TESTICULAR SPERM RESERVE AND PLASMA TESTOSTERONE LEVELS OF THE SOUTH-AMERICAN WHITE-BELLY OPOSSUM (DIDELPHIS-ALBIVENTRIS), MARSUPIALIA

Testicular sperm reserve was estimated through the haemocytometric met hod in eleven adult South American white-belly opossums, sacrified at mating and non-mating periods of the annual reproduction cycle. Mean v alues for the testicular sperm reserve were 29.7 +/- 1.9 x 10(6) sperm cells/g of testis parenchyma and 25.3 +/- 1.4 x 10(6) sperm cells/tes tis (mean +/- standard error of mean). No difference was observed betw een these two groups, however prostate weight showed a significant inc rease in the mating period. In order to investigate circadian variatio n in plasma testosterone levels during the mating and non-mating perio ds, plasma testosterone concentrations were quantified. The results ob tained indicate that the levels were significantly higher in the matin g period and only in blood samples collected at morning.