The role of prostaglandin F2 alpha and oxytocin in the reproductive behavior of a marsupial, Bettongia gaimardi.

Bettongs give birth on the night that their large pouch young finally vacates the pouch. We have hypothesized that hormones associated with this birth are also involved in pouch vacation. Injections of prostaglandin F2 alpha (PGF2 alpha) caused contractions of the pouch. In a separate experiment PGF2 alpha caused pouch vacation; oxytocin had a similar effect but with a longer latency. In addition both hormones induced birth behavior in adult and immature females as well as in males. When a prostaglandin synthesis inhibitor (Finadyne) was given first, oxytocin failed to produce birth behavior or pouch vacation. This finding leads us to suggest that oxytocin exerts its behavioral effects via prostaglandin synthesis. These experiments are the first to demonstrate an effect by oxytocin on reproductive behavior in a marsupial.

Effects of bromocriptine on lactation and plasma progesterone in Bettongia gaimardi, a Tasmanian macropodid marsupial.

Many macropodids exhibit lactational quiescence during which an embryo produced at post-partum mating is retained as a blastocyst in utero while a pouch young is sucking. The sucking stimulus maintains secretion of prolactin which may in some species inhibit the activity of the corpus luteum and, hence, the development of the embryo. When the sucking frequency decreases, the blastocyst resumes development. In the present study, the dopamine agonist bromocriptine, which in many mammals results in decreased secretion of prolactin from the pituitary gland, was administered to the Tasmanian bettong (Bettongia gaimardi) at two different doses (12.5 mg kg(-1) and 5 mg kg(-1)). Although lactation was affected by both doses, as evidenced by slower growth of the pouch young or their loss, in only two cases did the quiescent blastocyst activate at the time of injection. This occurred with the highest dose of bromocriptine and was reflected by earlier changes in plasma progesterone concentrations. It is concluded that the Tasmanian bettong is unusual in its lack of sensitivity to bromocriptine.