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A. J. Smith, M. Mondain-Monval, P. Simon, K. Andersen Berg, O. P. F. Clausen, P. O. Hofmo and R. Scholler

Summary. Bromocriptine administration in the form of slow-release injections to male blue foxes during March–May abolished the normal spring rise in plasma prolactin concentrations seen in May and June. The spring moult was prevented and the treated animals retained a winter coat of varied quality and maturity until the end of the study in August.

Plasma testosterone concentrations fell normally from March until August. Testicular regression was, however, delayed, although there were individual variations in response. Estimation by DNA flow cytometry in early July of the relative numbers of haploid, diploid and tetraploid cells in the testis showed that, in the treated animals, 74–80% of the cells were haploid (maturing germinal cells), 4–6% tetraploid (mainly primary spermatocytes) and the rest diploid cells (somatic cells and the remaining germinal cell types). In the control males, however, no haploid cells were detected and the majority of cells were diploid (93–99%). At castration in August, histological examination revealed various stages of testicular regression in the treated and control animals.

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A. J. Smith, M. Mondain-Monval, K. Andersen Berg, J. O. Gordeladze, O. P. F. Clausen, P. Simon and R. Scholler

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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A. J. Smith, M. Mondain-Monval, K. Andersen Berg, P. Simon, M. Forsberg, O. P. F. Clausen, T. Hansen, O. M. Møller and R. Scholler

Summary. Melatonin administration to male blue foxes from August for 1 year resulted in profound changes in the testicular and furring cycles. The control animals underwent 5-fold seasonal changes in testicular volume, with maximal values in March and lowest volumes in August. In contrast, melatonin treatment allowed normal redevelopment of the testes and growth of the winter coat during the autumn but prevented testicular regression and the moult to a summer coat the following spring. At castration in August, 88% of the tubular sections in the testes of the controls contained spermatogonia as the only germinal cell type, whereas in the treated animals 56–79% of sections contained spermatids or even spermatozoa. Semen collection from a treated male in early August produced spermatozoa with normal density and motility.

Measurement of plasma prolactin concentrations revealed that the spring rise in plasma prolactin values (from basal levels of 1·6–5·4 ng/ml to peak values of 4·1–18·3 ng/ml) was prevented; values in the treated animals ranged during the year from 1·8 to 6·3 ng/ml. Individual variations in plasma LH concentrations masked any seasonal variations in LH release in response to LHRH stimulation, but the testosterone response to LH release after LHRH stimulation was significantly higher after the mating season in the treated animals, indicating that testicular testosterone production was maintained longer than in the controls.

The treated animals retained a winter coat, of varied quality and maturity, until the end of the study in August.