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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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LYNN R. FRASER, PRAMILA V. DANDEKAR and MILDRED K. GORDON

Cortical granules are found in the unfertilized eggs of many invertebrates and vertebrates, including mammals, but are essentially absent in fertilized eggs (Austin, 1968). The extruded contents of the granules are thought to play a rôle in the prevention of polyspermy (Austin, 1961). In the sea urchin, the cortical granule breakdown occurs after sperm penetration has begun and appears to be a propagated reaction over the egg surface (Austin, 1961). Szollosi (1967), studying cortical granules in the hamster and rat, found that the granule breakdown in these species is generally activated by the attachment of a spermatozoon to an egg. Pikó (1969) reported that the reaction is triggered when membrane fusion and breakdown of the postnuclear cap region of the spermatozoon has begun. Thus, the presence

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Francois Paradis, Susan Novak, Gordon K Murdoch, Michael K Dyck, Walter T Dixon and George R Foxcroft

This study aimed to describe the abundance and localization of BMP2, BMP6, BMP15, GDF9, BMPR1A, BMPR1B, BMPR2 and TGFBR1 mRNA during pig preovulatory follicular development and to evaluate their implication in improving follicular maturity in the preovulatory period preceding the second versus first post-weaning oestrus. Oocytes, granulosa (GC) and theca cells (TC) were recovered from antral follicles of primiparous sows at day 1, 2 and 4 after weaning and at day 14, 16 and 20 of their subsequent oestrous cycle. Real-time PCR analysis revealed that with the exception of BMP6 mRNA, which was absent in GC, all genes were expressed in every cell type. Although BMP6, BMP15 and GDF9 mRNA were most abundant in the oocyte, their expression remained relatively constant during follicular development. By contrast, receptor BMPR1B and TGFBR1 expressions in the GC and TC were temporally regulated. BMPR1B mRNA abundance was positively correlated with plasma oestradiol (E2) suggesting that its regulation by oestrogen may be implicated in normal folliculogenesis. Interestingly, the increase in BMPR1B mRNA and protein abundance during the periovulatory period in GC and TC suggests a role for bone morphogenetic protein (BMP) 15 in the ovulatory process. Finally, expression of these ligands and receptors was not associated with potential differences in follicle maturity observed during the second versus first post-weaning preovulatory follicular wave. In conclusion, our results clearly demonstrate the presence of a complex signalling system within the pig follicle involving the transforming growth factor-β superfamily and their receptors, and provide evidence to support a role for BMP15 and BMPR1B during ovulation.

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K. Gordon, M. B. Renfree, R. V. Short and I. J. Clarke

Summary. Matched hypothalamo–pituitary portal and jugular blood samples were collected over about 6 h from 7 lactating Corriedale ewes penned with their lambs, and a careful record was kept of ewe/lamb behaviour. Hypothalamo–pituitary portal blood concentrations of β-endorphin were measured by radioimmunoassay and the secretion rates were calculated; these were related to peripheral plasma prolactin and LH concentrations, and the sucking bouts of the lambs.

Basal LH concentrations remained <1 ng/ml with 0–2 pulses of 1·5–3·5 ng/ml amplitude per 6-h collection period. Prolactin secretion was episodic with individual baselines varying from 24 to 286 ng/ml, and peak concentrations of 50–631 ng/ml. Portal β-endorphin was secreted in an episodic pattern with individual baseline secretion rates varying from 0·125 to 0·495 ng/min, and peak secretion rates of 0·768 to 3·216 ng/min. A close correlation was seen between sucking bouts and the secretion of portal β-endorphin and peripheral prolactin; 86% of sucking bouts resulted in a significant release of β-endorphin, and 46% of sucking bouts resulted in a significant release of prolactin.

These results show that hypothalamic β-endorphin is released in response to the sucking stimulus. This provides support for the hypothesis that, during lactation, β-endorphin acts within the hypothalamus to reduce GnRH release and hence depress pituitary gonadotrophin secretion.

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Cansu Agca, James E Ries, Sarah J Kolath, Jae-Hwan Kim, Lawrence J Forrester, Eric Antoniou, Kristin M Whitworth, Nagappan Mathialagan, Gordon K Springer, Randall S Prather and Matthew C Lucy

The LH surge initiates the luteinization of preovulatory follicles and causes hormonal and structural changes that ultimately lead to ovulation and the formation of corpora lutea. The objective of the study was to examine gene expression in ovarian follicles (n = 11) collected from pigs (Sus scrofa domestica) approaching estrus (estrogenic preovulatory follicle; n = 6 follicles from two sows) and in ovarian follicles collected from pigs on the second day of estrus (preovulatory follicles that were luteinized but had not ovulated; n = 5 follicles from two sows). The follicular status within each follicle was confirmed by follicular fluid analyses of estradiol and progesterone ratios. Microarrays were made from expressed sequence tags that were isolated from cDNA libraries of porcine ovary. Gene expression was measured by hybridization of fluorescently labeled cDNA (preovulatory estrogenic or -luteinized) to the microarray. Microarray analyses detected 107 and 43 genes whose expression was decreased or increased (respectively) during the transition from preovulatory estrogenic to -luteinized (P<0.01). Cells within preovulatory estrogenic follicles had a gene-expression profile of proliferative and metabolically active cells that were responding to oxidative stress. Cells within preovulatory luteinized follicles had a gene-expression profile of nonproliferative and migratory cells with angiogenic properties. Approximately, 40% of the discovered genes had unknown function.