Thyroid hormones control the functions of almost all body systems. Reproductive dysfunctions, such as abnormal sexual development, infertility, or irregularities in the reproductive cycle, might be associated with thyroid disorders. Uterine receptivity is the period when the uterus is receptive to the implantation of an embryo. During the receptivity period (implantation window), a newly formed blastocyst is incorporated into the uterine epithelium. Prostaglandins are well-known primary mediators of pathological conditions such as inflammation and cancer but are also essential for the physiology of female reproduction. The aim of this study was to evaluate the possible relationship between hypothyroidism and changes in the prostaglandin signaling pathways in the uterus and in the process of uterine receptivity in a rat model. The results show that hypothyroidism impaired uterine receptivity by decreasing the level of E2 as well as decreasing the expression of the uterine-receptivity factors homeobox A10 and osteopontin. Moreover, hypothyroidism caused changes in the expression of elements of the prostaglandin E₂, F_2α, and I₂ signaling pathways and changed the levels of those prostaglandins in the uterine tissue. The results suggest that the mechanisms by which hypothyroidism affects female reproductive abnormalities might involve the prostaglandin signaling pathway, resulting in a subsequent reduction in uterine receptivity.

The Polish draft horse (PDH) breed is a result of crossing local mares with imported cold-blooded stallions, such as Belgians, Ardennes, Fjords, and others. A part of the broodmare stock investigated in this study was also imported from various countries, such as Denmark. In this study, we investigate the genetic composition of the PDH by analyzing the whole mitochondrial d-loop variability and comparing it to previously demonstrated whole d-loop sequences of other cold-blooded breeds: Ardennais, Belgian, Breton, Clydesdale, Noriker, Norwegian Fjord, Percheron, and Suffolk. Our results show high nucleotide diversity within the PDH population (π = 0.011), and the existence of two main haplogroups: one of relatively concise origin, with strong kinship to the Belgian breed, and the second showing close relation to the majority of other analyzed cold-blooded breeds. Some of the PDH maternal strains clustered separately, which can be a result of the influence of other unidentified breeds that served as a foundation stock for the present population. This present study explains the genetic relationship of the PDH to other cold-blooded breeds and indicates the high genetic diversity of the breed.