The effects of moderate heating of the testes and epididymides of rams by scrotal insulation on body temperature, respiratory rate, spermatozoa output and motility, and on fertility and embryonic survival in ewes inseminated with frozen semen

Amelioration of heat stress-induced damage to testes and sperm quality

Heat stress (HS) occurs when temperatures exceed a physiological range, overwhelming compensatory mechanisms. Most mammalian testes are ∼4-5 °C cooler than core body temperature. Systemic HS or localized warming of the testes affects all types of testicular cells, although germ cells are more sensitive than either Sertoli or Leydig cells. Increased testicular temperature has deleterious effects on sperm motility, morphology and fertility, with effects related to extent and duration of the increase. The major consequence of HS on testis is destruction of germ cells by apoptosis, with pachytene spermatocytes, spermatids and epididymal sperm being the most susceptible. In addition to the involvement of various transcription factors, HS triggers production of reactive oxygen species (ROS), which cause apoptosis of germ cells and DNA damage. Effects of HS on testes can be placed in three categories: testicular cells, sperm quality, and ability of sperm to fertilize oocytes and support development. Various substances have been given to animals, or added to semen, in attempts to ameliorate heat stress-induced damage to testes and sperm. They have been divided into various groups according to their composition or activity, as follows: amino acids, antibiotics, antioxidant cocktails, enzyme inhibitors, hormones, minerals, naturally produced substances, phenolic compounds, traditional herbal medicines, and vitamins. Herein, we summarized those substances according to their actions to mitigate HS' three main mechanisms: oxidative stress, germ cell apoptosis, and sperm quality deterioration and testicular damage. The most promising approaches are to use substances that overcome these mechanisms, namely reducing testicular oxidative stress, reducing or preventing apoptosis and promoting recovery of testicular tissue and restoring sperm quality. Although some of these products have considerable promise, further studies are needed to clarify their ability to preserve or restore fertility following HS; these may include more advanced sperm analysis techniques, e.g. sperm epigenome or proteome, or direct assessment of fertilization and development, including in vitro fertilization or breeding data (either natural service or artificial insemination).

Mild experimental increase in testis and epididymis temperature in men: effects on sperm morphology according to spermatogenesis stages

Background

A mild increase in testicular and epididymal temperatures in men, bulls and rams (pendulous scrotum) inhibits spermatogenesis and increases the percentage of sperm with an abnormal morphology. However, the stages of spermatogenesis that are most sensitive to a mild increase in testicular temperature in men are unknown. The aim of the present study was to explore the effects of a mild induced increase in testicular and epididymal temperature (i.e., testicular temperature maintained below the core body temperature) on sperm morphology in humans depending on the physiological time of spermatogenesis and epididymal transit.

Methods

Five healthy volunteers were enrolled in an experimental study in which testicular and epididymal temperatures were increased by maintaining the testes in a supra-scrotal position with a specially designed underwear worn 15±1 h a day for 120 consecutive days. Semen collection was scheduled on specific days depending on spermatogenic stages and epididymal transit.

Results

Sperm morphology and the multiple anomalies index (MAI) were analysed before, during and after heating. This mild induced increase in testicular and epididymal temperatures resulted in a significant rise in the percentage of morphologically abnormal spermatozoa on day 34 of heating, which remained elevated throughout the heating period and persisted until 45 days after cessation of heating. The MAI was significantly increased on day 20 throughout the heating period and persisted 45 days after cessation of heating. An increase in the percentage of anomalies in the sperm head, acrosome or tail occurred on days 34 and/or 45 of heating. Abnormal sperm morphology and MAI reverted to control values 73 days after cessation of heating.

Conclusions

A mild sustained increase in testicular and epididymal temperature in man leads morphological abnormalities in spermatozoa mainly due to an impairment of spermiogenesis and meiosis.

Attenuation of heat stress-induced spermatogenesis complications by betaine in mice

High temperatures can induce oxidative stress, impairment of spermatogenesis, and reduction of sperm quality and quantity concomitant with transient periods of partial or complete infertility in male mammals. Promising beneficial effects of betaine supplementation on the epididymal spermatozoa have been reported in experimental studies; however, its effects on testicular heat stress (HS)-induced impairment have yet to be determined. In the present study, betaine (Bet) was orally administrated (250 mg/kg day) during a 14-day period, before (Bet + HS group) or after (HS + Bet group) induction of testicular HS in 7-9 week-old male mice. HS was induced by testicular immersion in water at 42 °C in stress groups. Epididymal spermatozoa and testes were collected at days 14 and 28 after HS induction in order to analyze sperm characteristics, testicular oxidative status, and histological changes. Our studies showed that HS reduced testicular weight, the quality and quantity of epididymal spermatozoa, and impaired maturation of germinal cells. The levels of MDA, catalase, SOD, and GPX were increased in the testes of HS-induced mice (P < 0.01). Although betaine treatment before and after exposure to HS enhanced antioxidant defense (P < 0.05) and accelerated germinal epithelium regeneration, its effects on the characteristics of epididymal spermatozoa were scarce. On the other hand, in the absence of heat stress, quality and quantity of epididymal spermatozoa were improved following 14 days of betaine consumption. Our study revealed the beneficial effect of betaine on HS-induced complications of spermatogenesis, as well as its potency to improve epididymal spermatozoa in intact mice.

