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S. AVENDAÑO, J. PELAEZ, and H. B. CROXATTO

There is little fundamental knowledge concerning the safe and timely transport of the developing egg into the uterus in the human. The present investigation was designed to test the feasibility of studying in vitro the transport of particulate matter by the human oviduct. In addition, since some of the oviducts were obtained from patients treated with megestrol acetate (MA = 17-alapha-acetoxy-6-methylpregna-4,6-diene-3,20-dione), a comparison was made of the transport in the tubes of these patients and in those obtained from a control group.

Twenty-two oviducts were obtained from healthy fertile women at the time of laparotomy for surgical sterilization. Nine of these were obtained from women who had been taking 0·5 mg MA daily for several months up to the

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G. D. Moore and H. B. Croxatto

Summary. Starch or dextran blue microspheres were transferred microsurgically to the infundibulum of the oviduct on Days 1, 2, or 3 of pregnancy of control and oestradiol-treated rats. The animals were killed a few hours to several days after transfer to assess the number and distribution of ova and microspheres in the tract.

After transfer on Day 1 of pregnancy, microspheres and eggs crossed the ampullary-isthmic junction (AIJ) 18 h after ovulation. After transfer on Day 2 of pregnancy, more than 50% of microspheres were retained in the ampulla, indicating that the AIJ changes again 34 h after ovulation. Treatment with oestradiol did not advance the passage of eggs or microspheres across the AIJ but caused accelerated transport through the isthmus as soon as the eggs or microspheres reached this segment. Dextran blue microspheres were seen to move back and forth in the isthmus of control anaesthetized rats at a frequency of 5–6 times/min. Between 7 and 20 h after treatment with oestradiol the frequency of these movements was significantly augmented, indicating that increased frequency of contractions of the smooth muscle of the isthmus precedes and accompanies accelerated transport of ova through this segment.

Keywords: rat; oviduct; embryo transport; oestradiol; microspheres

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C. V. Gómez and H. B. Croxatto

Summary. Changes in egg retention activity of the oviduct were assessed during the first 5 days after HCG-induced ovulation in rabbits. Dextran microspheres were used as ovum surrogates. They were injected into the peritoneal cavity at 0, 10, 32, 41, 50, 64, 72 and 80 h following HCG. The distribution of ova and surrogates in the genital tract was assessed 24 h following surrogate injection in all groups and at 8 h following surrogate injection in animals injected 50 h after HCG. The distribution of microspheres injected up to 50 h after HCG was similar to that of eggs. Surrogates were not retained at the ampullary–isthmic junction (AIJ) shortly after passage of ova through this region. Moreover, spheres injected 38 h after ovulation reached the eggs at the proximal isthmus in 8 h or less. Surrogates injected at 64 h following HCG or later were retained at the AIJ, indicating resumption of retaining activity at this level. It is suggested that egg passage through the AIJ is associated with a temporary reduction of the retaining activity lasting for approximately 16 h. Retaining activity at the AIJ is regained before eggs pass from the proximal isthmus into the uterus.

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G. D. Moore and H. B. Croxatto

Summary. Microspheres of various materials and diameters were transferred microsurgically to the rat oviduct on Day 1 of pregnancy and autopsies were done at various times thereafter up to Day 10 to assess the recovery and segmental distribution of microspheres and eggs in the genital tract or the viability of embryos. The number and distribution of eggs in the treated and control sides after unilateral transfers were not different on Day 4 and 5 and the number of embryos implanted on Day 10 was not significantly affected after bilateral transfers.

The segmental distribution of eggs and starch microspheres within the oviduct on Days 2, 3 or 4 showed that both are transported partly intermingled from ampulla to uterus. When microspheres of poly(dl-lactide-co-glycolide), starch, dextran or dextran blue were transferred, their distribution in the genital tract in the morning of Day 5 showed that poly(dl-lactide-co-glycolide) and dextran microspheres stayed longer in the oviduct while starch and dextran blue microspheres were transported to the uterus at the same time as the eggs. Transfer of starch microspheres of 40–60 μm to one oviduct and 180–200 μm in diameter to the opposite oviduct showed that distribution on one side was nearly identical to that of the other side from Days 2 to 5.

