Prolactin in the marsupial Macropus eugenii, during the estrous cycle, pregnancy and lactation

An heterologous double antibody radioimmunoassay (RIA) using a guinea-pig antiserum (33-9) raised against human prolactin and 125I-ovine prolactin has been developed to measure prolactin (Prl) in plasma and pituitary preparations of marsupials. In this system, purified tammar and kangaroo Prl preparations showed parallel dose-response curves as did serial dilutions of crude pituitary homogenates of tammar, possum and eastern grey kangaroo. Serial dilutions of plasma from ovariectomized and lactating female and castrate male tammars showed immunoreactivity, and plasma Prl levels increased after injection of TRH. The assay has been used to monitor changes in plasma Prl in female tammars in various reproductive states. Plasma Prl remained at basal concentrations of 20 to 30 ng/ml throughout the estrous cycle, at estrus and during pregnancy. However, just prior to parturition, there was a 2- to 3-fold increase in Prl concentrations which declined to basal levels after birth. During early lactation, Prl levels were low but increased to maximum concentration in the second half of lactation.