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B. P. SETCHELL

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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B. P. SETCHELL

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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ALIYA MIDDLETON and B. P. SETCHELL

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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J. SUOMINEN and B. P. SETCHELL

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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B. P. SETCHELL and B. W. BROWN

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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B. T. Hinton and B. P. Setchell

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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B. P. SETCHELL and G. M. H. WAITES

Summary.

The concentration of spermatozoa in the rete testis fluid of rats increased gradually with age and reached adult levels at about 250 g body weight, whereas fluid secretion per unit weight of testis reached adult rates at a body weight of about 100 g. Unilateral castration had no effect on the weight of the remaining testis or on its fluid secretion; sperm concentration in rete testis fluid was only affected in very young rats. Local heating of the testes of rats was followed by a fall in the sperm concentration in rete testis fluid beginning between 6 and 10 days, and lasting until 39 days, after heating. This fall was associated with a decrease in testis weight which persisted after the concentration of spermatozoa in rete testis fluid had returned to normal. However, there was no change in fluid secretion per unit weight of testis, nor was there any change in the concentration of inositol, glycine or potassium in rete testis fluid.

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R. W. Evans and B. P. Setchell

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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B. P. SETCHELL and G. M. H. WAITES

The unusual complexity of the testicular blood vessels of eutherian mammals has been shown to have haemodynamic and thermoregulatory significance. The pulse wave of pressure passing down the long, coiled internal spermatic artery of the ram (Waites & Moule, 1960), dog (Blombery, Gow & Waites, unpublished observations) and rat (Setchell, 1969) is attenuated to a small oscillation, but mean blood pressure is only marginally reduced. A similar pressure-damping action was described for the carotid rete mirabile of the dolphin (Nagel, Morgane, McFarland & Galliano, 1968). There is also plentiful evidence for countercurrent heat exchange between neighbouring arteries and veins (see Waites, 1969). As the spermatic veins closely surround the internal spermatic artery, Harrison & Weiner (1949) proposed that heat exchange was occurring between the counterflowing blood streams. This was confirmed by measuring the thermal gradients in the testicular circulation of dogs (Dahl & Herrick, 1959) and rams (Waites

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G. M. H. WAITES and B. P. SETCHELL

Summary.

The metabolic effects of elevated temperature on the testes of conscious rams have been investigated. Locally heating the testes above 39° C for 2 to 2½ hr caused moderate or severe seminal degeneration. Blood flow through the testes was not consistently changed by the heating applied. More oxygen was removed from a unit volume of the blood passing through the testes when testicular temperatures were higher than 36 ·3 to 37·2° C, than at control temperatures. The oxygen content of the blood in the spermatic veins fell to 2·7 to 4·9 ml 02/100 ml during heating, and oxygen uptake by the testis and epididymis increased by about 70%. In most testes glucose uptake was increased by heating; there was no consistent change in lactate production.

It was concluded that heat sufficient to cause spermatogenic damage results in hypoxia in the testis but does not consistently alter the blood flow or the supply of glucose or the important role of glucose in testicular metabolism.