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Yolk sac and endometrial tissue were obtained from tammar wallabies between 11 and 25 days after the removal of pouch young. Tissues were examined histologically and steroid-metabolizing enzymes were identified by incubation for 3 h at 37 °C in Medium 199 containing labelled steroid precursors. Yolk sac membrane (YSM) incubated with labelled pregnenolone produced a small amount of progesterone and pregnanediols; 80·5 ± 8·4 (s.e.m.) % of the original substrate remained unmetabolized. Labelled androstenedione was metabolized to 5α-androstane-3,17-dione and androsterone, and only 5·8 ± 3·8% of the original substrate remained at the end of incubation. Incorporation of androstenedione or dehydroepiandrosterone (DHA) into phenolic compounds was low (0·5 ± 0·1%). There was no evidence for the enzymes, arylsulphatase or sulphotransferase, in YSM. Endometrial tissue from the same animals metabolized pregnenolone, DHA and androstenedione, converted progesterone to androstenedione, and produced aqueous-soluble steroid conjugates. The results demonstrated that YSM contains enzymes associated predominantly with steroid catabolism and with incipient progesterone synthesis. The findings are discussed in relation to the histological appearance of the tissues and compared with placental steroid synthesis in eutherian mammals.
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The corpus luteum was removed from tammar wallabies during either lactational or seasonal quiescence, and the pouch young were replaced on the teat after lutectomy. Follicular development resumed and the animals came into oestrus 11–14 days later. Injections of oil, progesterone or androstenedione did not prevent follicular growth, although ovulation only occurred in one animal, but treatment with oestradiol-17β, either alone or mixed with progesterone, inhibited the development of follicles. These results suggest that oestrogen, of luteal origin, is responsible for the suppression of follicular development during lactational and seasonal quiescence.
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Mammary gland lactose concentrations in pregnant tammar wallabies remained low at 115 ± (s.e.m.) μg/g wet weight of tissue until immediately before parturition, then increased to 1274±262 μg/g after birth. Concentrations in non-pregnant cyclic animals were generally low 143±36 μg/g), but were raised in three animals around the time of oestrus.
Removal of the corpus luteum on day 18 of pregnancy or the oestrous cycle caused an increase in lactose concentrations in both lutectomized and sham-operated animals. This occurred despite a significant lowering of peripheral plasma progesterone concentration in only the lutectomized group. Plasma cortisol concentrations were high in some of these animals, but showed no consistent relationships with the raised lactose concentrations.
The increased peripartum lactose concentration normally coincides with a sharp fall in peripheral plasma progesterone concentration, but artificial maintenance of high progesterone levels had no effect on the increase of mammary gland lactose at parturition.
Mammary gland lactose concentrations in tammar wallabies are therefore a useful indicator of biosynthetic activity and as an index of lactogenesis but the role, if any, of progesterone withdrawal in lactogenesis remains unclear.
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ABSTRACT
Tammar wallabies (Macropus eugenii) were observed for 7 days, 24 h/day, at the expected time of birth in two consecutive breeding seasons. Blood was collected from the lateral tail vein 1–2 days before birth, then at 10- to 20-min intervals in the peripartum period and less frequently to 30-h post partum. Plasma was assayed for the prostaglandin metabolite 13, 14-dihydro-15-oxo-prostaglandin F2α (PGFM), progesterone and LH. An assay for PGFM was validated which allows direct measurement in 100 μl unextracted plasma with a sensitivity of 0·14 nmol/l (50 pg/ml).
There was a short-lived peak of PGFM immediately before or at birth (7·15 ± 2·52 nmol/l; 2536± 892 pg/ml) which declined to less than 0·28 nmol/l (100 pg/ml) within 2-h post partum. Progesterone concentrations declined about the time of birth, coincident with the peak of PGFM, and reached levels observed in lactationally quiescent animals by 16-h post partum, which was also the time of the LH peak. The transient prostaglandin pulse was detected only by frequent sampling and suggests that, as in other mammals, prostaglandin is important in parturition.
J. Endocr. (1986) 111, 103–109
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ABSTRACT
Ovaries were obtained from tammar wallabies at various stages of the reproductive cycle to examine the occurrence of oestrogens in corpora lutea, and the synthesis and metabolism of steroids in the corpus luteum and ovarian cortical and interstitial tissues. Corpora lutea contained oestradiol-17β and oestrone during embryonic diapause and at all stages of pregnancy studied after blastocyst activation. Aryl sulphatase, 3β-hydroxysteroid dehydrogenase and 17β-oxidoreductase were shown to be present in luteal and other ovarian tissues by incubation in vitro with labelled substrates. Aromatase was undetectable in corpora lutea or in interstitial tissue, but was present in the ovarian tissues (including follicles) which remained after removal of corpora lutea. The probable source of the oestrogens detected in the corpus luteum is discussed in relation to their role in the inhibition of follicular development during embryonic diapause.
J. Endocr. (1984) 101, 231–240
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ABSTRACT
Pituitary glands and corpora lutea collected at various stages of the reproductive cycle of the tammar wallaby (Macropus eugenii), were extracted and fractionated by high-performance liquid chromatography, and specific radioimmunoassays were used to measure mesotocin ([Ile8]-oxytocin) and oxytocin. Mesotocin, but not oxytocin, was identified in extracts of pituitary; the mean concentration of mesotocin in this tissue was 0·75 nmol/g wet weight. Neither mesotocin nor oxytocin was detected in extracts of corpus luteum. In female Bennett's wallabies passively immunized against mesotocin during seasonal reproductive quiescence, there was no significant effect on peripheral progesterone concentrations and there were no births, matings or changes in vaginal smears in the 2 months following treatment. Thus mesotocin is unlikely to act as a systemic luteostatic agent during seasonal quiescence.
J. Endocr. (1988) 117, 367–372
