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Summary.
Fluid secretion by the seminiferous tubules of the testes of rats, rams and goats has been calculated from measurements of weight and water content of the testes after ligation of the efferent ducts. Measurement of fluid secretion made in this way gave similar results to other studies where the volume of fluid flowing from a catheter in the rete testis was measured. Fluid secretion was absent in the testes of very young animals but had reached adult proportions before the first spermatozoa were shed. Surgically-induced cryptorchidism and hypophysectomy in rats had no immediate effect on fluid secretion. Hypophysectomy in rats 1 to 4 weeks before efferent duct ligation caused a reduction in fluid secretion, but this fluid secretion was the same as that by control testes of the same weight. Cryptorchidism of 2 to 7 days' duration led to a decrease in fluid secretion. The ionic composition of fluid secreted by the testis was calculated and found to be similar to that of fluid collected from a catheter.
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In recent years, it has become apparent that the testis produces, in addition to the androgens, considerable amounts of another type of secretion which flows from the lumina of the seminiferous tubules through the rete testis into the epididymis. Here a large part of the fluid part of the secretion is reabsorbed, but additional compounds are added as the spermatozoa pass down the epididymal duct. In this paper, attention will be largely confined to the most recent findings concerning this latter secretion, as the earlier observations have been reviewed by Setchell (1970a) and Setchell & Waites (1971).
Rate of flow and ionic composition
The fluid which flows from the rete testis of all species so far examined (ram, bull, boar, rat, hamster, wallaby) is a low-protein fluid, isotonic with plasma but containing about three times as much potassium, less sodium and bicarbonate and more chloride than plasma or testicular lymph.
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Summary.
Fluid secretion by rat testes was estimated from the gain in fluid content after efferent duct ligation. Fluid secretion was reduced by metabolic alkalosis induced by intravenous infusions of sodium acetate or bicarbonate but unaffected by the infusion of similar amounts of sodium as sodium chloride. Hypotension had no effect on fluid secretion nor did inhibitors of carbonic anhydrase given by mouth. However, acetazolamide injected intravenously and ethoxzolamide injected intraperitoneally decreased fluid secretion. The results support the theory that fluid secretion is an active process.
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Summary. Measurements were made on micropuncture samples of luminal fluids. The concentration of GPC was highest in the caput and corpus regions of the epididymis, that of phosphocholine changed little along the length of the rat epididymis and there was approximately a 3-fold increase of concentration of inorganic phosphate in the luminal fluid from caput epididymidis to ductus deferens. The estimated total phosphate appeared to equal that of the sum of the phosphate derived from the above compounds. The concentrations of these compounds in the luminal fluid of the testis and in blood plasma were very low.
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Summary.
Compared with blood plasma, rete testis fluid (RTF) from rams was found to contain a higher concentration per unit volume of the enzymes that occur in the sperm acrosome and in the kinoplasmic droplet, but the levels of these enzymes could be reduced by high-speed centrifugation. Other enzymes present in blood plasma were also found in RTF but at a lower concentration per unit volume. Because of the low concentration of protein in RTF, however, the activity of most of these enzymes per unit weight of protein was higher in RTF than in blood plasma. The concentrations of these enzymes and the total protein concentrations were only slightly reduced by high speed centrifugation. There was no appreciable concentration of the X-isoenzyme of lactic dehydrogenase in RTF and the activity of most enzymes per unit weight of protein was less in RTF than in the testis.
Epididymal plasma and RTF from rams and boars were found to contain appreciable concentrations of an inhibitor of trypsin and the activity of the inhibitor per unit weight of protein was comparable with the activity in seminal plasma.
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Summary.
Inositol is synthesized from blood glucose by the ram testis in vivo, and more of the inositol in rete testis fluid is derived from blood glucose than from blood inositol.
However, the turnover rate of the inositol pool in the rete testis fluid is so slow that steady-state conditions were not reached even during a 6-hr infusion.
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Summary. The flow rate and composition of boar rete testis fluid were similar to those in other species studied previously. The total phospholipid phosphorus and phospholipid fatty acid content of boar spermatozoa decreased during maturation in the epididymis but the level of phospholipid phosphorus was slightly higher in ejaculated spermatozoa than in epididymal spermatozoa. During passage of the spermatozoa from the testis to the cauda epididymidis, loss of the major saturated acids (palmitic, 16:0, and stearic, 18:0) was extensive but partly recovered in the ejaculated spermatozoa. The mass of docosapentaenoic (22:5) and docosahexaenoic (22:6) acids tended to decrease continuously during maturation but the percentage of 22:6 by weight of total phospholipid fatty acid reached a maximum in the epididymis.
Ejaculated boar spermatozoa contained considerably more phospholipid and phospholipid fatty acid than did ejaculated bull or ram spermatozoa.
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Summary. The phospholipid and phospholipid fatty acid content of ram spermatozoa decreased during maturation in the epididymis but interpretation of the results was complicated by a possible seasonal factor. Loss of individual fatty acids was selective, resulting in an increase in unsaturation during maturation. Testicular spermatozoa and fluid collected directly into chloroform—methanol contained about 7 times more neutral lipid fatty acid than testicular spermatozoa collected for 6–18 h, separated from the rete testis fluid and then extracted; the difference was not due to lipid in the rete testis fluid. Thin-layer chromatography indicated that cholesterol esters and triglycerides were the neutral lipids which were lost during collection. Epididymal spermatozoa contained only slightly less neutral lipid fatty acid than continuously collected testicular spermatozoa.
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Summary. Testicular lymph and regional lymph nodes consistently contained spermatozoa in rams and boars up to 3 months after vasectomy. Such direct access of spermatozoa to lymph nodes is likely to provide a powerful stimulus to the development of anti-sperm autoimmunity.
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Summary. The O2 uptake of spermatozoa collected from the rete testis of conscious rams and boars has been measured polarographically either in the rete testis fluid (RTF) in which they were collected or in a synthetic saline medium (S-RTF) made to resemble the ionic composition of RTF as closely as possible. In both species, O2 uptake of the testicular spermatozoa was higher in RTF than in S-RTF. The addition of some of the organic constituents of RTF was without effect on O2 uptake. Pyruvate, lactate, acetate or alanine increased the O2 consumption of ram spermatozoa in S-RTF. Lactate had no effect on but acetate increased the O2 consumption of pig testicular spermatozoa. Phospholipid phosphorus and fatty acids decreased during incubation of ram spermatozoa in RTF and S-RTF. The addition of substances which increased the O2 consumption of the spermatozoa in S-RTF was without effect on the lipid composition. The fatty acid composition of the phospholipids and the proportions of the various phospholipids were unaffected by incubation.
These results indicate that rete testis fluid has an appreciable effect on the metabolism of the spermatozoa it contains, and that this effect cannot be mimicked by any of the known organic constituents of the fluid.