We conclude that the behaviour of synthetic surrogate ova in rats differs from that in rabbits. The rat oviduct does not change the rate of transport of native eggs following transfer of synthetic surrogate ova. Also, in the rat the composition of the surrogates has greater influence than their size on their time of passage to the uterus. Some surrogates mimic quite well the oviducal transport of embryos and can be used therefore to study this process in species in which the eggs are not coated with additional layers after ovulation.

Keywords: rat; oviduct; embryo transport; egg surrogate; microsphere

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M. L. Forcelledo and H. B. Croxatto

Summary. The effects of decreasing oestrogen secretion upon the rate of oocyte transport achieved by the administration of 4-hydroxy-4-androstene-3,17-dione were investigated in cyclic rats. Control animals examined during late pro-oestrus showed that the majority of oocytes had entered the uterus. In contrast, when inhibitor was administered from the afternoon of metoestrus or from late dioestrus through prooestrus, oviducal retention of oocytes was observed. When treatment was delayed until the morning of pro-oestrus, only uterine retention of oocytes was observed. The inhibitor decreased oestradiol concentrations in ovarian vein, while systemic testosterone values were increased. Treatment with exogenous oestradiol counteracted the effect of the inhibitor on ovum transport. The elevation of systemic testosterone concentrations by means of subdermal implants of testosterone failed to alter the normal pattern of ovum transport. These results demonstrate that normal oestrogen secretion during late metoestrus and dioestrus is required for the movement of oocytes from the oviduct to the uterus, whereas the preovulatory oestrogen surge is needed for the expulsion of ova from the uterus.

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H. B. CROXATTO, C. VOGEL, and J. VASQUEZ

Experimental analysis of the influence of endogenous hormones on egg transport in the oviduct requires groups of animals in which the endocrine environment differs from that prevailing during the early postovulatory period. In order to measure transport in these animals, a substitute for the egg must be introduced. Eggs in cumulus obtained from donor rabbits (Noyes, Adams & Walton, 1959) or radioactive microspheres (Harper, Bennett, Boursnell & Rowson, 1960) have been used as substitutes, but both require surgical techniques and neither substitute is readily available.

The present study was undertaken to see if dextran microspheres injected into the peritoneal cavity would act as useful substitutes for the egg in rabbits. Their uptake and transport by the genital tract was assessed under various endocrine conditions and the influence of their size on the speed of transport was also investigated.

Female rabbits obtained at the local market were isolated and given 25

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J. Zenteno, C. Silva, H. Cárdenas, and H. B. Croxatto

Summary. Silastic devices impregnated with oestradiol and blank devices were placed around both oviducts and around skeletal muscle bundles in the forelegs to attain local and systematic delivery, respectively. Another group of mice received an oestradiol-impregnated device around one oviduct and a blank device in the contralateral oviduct. Implantation of blank devices around the oviducts and in the forelegs did not alter ovum transport. Devices impregnated with oestradiol placed around both oviducts produced a dose-dependent delay of ovum transport, which was more pronounced than the effect of devices located in the forelegs. Oviducts receiving an oestradiol-loaded device had a larger retention of ova than did the contralateral oviducts receiving a blank device. These results demonstrate a direct action of oestradiol upon the oviduct to delay ovum transport in the mouse.

