Protein synthesis and secretion by the epididymis of the tammar wallaby, Macropus eugenii (Macropodidae: Marsupialia)

Abstract

The objectives were to assess the following in a marsupial: which proteins are synthesized by the different regions of the epididymis and secreted into the lumen of the ductus; the effect of the experimental method on the detection of protein secretion; the role of the testis in regulating the protein synthesis and secretion; and whether any of the secreted proteins may associate with spermatozoa. Samples from untreated animals were collected for examination by perfusing Krebs-bicarbonate through the ductus epididymidis in vivo (microperfusion), and after incorporation of [35S]methionine during incubation of minced duct in vitro. Electrophoresis of the samples showed that the caput and corpus epididymidis (initial segments) secreted most of the proteins that were synthesized and secreted by the epididymal mucosa, and that the cauda epididymidis secreted mainly blood proteins. Also, many more proteins were secreted in vitro than into the microperfusates in vivo, or were found by Jones (1987) in micropuncture samples of epididymal plasma. The synthesis and secretion of five proteins was androgen dependent (M(r) 75,700, 30,000, 18,700, 17,400 and 12,800). Also, the luminal fluids from the testis stimulated the secretion of two proteins (M(r) 46,300 and 36,100) and inhibited the secretion of three proteins (M(r) 43,000, 32,300 and 21,400). Examination of detergent extracts of spermatozoa indicated that they lose three proteins (M(r) 28,000, 30,000 and 47,000) and gain one (M(r) 30,400) during passage through the epididymis. The method of determining protein secretion affected the findings. Protein secretion, its control and its association with spermatozoa are broadly similar in the tammar wallaby to the processes described in eutherian mammals.