The uterine tubal fluid: secretion, composition and biological effects
Anim Reprod, vol.2, n2, p.91-105, 2005
Gamete transport, sperm capacitation, fertilization, and early embryo development are all physiological events that occur in a very synchronized manner within the uterine tubal lumen. The tubal fluid that bathes the male and female gametes allows these events to occur in vivo much more successfully than in vitro. Collection of tubal fluid from domestic females has been performed by different methods. The amount of fluid secreted by the uterine tube increases during estrus and decreases during diestrus and pregnancy. The ampulla produces approximately two thirds of the total daily secretion, while the isthmus supplies the rest. Steroid hormones qualitatively and quantitatively modify the tubal fluid, through both a direct effect on epithelial cells and indirectly through their action on the vascular bed. Estrogen predominantly stimulates while progesterone inhibits tubal fluid secretion. The concentration of nutrients in tubal fluid is generally below plasma concentrations which suggests an overall transport of nutrients across the tube, mainly by diffusion. High potassium levels in the tubal fluid seem to be constant across species and is an important factor to consider when designing fertilization culture medium. The main energy substrates in tubal fluid are glucose and pyruvate derived from blood, although some sucrose and lactate are also present. In the rabbit tube, 25% of lactate is filtered from the blood and 75% is produced from vascular glucose by the tubal epithelial cells. Twenty-five free amino acids were present in the tubal fluid of cows, ewes, pigs, rabbits, and mice. Glycine was found in the highest concentrations in all the species studied, but levels of free amino acids varied across species and also during the estrous cycle. Protein concentration in the fluid is approximately 10-15% of that in serum. Albumin and immunoglobulin G, derived from the blood stream, are the most common proteins representing about 95% of the total protein of the tubal content. Tubal-specific glycoproteins produced by the epithelial cells have been identified and characterized in several species. Prostaglandins, steroid hormones, and growth factors have also been found in the tubal fluid and likely play important roles in tubal events. Continuous changes that occur in the secretory patterns throughout the estrous cycle and among the different regions of the tube indicate the existence of systemic and local controlling mechanisms of tubal fluid production.
uterine tube, oviduct, fluid, composition, secretion, fertilization