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The concentration of chromium⁵¹–EDTA in blood plasma after an intravenous infusion was found to be about 40 times that present in rete testis fluid and 20 times that in the additional seminiferous tubular fluid resulting from ligation of the efferent ducts. These values indicate the effectiveness of the blood–testis barrier to small water-soluble molecules, like Cr–EDTA. The volume of distribution in microlitres of Cr–EDTA in the parenchyma was about 60% of the volume of the interstitial tissue as determined on frozen sections by morphometry, and was similar, or slightly less, in the ligated testes, compared with the unligated testes. Heating the testes to 43°C for 30 min led to the expected reduction several days later in testis mass, but the volume of distribution of Cr–EDTA was no greater than that in the testes of control rats, and the ratio of Cr–EDTA space to interstitial tissue was not different, while the concentration of Cr–EDTA in the additional seminiferous tubular fluid increased only slightly as testis mass fell. These results indicate that the blood–testis barrier was only slightly less effective, if changed at all, during the period of spermatogenic disruption following local heating of the testis.

Summary. Motility of whole undiluted semen collected from different regions of the bull epididymis by micropuncture was determined by examining a droplet under paraffin oil. Bull caudal spermatozoa showed vigorous motility in undiluted semen. This motility was less in samples collected from nearer the testis: samples from the distal caput showed weak but detectable motility while those from the proximal and mid-caput were completely quiescent. Motility of spermatozoa from the distal caput and the proximal corpus was markedly increased after incubation at 34 or 37°C for 1 h, but was depressed by incubation at 25°C. Similar but smaller effects were observed with spermatozoa collected from the mid-corpus and the mid-cauda, except that motility of spermatozoa from the mid-corpus was reduced after incubation for 1 h at 37°C. The inhibitory effect of low temperature was completely reversible. Incubation of caudal spermatozoa under anaerobic conditions produced partial and reversible inhibition of sperm motility. The results suggested that bull epididymal spermatozoa may not be completely quiescent in their native environment as previously assumed.

Summary. After removal of the scrotal skin, one testis of each of 12 adult anaesthetized rams was kept at 33°C for 60 min, then heated either to 36°C for 60 min and then to 39°C for 60 min, or to 36°C for 120 min and then returned to 33°C for 100 min, while the other testis was maintained at 33°C. Flow of testicular blood plasma was measured every 10 min using the technique of dilution of sodium p-aminohippurate.

When the temperature of the testis was raised to 36°C, flow of blood plasma gradually increased and reached a higher than normal rate at the end of the first hour, without any further increase during the second hour. The increase in mean flow rate was 25·8 ± 3·4% (mean ± sem) during the second hour at 36°C, and 77·1 ± 12·8% during the hour at 39°C, compared with the respective values at 33°C. No significant changes were seen in testicular lymph flow determined by collection for 10 min in four rams at 36°C (60 min) and then at 39°C (60 min).

These results are different from those from earlier studies in which total blood flow was unchanged when the scrotum and testes were heated. The difference could be related either to lack of heating of the scrotum or to the lower temperatures used in the present study. Changes in the flow of arterial blood bypassing the testis through arterio–venous anastomoses in the spermatic cord might be involved, as a result of heating of the testes.

Keywords: testis; temperature; lymph; blood flow; sheep

Summary. Normal female rats were mated to control males or males which were subjected to unilateral testicular heating (43°C for 30 min), irradiation (500 R), efferent duct ligation, arterial ligation or castration; in all males, the contralateral ductus deferens was ligated. All treatments caused reduced fertility and eventually infertility, as judged by the percentage of females becoming pregnant; the infertility was temporary after heating and irradiation. During the periods of reduced fertility, the numbers of fetuses per pregnant female and the fetus/corpus luteum ratios were reduced. In subsequent experiments, after heating of the testis, there was not only failure of fertilization despite the presence of normal numbers of spermatozoa in the uterus, but also an increased rate of embryonic degeneration in normal females.

These results provide evidence that the male, while still fertile, can affect the fecundity of the female and the rate of embryo mortality.

Keywords: embryonic mortality; subfertility induced by heat; rat

Summary. Fertilization rate and embryonic mortality were assessed in 636 ewes inseminated in each uterine horn with 50 × 10⁶ frozen spermatozoa from four control rams and from four rams submitted to a moderate (1·4–2·2°C), but repeated, intermittent (16 h/day for 21 consecutive days) increase in their subcutaneous scrotal temperature by means of scrotal insulation. Pregnancy was assessed twice in each ewe from concentration of progesterone in blood plasma at 17 days and by ultrasound at 65 days after insemination. No differences were observed in the pregnancy rate at 17 days between ewes inseminated with semen collected from control rams (56·0, 65·2, 66·7 and 60·3% and from heated rams (60·6, 71·8, 63·6 and 48·2%) before or after 4, 15 and 21 days of heating, respectively. In contrast, the rate of embryonic mortality between 17 and 65 days after insemination was significantly higher at days 4, 15 and 21 in the heated rams (78·7, 78·6 and 93%) than in the control rams (55, 59 and 65·7%). These results indicate that an intermittent slight, but repeated, increase in the subcutaneous scrotal temperature could induce a significant increase in the embryonic mortality rate. As these changes were apparent on day 4 of heating, an effect must have occurred on sperm stored in the epididymis.

Keywords: embryonic mortality; fertility; scrotum; sheep; temperature