Showing papers on "Sperm published in 1993"

Evidence for Decreasing Quality of Semen During Past 50 Years

Abstract: OBJECTIVE--To investigate whether semen quality has changed during the past 50 years. DESIGN--Review of publications on semen quality in men without a history of infertility selected by means of Cumulated Index Medicus and Current List (1930-1965) and MEDLINE Silver Platter database (1966-August 1991). SUBJECTS--14,947 men included in a total of 61 papers published between 1938 and 1991. MAIN OUTCOME MEASURES--Mean sperm density and mean seminal volume. RESULTS--Linear regression of data weighted by number of men in each study showed a significant decrease in mean sperm count from 113 x 10(6)/ml in 1940 to 66 x 10(6)/ml in 1990 (p < 0.0001) and in seminal volume from 3.40 ml to 2.75 ml (p = 0.027), indicating an even more pronounced decrease in sperm production than expressed by the decline in sperm density. CONCLUSIONS--There has been a genuine decline in semen quality over the past 50 years. As male fertility is to some extent correlated with sperm count the results may reflect an overall reduction in male fertility. The biological significance of these changes is emphasised by a concomitant increase in the incidence of genitourinary abnormalities such as testicular cancer and possibly also cryptorchidism and hypospadias, suggesting a growing impact of factors with serious effects on male gonadal function.

Cold shock damage is due to lipid phase transitions in cell membranes: A demonstration using sperm as a model

Abstract: When cells are cooled to temperatures above the freezing point of water at rates greater than a few degrees per minute, they sustain irreversible injury. Reduction of this "cold shock" damage could increase the survival of animals and plants at low environmental temperatures and improve the cryopreservation of plant and animal cells. Leakage of solutes across membranes, associated with thermotropic phase transitions in membrane lipids, is thought to be responsible, but this hypothesis has not been tested directly. Using Fourier transform infrared spectroscopy (FTIR), we measured the lipid phase transitions in intact, living sperm, the animal cell in which cold shock has been studied most extensively. A shift in the CH2 absorbance peaks indicates the transition from liquid-crystalline to gel phase. The phase transition in sperm membranes occurred at a lower temperature for a marine shrimp than for the pig. In each case, potassium leakage, which is a hallmark of cold shock damage, increased abruptly near the end of the phase transition. Human sperm are quite resistant to cold shock, and an abrupt lipid phase transition was not detected. This phase behavior is typical of membranes containing a high proportion of cholesterol, and human sperm have an unusually high sterol content. High cholesterol levels are known to stabilize membranes during cooling. Overall, the lipid phase behavior was consistent with the temperature range over which cooling was damaging for pig and shrimp sperm, and the with the extent of damage produced in pig and human sperm. This is the first direct evidence that cold shock results from lipid phase transitions in cell membranes.

Lipids and calcium uptake of sperm in relation to cold shock and preservation: a review

Abstract: When sperm of the ram, bull, boar and stallion are cold-shocked by rapid cooling to near freezing point, motility and metabolic activity are irreversibly depressed and the acrosome and plasma membrane disrupted. Ram sperm become susceptible to cold shock in the proximal corpus region of the epididymis when the cytoplasmic droplet has moved backwards to the distal portion of the sperm midpiece. The membrane constituents phospholipids and cholesterol are important in cold shock which causes loss of lipid from sperm. The susceptibility of sperm to cold shock is linked with a high ratio of unsaturated:saturated fatty acids in the phospholipids and a low cholesterol content. The high unsaturated fatty acid content of sperm also makes them susceptible to damage from peroxidation which adversely affects motility, metabolism, ultrastructure and fertility. Hydroxynonenal, a product of fatty acid peroxidation, depresses the motility and oxygen uptake of ram sperm in vitro and may react with the -SH groups of the axonemal microtubules. High calcium concentrations in the external medium may decrease the motility and metabolism of sperm and 'calcium intoxication' may be a factor in cold shock. Lowering the environmental temperature increases calcium uptake by sperm and the effect is aggravated if the rate of cooling is rapid. Phospholipids, particularly those in egg yolk, protect sperm to some extent from cold shock and also prevent increased calcium flux into the sperm. Suggestions are made for increasing the life span of sperm during preservation and microencapsulation by adding agents that may stabilize membranes, counter peroxidation and decrease calcium uptake.

