Sperm transport and reservoirs in the pig oviduct in relation to the time of ovulation

The rate of establishment of a population of viable spermatozoa in the oviducts was studied using a technique of post-coital transection in conjunction with subsequent examination of the proportion of eggs fertilized. Gilts were mated early in oestrus (before ovulation) or on the 2nd day of oestrus (after ovulation), and 30, 45 or 60 min later the reproductive tract was sectioned just above or below the utero-tubal junction in a total of 48 animals; these were slaughtered 1 or 2 days after the operation. Some fertilized eggs were recovered from 40 animals, and 72.3% of the 679 eggs examined were fertilized. Mean percentage fertilization increased overall (a) with the time elapsing from mating to transection, (b) with transection below the utero-tubal junction compared with in the caudal isthmus, and (c) with a post-ovulatory versus pre-ovulatory mating. In a further 6 gilts, the results of transection in the lower third of the oviduct 3 h after mating at the onset of oestrus indicated that spermatozoa were initially sequestered in the caudal portion of the isthmus. It is concluded that a population of spermatozoa sufficient to give maximum fertilization is established in the oviducts within 1--2 h of mating, thereby affording protection from the uterine invasion of polymorphonuclear leucocytes.     

Capacitation status of hamster spermatozoa in the oviduct at various times after mating

Female hamsters were mated shortly after the onset of oestrus or immediately after ovulation. At various times after mating, spermatozoa were flushed from the isthmus of the oviduct using a modified Tyrode's medium supplemented with 20% hamster serum. Cumulus oophorus-free eggs were introduced into the suspensions of isthmic spermatozoa. Some eggs were removed every 30 min and examined for evidence of fertilization. For females mated shortly after the onset of oestrus, spermatozoa recovered from the oviducts 8 h after mating (about 1.5 h after ovulation) could penetrate eggs within 30 min and were considered fully capacitated. When spermatozoa were recovered at earlier times (1, 2, 4 and 6 h after mating) they required additional time (2, 1.5, 1 and 1 h respectively) in vitro before penetrating eggs. Therefore, when mating occurs shortly after the onset of oestrus, spermatozoa in the oviduct do not appear to become fully capacitated until about the time of ovulation. For females mated immediately after ovulation, spermatozoa recovered from the oviducts at 4 h after mating could penetrate eggs within 30 min. Spermatozoa recovered at 1 and 3 h after mating required 2 and 1 h respectively in vitro before penetrating eggs. These results suggest that sperm capacitation proceeds at a faster rate when mating occurs after ovulation.     

The viability of hamster spermatozoa stored in the isthmus of the oviduct: the importance of sperm-epithelium contact for sperm survival

When hamsters mate shortly after the onset of estrus, spermatozoa are stored in the lower oviduct (isthmus) during the preovulatory period. The present study was performed to determine what proportion of the spermatozoa in the isthmus survive until fertilization. Females were mated 5 to 6.5 h before ovulation. When spermatozoa in the isthmus were observed through the wall of oviducts excised 2 h after the onset of mating, spermatozoa were seen free in the lumen, attached to the mucosal surface of the wall, and in crypts. The vast majority of spermatozoa in the lumen were immotile, whereas most of those attached to the mucosal surface of the wall and almost all of the those in the crypts exhibited flagellar movement. This suggested that attachment to the mucosa and/or storage in the crypts is beneficial to the survival of spermatozoa. Sequential flushing of an oviduct at various times (2-8 h) after mating was used to remove spermatozoa from the lumen (first flush), from the mucosal surface (second flush), and from the crypts (third flush). The highest number of spermatozoa was always contained in the first flush, the next highest in the second flush, and the smallest in the third flush. When Trypan blue was included in the flushing medium to differentiate live and dead spermatozoa, the first flush recovered the smallest percentage of liver spermatozoa (2-22%), the second flush slightly more (16-37%), and the third flush the highest (51-69%), regardless of the time after mating. These data indicate that the majority of spermatozoa stored in the hamster isthmus die before ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution and number of spermatozoa in the oviduct of the golden hamster after natural mating and artificial insemination