Hormonal, chemical and thermal inhibition of spermatogenesis: contribution of French teams to international data with the aim of developing male contraception in France

Since the 1970s, international research on male contraception has been actively pursued. Hormonal and non-hormonal methods (thermal, chemical) have been tested, leading to clinical trials of interest to thousands of men and couples. The results showed that it was possible to develop methods of male contraception that inhibited spermatogenesis with good contraceptive efficacy. However, their side effects (mainly loss of libido), poorly accepted modes of administration, and the high frequency of poor responders prevented their widespread use. Based on earlier initiatives, new avenues were explored and significant progress was achieved, allowing the reasoned use of male contraception. For 40 years, several French teams have played an important role in this research. The aim of this paper is to outline the history and the progress of the experimental and clinical works of these teams who addressed hormonal, chemical and thermal approaches to male contraception. These approaches have led to a better comprehension of spermatogenesis that could be useful in fields other than male contraception: effects of toxic compounds, fertility preservation.

Effect of short-term scrotal hyperthermia on spermatological parameters, testicular blood flow and gonadal tissue in dogs

The objective was to assess the effect of a short-term scrotal hyperthermia in dogs on quantitative and qualitative ejaculate parameters, testicular blood flow and testicular and epididymal histology. After a control period, the scrotum of seven normospermic adult beagle dogs was insulated with a self-made suspensory for 48 h. Nine weeks later, two animals were castrated, while in five animals, scrotal hyperthermia was repeated. Dogs were castrated either 10 or 40 days thereafter. In each phase of scrotal insulation, average scrotal surface temperature increased by 3.0°C. Semen was collected twice weekly throughout the experiment. Total sperm count did not change after the first hyperthermia, but it slightly decreased after the second (p < 0.05). Profiles of sperm morphology and velocity parameters (CASA) rather indicated subtle physiological variations in sperm quality than effects of a local heat stress. Chromatin stability of ejaculated spermatozoa as indicated by SCSA remained constant throughout the experiment. Perfusion characteristics of the gonads, that is, systolic peak velocity, pulsatility and resistance index at the marginal location of the testicular artery, did not change due to hyperthermia (p > 0.05). Histological examination of excised testes and epididymides for apoptotic (TUNEL and activated caspase-3) and proliferating cells (Ki-67 antigen) indicated only marginal effects of scrotal insulation on tissue morphology. In conclusion, a mild short-term scrotal hyperthermia in dogs does not cause substantial changes in sperm quantity and quality. In contrast to other species, canine testes and epididymides may have a higher competence to compensate such thermal stress.

Heat stress on reproductive function and fertility in mammals

In most mammalian species including cattle, heat stress has deleterious effects on nutritional, physiological and reproductive functions. Exposure of animals to a hot environment causes an increase in body temperature in mammals, including domestic animals. High ambient temperature also causes a decrease in the length and intensity of estrus by disturbing ovarian function as well as decreasing pregnancy rate after artificial insemination. Therefore, it is important to understand the effects of heat stress on reproductive function in order to improve the production of domestic animals. Heat stress decreases appetite, weight gain, and milk yield in dairy cattle. It also adversely affects the reproductive performance of both sexes. In males, it reduces spermatogenic activity, while in females it adversely impacts oogenesis, oocyte maturation, fertilization development and implantation rate. Detection and evaluation of the deteriorating effects of heat stress on reproductive organs and cells can help to design measures to prevent them and improve reproductive functions. In this review, we discuss the impacts of heat stress on reproductive functions.

Scrotal heat stress effects on sperm viability, sperm DNA integrity, and the offspring sex ratio in mice

Evidence exists to suggest detrimental effects of heat stress on male fertility. This study was designed to assess the effects of scrotal heat stress on mature and developing sperm in a mouse model. After receiving shock heat treatment (42 degrees C for 30 min), mature spermatozoa were recovered from the epididymis hours (6) or Days (7, 14, 21, 28, 60) later, to determine the variables: number of spermatozoa, sperm viability, motility and progressive motility, sperm DNA integrity as established by the TUNEL method, embryo implantation rate, and sex ratio of the fetuses conceived using the heat-exposed spermatozoa. Our results indicate that transient mild heat treatment does not affect in the same way the different types of male germ cells. Spermatocytes present within the testis at the time of heat stress resulted into a lower concentration of spermatozoa with reduced viability and low motility. Even though, DNA integrity of spermatozoa resulting from spermatocytes was also compromised by heat stress, the higher degree of DNA damage was found among spermatozoa resulting from spermatids present within the testis at the time of heat stress. At last, heat shock effect on spermatozoa present in the epididymis at the time of thermal stress resulted into a sex ratio distortion. These findings point to a higher sensitivity of spermatocytes to heat exposure and also suggest a different response of X and Y chromosome-bearing spermatozoa to heat stress that warrants further investigation.

