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Summary.

(I) Fourteen adult male rabbits have been subjected to unilateral isolation of the tail of the epididymis in the abdomen, with subsequent retention of the organ in an abdominal position. Isolation of the contralateral cauda epididymidis in each rabbit was effected in the scrotum as a control measure. (2) Estimates of the proportion of dead and decapitated spermatozoa as well as the incidence of spermatozoa with coiled tails, at different levels of the tubule distal to the point of isolation, have demonstrated a delayed response of so-called mature spermatozoa to the conditions of experimental cryptorchidism. (3) Quantitative assessments of these criteria have suggested that spermatozoa in the body of the epididymis are more susceptible to degeneration than those in the tail of the epididymis, but it is pointed out that more evidence is yet required on this matter. (4) The overall results are discussed in relation to previous work concerning the origin of similar sperm abnormalities.

Summary.

A comparison of certain features of the testis and epididymis has been made in five species of East African mammals, two of which, the rock hyrax and elephant, have abdominally situated testes.

The artery to the testes was straight in the species with abdominally situated testes and there was no pampiniform plexus while in the species with scrotal testes, it was coiled in the region of the plexus. It is suggested that where the testicular artery is coiled, the testes should be regarded as basically scrotal, even if they are usually found in the abdomen post mortem.

A striking increase in blood flow in the testis of the rock hyrax during sexual activity suggests that the simpler arterial pattern of the testis in testicond mammals allows a greater variation in blood flow than the more complicated arterial design associated with scrotal testes.

Characteristic signs of sperm maturation occur in the epididymis of testicond mammals in contrast to the situation in artificial cryptorchidism, where normal epididymal function is completely disrupted. It is suggested that epididymal function, as well as spermatogenesis, has become modified during evolution. Evidence is given that a need for prolonged survival of spermatozoa in the mesonephric duct might have been an important primary factor in the caudal migration of gonads into a scrotum.

Summary.

Rabbit does were killed at intervals between 2 min and 90 hr after mating and spermatozoa were flushed from the genital tract and counted. A technique is described which facilitates the counting of small numbers of spermatozoa with reasonable accuracy. Evidence was found to suggest that the rabbit's cervix functions as a sperm reservoir and factors influencing the formation of the reservoir and transcervical migration are discussed. It was noted that spermatozoa reached the oviduct within 30 min of coitus.

Summary.

Ovariectomized oestrogen-treated rabbits were inseminated with semen of variable sperm density and volume. Does were killed 10 hr after insemination and the number of spermatozoa in the vagina, cervix, uterus and oviduct was determined. It was found that sperm counts from all regions of the genital tract were directly related to the total number of spermatozoa in the inseminate. When the number of spermatozoa in the inseminate was held constant, more spermatozoa were recovered from the cervix and uterus with the smaller inseminate volumes. All regional counts were positively correlated with one another. Proportionately fewer spermatozoa were recovered from the genital tract when the inseminate contained larger sperm numbers.

Summary.

A technique is described for collection of the epididymal contents from the cauda epididymidis of anaesthetized rabbits. The technique avoids undue contamination of the epididymal contents with blood or tissue fluid and overcomes the difficulty of post-mortem change.

The effects of high-speed centrifugation and cold shock on the composition of epididymal plasma have also been investigated, and it has been shown that lactic dehydrogenase and glutamic-oxaloacetic transaminase are largely intracellular constituents, whilst sodium, potassium, acid phosphatase, alkaline phosphatase and β-N-acetylglucosaminidase are extracellular. Finally, some results are presented on the overall composition of epididymal plasma in the rabbit.

Summary.

The composition of luminal plasma from the cauda epididymidis of rabbits has been investigated after prolonged retention of spermatozoa in the cauda epididymidis of entire animals, and of castrated animals both with and without hormone replacement. The morphology of the contained spermatozoa and the epididymal cells has also been examined.