A group of female hamsters was mated with males of proven fertility either several hours before or during ovulation. Another group of females was artificially inseminated several hours before ovulation. Females were killed at various times after the onset of mating or artificial insemination, oviducts were fixed and sectioned serially, and spermatozoa were counted individually as to their location in the oviduct. Regardless of the type or time of insemination, the vast majority of spermatozoa that entered the oviduct remained in the lower segments of the isthmus (the intramural and caudal isthmus) without ascending to the ampulla. The lower segments of the oviduct, particularly the caudal isthmus, appeared to be acting as a "sieve" and/or "sperm reservoir." In females mated or artificially inseminated prior to ovulation, virtually no spermatozoa reached the cephalic isthmus or ampulla until the commencement of ovulation. Although a few spermatozoa reached the ampulla by 1 h after the onset of mating, they were the exception rather than the rule. When females were mated during ovulation, spermatozoa spent a minimum of about 3 h in the caudal isthmus before ascending to the ampulla. The number of spermatozoa that entered the oviduct after artificial insemination was considerably lower than in naturally mated animals, but this low number was apparently large enough to ensure complete fertilization.     

Capacitation potential of the fallopian tube: A study involving surgical insemination and the subsequent incidence of polyspermy

In an attempt to demonstrate limitations in the capacitating potential of the Fallopian tube, ejaculated boar spermatozoa were introduced directly into the isthmus at varying intervals before ovulation. The incidence and degree of polyspermy subsequently observed were taken as indicators of the population of capacitated spermatozoa confronting the newly ovulated eggs: the more extensive the condition of polyspermy, the greater the number of capacitated spermatozoa presumed to have been available at the site of fertilization. Results are based on 673 eggs from 53 animals. When suspensions containing 2.21–3.87 × 10⁸ sperm per ml were introduced 36–40 hours and 26–30 hours before ovulation, 85% and 61% respectively of the eggs were polyspermic, such eggs exhibiting mainly dispermy and trispermy. By contrast, when comparable sperm suspensions from the same boar were instilled 17–18 hours before ovulation, 70% of the eggs were polyspermic but the degree of polyspermy had increased dramatically: most eggs contained 40 or more sperm heads in the vitellus, invariably forming swollen chromatin aggregates rather than male pronuclei. Surgical insemination at times closer to ovulation significantly reduced the incidence and degree of polyspermy, reaching a low of 2% with insemination 1–2 hours before ovulation. These results therefore support the concept of a limited capacitation potential of the Fallopian tube. In a separate series of observations, mating animals shortly before surgical insemination with sperm suspensions from the same boar markedly reduced the incidence of polyspermy. This latter observation may be of clinical significance in procedures of laparoscopic or transcervical insemination into the tubes to alleviate human infertility. The manner whereby myosalpingeal physiology could be modified in response to coital stimulation is discussed.     

Pre- and peri-ovulatory distribution of viable spermatozoa in the pig oviduct: a scanning electron microscope study

Using sexually mature animals, the distribution of spermatozoa has been examined at the utero-tubal junction and in the distal and proximal portions of the oviduct isthmus. Mating occurred during early oestrus and, with one exception, specimens were prepared shortly before or after ovulation. Distinct reservoirs of spermatozoa were identified in furrows between the terminal folds of the isthmus, and particularly within the troughs and transverse ridges of this region. The density of spermatozoa diminished steeply from the utero-tubal junction towards the isthmus, especially in the pre-ovulatory specimens. The membranes of most spermatozoa in the isthmus were intact up to the time of ovulation, suggesting that the acrosome reaction is a peri- or post-ovulatory event. Whilst the flagella of spermatozoa in the reservoirs were usually straight or only slightly curved, those on the surface of the epithelial folds were undulating (S-shaped). Specific microenvironments may therefore exist in the distal portion of the isthmus to regulate sperm motility; droplets of secretion were a notable feature in this region. In specimens prepared 24 hr after ovulation, spermatozoa were almost absent from the utero-tubal junction and isthmus. However, denuded eggs were observed in the proximal portion of the isthmus in this animal, and they had spermatozoa associated with the zona pellucida. Arguments are presented for a peri-ovulatory endocrine regulation of sperm redistribution and capacitation.     