Ram sperm motility after intermittent scrotal insulation evaluated by manual and computer-assisted methods

AIM

To study whether additional measurements of motility characteristics of spermatozoa by computer assisted semen analysis (CASA) were more sensitive indicators of reduced semen quality than estimates of percentages of motile, rapid or progressive cells.

METHODS

Intermittent scrotal insulation was applied to 6 rams for 16 h per day for 21 days or to 2 of these for 12 h per day for 28 days in the following year. Semen was collected and evaluated by CASA immediately and either frozen or stored at 30 degrees Celsius or 5 degrees Celsius before re-evaluation.

RESULTS

Intermittent scrotal insulation caused falls in the percentage of motile, progressive and rapid sperm, as did freezing-thawing and storage at 30 degrees Celsius or 5 degrees Celsius. Motility characteristics (amplitude of lateral head displacement, mean path velocity, mean progressive velocity and curvilinear velocity), as determined by CASA fell only when the percentage of motile sperm was already reduced. Freezing and thawing or liquid storage of the semen from insulated rams caused a greater fall in the percentage of motile and rapid sperm than control semen, but only affected the motility characteristics when the percentage of motile sperm was already reduced.

CONCLUSION

Intermittent scrotal insulation affected not only the motility of the freshly collected sperm, but also their ability to withstand the additional stress of storage. The additional data on motility characteristics obtained by CASA appeared to be no more a sensitive indicator than the percentage of motile cells of reductions in semen quality.

Semen quality and sedentary work position

Increased scrotal temperature can, in experimental settings, markedly disturb the production of semen. Sedentary work position may increase the temperature of the scrotum, but previous studies have failed to determine whether changes in scrotal temperature caused by sedentary work actually do affect semen quality. This study was carried out to elucidate the possible harmful effects of sedentary work on sperm count and other semen characteristics. In 1981-1983 a semen sample was obtained from 3119 men who attended an infertility workup in one of four Danish fertility centres. A total of 2517 men returned a postal questionnaire with information on life style, leisure time activities, occupational history and job duties. Information on job specific work position was obtained from The Danish Work Environment Cohort study 1990 (DWECS). In this analysis DWECS data for a total of 1747 men was included from men aged 18-39 years with >30 h of work per week. For all job titles represented in the DWECS, the mean proportion of sedentary work was estimated. The sperm cell concentration was 30.6 million/mL among men in the quintile with lowest job specific sedentary work compared with 40.5 million/mL in the highest quintile. The difference was, however, not statistically significant. Stratification on infertility period, educational level of the man, fertility centre, and fertility-related disease of the spouse did not influence the results. The analyses do not suggest that sedentary work is a risk factor for abnormal semen characteristics.

Diurnal scrotal skin temperature and semen quality. The Danish First Pregnancy Planner Study Team

It is well established that heat is associated with reduced sperm production, but the role of physiological variation in temperature has never been scrutinized in humans. We studied diurnal scrotal temperature and markers of male fertility in a population of couples planning their first pregnancy. Sixty men from a cohort of couples who were planning their first pregnancy were included and scrotal skin temperature was monitored during 3 days using a portable data recorder. Working hours and working postures were recorded daily in a questionnaire. Each man provided a fresh semen sample and the couples were followed for six menstrual cycles or until a clinical pregnancy was recognized. The median value of scrotal skin temperature was 33.3 degrees C in the daytime and 34.8 degrees C at night. In periods of sedentary work, the median temperature was on average 0.7 degrees C higher (SE=0.2 degrees C). In addition, scrotal temperature was higher in the daytime, in summer, and in leisure time compared with working hours. Median sperm concentration among men with more than 75% of their daytime readings above 35 degrees C was 33.4 x 10(6)/mL, compared with 91.8 x 10(6)/mL for men with less than half of their readings above 35 degrees C (difference 58.4; 95% CI: 25.9-77.8 x 10(6)/mL). It is concluded that a sedentary position is a significant source of increased scrotal skin temperature, and even moderate and physiological elevation in scrotal skin temperature is associated with a substantially reduced sperm concentration. Sedentary work should be considered as an important potential confounder for reduced sperm count in epidemiological research.