John Hopkins Hosp. Bull., methods of fertility control. 42: 335-357. ACKNOWLEDGMENTS This is a contribution from the Research Professorship In Human Reproduction. The research was supported by grant HD00596-04 from the NIH-U.S.P.1I.S. and by the Ford Foundation. LITERATURE CITED Andersen, D. H. 1928 Comparative anatomy of the tubo-uterine junction. Histology and physiology in the sow. Am. J. Anat., 42: 255305. Banik, U. K., and G. Pincus 1964 Estrogens and transport of ova in the rat. Proc. Soc. Exp. Biol. & Med., 116: 1032-1034. Parkes, A. S., and C. W. Bellerby 1926 Studies o n the internal secretions of the ovary. 2.The effects of injection of the oestrus producing hormone during pregnancy. J. Physio., 62: 145- 155. Pincus, G., and R. Kirsch 1936 The sterility in rabbits produced by injections of oestrone and related compounds. Am. J. Physio., 115: 219228. Smith, M. G. 1926 On the interruption of pregnancy in the rat by the injection of ovarian follicular extract. Bull. Johns Hopkins Hosp., 39: 203-214. Walpole, A. L. 1965 Non-steroidal agents inhibiting pituitary gonadotrophic function. In: Agents Affecting Fertility. Ed. by C. R. Austin and J. S. Perry, Little, Brown & Co., Boston, Mass., pp. 159-179. 172 GILBERT S. GREENWALD Whitney, R., and H. 0. Burdick 1936 Tubelocking of ova by oestrogenic substances. Endocrinology, 20: 643-647. - 1938 Acceleration of the rate of passage of fertilized ova through the fallopian tubes of rabbits by massive injections of Progynon B. Endocrinology, 22; 639-642.