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C. SERNIA
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C. H. TYNDALE-BISCOE
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SUMMARY

Specific binding of radio-iodinated ovine prolactin to subcellular tissue fractions of the tammar wallaby (Macropus eugenii) was investigated. Specific binding was found, in order of decreasing binding activity, in the lactating mammary gland, corpus luteum, corpus albicans, adrenal gland and ovary. Specific binding was absent in kidney, liver, brain and inactive mammary gland.

The mean association constant (Ka at 23 °C) was determined as 0·90 × 109, 2·20 × 109, 2·44 × 109, 3·38 × 109 and 10·98 × 1091/mol for mammary gland, adrenal, corpus albicans, corpus luteum and ovary respectively. The mean receptor concentration (N) varied from 92·87 × 10−14 mol/mg protein for the mammary gland to 1·03 × 10−14 mol/mg protein for the ovary. The concentration in the corpus luteum varied between tissue pools collected at different times of the annual breeding cycle.

The specificity for prolactin was shown in the mammary gland and corpus luteum by the failure of ovine FSH, LH, GH and TSH to displace 125I-labelled ovine prolactin, whereas it was displaced readily by both ovine and bovine prolactin.

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FRANCESCA STEWART
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C. H. TYNDALE-BISCOE
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Prolactin and LH receptor concentrations in tammar wallaby corpora lutea (CL) have been examined and related to the control of luteal function in this and other marsupial species. During embryonic diapause, quiescent CL contained high concentrations of prolactin receptors. This was consistent with an earlier suggestion that prolactin may act directly on the CL to maintain its quiescent state. However, despite an apparent seasonal change in the mechanism by which the CL is maintained in quiescence, the number of luteal prolactin receptors remained constant throughout the year. Reactivation of quiescent CL led to an approximate halving of prolactin receptors on a per cell basis, but pregnancy had no effect. None of the wallaby CL showed any significant degree of LH binding, although wallaby follicles and testicular tissue did show binding. This lack of LH binding was consistent with previous findings that quiescent wallaby CL reactivate in response to hypophysectomy and are refractory to LH when cultured in vitro. Parturition, which occurs approximately 2 days before ovulation in this species, had no effect on numbers of either prolactin or LH receptors despite the occurrence of a peak of plasma prolactin at this time. The red kangaroo, which also exhibits embryonic diapause, showed a similar pattern of luteal receptor numbers with high prolactin and negligible LH binding, whereas the brush-tailed possum, which does not exhibit embryonic diapause, gave a pattern more like that seen in Eutheria with many more LH than prolactin receptors.

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K. R. Nicholas
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C. H. Tyndale-Biscoe
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ABSTRACT

The minimal hormonal requirements for the in-vitro accumulation of α-lactalbumin have been investigated in a marsupial, the tammar (Macropus eugenii). Mammary gland explants from 24-day pregnant tammars cultured in medium containing bovine insulin, cortisol and ovine prolactin showed a progressive increase in accumulation of α-lactalbumin during 4 days of incubation. No increment was observed if prolactin was omitted from the medium. However, a similar rate of increase was observed after 3 days of culture in medium containing prolactin alone. This induction of α-lactalbumin was maximal at a prolactin concentration of approximately 0·02 mg/l, which corresponds to physiological levels during pregnancy and early lactation. The absence of an effect of bovine insulin on tammar explants is not due to a general unresponsiveness to this hormone since insulin-stimulated DNA synthesis and amino acid uptake was evident after 3 days of culture. The inclusion of tri-iodothyronine and raised concentrations of cortisol in culture media have been shown to modulate α-lactalbumin synthesis in eutherian mammals but were without effect in the tammar. In addition, increased levels of progesterone did not inhibit the induction of α-lactalbumin, confirming an earlier invivo study suggesting that progesterone withdrawal may not be the lactogenic trigger in this species. Thus the pregnant tammar is the only species yet described in which α-lactalbumin is induced maximally in vitro in response to a single hormone.

J. Endocr. (1985) 106, 337–342

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L. A. Hinds
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C. H. Tyndale-Biscoe
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The plasma progesterone concentrations were measured in one group of tammars undergoing non-delayed oestrous cycles and pregnancy, and in another group undergoing pregnant and non-pregnant cycles which had been inhibited by lactation and initiated by removal of the pouch young. The basal concentrations of progesterone during lactation and for the first 5 days of the cycle were less than 200 pg/ml. In all animals there was a transient peak of about 450 pg/ml lasting 1–2 days, on days 5–8, and this was followed by a return to the basal concentrations. From day 10 the concentration rose and remained at 500 pg/ml until the day of parturition and/or oestrus when it again returned to the basal concentration. There was no difference in pattern of the early peak associated with pregnancy but the peak concentration in the delayed pregnant cycles was just significantly higher than in the non-pregnant cycles of the same animals. These data do not support the hypothesis for the maternal recognition of early pregnancy in the tammar.

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FRANCESCA STEWART
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R. L. SUTHERLAND
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C. H. TYNDALE-BISCOE
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The interactions of several mammalian follicle-stimulating hormones and luteinizing hormones with specific gonadotrophin receptors in macropodid marsupial testicular homogenates were investigated with a view to developing radioreceptor assays for marsupial FSH and LH. Testes from Eastern grey kangaroos and tammar wallabies possessed high affinity (dissociation constant ≃10−10 mol/l) saturable receptor sites which were highly specific for LH or FSH. Luteinizing hormone receptor sites bound only highly purified LH preparations (human, ovine and rat) but did not bind highly purified FSH, TSH or prolactin while FSH receptor sites were equally specific for highly purified FSH preparations. These sites demonstrated a degree of species specificity in that marsupial pituitary extracts were relatively more potent in these assays than in assays using gonadotrophin receptors from rat testes. Serum from hypophysectomized female tammar wallabies had little effect on the slope and position of the LH standard curve but significantly depressed the dose–response curve for FSH. For this reason it was not possible to develop a radioreceptor assay for serum FSH using marsupial testicular FSH receptors. However, gonadotrophin receptors from both rat and marsupial testes have been emplpyed in the successful development of radioreceptor assays for marsupial pituitary LH and FSH and marsupial serum LH.