In the presence of androgen, spermatozoa survived for 4 to 5 weeks before degenerative changes became apparent and the composition of the epididymal plasma and the histological characteristics of the lining cells were not seriously affected during this period. The only change in the plasma which could be due to sperm death was an increase in the lactic dehydrogenase (LDH) activity. After androgen withdrawal, spermatozoa degenerated rapidly and there were considerable changes in the composition of the luminal plasma. There was a rapid increase in the level of sodium ions and pH, and a decrease in the concentrations of glycerylphosphorylcholine (GPC) and protein. The activity of acid phosphatase and LDH also decreased. Initially, the concentration of inorganic phosphate and potassium increased but this was soon followed by a decrease. Five weeks after castration, all the spermatozoa disappeared from the epididymis and the epididymal cells had regressed. If testosterone replacement was given at this stage, the level of sodium ions in the plasma decreased and the concentration of GPC increased. The epididymal cells were also restored to their normal histological appearance.

These results provide evidence that, in the presence of androgen, the epididymal cells in the cauda epididymidis actively maintain a constant milieu in the lumen of the duct by their capacity for absorption and secretion. If androgen is withdrawn, these functions cease and considerable changes take place in the lumen.

Summary. The testes of rams were insulated for 28 days. After 28 days typical degenerative changes occurred in the tubular compartment of the testis. Spermatozoa, spermatids and, in many tubules, spermatocytes were absent. A pronounced dilatation of the testicular lymph vessels was noted, and a morphometric study indicated that the volume fraction occupied by Leydig cells was greater than in controls. A serial bleeding regimen showed that peripheral plasma concentrations of FSH were elevated and of testosterone were usually reduced after scrotal insulation. Although mean testosterone levels were unchanged after 7 days of treatment, there were more hormone episodes, each of significantly reduced amplitude. LH values were elevated at this time and there was an increase in the number and amplitude of LH episodes. After 14 days of scrotal insulation, mean and basal levels of testosterone were significantly reduced, and episodes of secretion were much smaller in amplitude. Mean LH values were elevated and each secretory episode was of significantly greater amplitude than in control blood. These results show that the testes of scrotally insulated rams are relatively insensitive to endogenous LH and that this treatment affects cells within the seminiferous tubule and those in the interstitial compartment.

Summary.

Experiments have been carried out to investigate the reaction of epididymal spermatozoa to interruption of their normal passage through the epididymis. In eighteen rabbits, the epididymis was ligated unilaterally at the distal end of the body, and in a further fifteen the ligature was placed at a point just distal to the head of the epididymis. Samples of spermatozoa from different regions proximal to the ligature were examined in each case for changes in motility, morphology and reactions to certain staining techniques.

It was found that ligation resulted in a distinct pattern of changes in the contained spermatozoa, irrespective of the level at which the epididymis was ligated. Initially these changes involved an enhanced capacity for motility in vitro, decreased eosinophilia and an increased number of coiled tails. In addition, maturation changes in the acrosome and in the location of the protoplasmic droplet occurred. After 14 days of ligation, however, degeneration of the spermatozoa was widespread.

The significance of these events is discussed in relation to the normal maturation of spermatozoa. It is suggested that spermatozoa can mature in situ when the epididymis is ligated, but that the changed environment resulting from ligation appears to superimpose a number of morphological abnormalities on the spermatozoa.

Summary.

Alkaline phosphatase activity has been examined in ram, rabbit, hamster and rat spermatozoa. Results have shown that the enzyme is restricted to the cytoplasmic droplet in rabbit and ram spermatozoa but that the intensity of reaction is highest in rabbit spermatozoa. The enzyme could not be demonstrated at all in the spermatozoa of the hamster or rat.

It has also been shown that alkaline phosphatase activity in the droplet of rabbit spermatozoa decreases during epididymal transit and that there is a reduction in activity in degenerating spermatozoa. Degeneration in spermatozoa was produced in rabbits by means of artificial cryptorchidism, and after 2 weeks, activity in the droplets was completely lost.

Summary.

Artificial cryptorchidism produced sterility in male rabbits within 7 days. Progressive infertility, which first appeared on the 2nd day after operation, resulted from a failure of a normal number of live motile spermatozoa to fertilize. Many such spermatozoa had not discarded their cytoplasmic droplets, and it is thought that these were heat-affected and incapable of fertilization. This is because fertilization rate and implantation rate were significantly (P<0·001) correlated with the number of live (droplet-free) spermatozoa in the inseminates.

There were no adverse effects on the ability of embryos to implant or to survive gestation, and the morphology and sex ratio of foetuses at term were normal. Before fertilization failure became apparent, there were significant (P<0·001) improvements in embryonic survival rates and a theory is advanced to explain these findings.