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C. Jeulin, J. C. Soufir, J. Marson, M. Paquignon and J. L. Dacheux

Summary. In the epididymal fluid of boars, the concentration of carnitine (nmol/mg protein) began to increase from 20 in the distal caput, then rose progressively to 700 in the distal cauda. By contrast, the carnitine content of spermatozoa only started to increase in the proximal cauda where the concentration of carnitine in the fluid was 200–300 nmol/mg protein then gradually increased in spermatozoa from more distal sites. The increase in the acetylcarnitine content of spermatozoa paralleled that of the carnitine amount and represented 50% of the total carnitine (carnitine + acetylcarnitine). We conclude that the acetylcarnitine content of epididymal spermatozoa may be used as a marker of maturation.

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J. Marson, S. Meuris, F. Moysan, D. Gervais, R. W. Cooper and P. Jouannet

Summary. Semen characteristics were studied in 6 wild-born chimpanzees with dental ages ranging approximately from 6 to 12 years. The animals formed 2 groups, early pubertal (EP, N = 3, 6–9 years) and late pubertal (LP, N = 3, 11–12 years). Mean body weight, testicular volume and serum androgen concentration were significantly lower in Group EP (32·2 ± 1 ·6 kg, 34·0 ± 7·7 cm3, 2·1 ± ng/ml) than in Group LP (55·7 ± 5·7 kg, P < 0·01; 100·5 ± 11·9 cm3, P < 0·01; 3·6 ± 0·7 ng/ml, P < 0·05).

Ejaculates were obtained by masturbation in all subjects. The mean ejaculate volume was lower in Group EP (0·56 ± 0·20 ml) than in Group LP (3·77 ± 0·73 ml, P < 0·01).

In Group EP, 2 animals were azoospermic while the third produced semen with means of 57·1 × 106 spermatozoa per ml, 20% motility and 40% vitality. These values were low when compared with the mean values of Group LP (376 × 106 spermatozoa per ml, 67% motility and 78% vitality). Mean total sperm count was correlated with testicular volume (r = 0·84) and serum androgen concentration (r = 0·96).

The mean concentrations of l-carnitine, fructose, citrate and acid phosphatase for the two groups were not significantly different; but, related to the differences in ejaculate volumes, their total amounts in total ejaculate were lower in Group EP than in Group LP.

These results suggest that, in chimpanzees, mechanisms of seminal plasma production and ejaculation are functional early in the reproductive life and that the emission of spermatozoa occurs later.

Keywords: semen; chimpanzee; puberty; masturbation

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J. Marson, D. Gervais, S. Meuris, R. W. Cooper and P. Jouannet

Summary. Semen samples were obtained by masturbation from 6 chimpanzees and the spontaneously liquefied fraction and the remaining coagulum were studied separately. When semen was collected once or twice a week, large intra-individual variations were observed for all measures. The liquefied fraction represented 26·5 ± 3·2% (weighted mean ± s.d.) of the total ejaculate but contained 51·3 ± 3·8% of all emitted spermatozoa. Fructose concentration was higher in the coagulum than in the liquefied fraction (29·3 ± 3·0 μmol/ml vs 12·0 ± 2·7 μmol/ml, P < 0·001) whereas acid phosphatase was less concentrated in the coagulum than in the liquefied fraction (3·5 ± 0·3 × 103 IU/ml vs 13·0 ± 0·9 × 103 IU/ml, P < 0·001). l-Carnitine and citrate concentrations did not differ between the two fractions of the ejaculate.

When semen collection was repeated every hour for 5 h, the ejaculate volume increased from 2·6 ± 0·7 to 4·7 ± 0·6 ml (P < 0·001), whereas total sperm count decreased from 1278 ± 872 × 106 to 587 ± 329 × 106 (P < 0·05) between the 1st and the 6th ejaculate. In the spontaneously liquefied fraction, the sperm count decreased from 984 to 369 × 106. The 6 successive ejaculates gave a total of 20·2 ± 7·6 ml and 4278 ± 2884 × 106 spermatozoa. The increase of the ejaculate volume was essentially due to an increase of the volume of the coagulum which closely correlated with total amount of fructose (from seminal vesicles) (r = 0·913, P < 0·001). The volume of the liquefied fraction and total amounts of l-carnitine (from epididymis), citrate and acid phosphatase (both from prostate) did not show any significant variations.

These results suggest (1) a high reserve capacity of the male genital tract in chimpanzees and (2) an increase in seminal vesicle secretion resulting from sexual stimulation induced by high masturbation frequency.

Keywords: semen; chimpanzee; ejaculation frequency; masturbation; fructose