Comparative study on the effects of taurine and glutamic acid on fowl sperm motility, ATP and intracellular free Ca 2+ concentrations

The aim of the study was to elucidate some details of those biochemical processes that influence the motility of fowl spermatozoa in vivo near the sperm storage tubules (SSTs) of the hen’s oviduct. Several studies demonstrate that the putative transmitter amino acids such as glutamic acid, glycine, gammaaminobutyric acid and taurine/hypotaurine occur in high concentrations in the male and female reproductive tract of different species, compared to other amino acids (Lake and McIndoe, 1959; Van der Horst and Grooten, 1966; Johnson et al., 1972; Ibrahim and Boldizsár, 1981). Glutamic acid was found to be the principal amino acid in the fowl seminal plasma and in the utero-vaginal junction and shown to have an inhibitory effect on sperm metabolism (El Zayat and van Tienhoven, 1961; Howarth, 1974). Of the free amino acids in the oviductal fluid of hen, taurine and glutamic acid were demonstrated to be present at the highest concentrations during the egg formation cycle. Also, their concentrations change independently of other amino acids involved in protein synthesis (Barna et al., 1996). The effect of some amino acids on mammalian sperm motility has already been investigated. Glutamic acid was found to stimulate mouse sperm motility at low concentrations and to arrest it at high concentrations (Sliwa, 1990). Taurine/hypotaurine has been identified as a sperm motility factor as it stimulated hamster sperm motility in vitro (Mrsny et al., 1979; Boatman et al., 1990). Pooled, washed semen samples of White Leghorn roosters were used throughout the study. Taurine and glutamic acid were added to the semen samples at a concentration of 0–5 mM. The analysis of intact and de-membraned sperm motility was carried out objectively by video microscopy at 25°C and at 40°C. The ATP content of spermatozoa was assayed by firefly bioluminescence in boiled extracts (Wishart, 1982) and the intracellular free Ca concentration was determined with the fluorescent indicator fura-2, according to Grynkiewicz et al. (1985) with certain modifications (Ashizawa et al., 1992). The percentage of motility was transformed using arc sine transformation and analysed by Duncan’s multiple-range test (Duncan, 1955). The addition of taurine to the washed fowl spermatozoa within the range of 0–5 mM did not appreciably affect the motility of either intact or de-membraned spermatozoa. Motility was almost negligible at body temperature (40°C) and maintained vigorous movement at room temperature (25°C). Even in the presence of Ca that stimulates sperm motility and before the addition of taurine, no stimulation or inhibition of motility werer observed. As the concentration of glutamic acid was increased from 0 to 5 mM, the motility of intact spermatozoa was reduced and inhibited at both 25°C and 40°C, even in the presence of Ca, while the motility of de-membraned spermatozoa did not change. Neither the ATP concentration nor the intracellular free Ca content of spermatozoa was influenced significantly in the presence of taurine or glutamic acid at any concentrations. The results suggest that glutamic acid, which inhibits the motility of intact fowl spermatozoa, affects presumably the plasma membrane and/or cytoplasmic matrix, since inhibition occurred without the change of intracellular levels of ATP or Ca and it only acted in intact spermatozoa. Either it is presumed to affect the transmembrane ion transport, similar to its effect in the central nervous system, or it affects some parts of the regulatory cascade initiated by Ca. It may also be involved in the inactivation processes of spermatozoa in the SSTs as well. Interestingly, taurine, despite its high concentration in oviductal fluid, has no effect on fowl sperm motility. Its reactivating effect, which was previously demonstrated in hamster spermatozoa, could not be proven either (Boatman et al., 1990). Its role in the reproductive processes of birds requires further investigations. This study was supported by a Grant-in-aid for Scientific Research from Ito Memorial Foundation and by a grant from the Ministry of Education, Science and Culture, Japan (no. 11460130).