Testicular development and maturation of the hypothalamic–pituitary–testicular axis in the male tammar, Macropus eugenii
in ReproductionSummary. Testicular growth and maturation of the hypothalamic–pituitary–testicular axis were assessed in male tammars from 12 to 25 months of age to establish the time of sexual maturity. The testicular dimensions and body weights of 20 male tammars, ∼12 months of age at the beginning of the study, were measured monthly for 1 year. Groups of 3 animals were castrated at 13, 19 and 25 months of age and their testes sectioned for histological examination. Testicular volume increased between 12 and 24 months of age and was highly correlated with body weight (r = 0·91). In the 13-month group the seminiferous tubules were closed with few mitotic figures. Spermatogenesis had begun in 2 of the 19-month animals. All stages of spermatogenesis were present in the other 19-month male, and in all of the 25-month males.
Basal FSH concentrations increased with the age of the animal (21·0 ± 32·48, 94·40 ± 55·18 and 193·05 ± 40·21 ng/ml (mean ± s.d.) at 19, 20 and 25 months respectively) while basal LH concentrations were similar at 20 months and 25 months (0·43 ± 0·18 and 0·58 ± 0·25 ng/ml respectively). Basal testosterone concentrations were also similar 0·11 ± 0·04, 0·35 ± 0·16 and 0·22 ± 0·10 ng/ml in 13-, 19- and 25-month-old animals.
LHRH injection in tammars at 13, 19 and 25 months of age induced release of both LH and testosterone 10#x2013;30 min after injection. The hormone concentrations increased in both magnitude and duration with increasing age. At 13, 19 and 25 months, peak testosterone values of 1·13 ± 0·27, 1·90 ± 0·45 and 6·58 ± 0·91 ng/ml (mean ± s.d.), respectively, were measured by 90–120 min after injection and peak LH values at 13, 19, 20 and 25 months of age were 2·46 ± 0·82, 8·31 ± 2·02, 9·0 ± 2·18 and 7·86 ± 1·41 ng/ml, respectively, when measured 30 min after injection. By contrast, LHRH injection did not increase FSH concentration at 20 or 25 months of age above the basal concentration.
Taken together, the morphological and endocrinological data show that puberty in male tammars begins around 19 months and is complete by 25 months of age.
Keywords: testis, testosterone; LH; FSH; LHRH; spermatogenesis; marsupial; puberty
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