Distribution of spermatozoa in the utero-tubal junction and isthmus of pigs, and their relationship with the luminal epithelium after mating: a scanning electron microscope study

The effect of induced standing reflex, cervical stimulation and insemination on intraluminal pressure variations in the isthmus of the oviduct in unrestrained gilts

Four gilts were each equipped with 2 ultra-miniature pressure sensors, placed at 2 different points along the same isthmus of the oviduct, on the morning of the first day of standing oestrus (Day 1). Intraluminal pressure recordings were started the same afternoon. After an initial recording period, intraluminal pressure was recorded while the gilts showed standing oestrus and during cervical stimulation followed by insemination with either 100 ml saline or 100 ml boar semen. Monitoring of the pressure variations in the isthmus was continued for up to 6.5 h after the last insemination. Blood samples for monitoring oestradiol-17 beta, progesterone and 15-ketodihydroprostaglandin F2 alpha were collected before and after each manipulation of the gilt and every 30 min during the rest of the test period. None of the above manipulations had any consistent effect on the intraluminal pressure in the porcine isthmus, although, a clear 15-ketodihydroprostaglandin F2 alpha peak could be seen after insemination with boar semen.

The mucosa of the rabbit vagina: a proposed experimental model for correlated morphofunctional studies in humans

In order to suggest a valid experimental model for correlated studies regarding the complex phenomena of reproductive biology in humans, light (LM), transmission (TEM) and scanning electron microscopic (SEM) observations were carried out on vaginae of sexually mature New-Zealand albino rabbits, both in estrus and at 5 h after mating. To avoid artifacts depending upon the operative times for specimen removal and, in particular, to well visualize the inner surface of this organ, vaginal irrigation with fixative was performed prior to the surgical removal. Our data demonstrate that the upper 2/3 of the vaginal duct form a kind of 'cervico-vaginal canal' which shares many histological features with the human endocervix. In fact, this portion is lined within by a monostratified epithelium provided with tall microvillous and ciliated cells and often invaginated in crypts. After mating, the microvillous cells showed evidence of secretory activity, exhibiting dome-like luminal surfaces. Secretory droplets often contacted cilia and spermatozoa present in the mucosal furrows and crypts. Because of these singular features and the morphofunctional interactions between vaginal epithelium and male gametes, we believe the rabbit to be a helpful model for comparative biology in humans, concerning sperm capacitation and the general reactivity of the female genital tract during the reproductive cycle.

Precontact mammalian sperm-egg communication and role in fertilization

In creatures with external fertilization, e.g., metazoa, it is well established that there is precontact sperm-egg communication in the form of chemotaxis. An intriguing question is whether also in mammals, where fertilization is internal and the need for precontact sperm-egg communication is not self-evident, such a process occurs and what its physiological significance may be. Here we review the evidence related to such a process in mammals, evidence which suggests that sperm attraction to the ovulated egg may indeed occur. On the basis of the available data we propose a hypothesis, according to which a sperm population is heterogeneous with respect to its physiological state; some spermatozoa are at a physiological state ready for fertilizing an egg, while others are premature or overmature. According to the hypothesis this is a dynamic state; the population of fertilizing spermatozoa gradually loses its potency and, at the same time, other spermatozoa mature and acquire fertilizing ability. After ovulation, only the fertilizing spermatozoa are attracted to the egg, while the rest are either repelled or inhibited and thus prevented from reaching the egg. The potential significance of sperm-egg communication is discussed.

Distribution, morphology and epithelial interactions of bovine spermatozoa in the oviduct before and after ovulation: a scanning electron microscope study

In cows undergoing spontaneous oestrous cycles and mated during the first 6 hours of oestrus, the distribution of spermatozoa in the oviduct isthmus and changes in their surface membranes and neighbouring epithelium have been examined shortly before and after ovulation. In agreement with previous histological studies, relatively few spermatozoa were detected in the oviduct lumen: most were located in the caudal isthmus before ovulation, frequently among folds and in the presence of a viscous secretion. A majority of spermatozoa in this region showed strands and droplets of secretory material distributed over the anterior portion of an intact head before ovulation, whereas distribution of material over the post-nuclear cap of spermatozoa close to vesiculation or already acrosome-reacted was characteristic of the post-ovulatory situation. These changes in sperm head membranes were viewed as an expression of the completion of capacitation, and seemingly permit microvillous engagement with the rostral tip of the head. In conjunction with a narrow lumen and viscous secretions in the caudal isthmus, microvilli may thus serve to regulate periovulatory sperm progression towards the site of fertilisation, and be the basis of intermittent phases of adhesion to the oviduct epithelium as seen by phase-contrast microscopy. Although cilia do not similarly engage the heads of bull spermatozoa (cf. boar spermatozoa), they may act to regulate progression of capacitated spermatozoa by contacting the principal piece of the flagellum. In the light of these observations, changes in the molecular composition of sperm surface domains during the process of capacitation in vivo now require specific definition.

Ultrastructure of the uterotubal junction in preovulatory pigs

The ultrastructure of the surface epithelia from the uterotubal junction (UTJ), and the adjacent tubal isthmic and endometrial regions, was studied in preovulatory oestrus gilts, either unmated or inseminated 12 h before with fresh boar semen. The simple columnar epithelium of the UTJ consisted of non-ciliated (secretory) and ciliated cells. Secretory vesicles occurred in the secretory cells, especially in inseminated gilts. Lymphocytes, monocytes and macrophages were found dispersed basally among the epithelial cells. Phagocytosis of epithelial cells undergoing apoptosis was seen throughout the UTJ at oestrus, increasing after insemination. Neutrophilic granulocytes were found in the lamina propria of the uterine component of the UTJ, but only occasionally in the epithelium. After insemination, neutrophils invaded the uterine epithelium, to actively participate in intraepithelial phagocytosis or move into the lumen, engulfing spermatozoa. Neutrophils were absent from the UTJ proper and the isthmic epithelium, irrespective of the presence of spermatozoa in the lumen. Those spermatozoa in the uterine lumen that escaped phagocytosis had severely damaged plasma membranes, whereas those in the UTJ proper--concentrated towards the deep furrows of the diverticulae--mostly showed normal sperm ultrastructure.

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.