Distribution of spermatozoa in the female reproductive tract of the domestic cat in relation to ovulation induced by natural mating

The purposes of this study were to demonstrate the localization of spermatozoa in the reproductive tract of female domestic cats before (30 min and 3 h after mating) and after ovulation (48 and 96 h after mating), and to evaluate the efficiency of two techniques for studying sperm distribution. Estrus was induced in twenty-four female cats using 100 IU eCG and the females were divided into four groups with six females per group. The same male cat was used for mating with all the females. One group of six females was mated once; the others were mated four times in 1 h. Ovariohysterectomy was performed at 30 min, 3 h, 48 h, and 96 h after mating and the excised reproductive tracts were divided into seven segments on each side: infundibulum, ampulla, isthmus, uterotubal junction (UTJ), cranial and caudal uterine horn, and uterine body. The vagina and the lumina of the segments from one side were flushed with 0.5 ml PBS. The flushed and the non-flushed segments from the contralateral side were then fixed in 3% neutral buffered formalin and processed for routine histology. The numbers of spermatozoa in the flushings and in 40 histological sections from each segment were counted. Before ovulation, the majority of spermatozoa was detected in the vagina and the uterine segments, whereas after ovulation, significantly higher numbers of spermatozoa were present in the uterine tubal segments. The decreasing gradient in sperm numbers at 30 min and 3 h after mating between the vagina, the uterine segments, including the UTJ, and the uterine tubal segments indicated that the cervix and the UTJ served as barriers for sperm transport in the cat. The UTJ and the uterine crypts acted as sperm reservoirs before ovulation whereas the isthmus was a sperm reservoir around the time of ovulation. There was no difference in sperm numbers in the tissue sections between flushed and non-flushed segments, implying that the flushing technique only recovered some intraluminal spermatozoa while most of the spermatozoa remained in the epithelial crypts. This was further supported by the finding that significantly higher numbers of spermatozoa were recovered in the flushings at 30 min and 3 h after mating, when more spermatozoa were free in the lumina, than at 48 and 96 h after mating, when the majority of the spermatozoa were entrapped in the uterine epithelial crypts.     

Effect of ovulation on sperm transport in the hamster oviduct

When hamsters mate shortly after the onset of oestrus (4.5-6 h before the onset of ovulation), spermatozoa are stored in the caudal isthmus of the oviduct until near the time of ovulation. At this time, a few spermatozoa ascend to the ampulla to fertilize the eggs. Superovulation resulted in a significant increase in the number of spermatozoa in the caudal isthmus at 6 h post coitus (p.c.) and in the ampulla and bursal cavity at 12 h p.c. Precocious ovulation resulted in a highly significant reduction in the total number of spermatozoa in the oviduct at 3 and 6 h p.c. This effect was completely overcome by intrauterine artificial insemination, suggesting lack of cervical patency as the block to sperm transport in precociously ovulated animals. Ligation of the ampulla-infundibulum junction in naturally ovulating hamsters resulted in significantly fewer spermatozoa in the caudal isthmus and ampulla at 12 h p.c. Preclusion of ovulation also resulted in fewer spermatozoa in the caudal isthmus and ampulla at 12 h p.c., suggesting that the products of ovulation stimulate sperm transport in the oviduct.     

Ovarian programming of gamete progression and maturation in the female genital tract

Whilst the rate of displacement and migration of sperm cells in the female reproductive tract of rodents, farm animals and humans has attracted attention for at least 50 years, the overriding purpose of sperm transport has not always been kept in focus. This report is concerned with spermatozoa that can penetrate the egg investments and promote formation of a zygote, judgements involving a surgical approach and subsequent phase-contrast microscopy. A minimum period of 6–8 hours was required for such spermatozoa to be established in the oviducts in sheep and cows mated at the onset of oestrus. Sperm were then arrested in the caudal 12 cm of the isthmus for 17–18 hours or more until just before the moment of ovulation, when they were activated and displaced onwards to the site of fertilization at the ampullary-isthmic junction. The time-scale of these events differs in pigs as a result of the intra-uterine site of ejaculation and the 40-hour interval between the onset of oestrus and ovulation, but the pre-ovulatory sequestering of viable spermatozoa in the caudal tip of the oviduct is conspicuous for 36 hours or more. This function of the oviduct appears to be under local control from ovarian follicular hormones and, as judged by sperm motility and membranous changes, so does the process of capacitation. Completion of capacitation is interpreted as a peri-ovulatory event.     

