Oestradiol-17β in the blood during seasonal reactivation of the diapausing blastocyst in a wild population of tammar wallabies

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Abstract
Oestradiol-17β was measured by radioimmunoassay in cardiac blood from 143 pregnant and post-partum tammar wallabies shot in the wild during reactivation of the diapausing blastocyst, embryonic development, birth and post-partum oestrus. A transient rise in circulating oestradiol on 3 January coincided with or shortly preceded corpus luteum growth and blastocyst expansion; before 5 January mean corpus luteum weight was 14·3± 0·44 mg (n = 65), while thereafter it exceeded 20 mg in two-thirds of the animals. Expanded blastocysts were first noted on 5 January. A second rise in the concentration of oestradiol in plasma, which occurred in late January, preceded parturition and coincided with follicular maturation; the mean (± s.e.m.) oestradiol concentration before 17 January was 27·9 ±1·10 pmol/l (n = 110), whereas on or after this date it was 57·3 ± 4·15 pmol/l (n = 33). Thus oestradiol levels in peripheral plasma increased at parturition and post-partum oestrus, and showed a rise early in gestation which may be related to the termination of diapause.

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