Sexual development in the immature male blue fox (Alopex lagopus), investigated by testicular histology, DNA flow cytometry and measurement of plasma FSH, LH, testosterone and soluble testicular Mn2+-dependent adenylate cyclase activity

in Reproduction

Summary. Testicular weight in young male blue foxes increased steadily from 12 weeks of age (0·4–0·7 g) to reach peak values at the time of the mating season in March–April (5·2–6·6 g), before declining rapidly during May to low values in August at 63 weeks of age (1·3–1 ·6 g). Primary spermatocytes were found in the spermatogenic epithelium at 20 weeks of age and by late December (29 weeks of age) elongated spermatids were seen. There was a good correlation between the seasonal variations in the presence of germ cell types assessed by quantitative analysis of testicular histology and the variations in numbers of haploid, diploid and tetraploid cells measured by DNA flow cytometry: no haploid cells were found before the end of November and peak numbers were observed in March.

Plasma FSH concentrations were increased from December onwards (with the exception of April). There were no clearcut seasonal variations in plasma LH concentrations although values were consistently lower in April. Testosterone concentrations were low for most of the year but increased from the end of January to the middle of April. There was no detectable seasonal variation in LH release in response to LHRH injection, and no typical pattern in plasma FSH concentrations during the first 100 min after injection. Plasma testosterone concentrations after LHRH injection rose gradually during testicular development.

There were large seasonal variations in soluble Mn2+-dependent adenylate cyclase activity in the testis, that paralleled the changes in testicular weight and haploid cell content. Values were low until December and reached a peak at the time of the mating season before falling to basal levels again by June.

The results suggest that immature male blue foxes reach full testicular development (indistinguishable from that of older animals) by the first mating season after birth, at an age of about 40 weeks.

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