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C. H. TYNDALE-BISCOE
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J. P. HEARN
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MARILYN B. RENFREE
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Department of Zoology, Australian National University, Canberra 2600, Australia

(Received 13 May 1974)

CONTENTS

PAGE

Introduction 589

The oestrous cycle 590

Control of quiescence 592

Role of the corpus luteum 592

Lactational quiescence 592

Seasonal quiescence 592

Role of the pituitary 594

Patterns of breeding in Macropodidae 596

Control of pregnancy 599

The free vesicle stage 599

The control of diapause 599

Activation and maintenance of the embryo 599

Role of the uterus 602

Uterine secretions 602

Diapause and delayed implantation 604

Attachment stage 604

Determination of gestation length 605

Foeto-placental influence 605

Non-macropodid marsupials 606

The Macropodidae 607

Parturition 609

Role of the corpus luteum 609

Role of the pituitary 610

Conclusion 610

References 611

INTRODUCTION

Two features distinguish reproduction in the Macropodidae from all other marsuppials. A period of embryonic diapause of variable duration may supervene after blastocyst formation, and the duration of pregnancy is

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R. L. SUTHERLAND
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SUSAN M. EVANS
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C. H. TYNDALE-BISCOE
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A heterologous double antibody radioimmunoassay employing a rabbit anti-ovine LH antiserum (GDN no. 15) has been developed for the assessment of concentrations of LH in macropodid marsupial pituitary extracts and plasma. In this radioimmunoassay system highly purified ovine, rat, human and kangaroo LH preparations demonstrated apparently parallel dose–response curves, as did serial dilutions of crude pituitary extracts from a wide range of Australian marsupial species and serial dilutions of plasma from ovariectomized, oestrous and LH releasing hormone (LH-RH)-treated marsupials. The assay has been used to monitor changes in immunoreactive LH in the plasma of the female tammar wallaby. Basal concentrations of LH in non-oestrous female wallabies were in the range < 0·20–1·90 ng/ml with many animals having values at or near the limit of detection of the assay. Concentrations of LH were markedly increased following ovariectomy (1·7–7·0 ng/ml), on the day of oestrus (10·0–> 50 ng/ml) and following administration of LH-RH (9·5–> 25·0 ng/ml). Plasma from hypophysectomized animals had no detectable LH immunoactivity, A well-defined LH surge, lasting approximately 12 h, was associated with oestrus. Mating occurred approximately 8 h before, and ovulation approximately 24 h after, the maximal concentration of LH in plasma.

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SUSAN M. EVANS
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C. H. TYNDALE-BISCOE
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R. L. SUTHERLAND
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A heterologous radioimmunoassay for tammar wallaby FSH, using an ovine FSH antiserum and a human FSH tracer, is described. With this assay concentrations of FSH in plasma of intact female tammars are not detectable except rarely at the time of oestrus. However the assay has proved useful in studies of the control of gonadotrophin secretion in intact male and in ovariectomized tammars.

In the female tammar, concentrations of LH and FSH in plasma rose within a few days of bilateral ovariectomy. Ovariectomized tammars respond to a luteinizing hormone releasing hormone stimulus (10 μg, i.v.) with a prompt release of LH, peak levels of 16·9 ± 1·4 ng NIH-LH-S19/ml plasma (n = 12) being reached within 25 min of injection. Concentrations of LH and FSH in plasma were reduced to preoperative values in ovariectomized tammars when lutein tissue developed in ovarian cortex grafts autotransplanted under the pouch skin. Ovarian interstitial tissue was not necessary for this effect.

After lutectomy during quiescence, the female tammar ovulates again in about 14 days. Injections of progesterone (700 μg/kg per day, i.m.) for 7 days after the operation did not delay this response, but follicular development and ovulation appeared to be retarded in animals given oestradiol-17β (5 μg/kg per day, i.m.) with or without progesterone.

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C. H. Tyndale-Biscoe
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L. A. Hinds
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C. A. Horn
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G. Jenkin
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Concentrations of progesterone, prolactin, LH and 13,14 dihydro-15-keto-prostaglandin F (PGFM) were measured in plasma of eight tammar wallabies at 8-hourly intervals during the end of pregnancy and post-partum oestrus initiated by removing the pouch young, and during the end of the oestrous cycle, similarly initiated. In the non-pregnant cycle oestrus occurred 29·7 ± 0·7 (mean ±s.e.m.) days after initiation of the cycle, was preceded by a slow decline in progesterone concentration from 1·6 nmol/l to less than 0·64nmol/l and was followed by a preovulatory peak of LH 5·3± 3·9 h later. In the pregnant cycle birth occurred 26·1±0·2 days after removing the pouch young and was followed 8·0 ± 2·1 h later by oestrus and 16·0± 2·5 h by an LH peak. The latter events thus occurred 3·2 days earlier in the pregnant than in the non-pregnant cycle. Parturition coincided with a very rapid decline in progesterone and a transient high peak of prolactin. In two females sampled less than 25 min after parturition there was a transient peak of PGFM but in all others the concentrations of PGFM remained basal throughout. It is suggested that the fetus and/or placenta is involved in both the premature decline in progesterone and the initiation of parturition and that onset of oestrus and ovulation, being a consequence of a decline in progesterone, are therefore also determined by the fetus.

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