Use of a xanthine oxidase free radical generating system to investigate the cytotoxic effects of reactive oxygen species on human spermatozoa

Abstract: The reaction between xanthine and xanthine oxidase results in the univalent and divalent reduction of dioxygen to generate superoxide (O2-.) and hydrogen peroxide (H2O2), respectively. With the aid of this system, the direct effect of reactive oxygen species (ROS) on human sperm function has been investigated. A protocol involving the addition of xanthine oxidase to the reaction mixture at 0 and 15 min resulted in a loss of motility involving every component of sperm movement examined. Lower doses of xanthine oxidase, which did not influence sperm motility, were also found to suppress the competence of human spermatozoa to exhibit oocyte fusion in response to the ionophore, A23187. The reactive oxygen species responsible for the disruption of human sperm function was not influenced by the presence of superoxide dismutase (SOD) or scavengers of hypochlorous acid or hydroxyl radicals. However, the cytotoxic species was shown to be extremely stable and could be completely eliminated by catalase, which selectively eliminates H2O2. Confirmation that it is H2O2, and not O2-., which is cytotoxic to human spermatozoa was obtained in studies in which the direct addition of this oxidant was shown to influence both the movement of human spermatozoa and their competence for oocyte fusion. These results carry implications for the diagnosis of defective sperm function and the design of optimized culture media for the treatment of male factor infertility.

Sexual selection and the temporal separation of reproductive events: sperm storage data from reptiles, birds and mammals

Abstract: The duration of sperm storage by females differs markedly between reptiles (maximum: 2555 d [7 years] and birds (maximum: 117 d), with mammals showing both very short (

Relationship between iron-catalysed lipid peroxidation potential and human sperm function

Abstract: The relationship between lipid peroxidation and the functional competence of human spermatozoa has been investigated in a cohort of 31 infertility patients. Lipid peroxidation was assessed using a sensitive fluorometric assay for the generation of malondialdehyde in response to the presence of a ferrous ion promoter. Sperm function was evaluated by monitoring the movement characteristics of these cells and their capacity for sperm-oocyte fusion. Each sample was separated into high- and low-density sperm populations on discontinuous, two-step (40%:80%), Percoll gradients prior to analysis. The way in which individual ejaculates fractionated on these gradients was highly positively correlated (P < 0.001) with the lipoperoxidation status of the spermatozoa; the greater the potential for malondialdehyde generation, the higher the proportion of cells entering the low density region of the gradients. The lipoperoxidation potential of the freshly prepared spermatozoa was also highly predictive (P = 0.0001) of their capacity for movement at 3 and 24 h and their ability to exhibit sperm-oocyte fusion in response to the ionophore A23187. The potential for malondialdehyde generation in the 40% and 80% Percoll fractions was positively associated with midpiece abnormalities in the spermatozoa. These results emphasize the importance of lipid peroxidation in the pathophysiology of male infertility and suggest a mechanism by which such damage might arise.

The Importance of Sperm Limitation to the Evolution of Egg Size in Marine Invertebrates

Abstract: Interspecific variation in egg size of marine invertebrates has been previously explained by a trade-off between gamete quality and quantity: the production of many small eggs with high mortality or fewer large eggs that develop quickly and experience reduced planktonic mortality. This theory assumes 100% fertilization of eggs and predicts that either strategy results in a similar number of settling offspring per unit of energy invested in reproduction. Empirical support for the theory has been equivocal. Here I offer an alternative hypothesis: larger eggs present a larger target for sperm and thus are fertilized at a higher rate. This theory suggests a trade-off between the production of many small eggs with a low probability of fertilization or fewer large eggs with a higher probability of fertilization. This hypothesis is tested with three congeneric sea urchins, Strongylocentrotus purpuratus, Strongylocentrotus franciscanus, and Strongylocentrotus droebachiensis, with a fivefold difference in egg volu...

