Distribution of embryos and 500-microM microspheres in the rabbit oviduct: controls for acute motion analysis during transport.

Distributions of embryos and 500-micron diameter microspheres were measured in the cleared oviducts of 32 rabbits at 8 intervals post coitus (pc) and normalized to percentage of isthmic length. By 18 h pc, 46% of the embryos had entered the isthmus and were denuded of the cumulus, while 55% of the microspheres had entered the isthmus. By 24 h pc, all embryos and microspheres were in the isthmus. At 72, 78, and 84 h pc, 6.5, 37, and 93% of embryos and 21, 73, and 95% of microspheres were in the cornu, respectively. The mean positions of embryos and microspheres progressed at approximately 1% of isthmic length per hour between 24 and 72 h pc. Throughout isthmic transport, embryos and microspheres in individual oviducts were tightly grouped and had similar statistical distributions. Although microspheres began to transfer into the uterine horns earlier than embryos, the data suggest that 500-micron microspheres can be used in studies to quantify discrete movements within the oviduct prior to 72 h pc. The data further suggest that opposing forces may be generated by contractile events that keep embryos grouped and possibly control their rate of progress through the oviduct.

Quantification of intraluminal motion of surrogate ova in the rabbit oviductal isthmus.

The feasibility of using black polystyrene microspheres as surrogate ova to obtain quantitative information regarding ovum motion in the oviductal isthmus was tested in rabbits. The 175-microns diameter surrogates were instilled into the ampulla at the time of ovulation, and later the oviducts were exposed for direct observation of surrogate movements in the isthmic lumen. With the aid of transillumination, the black spheres were visible through the intact tubal wall and cinematographic records were made to quantify their movements. The frequency of surrogate movements was 5/min at 24, 36 and 48 h after coitus an 10/min at 60 and 72 h. The motion was typically oscillative with individual movements less than 4 mm in length; usually no net displacement occurred during 1-2 h of observation. These preliminary data, when used to test the stochastic model of ovum transport proposed by Verdugo et al. (1980), predicted isthmic transit times of only a few hours. Thus, the long duration of ovum residence in the rabbit isthmus may not be due to a slow transport process governed by random motion.

Differential steroidogenic responses of ovine luteal cells to ovine luteinizing hormone and human chorionic gonadotropin.

Experiments were conducted in vitro on ovine small luteal cells to evaluate their steroidogenic response to ovine luteinizing hormone (oLH) and human chorionic gonadotropin (hCG) administered continuously throughout the experimental period or as a 15-min pulse. Both oLH and hCG stimulated a significant increase in progesterone secretion (P less than 0.001) by small luteal cells. Human chorionic gonadotropin administered continuously or as a pulse maintained progesterone secretion at 40-55% of experimental maximum at least 6 hr while oLH-stimulated progesterone secretion declined to basal levels by 4 hr after a 15-min pulse or declined to 25% of the experimental maximum within 6 hr under constant stimulation. The responses of small luteal cells to oLH and hCG were found to differ (P less than 0.001). The sustained progesterone secretion of luteal cells in response to a pulse of hCG may be due to longer residence of occupied receptor complex on the cell membrane. In contrast, the decline in oLH stimulated progesterone secretion, even when hormone is continuously present in the medium, may be related to a rapid internalization of receptor-hormone complexes and down-regulation of receptors.

The structural and functional impact of microsurgical anastomosis on the rabbit oviductal isthmus.

Microsurgical transection and anastomosis of the left isthmus in 7 rabbits caused fertility to be reduced 40%. Following rebreeding artificial eggs were introduced into the anastomosed and control oviducts. Sixty-three to 65 hours after mating, direct in vivo observations disclosed varied forms of motion of the artificial eggs within the isthmus, including both small oscillations and occasionally, large precipitous excursions covering more than 1 cm. Subsequent clearing of the genital tracts revealed that the anastomosis in the isthmus had detained most of the natural and artificial eggs, whereas both forms of ova were predominantly past the equivalent site on the control side; yet all anastomosed oviducts were fully patent. We conclude that the decreased fertility after isthmic anastomosis is due not to a physical obstacle but to an inability of the isthmus near the anastomosis to dilate as do other regions of the tube.

In vivo recording of oviductal contractions in rabbits during the periovulatory period.

Muscular activity of the oviductal isthmus was recorded in intact awake rabbits with an extraluminal optoelectronic transducer. Telemetered data were collected continuously during the periovulatory period to relate changes in contraction frequency to oviductal transport function. Mean frequencies during estrus ranged from 11.7 to 18.7 contractions/min. Animals stimulated to ovulate either by luteinizing hormone (LH) or by mating showed equivalent responses. Within 2 h following the stimulus, the frequency increased rapidly and remained elevated more than 50% above the estrous control level for approximately 10 h. Thereafter, the frequency declined slowly to reach a second plateau, 30% below the control level, which was maintained throughout the 2nd and 3rd poststimulus days. Subsequently, the activity returned to the prestimulus level. The periods of elevated and depressed activity correspond closely in time to the periods of rapid preovulatory transport of sperm and slow postovulatory transport of ova through the isthmus, suggesting the possibility of regulation of gamete transport by the oviductal musculature.

Optoelectronic transducer for in vivo recording of oviductal contractile activity.

An optoelectronic instrument to record oviductal muscular activity in chronically instrumented animals was evaluated in in vitro and in vivo experiments. The intensity of red light transmitted through the oviduct was modulated by contractions of the oviductal wall producing an optical analog of the mechanical events. Accuracy of the analog was tested by Fourier analysis of signals from mechanical and optoelectronic transducers placed at the same site on the oviduct; the results validated the use of the optical device as a contraction event sensor. Contractions of the tubal mesenteries had less effect on the optical signal than on signals from extraluminal mechanical transducers. Optical and photographic recordings of luminal transport in exposed oviducts showed a correspondence of intraluminal movements to events in the optical contraction signal. This instrument does not alter tubal function, and thus it is an especially useful experimental tool to investigate the role of oviductal muscular activity in fertility.