A QUANTITATIVE MORPHOLOGICAL-STUDY OF AGE-RELATED-CHANGES IN THE DONKEY TESTIS IN THE PERIOD BETWEEN PUBERTY AND SENIUM

The testis of the donkey was used as a model to study age-related chan ges in the period between puberty and senium. From the age of 1.5 year s to the middle of sexual maturity (5 to 6 years) a number of histophy siological features, all indicative of the spermatogenetic efficiency, increase continuously. Then without a longer-lasting plateau of maxim al performance these features undergo continuous retrogression. Thus, the adult testis is an organ in permanent change. During its progressi ve period (1.5 to 5 years) the average testicular and tubular volumes treble. The increase in tubular volume is due to an increase in tubula r length (from 700 m to 1600 m per testis) and tubular diameter (from 205 mu m to 250 mu m) Parallel to this growth, the spermatogenetic eff iciency of the seminiferous epithelium rises: the number of germ cells entering meiosis increases and the cell loss by apoptosis or exfoliat ion decreases. During the following regressive period of the testis (5 -10 years) seminiferous epithelial height and tubular diameter are aga in gradually reduced to 70 mu m and 205 mu m, respectively. The absolu te number of Sertoli cells per testis decreases continuously from pube rty onwards. The tubular lamina propria thickens with advancing age an d at the age of 10 years, displays long irregular projections into the seminiferous epithelium.