In-vitro secretion of progesterone by the corpus luteum of the tammar wallaby, Macropus eugenii.

Luteal tissue collected from tammars 0, 5, 9 and 16 days after removal of pouch young actively produced progesterone in vitro. On Days 5, 9 and 16 luteal progesterone concentration was not significantly different from Day 0 (quiescence). However, the net production of progesterone was significantly higher on Day 5 (P less than 0 X 05) than at any other stage, and we suggest that the corpus luteum is the main source of the rise in progesterone in the peripheral circulation at Days 5-8 of the delayed or non-delayed cycle. Addition of ovine prolactin to corpora lutea incubated on Day 5 after removal of pouch young had no effect on luteal progesterone concentration or the production of progesterone. We therefore conclude that the tonic inhibition exerted by prolactin on the corpus luteum does not affect the steroidogenic capacity of the luteal tissue but may inhibit luteal cell growth during quiescence.