Attachment and release of spermatozoa from the caudal isthmus of the hamster oviduct

Female hamsters were mated shortly after the onset of oestrus. At 3 or 6 h after mating, the right oviduct was flushed in situ with 30, 90 or 180 microliters medium to remove spermatozoa from the lumen, leaving only those firmly attached to the isthmic mucosa of the oviduct. When eggs were recovered from oviducts at 20 h after flushing the majority were fertilized, indicating that the spermatozoa that were firmly attached to the mucosa were capable of detaching and ascending to the ampulla to fertilize eggs. Neither the time of flushing nor the volume of flushing medium had a significant effect on the percentage of spermatozoa that remained in the isthmus after flushing. These results suggest that there is no change in the surface of the oviduct mucosa that causes the release of spermatozoa from the caudal isthmus near the time of ovulation. When incapacitated spermatozoa were introduced into the oviduct, many of them attached to oviductal mucosa, while capacitated spermatozoa did not. This indicates that it is a change in the sperm surface, rather than the mucosal surface, that causes the release of spermatozoa, i.e. spermatozoa remain attached to the isthmic mucosa until they become capacitated and then detach and migrate to the ampulla to fertilize the eggs.     

The rate of functional sperm transport into the oviducts of mated cows

The technique of ligation and transection of the oviducts from the uterus, together with subsequent examination of the eggs, has been used to establish how soon after mating a population of spermatozoa competent to fertilise enters the oviducts. Animals were mated within 8 h of the onset of oestrus, and the uterotubal junction ligated under local anaesthesia 6, 8 or 12 h later.Nineteen eggs were recovered from 29 animals. Fertilisation was not found as a sequel to ligation 6 h after mating, whereas 3 of 6 and 5 of 6 eggs, respectively, were fertilised when the operation was performed 8 or 12 h after mating. The mean number of spermatozoa associated with the zona pellucida increased over the interval examined from 0.2 to 4.5 (range 0–11). These results suggest that only a slow progression and displacement of viable spermatozoa occurs in the female tract after mating early in oestrus. They also infer that the functional sperm reservoir — the one drawn on at the time of ovulation — is in the oviductal isthmus rather than in the cervix, a consideration that may have a bearing on procedures of artificial insemination.     

Ovarian follicular fluid, progesterone and Ca2+ ion influences on sperm release from the fallopian tube reservoir.

As a means of determining whether ovarian follicular fluid reaches the functional sperm reservoir in the caudal isthmus of the Fallopian tube shortly after ovulation, 0.01-0.02 ml aliquots of whole or steroid-free follicular fluid were introduced into the distal extremity of the isthmus within 1 hr before ovulation. Eggs were recovered during a second intervention 4 hr 45 min-6 hr 10 min after treatment and examined by phase-contrast microscopy for the normality of fertilisation. In a separate experiment, 0.01-0.02 ml aliquots of 10 microM calcium ionophore solution were introduced into the same site in comparable animals. Sixty-nine fertilised eggs were recovered from 12 fallopian tubes treated with whole follicular fluid, of which 24 (34.8%) were polyspermic. The 12 contralateral control tubes (PBS-treated) yielded 47 fertilised eggs, of which only one (2.1%) was polyspermic (P < 0.001). Steroid-free aliquots of the same follicular fluid introduced bilaterally into eight fallopian tubes (4 animals) resulted in recovery of 59 fertilised eggs, of which only one (1.7%) was polyspermic. Treatment with ionophore solution yielded a 41.6% incidence of polyspermy (10 of 24 eggs from four tubes) compared with 3.8% polyspermy (1 egg) from the control tubes (P < 0.01). Dispermy was the principal form of polyspermy. The numbers of accessory spermatozoa on/in the zona pellucida were increased by the experimental treatment. Follicular fluid passing down the fallopian tube ampulla at ovulation was therefore considered not to be the physiological stimulus for an initial, tightly-controlled release of spermatozoa from epithelial binding in the caudal isthmus. Indeed, because such sperm activation commences shortly before ovulation, a locally transmitted ovarian programming with relatively high concentrations of follicular hormones remains the favoured model. Although pre-ovulatory progesterone is considered to be the coordinating steroid of increasing influence in these pre-fertilisation events, its effects are proposed to be modulated in the endosalpinx by mobilisation of Ca2+ ions into a discrete population of bound spermatozoa. Results of the steroid-free follicular fluid and calcium ionophore treatments stand in support.     

