Of all cases of infertility in humans, ≈20% are due entirely to a male factor, with an additional 30–40% involving both male and female factors [1]. One of the goals when evaluating an infertile man is to identify reversible conditions that are responsible for infertility. Various conditions can cause infertility. Moreover, there are many controversies about environmental factors and occupational exposure to physical agents that might affect fertility [2]. Exposure to chemical toxins, and the effect of heat and cigarette smoking, have long been studied [3]. However, the effects of noise stress on different systems related to fertility have yet to be elucidated. Some have suggested that the teratogenic action of noise is primarily the result of decreased uroplacental blood flow, resulting in foetal hypoxia, and increased secretion of maternal catecholamines [4]. Geber [4] reported a significantly reduced litter size and a significant increase in the number of resorptions per litter amongst pregnant rats exposed to noise. Others [5] exposed mice to noise at 83–95 dB during gestation, and reported increased pre-implantation mortality, decreased litter size, and decreased embryo size and weight amongst the exposed offspring. There was no significant effect on the number of litter resorptions. However, these data are inconsistent amongst the various experimental conditions [6], [7] and [8]. These different results might be due to variability in acoustic stimuli, exposure regimens, test species, and other variables [9].
Antioxidants are the main defence against oxidative stress induced by free radicals. There are preventive antioxidants and scavenger antioxidants. Preventive antioxidants, e.g. metal chelates and metal-binding proteins, block the formation of new free radicals, whereas scavenger antioxidants remove the free radicals that have already formed [10].
Oxidative stress can be limited by using chain-breaking antioxidants such as vitamins E and C as drug supplements [11]. More specifically, these vitamins have been shown to have protective effects on the testis and on fertility [3] and [12].
In the present study we evaluated the effect of noise stress on male rat fertility and administered vitamins C and E to assess any change in the effects of noise.
Materials and methods
This experimental study was conducted in the Physiology Research Centre of Ahwaz Joundi Shapour University of Medical Sciences from September 2010 to December 2010. Male rats (200–250 g) of the Wistar strain (Rattus norvegicus) were used, acclimated to 22 ± 1 °C and maintained under conditions of 12-h of light and dark, with free access to tap water and commercial rat food. All procedures were approved by international guidelines and by the Institute Research Ethics and Animal Care and Use Committee of the authors’ institution. Every effort was made to minimise the number of animals used and their suffering.
Experimental design
The rats were randomly divided into five groups of eight each, and thus the fertility of each group was considered comparable to the other groups at the baseline. Group 1 (controls) was not exposed to noise. The rats in groups 2–5 were exposed to noise at 90–130 dB and 300–350 Hz from 19.00 to 07.00 h each day for 50 days. For this exposure the groups were transported to a room of 3 × 4 × 3 m, lined by wood and acoustic segments (‘anti-loud’ voice), within which ‘white noise’ was produced [13], and a timer was arranged so that after 1 h of exposure the noise was turned off for 15–60 min before continuing the exposure. This intermittent exposure was to prevent the rats from becoming adapted to the noise. The intensity and frequency of the noise was changed automatically within the range of minimum and maximum every 2–3 min, and this also contributed to preventing adaptation to the noise [14]. The amount and intensity of noise were measured using a noise level meter and the rate and intensity were controlled in this way. Group 2 received vitamin C (125 mg/kg/day) and group 3 received vitamin E (75 mg/kg/day) [3]. Group 4 received vitamins C and E concomitantly. Group 5 received no vitamins.
After 50 days (7 weeks is the time needed for a complete spermatogenesis cycle in male rats) a blood sample was drawn with a syringe from each rat’s tail, between 08.00 and 11.00 h, and analysed for serum FSH, LH and testosterone levels using an ELISA technique. As all rats had been assigned randomly to the groups at the beginning of study, serum levels in the control group were referred to as the normal range and levels in the other groups were compared with those. Each rat was then left with three female rats, for mating, for 1 week. Every morning, females with positive vaginal plaques (pregnant females) were identified and separated. Pregnant females were killed humanely on the 19th day of pregnancy (the duration of normal pregnancy in the rat is 21 days) by cervical dislocation under anaesthesia (an acceptable method of euthanasia of rats used for scientific purposes). Their uteri were then evaluated for the presence and number of viable, dead and absorbed fetuses.
Data are reported as the mean (SD) and percentage, where appropriate. The statistical significance of differences between the control and experimental groups was determined by anova for the hormonal studies. The pregnancy rate and number of dead/absorbed fetuses were compared amongst groups using the chi-square test. Differences between the means were considered to be significant at P < 0.05.
Results