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The Tasmanian bettong (Bettongia gaimardi) is a small rat-kangaroo (marsupial) found only in Tasmania, Australia. The duration of pouch life is 15 weeks. Adults and older young display non-shivering thermogenesis and this paper examines the role of thyroxine in the development of endothermy in pouch young. Free thyroxine (T4) concentrations varied throughout pouch life. The mean (+/-SE) concentration was 6.2+/-1.9 pmol L(-1) in week 7, increased and peaked at 19.2+/-4.3 pmol L(-1) in week 12, and declined to 5.6+/-0.4 pmol L(-1) by week 20. This was similar to adult levels (3.2+/-3.8 pmol L(-1)). These concentrations showed significant differences. From pouch week 12 onwards, T4 injection raised oxygen consumption. Maximum levels of VO2 after T4 injection occurred at weeks 14-15. Although adult levels were lower, the increase in adult oxygen consumption after T4 injection was about 50%. Peak free T4 levels and metabolic responses to nor-adrenalin occur at week 12 and we hypothesize that thyroid hormone may facilitate the development of adrenergic-receptors in this species. The data presented in the paper further attest to the likely important role of the thyroid gland in the development of endothermy in marsupial pouch young.

Plasma progesterone levels were measured in female bettongs (small macropodid marsupials) under two natural regimes: (1) during "delayed" gestation (initiated by removal of pouch young, RPY) and (2) during the pregnancy prior to pouch vacation when a young still occupies the pouch (i.e., during lactation). Basal levels of progesterone were 0.15-0.5 ng/ml. There was a transient peak of progesterone (0.7 ng/ml) early in gestation at Day 4 RPY. After Day 6 RPY, progesterone levels remained elevated (1.2-1.5 ng/ml) until they dropped sharply to basal levels on the day of birth. This pattern of progesterone secretion during delayed gestation is similar to that seen in other marsupials, such as the tammar wallaby. There was no significant difference between the progesterone profiles of the two experimental groups. We deduce, then, that lactation had no effect on corpus luteum function (as assessed by plasma progesterone levels) in the pregnant bettong.

The Tasmanian bettong (Bettongia gaimardi) is a small macropodid marsupial that is a continuous breeder. This study has partitioned testosterone into three fractions that vary to some extent throughout the year, coinciding with peaks and troughs in breeding, body weight, and testes volume. The three fractions determined were free, albumin bound, and sex hormone binding globulin (SHBG) bound testosterone. Concentrations of both albumin and SHBG varied significantly throughout the year with peaks in SHBG coinciding with lowered levels of free testosterone. Testosterone was also measured during maturation of male bettongs. There were significant regressions between weight or testes volume and the combined free and albumin bound testosterone. Maturity started near age 30 weeks and a body weight of 1.5 kg and was accompanied by a brief surge in testosterone levels.