Keywords: oviduct; egg transport; oestradiol; mouse

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C. R. Prieto, H. Cardenas, and H. B. Croxatto

Quantitative relationships between physical parameters of sucking, milk transfer and the duration of amenorrhoea were examined in normal mother–baby pairs under exclusive breastfeeding. Sucking pressures were recorded twice on the second and once on the fifth month after birth, during complete breastfeeding episodes, by means of a catheter attached to the nipple and connected to a pressure transducer, the signals of which were analysed by computer. Babies were weighed before and after each sucking episode to estimate milk transfer. In the first nursing episode after noon, 2-month-old babies sucked from 140 to > 800 times during 4–15 min from the first breast, obtaining from 20 to > 100 g milk. The physical parameters of sucking and milk transfer exhibited high inter-individual but low intra-individual variabilities. There were significant differences in the physical parameters of sucking and milk transfer efficiency between first and second breast and between the second and fifth months after birth. Milk transfer efficiency was inversely correlated with time occupied by non-sucking pauses ≥ 1.5 s, and was directly correlated with mean intersuck intervals in the first breast and with duration of the sucking episode, number of sucks, mean pressure and area under the pressure curve in the second breast. There was no correlation between the physical parameters of sucking and duration of lactational amenorrhoea (n = 62). However, significantly more mothers had amenorrhoea lasting > 180 days among those whose babies spent a longer proportion of the nursing episode in non-sucking pauses ≥ 1.5 s. This finding indicates that sensory stimulation of the nipple produced during a nursing episode by stimuli other than sucking itself may have an important role in sustaining lactational amenorrhoea. It is concluded that nursing episodes have a complex structure that allows the development of a breastfeeding phenotype in each mother–baby pair, exhibiting important inter-individual variability. The present analysis does not support the contention that this source of variability accounts for the variability in the duration of lactational amenorrhoea.

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H. B. Croxatto, M. E. Ortiz, S. Díaz, and R. Hess

Summary. The effect of various compounds upon ovum transport was investigated by comparing the location of the ovum in treated and untreated subjects between 24 and 120 h following the LH peak. The compounds were administered in the immediate post-ovulatory period. Methyl ergonovine and 15(S)15-methyl-prostaglandin F-2α were given at doses which stimulate human tubal contractility in vivo. Ergonovine maleate, also at a dose which stimulates tubal contractility, was given in conjunction with a βadrenergic agonist (Ritodrine) in order to prevent closure of the lumen in the narrow portions of the oviduct. Oestradiol-17β was given i.m. as a single dose of 5 mg. Utilizing overall recovery of ova, their segmental distribution within the Fallopian tube or their distribution between Fallopian tubes and uterus as the criteria for comparison between control and treatment groups, no evidence was obtained that any of the treatments accelerated transport. Oestradiol and Ritodrine should be tested at higher doses and an experimental design to disclose delayed transport should be used before concluding that these treatments have no effect upon ovum transport in women. The present results permit the conclusion that compounds which stimulate tubal contractility do not necessarily accelerate ovum transport. The implications of these findings for our current concepts on the physiology and pharmacology of ovum transport are discussed.

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L. A. Velasquez, S. R. Ojeda, and H. B. Croxatto

Platelet-activating factor (PAF) is a lipid mediator that has a range of biological effects on various cells and tissues. PAF-like activity has been detected in the spent media of two-cell to morula stage hamster embryos, leading to the suggestion that PAF may be the embryonic signal that hastens embryo transport to the uterus in this species. The present study was undertaken to examine whether the PAF receptor (PAFr) gene is expressed in hamster oviduct, and to identify the cell types in which the gene is expressed. DNA fragments complementary to the coding region of mRNA encoding hamster PAFr were cloned by reverse transcription–polymerase chain reaction (RT–PCR), identified by sequencing and used to prepare hamster specific cRNA probes. The presence of mRNA transcripts encoding the PAFr receptor in the oviduct was investigated by subjecting oviduct mRNA to RT–PCR. Southern blot analysis of the RT–PCR products verified the identity of the presumptive PAFr cDNAs. The cloned cDNA fragment of hamster PAFr was found to be highly conserved with respect to the receptor of other species, having 94.3% sequence similarity to the rat PAFr receptor. Hybridization histochemistry demonstrated that PAFr is expressed in the subepithelial cells and occasionally in the epithelium. In conclusion, expression of PAFr in the hamster oviduct is compatible with the proposed paracrine role of early embryo-derived PAF.