Role of the oviduct in sperm capacitation

Following insemination of spermatozoa pre-ovulation, the mammalian oviduct ensures, by the formation of a functional sperm reservoir (SR), that suitable (low) numbers of viable and potentially fertile spermatozoa are available for fertilization at the ampullary isthmic junction (AIJ). As ovulation approaches, a proportion of the SR-stored spermatozoa is continuously distributed towards the AIJ and individually activated leading to step-wise capacitation and the attainment of hyperactivated motility. This paper reviews in vivo changes in the intra-luminal milieu of the oviduct of pigs and cows, in particular the SR and the AIJ which relate to the modulation of sperm capacitation around spontaneous ovulation. In vivo, most viable spermatozoa in the pre-ovulatory SR are uncapacitated. Capacitation rates significantly increase after ovulation, apparently not massively but concurrent with the individual, continuous sperm dislocation from the SR. Bicarbonate, whose levels differ between the SR and the AIJ, appears as the common primary effector of the membrane destabilizing changes that encompasses the first stages of capacitation. Sperm activation can be delayed or even reversed by co-incubation with membrane proteins of the tubal lining, isthmic fluid or specific tubal glycosaminoglycans, such as hyaluronan. Although the pattern of response to in vitro induction of sperm activation - capacitation in particular - is similar for all spermatozoa, the capacity and speed of the response is very individual. Such diversity in responsiveness among spermatozoa insures full sperm viability before ovulation and the presence of spermatozoa at different stages of capacitation at the AIJ, thus maximizing the chances of normal fertilization.     

Relationship between longevity of spermatozoa after insemination and the percentage of normal embryos in brown marsupial mice (Antechinus stuartii)

Twenty-six female brown marsupial mice in a laboratory colony were mated at intervals ranging from 1 to 20 days between coitus and ovulation. The numbers of corpora lutea and normal embryos were counted. A multiple regression model examined the parabolic relationship between the proportion of normal embryos and the time from coitus to ovulation. The proportion of normal embryos increased until a mean of 9.5 days and decreased thereafter. This relationship was independent of the year of breeding and the number of corpora lutea. After survival of spermatozoa for up to 13 days in the female reproductive tract, the fertility levels of females was 88-92%. Low fertility levels after 13 days appeared to be due to a decrease in the number of spermatozoa. Reproductive tracts from 7 females killed after insemination and examined histologically showed many spermatozoa in the isthmus of the oviduct and the uterus at 5 days post coitum; spermatozoa confined to the isthmus between 6 and 13 days; and few spermatozoa in the isthmus at 14 days after copulation. A comparison between the fertility levels in the females which had been inseminated once and a further 17 females which had been inseminated 2 or 3 times suggested that spermatozoa from 2nd and 3rd inseminations can contribute spermatozoa for fertilization. In these females fertility levels did not decline with time after the first mating.     

The effect of pre-ovulatory anaesthesia on ovulation in laparoscopically inseminated domestic cats.