Sperm Competition Games: Sperm Size and Sperm Number under Adult Control

Abstract: Evolutionary games of sperm competition in which two males mate with the same female have previously considered sperm size to be fixed at some (small) constant level. Although male gametes in multicellular organisms are typically small compared with ova, they vary greatly both between and within groups, and sperm size sometimes correlates with the probability of sperm competition. This paper examines `raffle principle' sperm competition games in which both size and number of gametes can be varied strategically under control of the diploid parent. If ejaculate investment trades off against the number of matings that a male can achieve, the evolutionarily stable strategy (ESS) ejaculate expenditure (as a fraction of reproductive effort per mating) approximates to p/4 when the probability, p, of sperm competition is low. Sperm size may either: (i) increase a sperm's competitive weight (a measure of its advantage in the fertilization raffle), or (ii) influence its mortality rate in the female tract. On the simplest model, size is optimized after the marginal value theorem, and may be large or small depending on how size influences competitive weight or survivorship. Further, sperm size is independent of the risk of sperm competition, and only sperm numbers increase with this risk. However, some recent studies show sperm size to increase with sperm competition. The present analysis offers the following possibilities: (i) there are unidentified constraints on sperm number, so that ejaculate mass can increase only by increase in sperm size; (ii) competitive benefits of size become more important as sperm numbers increase; (iii) size mainly increases survivorship, and sperm competition risk increases with the mean duration between mating and fertilization; and (iv) size increases competitive ability at the expense of survivorship, and sperm competition risk decreases with time between mating and fertilization. These conclusion relate to advantages conferred by size on sperm before fertilization; they do not affect the prediction of previous models that no component of sperm size should evolve for provisioning the zygote.

Effect of deoxyribonucleic acid protamination on fluorochrome staining and in situ nick-translation of murine and human mature spermatozoa.

Abstract: A major event in enhancing sperm chromatin stability is the replacement of the histones by protamines during spermiogenesis. In this study, we present results indicating that chromomycin A3 (CMA3 ) can be used to show protamine deficiency in sperm chromatin. Fixed chromatin of mature mouse spermatozoa showed high fluorescence after treatment with ethidium bromide (EB), but was completely unstained after treatment with CMA3. The same chromatin was found to be highly resistant to in situ nick-translation. In contrast, a substantial fraction of human spermatozoa were positive for CMA3. The accessibility of CMA to the DNA of human sperm was eliminated if the slides were previously treated with protamine in situ. This treatment did not affect the accessibility of EB to the chromatin. Individual human sperm samples revealed a substantial frequency of spermatozoa with endogenous nicks, which was found to be the same as the frequency of spermatozoa responding positively to CMA3 staining. Treatment of preparations with protamines prevented the identification of the endogenous nicks. These data as a whole suggest that CMA3 could represent a useful tool for the detection of protamine deficiency in sperm chromatin. Furthermore, confirmation of experiments relating sensitivity to nick translation and positivity to CMA3 may allow an indirect in situ visualization of nicked and partially denatured DNA, which could correlate with certain forms of male factor infertility.

Multiple mating, lifetime fecundity and female mortality of the bruchid beetle, Callosobruchus maculatus (Coleoptera: Bruchidae)

Abstract: Females of most insect species mate frequently. Many hypotheses have been proposed to account for the evolution of multiple mating in female insects. In this paper, I test the hypothesis that females of the bruchid beetle, Callosobruchus maculatus, mate frequently to replenish depleting sperm supplies. I also test the hypothesis that females obtain a nutritional contribution from males during copulation, and that this has a positive effect on the female's life history. For C. maculatus, there is no difference in lifetime fecundity between females that mate one time and females that are confined with males throughout life. However, when females are mated at 48-h intervals, but are not confined with males, they lay more eggs than females which have mated only once

Probing the function of Drosophila melanogaster accessory glands by directed cell ablation

Abstract: The female Drosophila melanogaster fly undergoes behavioral changes after mating, including an increase in egg laying and an avoidance of remating. Accessory-gland products elicit these changes transiently when introduced into unmated female flies. We report here the generation and phenotype of flies that lack functional accessory-gland main cells as a consequence of genetically directed delivery of diphtheria toxin subunit A to those cells. Only main-cell secretions are essential for the short-term inhibition to remating; no other products of the genital tract can replace their function. Long-term inhibition to remating depends only on the storage of sperm in the female. Both sperm and main-cell secretions have roles in the increase of egg laying by the mated female. In addition to full-strength diphtheria toxin, we used low-activity toxins to kill only those cells that express toxin at high levels. These transgenic strains that express diphtheria toxins of different strengths in accessory-gland main cells will be useful in further defining the role of these cells.

In vitro fertilization with isolated, single gametes results in zygotic embryogenesis and fertile maize plants

Abstract: We demonstrate here the possibility of regenerating phenotypically normal, fertile maize plants via in vitro fertilization of isolated, single sperm and egg cells mediated by electrofusion. The technique leads to the highly efficient formation of polar zygotes, globular structures, proembryos, and transition-phase embryos and to the formation of plants from individually cultured fusion products. Regeneration of plants occurs via embryogenesis and occasionally by polyembryony and organogenesis. Flowering plants can be obtained within 100 days of gamete fusion. Regenerated plants were studied by karyological and morphological analyses, and the segregation of kernel color was determined. The hybrid nature of the plants was confirmed.

