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Summary.

Pregnant tammars were ovariectomized during anoestrus or on Day 8 of the reproductive cycle that follows removal of the pouch young. Quiescent and Day-8 blastocysts were transferred to the uteri of anoestrous or Day-8 non-pregnant recipients, some of which were ovariectomized at the time of transfer.

Blastocysts did not develop after ovariectomy performed during anoestrus or after transfer to anoestrous recipients. Pregnancy continued normally after ovariectomy on Day 8 and both quiescent and Day-8 blastocysts developed in the uteri of intact and ovariectomized recipients.

These results indicate that the uterus by Day 8 is competent to nourish an embryo to full term without further ovarian stimulation. They also show that the quiescent blastocyst can resume development without the direct stimulus of ovarian hormones. The hypothesis most in accord with the results is that blastocyst development is inhibited during lactation by a principle of the uterus, which is inactivated during the first 8 days by corpus luteum secretions, and that these secretions also induce the endometrial changes upon which subsequent embryonic development depends.

Summary.

The effects of bilateral and unilateral ovariectomy performed on various days of the delayed cycle are described and it is concluded that the corpus luteum is essential for the resumption of embryonic development and for induction of the secretory phase in the endometrium. It can wholly fulfil these functions by Day 7 and is not necessary for the subsequent progress of pregnancy. The corpus luteum after Day 2 also inhibits premature follicular development and ovulation from the remaining ovary in unilaterally ovariectomized animals. The first two of these functions of the corpus luteum, but not the latter one, have been fully substituted with injections of progesterone given during the first 7 days of the cycle.

Parturition failed to occur in all bilaterally ovariectomized animals and occurred in only one unilaterally ovariectomized animal. Birth occurred in two bilaterally ovariectomized animals given a relaxin preparation, but in none that was given either oestrogen or oxytocin. It is suggested that failure to give birth may be due to a lack of relaxin secretion after ovariectomy and a consequent inadequacy of the pseudo-vaginal canal for parturition.

Summary.

The inter-relationships of the ovaries, uterus and blastocyst in Setonix during the resumption of reproductive activity that follows lactation have been examined by transferring blastocysts of various stages of development to recipients at corresponding or different stages of the cycle.

The uterus of the non-pregnant animal is fully competent to nourish a blastocyst after synchronous transfer. Quiescent blastocysts from lactating animals developed in the uteri of recipients that were at the 6th day of the cycle, but developing blastocysts failed to maintain normal development in the uteri of lactating recipients or in those at an earlier stage of the cycle than the donor.

The results suggest that the luteal-phase uterus, although essential in later development, does not stimulate the blastocyst to resume development; this stimulation may come from the corpus luteum, possibly in conjunction with other secretions of the ovaries, and can be effected in the ovariectomized recipient by progesterone and oestrogen.

Summary. Ovulation in the tammar wallaby alternates between the ovaries. The genital duct of each side enters the median vaginal culs-de-sac separately. Post-partum oestrus occurred 0·4 days after birth and ovulation 1 day later. After a single copulation spermatozoa were found in both cervical canals at 0·5 h and extended to the oviduct on the non-parturient side only by 8 h. Very few spermatozoa were found in sections of the post-partum uterus or its associated oviduct at any time. Spermatozoa were recovered by flushing from both sides but the numbers were 2–20 times greater in the non-parturient than in the post-partum side: the greatest difference occurred in the cervical canals 2–5 h after copulation. In females which had undergone a previous infertile cycle, spermatozoa were abundant in both cervices and both uteri. It is concluded that the differential distribution of spermatozoa in post-partum animals was (1) due to failure of transport in the recently pregnant side of the tract, rather than attraction of spermatozoa to the ovulation side, and (2) established at the cervix which, on the ovulation side, provides a reservoir of spermatozoa for 24 h after copulation.

Summary. Metabolic clearance rate (MCR), production rate (PR) and plasma protein-binding of progesterone were measured during embryonic diapause and after ovariectomy in the tammar wallaby. The effect of ovine prolactin and LH on the secretion of progesterone by the quiescent corpus luteum in vitro was also examined.

During embryonic diapause, a low plasma progesterone concentration of 196 ± 24 (s.e.m.) pg/ml (n = 7) was associated with a low PR of 20·2 ± 1·4 ng/kg/min and a high MCR of 111·0 ± 7·6 ml/kg/min. Similar values were obtained for the 4 animals ovariectomized 9 or 12 months previously (plasma progesterone = 156 ± 14 pg/ml; MCR = 147 ± 16 ml/kg/min; PR = 20·4 ± 2·2 ng/kg/min) although plasma progesterone concentration was decreased by about 50% within 14 days of ovariectomy. An increased adrenal cortical secretion of progesterone in long-term ovariectomized tammars is suggested.