Laparoscopic intrauterine artificial insemination (AI) of electroejaculated spermatozoa was used to compare embryo development and conception rates in domestic cats inseminated either before or after ovulation. Females were given a single (100 iu) injection of pregnant mares' serum gonadotrophin (PMSG) followed by either 75 or 100 iu human chorionic gonadotrophin (hCG) 80 h later. Cats were anaesthetized (injectable ketamine HCl/acepromazine plus gaseous halothane) 25-50 h after administration of hCG for laparoscopic assessment of ovarian activity and for transabdominal AI into the proximal aspect of the uterine lumen. At the time of AI, 23 cats were pre-ovulatory (25-33 h after hCG injection) and 30 were post-ovulatory (31-50 h after hCG injection). Pre-ovulatory females produced 10.5 +/- 1.1 follicles and no corpora lutea compared with 1.9 +/- 0.5 follicles and 7.5 +/- 0.9 corpora lutea for the post-ovulatory group (P < 0.05). Six days later, the ovaries of nine pre-ovulatory and 12 post-ovulatory females were re-examined and the reproductive tracts flushed. On this day, pre-ovulatory cats produced fewer corpora lutea (2.8 +/- 1.5; P < 0.05) and embryos (0.4 +/- 0.3; P < 0.05) than post-ovulatory females (18.9 +/- 3.3 corpora lutea; 4.6 +/- 1.2 embryos). Two of the 14 cats (14.3%) inseminated before ovulation and not flushed became pregnant compared with 9 of 18 cats (50.0%) inseminated after ovulation and up to 41 h after hCG injection (P < 0.05). These results indicate that ovulation in cats is compromised by pre-ovulatory ketamine HCl/acepromazine/halothane or laparoscopy or by both and that electroejaculated spermatozoa deposited by laparoscopy in utero, after ovulation, result in a relatively high incidence of pregnancy. Because ovulation usually occurs 25-27 h after injection of hCG, the lifespan for fertilization of the ovulated ovum appears to be at least 14 h in vivo in cats.     

Effect of ovulation and sperm motility on the migration of rabbit spermatozoa to the site of fertilization.

Few spermatozoa were present in the ampullae of females 12 h after intravaginal artificial insemination (AI) when there was no ovulation-inducing stimulus. When ovulation was induced, sperm distributions in the female tract 12 h after AI did not differ from those observed 12 h after natural mating. The number of spermatozoa in the oviductal isthmus was similar in all 3 groups as was the percentage of isthmic spermatozoa exhibiting 'activated' motility. When fertile mating was delayed for 8 or 12 h after coitus with a vasectomized male (i.e. 2 h before or after ovulation), spermatozoa were not present in the ampulla 4 h later. The numbers of spermatozoa recovered from the cranial isthmus after delayed matings and 12 h after natural matings did not differ, but after delayed matings the motility of isthmic spermatozoa was non-progressive or poorly progressive and none exhibited 'activated' motility. Flagellar activity of isthmic spermatozoa recovered 4 h after delayed matings and after natural matings was similarly depressed. These observations indicate that sperm ascent to the tubal ampulla in the sustained phase of transport, though enhanced by ovulation, must also depend on changes in flagellar activity and a specific pattern of motility, both of which appear only after spermatozoa have resided for more than 4 h in the female tract.     

Boar spermatozoa in the oviduct

In the pig, a functional tubal sperm reservoir (SR) is established before ovulation to ensure availability of suitable numbers of viable spermatozoa for fertilization. The boar's large ejaculate is split: most spermatozoa are delivered in a sperm-rich fraction (SRF) followed by a post-SRF fraction containing increasing amounts of the spermadhesin PSP-I/PSP-II-rich seminal vesicle secretion. This heterodimer acts as leukocyte chemoattractant both in vitro and in vivo, contributing to the phagocytosis of those spermatozoa not reaching the SR. Sequential ejaculate deposition of marked spermatozoa and SR screening showed that most spermatozoa in the SR arose from the fortuitous PSP-poor, first portion of the SRF fraction, escaping phagocytosis and replenishing the SR within 2-3 h. The SR-sperm numbers diminish gradually in relation to ovulation, spermatozoa being continuously redistributed toward the upper isthmus. In vitro, only uncapacitated spermatozoa bind to epithelial explants, suggesting that the SR influences sperm capacitation. In vivo, most viable spermatozoa--usually harbored in the deep furrows in the pre- or peri-ovulatory SR during spontaneous standing estrus--are uncapacitated, but capacitation significantly increases after ovulation. Pre-/peri-ovulatory SR spermatozoa promptly capacitate in vitro when exposed to the effector bicarbonate, an influence that can be reversed by co-incubation with SR fluid or its component hyaluronan. Fluid collected from the ampullar segment (rich in bicarbonate) induces capacitation in vitro. In conclusion, the lack of massive sperm capacitation in the SR and the diverse individual response to capacitation shown by tubal spermatozoa would relate both to the insurance of full sperm viability before ovulation and the presence of spermatozoa at different stages of capacitation in the upper oviduct, thus maximizing the chances of normal fertilization.     