Intracellular calcium increases with hyperactivation in intact, moving hamster sperm and oscillates with the flagellar beat cycle.

Abstract: At some time before fertilization, mammalian sperm undergo a change in movement pattern, termed hyperactivation. There is evidence that hyperactivation offers an advantage to sperm for detaching from the oviductal mucosa, for penetrating viscoelastic substances in the oviduct, and for penetrating the zona pellucida. Hyperactivation is known to require extracellular calcium, but little else is known about the mechanisms by which calcium affects sperm movement. The calcium-sensitive fluorescent dye indo-1 was used to follow intracellular calcium levels ([Ca2+]i) in individual moving sperm. Sperm were loaded with 10 microM of the acetoxymethyl ester form of the dye and then rinsed. The dye was excited at 340 nm by using a filtered xenon stroboscope, and images at the 405-nm and 490-nm excitation maxima were simultaneously digitized at 30 per sec for 2.1 sec. [Ca2+]i was significantly higher in the acrosomal and postacrosomal regions of the head and in the flagellar midpiece (the principal piece could not be measured) in hyperactivated than in nonhyperactivated sperm (P < 0.0001). [Ca2+]i oscillations were detected in the proximal half of the midpiece that were identical in frequency to the flagellar-beat-cycle frequency in 12 of 17 hyperactivated sperm (median, 3.5 Hz). Rapid [Ca2+]i oscillations were also detected in the acrosomal and postacrosomal regions, as well as in the distal midpiece. Oscillations were not eliminated by dampening the flagellar bending with methyl cellulose. The [Ca2+]i oscillations detected in sperm are significantly more rapid than oscillations detected in other cell types.

The epididymis and sperm maturation: a perspective.

Abstract: In common mammals, sperm leaving the testis are incapable of fertilizing a female gamete. Sperm have limited biosynthetic capability and need to minimize demand for ATP. Hence, modification of sperm to achieve their maturation requires pre-programmed cleavage of integral molecules (planned self-modification) and remodelling by action of molecules found in the suspending fluids. Most of these biocatalysts are secreted by a series of specialized regions in the epididymal epithelium, but some are provided in seminal plasma. The role of the epididymis in sperm maturation is postulated to be 'setting a series of triggers' each capable of initiating cellular changes either at emission or near or in the oocyte, and 'setting a safety' for each trigger to prevent premature occurrence of the event. The attributes required in a spermatozoon for in vitro fertilization and natural mating are different, and their expression is dependent on the site of sperm sampling. Some attributes needed for fertility are probably like an on-off switch, whereas others probably allow a gradually reduced probability of success before going to the off position (analogous to a conventional light switch and a dimmer-type light switch). All essential attributes of a spermatozoon must be expressed in a 'combined effective amount' for that cell to be fertile. Because of mixing, in any segment of the epididymal duct the population of sperm is heterogeneous in age and biological status. Thus, when assessing sperm maturation it is necessary to establish the proportion of sperm that has completed and retained all steps of maturation necessary to achieve fertilization of oocytes under the conditions imposed. In a normal animal, most sperm leaving the epididymis have a 'combined effective amount' of attributes, and the population has a high fertilizing potential.

Liquid storage of ram semen: a review.

Abstract: Research from 1930 to 1992 is reviewed with regard to storage of semen at reduced (0-5 degrees C or 10-15 degrees C) and at ambient temperatures. Diluents investigated have included synthetic buffers combined with sugars and egg yolk or its fractions, milk from various sources, glycine, and other substances. Irrespective of the diluent, dilution rate, temperature or conditions of storage, the spermatozoa deteriorate with time of storage. Changes include reduction in motility and morphological integrity of spermatozoa, accompanied by a decline in their survival in the female reproductive tract, reduction in fertility and increased embryonic loss. In critical studies, fertility declined rapidly when semen stored for more than 24 h was used for cervical insemination, but after intrauterine insemination some spermatozoa maintained their fertilizing capacity up to 10 days. Laparoscopic intrauterine or transcervical inseminations could be the means of improvement of fertility. These methods may eliminate the problem of sperm transport through the cervix and ageing of spermatozoa in the reproductive tract, thereby improving fertilization of ova and reducing embryonic loss.

