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Gonadotrophin releasing hormone (GnRH) facilitates the migration of mast cells (MCs) into the involuting mammary gland. As GnRH is also expressed in the ovary, we examined changes in ovarian MCs. MCs in the ovary were mainly in interstitial tissue and their number increased during the estrous cycle to produce 2 peaks, one at diestrus 2 (20:00 hours) and another at proestrus (17:00 hours). Laser microdissection demonstrated that GnRH mRNA is expressed throughout ovarian tissues (corpora lutea, follicles, and interstitial tissues). GnRH immunoreactivity was also ubiquitous, but MCs were the most strongly immunostained. Analysis of GnRH mRNA in the ovary showed it to fluctuate similarly to the variation in MC number during the estrous cycle, and MCs also expressed GnRH. Local administration of a GnRH agonist (GnRHa) into the hemilateral ovarian bursa increased MCs in the administered ovary. MC number and GnRH mRNA were significantly lowered in the pregnant ovary. Prolactin administration suppressed the normal peaks in MC number in the ovary at both diestrus and proestrus. By contrast, a dopamine agonist, administered when prolactin was elevated during pseudopregnancy, increased ovarian MC number. Furthermore, prolactin inhibited GnRHa-induced peritoneal MC migration in a Transwell assay. These data clearly demonstrate that ovarian MC number is regulated positively by local GnRH expression and negatively by prolactin. The suppressive effect of prolactin on GnRH and MCs would be part of its luteotrophic action., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

It has been demonstrated that mammary gland involution after lactation is initiated by accumulation of milk in alveoli after weaning. Here, we report that involution is also dependent on mammary GnRH expression that is suppressed by PRL during lactation. Reduction of plasma prolactin (PRL) by the withdrawal of suckling stimuli increased GnRH and annexin A5 (ANXA5) expression in the mammary tissues after lactation with augmentation of epithelial apoptosis. Intramammary injection of a GnRH antagonist suppressed ANXA5 expression and apoptosis of epithelial cells after forcible weaning at midlactation, whereas local administration of GnRH agonist (GnRHa) caused apoptosis of epithelial cells with ANXA5 augmentation in lactating rats. The latter treatment also decreased mammary weight, milk production, and casein accumulation. Mammary mast cells were strongly immunopositive for GnRH and the number increased in the mammary tissues after weaning. GnRHa was shown to be a chemoattractant for mast cells by mammary local administration of GnRHa and Boyden chamber assay. PRL suppressed the mammary expression of both ANXA5 and GnRH mRNA. It also decreased mast cell numbers in the gland after lactation. These results are the first to demonstrate that GnRH, synthesized locally in the mammary tissues, is required for mammary involution after lactation. GnRH is also suggested to introduce mast cells into the regressing mammary gland and would be in favor of tissue remodeling. The suppression of these processes by PRL is a novel physiological function of PRL.

Antiphospholipid syndrome is associated with an increased risk of thrombosis and pregnancy loss. Annexin A5 (Anxa5) is a candidate autoantigen. It is not known, however, whether endogenous Anxa5 prevents foetal loss during normal pregnancy. We found significant reductions in litter size and foetal weight in Anxa5-null mice (Anxa5-KO). These changes occurred even when only the mother was Anxa5-KO. A small amount of placental fibrin deposition was observed in the decidual tissues, but did not noticeably differ between wild-type and Anxa5-KO mice. However, immunoreactivity for integrin beta 3/CD61, a platelet marker, was demonstrated within thrombi in the arterial canals only in Anxa5-KO mothers. Subcutaneous administration of the anticoagulant heparin to pregnant Anxa5-KO mice significantly reduced pregnancy loss, suggesting that maternal Anxa5 is crucial for maintaining intact placental circulation. Hence, the presence of maternal Anxa5 minimises the risk of thrombosis in the placental circulation and reduces the risk of foetal loss.

The distribution of annexin A5, a cytosolic protein related to gonadotropin releasing hormone action, was examined in the mammary gland of rats by immunohistochemistry with special reference to changes by lactation. Annexin A5 was observed in the interstitial tissues but not alveolar cells in virgin rats, while mammary epithelial cells became positive for annexin A5 in pregnant rats. The intensity of annexin A5 was decreased in lactating rats and dramatically increased after weaning, especially on the nucleus. When pups were removed from their dam at mid-lactation (day 10), annexin A5 was also increased on day 12. Apoptotic epithelial cells detected by terminal deoxynucleotidyl transferase nick end labeling were simultaneously increased. Annexin A5 mRNA expression of mammary tissues was increased after pup removal. These results are the first to demonstrate the distribution of annexin A5 in the mammary glands of lactating rats, and the enhanced expression in mammary epithelial cells after lactation suggests its involvement in mammary epithelial cell involution.

Objectives: To examine the expression of annexin A5, a recently emerged multifunctional protein, in the testis after experimental cryptorchidism., Methods: The hemilateral testes of rats were surgically relocated from the scrotum into the abdomen. The annexin A5 content was evaluated by Western blot analysis, and its distribution was determined by immunohistochemistry. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) was performed to detect the apoptotic cells., Results: Although annexin A5 content was not changed in the scrotal testis, it was dramatically increased in the abdominal testis during the 4-week observation period. TUNEL-positive apoptotic spermatogonia appeared in some of the seminiferous tubules only 1 day after the surgery. The appearance of TUNEL-positive cells was accompanied by augmented expression of annexin A5. Spermatocytes disappeared by 1 week after cryptorchidism, and annexin A5 expression was significantly increased inside the seminiferous tubules. In the cryptorchid testis, annexin A5 of the interstitial cells disappeared, as did 3beta-hydroxy steroid dehydrogenase. Annexin A5 on endothelial cells was not changed by the cryptorchidism., Conclusions: These data demonstrate first that the expression of annexin A5 is increased in the seminiferous tubules of cryptorchid testes and suggest that it is related to the degenerative response of germ cells.