Oviductal sperm storage structure and their changes during the seasonal (dissociated) reproductive cycle in the soft-shelled turtle Lissemys punctata punctata

The oviduct of the Indian fresh water soft-shelled turtle Lissemys punctata punctata was examined throughout the year under light and scanning electron microscopes to determine the location, histomorphological characteristics, and function of sperm storage structure, as well as their changes at different phases of the seasonal reproductive cycle. Sperm storage structures in the form of tubules were observed in the wall of isthmus throughout the year. These tubules developed either by folding or fusion of the oviductal mucosal folds and were lined by both ciliated and nonciliated epithelial cells. The height and secretory activities of the epithelia were markedly high during the breeding phase (August to September) but low in the nonbreeding phase (October to June). A few short tubules lined by cuboidal epithelium appear in the wall of infundibulum only during the breeding phase. Following mating (May), inseminated sperm were stored within the tubules of isthmus up to the pre-ovulatory stage (August). Thereafter, sperm associated with PAS-positive materials secreted from the epithelium (referred to as a carrier matrix) moved forward to the infundibulum and were stored within the storage tubules of the infundibulum for a short time. Subsequently, sperm evacuated the storage tubules and entered the oviductal lumen to fertilize the subsequently ovulated eggs during or prior to ovulation. The isthmus-tubules become shorter and narrower in the regressive phase (October to November) and remained so until the early preparatory phase (April). Sperm release might have been stimulated by estrogen secreted from the ovarian follicles of pre-ovulatory turtles. Stored sperm not utilized for fertilization remained viable not less than six months in the present turtle species.     

Peripheral plasma progesterone during egg transport in the rabbit.

Peripheral plasma progesterone concentrations were measured in New Zealand rabbits every 6 hr beginning 12 hr before and continuing until 96 hr after either natural mating, hCG injection, or saline injection. The number of ovulation points in naturally mated animals (9.3 +/- 0.6, mean +/- SE) was not significantly different from that in hCG-injected animals (8.6 +/- 1.5). There was a surge in progesterone secretion following both mating and hCG injection. Plasma progesterone concentrations reached a peak prior to ovulation and then fell to basal levels at the time of ovulation. Beginning at approximately 30 hr after the ovulation-inducing stimulus, there was a progressive, significant (P less than 0.001) increase in plasma progesterone concentration, which continued for the duration of the sampling period. The initiation of the postovulatory increase in progesterone secretion corresponds temporally with the movement of eggs from the ampullary-isthmic junction into the isthmus. The progressive increase in plasma progesterone between 30 and 72 hr after the induction of ovulation corresponds with the gradual movement of eggs through the isthmus into the uterus. The data suggest that movement of eggs through the oviductal isthmus is influenced by the postovulatory secretion of progesterone.     

The Fallopian tubes in domestic mammals: how vital is their physiological activity?

Set in an historical perspective, this essay examines diverse physiological aspects of Fallopian tube function in domestic animals and man. Microsurgical experiments are described that established the role of the isthmus in imposing a sperm gradient up to the site of fertilisation. Resection of the isthmus followed by reanastomosis of the remaining portions of the tube generated a high incidence of polyspermy in mated animals. Scanning electron microscopy and surgical studies revealed that spermatozoa were arrested and stored in the caudal portion of the isthmus before ovulation, the so-called functional sperm reservoir. There were specific adhesion contacts between the sperm head and endosalpingeal microvilli or cilia. Further experiments indicated that very large numbers of competent spermatozoa could be released from pre-ovulatory binding by microinjections of a solution of progesterone in oil under the serosal layer of the tube: when suitably timed, such treatment led to a high incidence of polyspermic fertilisation. Avid sperm binding in the caudal isthmus before ovulation prevents myosalpingeal activity leading to abnormal fertilisation, as might occur with multiple mating. Temperatures in the reproductive system were assessed and the caudal isthmus was found to be cooler than the ampulla during the pre-ovulatory phase of sperm storage. Finally, the existence of fluid microenvironments within the Fallopian tubes was reported, and the role of suspended cumulus-corona cells in amplifying signals from the zygote examined. An impact of Fallopian tube fluids on embryonic gene expression was also considered--an influence that may be further imposed if such fluids have access to the uterine lumen.