Neonatal goitrogen treatment increases adult testis size and sperm production in the mouse

Abstract: Male rats made hypothyroid during neonatal life show unprecedented increases in adult testis size and daily sperm production (DSP). To determine if this effect was unique to the rat or could also be demonstrated in other species, we examined the effects of neonatal treatment with the reversible goitrogen 6-propyl-2-thiouracil (PTU) on adult testis size and function in the mouse. Male Swiss-Webster mice were untreated (control) or given PTU by adding 0.1% (w/v) to their mother's water from birth to day 25 postpartum. All pups were then weaned and given no further treatment. Sertoli cell proliferation was examined using tritiated thymidine autoradiography in some control and treated mice at 0, 5, 10, 15, 20, and 25 days, while the remainder were killed at 90 days to determine a variety of reproductive parameters. Neonatal PTU treatment decreased growth; body weight of treated mice at 4 weeks of age was 57% less than controls. Treated mice grew rapidly following cessation of PTU treatment, although their weights never equalled controls, remaining 17% smaller at 90 days of age. At 90 days of age, testis weight and DSP were increased by approximately 30% and 50%, respectively, in PTU-treated mice compared to controls. Despite the increased testis weight and function, serum testosterone concentrations were not different in control and treated mice. Testicular and epididymal histology in treated mice was similar to controls, while epididymal sperm in treated mice were motile and morphologically normal. Sertoli cell proliferation was altered in treated mice. The normal decrease in proliferative rate seen during early postnatal life was slowed, and by day 10 postnatal, the labeling index of treated Sertoli cells was about fourfold greater than that of controls. Furthermore, Sertoli cells in treated mice proliferated until day 25, whereas proliferation ceased in controls by day 15. In summary, neonatal PTU treatment increases testis weight, DSP, and the efficiency of sperm production (DSP/g testis) in the mouse, indicating that the PTU effect on testis development clearly occurs in other species. Furthermore, increased Sertoli cell proliferation appears to be the critical event for the development of this phenomenon in mice, as it is in rats. The existence of unique mutations that affect testicular development make the mouse an advantageous model for determining the mechanism of this effect. This technique may also be useful for increasing testicular size, sperm production, and fertility in various mutant mouse strains and transgenic mice in which these parameters are reduced.

Olfactory receptors are displayed on dog mature sperm cells.

Abstract: Olfactory receptors constitute a huge family of structurally related G protein-coupled receptors, with up to a thousand members expected. We have shown previously that genes belonging to this family were expressed in the male germ line from both dog and human. The functional significance of this unexpected site of expression was further investigated in the present study. We demonstrate that a few dog genes representative of various subfamilies of olfactory receptors are expressed essentially in testis, with little or no expression in olfactory mucosa. Other randomly selected members of the family show the expected site of expression, restricted to the olfactory system. Antibodies were generated against the deduced amino acid sequence of the most abundantly expressed olfactory receptor gene in dog testis. The purified serum was able to detect the gene product (DTMT receptor) in late round and elongated spermatids, as well as in the cytoplasmic droplet that characterizes the maturation of dog sperm cells, and on the tail midpiece of mature spermatozoa. Western blotting further confirmed the presence of a 40-kD immunoreactive protein in the membrane of mature sperm cells. Altogether , these results demonstrate that the main expression site of a subset of the large olfactory receptor gene family is not olfactory mucosa but testis. This expression correlates with the presence of the corresponding protein during sperm cell maturation, and on mature sperm cells. The pattern of expression is consistent with a role as sensor for unidentified chemicals possibly involved in the control of mammalian sperm maturation, migration, and/or fertilization.

Human male infertility may be due to a decrease of the protamine P2 content in sperm chromatin.

Abstract: Basic chromosomal proteins were extracted from the sperm of fertile and infertile human males. The relative proportions of protamine 1, 2, and 3 were determined by scanning microdensitometry following electrophoresis of total protamine in polyacrilamide gels. The findings were as follows: (1) The proportion of protamine P(2 + 3) in sperm obtained from infertile males was lower than that in fertile males. (2) Protamine P(2 + 3) in infertile human males showed reduced affinity to DNA. The possibility that some cases of human male infertility may be due to mutation within the protamine P2 gene is discussed. © 1993 Wiley-Liss, Inc.