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T. P. Fletcher and M. B. Renfree

Summary. The quiescent corpus luteum of female tammars was reactivated by removal of the pouch young (RPY). The reactivated corpus luteum was ablated 3 days after RPY. Plasma progesterone and oestradiol concentrations were measured by radioimmunoassay in these and in sham-operated controls. Excision of the CL abolished the rise in progesterone seen at Day 5–6 in the sham-operated animals (130·7 ± 56·6 vs 452·4 ± 176·0 pg/ml, mean ± s.d.). By contrast, oestradiol-17β values increased within 6–16 h of CL excision to 16·3 ± 6·9 pg/ml and remained high for 1–3 days while in the sham-operated animals there were less sustained and more variable peaks of 10–20 pg/ml between Days 3 and 5 (mean 12·0 ± 3·6 pg/ml at Day 4–5). We conclude that the early transient increase in peripheral plasma of progesterone is of luteal origin but the source of the oestradiol remains unknown.

Keywords: corpus luteum; progesterone; oestradiol-17β; early pregnancy; marsupial

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P. Williamson, T. P. Fletcher and M. B. Renfree

Summary. Testicular growth and maturation of the hypothalamic–pituitary–testicular axis were assessed in male tammars from 12 to 25 months of age to establish the time of sexual maturity. The testicular dimensions and body weights of 20 male tammars, ∼12 months of age at the beginning of the study, were measured monthly for 1 year. Groups of 3 animals were castrated at 13, 19 and 25 months of age and their testes sectioned for histological examination. Testicular volume increased between 12 and 24 months of age and was highly correlated with body weight (r = 0·91). In the 13-month group the seminiferous tubules were closed with few mitotic figures. Spermatogenesis had begun in 2 of the 19-month animals. All stages of spermatogenesis were present in the other 19-month male, and in all of the 25-month males.

Basal FSH concentrations increased with the age of the animal (21·0 ± 32·48, 94·40 ± 55·18 and 193·05 ± 40·21 ng/ml (mean ± s.d.) at 19, 20 and 25 months respectively) while basal LH concentrations were similar at 20 months and 25 months (0·43 ± 0·18 and 0·58 ± 0·25 ng/ml respectively). Basal testosterone concentrations were also similar 0·11 ± 0·04, 0·35 ± 0·16 and 0·22 ± 0·10 ng/ml in 13-, 19- and 25-month-old animals.

LHRH injection in tammars at 13, 19 and 25 months of age induced release of both LH and testosterone 10#x2013;30 min after injection. The hormone concentrations increased in both magnitude and duration with increasing age. At 13, 19 and 25 months, peak testosterone values of 1·13 ± 0·27, 1·90 ± 0·45 and 6·58 ± 0·91 ng/ml (mean ± s.d.), respectively, were measured by 90–120 min after injection and peak LH values at 13, 19, 20 and 25 months of age were 2·46 ± 0·82, 8·31 ± 2·02, 9·0 ± 2·18 and 7·86 ± 1·41 ng/ml, respectively, when measured 30 min after injection. By contrast, LHRH injection did not increase FSH concentration at 20 or 25 months of age above the basal concentration.

Taken together, the morphological and endocrinological data show that puberty in male tammars begins around 19 months and is complete by 25 months of age.

Keywords: testis, testosterone; LH; FSH; LHRH; spermatogenesis; marsupial; puberty

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T. P. Fletcher, A. E. Jetton and M. B. Renfree

Summary. Forty tammar wallabies, presumed to be carrying quiescent blastocysts, were injected with progesterone and oestradiol alone, or in combination, during seasonal quiescence when the corpus luteum is inactive. Plasma progesterone concentrations were increased to values equivalent to those of late pregnancy for the duration of the treatment in progesterone-treated groups but otherwise remained at values equivalent to seasonal quiescence. Tammars treated with low doses of oestradiol showed no measurable increase in plasma oestradiol concentrations but in those treated with high doses plasma concentrations were increased to oestrous levels. At autopsy on Day 18 after the start of treatment the embryos and reproductive tracts were assessed. While progesterone alone caused reactivation of about 50% of the embryos, blastocysts in tammars treated with oestradiol alone remained in diapause (low dose) or disappeared from the uterus (high dose): 2 blastocysts collapsed after some slight expansion. No synergistic effect on pregnancy was noted in tammars receiving both oestradiol and progesterone. We conclude that oestrogen alone is not capable of stimulating normal growth of blastocysts, and its role during early pregnancy in tammars remains unclear.

Keywords: progesterone; oestradiol-17β blastocyst; seasonal diapause; marsupial

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C. A. Horn, T. P. Fletcher and S. Carpenter

Summary. Two experiments, each using 8 animals, were conducted in the non-breeding and breeding seasons, respectively, and each animal was injected with 4 different doses of oestradiol benzoate over 4 trials. The resulting physiological concentrations of plasma oestradiol caused depression of both LH and FSH values. The highest dose elicited a biphasic response in LH with a pulse-like surge at 24 h after injection. There was no significant difference between the response of either hormone at the two times of the year and it is concluded that, in tammars, there is no seasonal difference in the responsiveness of the hypothalamus/pituitary to the negative feedback effect of oestradiol.

