Physical properties and non-enzymic components of human ejaculates. Relationship to spontaneous liquefaction

Male Genital Morphology and Function: An Evolutionary Perspective

PURPOSE

The genitals are at the forefront of evolution. Advantageous features of genital form and function determine which individuals pass their genes to future generations. The male genitalia are primarily for sperm deposition but additional functions of the penis and its accessory structures are being identified.

MATERIALS AND METHODS

The literature regarding genital evolution was reviewed.

RESULTS

This review explains key theories regarding the mechanisms of genital evolution. Also discussed are the anatomical and functional adaptations among different species that have evolved to optimize fertilization success. Finally, these evolutionary influences are discussed in the context of clinically relevant human genital morphology and function.

CONCLUSIONS

The function of the genitalia extends beyond simple sperm transfer. Genital morphology evolves to provide the primary and secondary functionality that is critical for successful mating. By considering the form and function of human genital morphology in an evolutionary context we gain not only an appreciation for its design, but also the potential for a deeper understanding of our treatment goals.

Semen Displacement as a Sperm Competition Strategy in Humans

We examine some of the implications of the possibility that the human penis may have evolved to compete with sperm from other males by displacing rival semen from the cervical end of the vagina prior to ejaculation. The semen displacement hypothesis integrates considerable information about genital morphology and human reproductive behavior, and can be used to generate a number of interesting predictions.

Deficiency in major high molecular-weight seminal proteins in men producing poorly coagulating and alkaline liquid ejaculates

Using SDS-PAGE three major high molecular-weight coagulum proteins (57, 75 and 79 kD) were identified in unliquefied human ejaculates. Washed coagulum was prepared at pH 4.5 and demonstrated negligible proteolysis as determined by a highly sensitive fluorescamine-based method. Laser densitometric scanning of these high molecular-weight proteins in unliquefied ejaculates in relation to their coagulational failure revealed that the total content of 57, 75 and 79 kD proteins in whole semen represented approximately 44% of levels in the normally coagulated, approximately 24% in poorly coagulated (P less than 0.005) and approximately 3% in the non-coagulated (alkaline liquid, P less than 0.001) samples. The findings imply that these predominant high molecular-weight proteins play a major role in human seminal coagulum formation.

Prolactin and alpha-1,4-glucosidase activity in normal and poorly coagulated human semen

Prolactin and alpha-1,4-glucosidase levels in seminal plasma were measured in poorly coagulated (I), deficiently coagulated (II) and normally coagulated (III and IV) human ejaculates having 0-20%, 21-50% and 51-100% coagulum respectively 4 min after emission. The prolactin concentration (ng ml-1, mean +/- SEM) in poorly coagulated (5.2 +/- 0.48) and deficiently coagulated (7.6 +/- 0.72) samples was significantly lower than in the normally coagulated groups III (51-75% coagulum, 8.2 +/- 0.43) and IV (76-100% coagulum, 9.9 +/- 0.59) as well as the presumably fertile samples (9.2 +/- 0.74). A highly significant positive correlation was observed between the prolactin level and the percentage coagulum of the ejaculates (r = 0.686, n = 58, P less than 0.001). In contrast, the epididymal marker, alpha-glucosidase showed no relationship to seminal coagulation.

Functional structure and ultrastructure of seminal vesicles

The function of the seminal vesicles in animals and man is under androgen control. The use of a new marker of the seminal vesicle function, termed corrected fructose, demonstrates an association between serum testosterone levels and seminal corrected fructose levels. The human seminal vesicles secrete a variety of products, and there is good evidence of a close relationship between functions of the seminal vesicles and sperm motility. Some of their products of secretion, such as potassium, bicarbonate, prostaglandins, and prolactin, directly stimulate the motility of the sperm through actions at the level of the mechanisms of production of the energy necessary for the motion. Several constituents are secreted by the seminal vesicles, some of which have no specific functions.

Differences in osmolality, pH, buffering capacity, superoxide dismutase and maintenance of sperm motility in human ejaculates according to the degree of coagulation

The purpose of this study was to compare various seminal plasma parameters in fresh human ejaculates exhibiting different amounts of coagulum. Poorly coagulating samples demonstrated significantly lower osmolality and buffering capacity but had a higher pH than did samples with good coagulation. However, no correlation was obtained between the activity of superoxide dismutase and the amount of coagulum. Eight hours after ejaculation, sperm motility had decreased by 15 and 80% in samples with good and poor coagulation, respectively. It is suggested that subfertility may be associated with poor coagulation of ejaculates.

Biochemical parameters of slowly liquefying human ejaculates

Abnormality in liquefaction of human semen is associated with poor scoring in postcoital tests and may lead to subfertility. A relative study on the seminal plasma characteristics of slowly and normally liquefying human ejaculates has been made. A multitude of seminal vesicular and prostatic components in the seminal plasma of eight slow-liquefying ejaculates from 4 men were compared with ten normally liquefying ejaculates from different healthy volunteers. For 60% liquefaction, the time taken by these two types of ejaculates was 46 and 7 min, respectively. The levels of the components that are mainly secreted by the seminal vesicles were similar in both the groups. But all the prostatic components demonstrated significantly (p less than 0.001) decreased levels in the slow-liquefying group from those in the group being compared. It was concluded that relative decrease in the prostatic activity with respect to that of the seminal vesicles appears to be the cause of slow-liquefaction.

Phosphate, zinc, calcium, citric acid, and acid phosphatase in human ejaculates as related to coagulation/liquefaction

Variations in the coagulation-liquefaction property of human seminal coagula have rarely been correlated to their ingredients. A number of seminal components were evaluated in relation to the degree of coagulation and the liquefaction time of human ejaculates. Correlation analyses suggested that the vesicular coagulatory activity can better be assessed by the phosphate level rather than the fructose and N-acetylamino sugar levels. The results showed that the fresh ejaculates with a smaller amount of coagulum possess significantly higher prostatic but lower vesicular activities in comparison with that of the better coagulating samples. The study also revealed that liquefaction time-based fractionation of the whole ejaculate seems to give an idea about the origin of some seminal components like split ejaculation technique. It was concluded that the material characteristics of human ejaculate can be approximated simply by determining its degree of coagulation or liquefaction time.

Grouping of human ejaculates according to the degree of coagulation and the relationship to the levels of choline and cholinesterase

Human ejaculates were divided into 3 groups (I, II and III) according to the extent of their coagulation and the levels of free choline and cholinesterase were determined together with seminal vesicular N-acetylamino sugar and prostatic (zinc) marker components. Coagulation was determined as the percent coagulum (CG) at 5 min after ejaculation. The mean (+/- SEM) values for CG at 5 min in groups I, II and III were 6 +/- 2, 43 +/- 4 and 79 +/- 2, respectively. The time for 100% liquefaction in the 3 groups were 4.7 +/- 0.8, 12.9 +/- 1.4 and 19.1 +/- 2.1 min, respectively. Group III had significantly higher levels of choline and cholinesterase activity than groups I and II. The choline level was correlated significantly (r = 0.58) with the concentration of N-acetylamino sugar, but there was no correlation with the level of zinc. Evaluation of the level of choline in prostatic fluid, in semen from azoospermic men and in ejaculates with different CG values suggested that the level of choline may provide valuable information about activity of the seminal vesicles. Release of choline in group I was only 33 and 50% of that groups III and II, respectively. 60% of the total release of choline occurred during the liquefaction phase. The mean activity of cholinesterase in the prostate was only 27% lower than that found in seminal plasma. The liquefaction time and the concentration of choline, N-acetylamino sugar and zinc decreased significantly in ejaculates after 2 days of abstinence.