Progesterone was bound by plasma protein. The association constant at 20°C was similar for intact (2·31 × 10⁸ m ⁻¹) and ovariectomized (2·27 × 10⁸ m ⁻¹) tammars while the concentration of binding sites was significantly lower in ovariectomized (1·41 × 10⁻⁷ m) than in intact (2·28 × 10⁻⁷ m) tammars. Cortisol and 17α-hydroxyprogesterone competed with progesterone for binding sites while 20α-hydroxyprogesterone, oestradiol-17β and testerone did not.

Progesterone was secreted by quiescent corpora lutea in vitro but neither LH nor prolactin changed its rate of secretion.

The placenta of the tammar wallaby, like that of most marsupials, is formed by close apposition of the yolk-sac membrane to the uterine epithelium. The yolk-sac fluid is rich in a variety of substances such as amino acids, glucose and protein which change quantitatively and qualitatively throughout gestation, the most marked changes occurring after attachment of the membrane to the uterus (Renfree, 1970).

Since many of the proteins resemble maternal proteins, they may have been transferred unchanged after attachment; conversely, they may have been synthesized by the embryo and the similarities may be due to the genetic similarities of the embryo and its mother. We have examined these two possibilities in the β-globulin proteins of yolk-sac fluid. The transferrins in this moiety of serum can be detected by virtue of their capacity to

Summary. The role of the corpus luteum, the ovarian interstitial tissue and the ovarian cortex in the maintenance of the diapausing embryo was investigated by selective excision of the component tissues from female tammars undergoing seasonal quiescence. The response of the pituitary was assessed by measuring LH in peripheral plasma. No part of the ovary was necessary for the continued survival of the blastocyst in diapause for up to 4 months after ovariectomy, but at 8 months no blastocyst reactivated normally when the mother was treated with progesterone. Reactivation and the normal progress of pregnancy occurred in females deprived of the quiescent CL or the interstitial tissue only if a luteinized follicle or corpus luteum developed in the remaining ovary or a graft of ovarian cortical tissue. Plasma LH became elevated in bilaterally ovariectomized females, but not in unilaterally ovariectomized females or those carrying grafts of ovarian cortex.

Summary. During the light phase of each of 3 photoperiods tested, plasma melatonin concentrations were < 16 to 62 pg/ml and during the dark phase they were 31 to 169 pg/ml. When the photoperiod to which the tammars were exposed was altered from 15 h light: 9 h dark to 12L:12D the onset of the nocturnal rise in melatonin was advanced from the first day, thereby extending its duration, and the females gave birth 32 ± 0·4 (mean ± s.e.m.) days later. To test whether melatonin mediated this effect of photoperiod change, tammars in a second group were injected s.c. with melatonin (400 ng/kg, N = 6) or the arachis oil vehicle (N = 6), 2·5 to 2·25 h before dark during 15L:9D for 15 days before exposure to 12·5L:11·5D. The melatonin injections mimicked the endogenous melatonin profile of 12L:12D and the melatonin-injected tammars gave birth 32 ± 0·8 days after the start of injections, which was the same as the interval from photoperiod change in Exp. 1 but was significantly different (P < 0·005) from the interval in the control group (46·0 ± 1·1 days). These results show that exogenous melatonin given 2·5 to 2·25 h in advance of the endogenous rise fully mimics the response of the tammar to photoperiod change.

Summary. Prolactin was measured in peripheral plasma of female tammars once a week for 14 months and every 2 months it was measured in a subgroup of 7 tammars at hourly intervals for 28 h to determine short-term changes in concentration.

During the course of the study 6 females gave birth in January/February and reared their young to weaning in October—November, while another 4 gave birth 1·5–3·0 months later and weaned their young in November—December. Concentrations of prolactin were < 40 ng/ml in a non-lactating animal and for the first 140 days of lactation in the others. Between 140 and 180 days of lactation the concentrations of prolactin fluctuated between 10 and > 100 ng/ml and thereafter remained high until the young vacated the pouch for the last time at about 250 days. After pouch exit the concentrations declined to about 40 ng/ml even though lactation continued for a further 21–35 days. Although the short-term patterns of prolactin concentrations showed no consistent relationship between light—dark phases there was an increase in the magnitude and duration of peaks of plasma prolactin which correlated with the stage of lactation. Removal of pouch young aged between 203 and 242 days for 24 h resulted in a rapid decrease in plasma prolactin concentration which was reversed when the young was returned to the pouch, indicating that the high levels of prolactin in the second half of lactation may be maintained by the sucking stimulus of the pouch young. This period of lactation, therefore, may be equated with lactation in eutherians, but there appears to be no eutherian equivalent to early lactation in the tammar.