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K. Gordon, T. P. Fletcher and M. B. Renfree

Summary. Pouch young of wallabies presumed to be carrying diapausing blastocysts were removed from the teat for times varying between 24 and 96 h and then returned to the same teat. The mothers were monitored for termination of diapause and checked for births or oestrus. In this way we were able to determine the critical time required to reactivate the quiescent corpus luteum and diapausing blastocyst after withdrawal of the sucking stimulus. When pouch young were removed from the teat for 76–96 h the corpus luteum and blastocyst were reactivated, with birth and/or oestrus occurring in 10/11 animals. When pouch young were removed for 72 h or less (n = 22) reactivation did not take place.

We conclude that it takes longer than 72 h for the maternal endocrine system to become committed to reactivation. The precise sequence of endocrine events which precede blastocyst reactivation still remains to be determined.

Keywords: corpus luteum; sucking; tammar; diapause; blastocyst

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M. B. Renfree, G. Shaw and T. P. Fletcher

Female tammar wallabies were treated prepartum with the prostaglandin synthase inhibitor indomethacin, with or without the dopamine agonist bromocriptine, to suppress the peripartum pulses of plasma prostaglandin and prolactin. The animals were observed continuously to detect birth, and a series of blood samples taken to define the hormonal profiles before and immediately after parturition. Birth was observed in ten of twelve control animals but not in the six animals treated with indomethacin alone or the six animals treated with indomethacin and bromocriptine. Indomethacin disrupted the normal profile of PGF metabolite 13,14-dihydro-15-keto-prostaglandin F (PGFM) concentrations, and in the females treated with bromocriptine plus indomethacin the pulse of prolactin normally seen at parturition was completely abolished. Plasma progesterone concentrations fell slowly in treated animals, whereas in control animals they fell steeply immediately after parturition. Postpartum oestrus was delayed or absent in treated and most control animals, suggesting that the frequent blood sampling and disturbances in the peripartum period interfered with these endocrine processes. We conclude that prostaglandin is essential for normal birth. Prolactin, in the apparent absence of a prostaglandin peak, does not induce birth or rapid luteolysis. Prostaglandin release may synchronize the rapid fall in progesterone concentrations associated with birth, but in the absence of this signal, the corpus luteum undergoes a less rapid, autonomous decline.

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L. J. Parry, F. J. Guymer, T. P. Fletcher and M. B. Renfree

The oxytocic peptide mesotocin was measured in plasma samples collected throughout pregnancy in the conscious tammar wallaby, Macropus eugenii. Plasma mesotocin and the prostaglandin metabolite 13,14-dihydro-15-oxo-prostaglandin F were also assessed immediately prepartum and during parturition. A radioimmunoassay for mesotocin was validated in the tammar and this assay allowed direct measurement in 50 μl unextracted plasma with a sensitivity of 12.5 pmol l−1. Plasma concentrations of mesotocin remained basal (approximately 15 pmol l−1) at all stages of pregnancy, including prepartum. A significant (P < 0.05) increase in plasma mesotocin was observed only immediately after delivery of the neonate and this increase was maintained for at least 15 min postpartum. Mesotocin concentrations returned to basal values 2 h after birth. Peak concentrations of mesotocin of 516.7 ± 108.1 pmol l−1 were measured within 2 min of birth. This peak coincided with a short-lived peak in concentration of prostaglandin F metabolite immediately after birth (2.1 ± 0.4 nmol l−1) which decreased to less than 0.3 nmol l−1 within 2 h postpartum. These data demonstrate that mesotocin is released during, or immediately after, delivery and appears to parallel the profile of circulating prostaglandin F metabolite in this marsupial.

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L. A. Hinds, C. H. Tyndale-Biscoe, G. Shaw, T. P. Fletcher and M. B. Renfree

Summary. In Exp. 1 non-pregnant female tammars were injected, on Day 26 (the day parturition would normally occur) after removal of pouch young, with saline, 200 μ ovine prolactin or 5 mg PG and changes in plasma concentrations of progesterone, prolactin, PGF-2α metabolite (PGFM), oestradiol-17β and LH were determined. Luteolysis occurred in females treated with prolactin alone, while treatment with PG first induced a rapid rise in prolactin and subsequently a significant decrease in plasma progesterone. After prolactin treatment the oestradiol peak, oestrus and the LH surge were advanced significantly compared to the saline-treated females.

In Exp. 2 the effects of the same treatments as used in Exp. 1 were determined on Day 23 and again on Day 26 after removal of pouch young in non-pregnant females. On Day 23 both prolactin and PG induced significant elevations in plasma progesterone, but luteolysis did not occur. On Day 26 the treatments initially induced significant elevations in plasma progesterone but these were followed by luteolysis within 8–12 h after treatment. PG treatment induced parturient behaviour in the non-pregnant females within 3–21 min and this persisted during the period that plasma concentrations of PGFM were elevated.

The results show that PG induces birth behaviour and the release of prolactin, while prolactin first induces an elevation of plasma progesterone concentrations and, in the mature CL on Day 26, subsequently induces luteolysis.

Keywords: progesterone; prolactin; LH; oestradiol; PG; tammar