Hypothyroidism compromises the testicular redox status and is associated with reduced sperm quality and infertility in men. In this regard, studies have demonstrated the antioxidant potential of kisspeptin in reproductive and metabolic diseases. In this study, we evaluate the effects of kisspeptin-10 (Kp10) on the testicular redox, as well as mediators of the unfolded protein response (UPR) in adult rats with hypothyroidism. Adult male Wistar rats were randomly separated into the Control (n = 15), Hypo (n = 13) and Hypo + Kp10 (n = 14) groups, and hypothyroidism was induced with 6-propyl-2-thiouracil (PTU) for three months. In the last month, half of the hypothyroid animals received Kp10. Testis samples were collected for enzymatic, immunohistochemical and/or gene evaluation of mediators of oxidative stress (TBARs, lipid hydroperoxides (LOOH), ROS, peroxynitrite, SOD, CAT and GPX), endoplasmic reticulum stress (GRP78, ATF6, PERK, CHOP, HO-1 and sXBP1) and antiapoptocytes (BCL-2). Hypothyroidism increased apoptosis index, TBARS and LOOH concentrations, and reduced testicular gene expression of Sod1, Sod2 and Gpx1, as well as the expression of Grp78, Atf6, Ho1 and Chop. Treatment with Kp10, in turn, reduced testicular apoptosis and the production of peroxynitrite, while increased SOD1 and GPX ½ expression, and enzymatic activity of CAT, but did not affect the lower expression of UPR mediators caused by hypothyroidism. This study demonstrated that hypothyroidism causes oxidative stress and dysregulated the UPR pathway in rat testes and that, although Kp10 does not influence the low expression of UPR mediators, it improves the testicular redox status, configuring it as an important antioxidant factor in situations of thyroid dysfunction.

Hypothyroidism causes ovarian dysfunction and infertility in women and animals and impairs the hypothalamic expression of kisspeptin (Kp). However, kisspeptin is also expressed in the genital system, and the lack of the Kp receptor (Kiss1r) in the uterus is linked to reduced implantation rates. This study investigated the impact of hypothyroidism on the uterine expression of Kp and Kiss1r in female rats throughout the estrous cycle and the associated changes in uterine activity modulators. Hypothyroidism was induced through daily administration of propylthiouracil (PTU) over a period of 14 days. Plasma levels of LH, E₂, and P₄, cyclicity, body and uterine weight, uterine histomorphometry, and the gene and/or protein expression of Kiss1, Kiss1r, estrogen receptor α (ERα), progesterone receptor (PR), and thyroid hormone receptor α (TRα) were assessed. Additionally, proliferative activity (CDC-47) and the gene expression of uterine receptivity mediators (SMO, WNT4, BMP2, HAND2, MUC1, and LIF) were evaluated. Hypothyroidism prolonged the diestrus and increased progesterone levels during this phase, while decreasing luteinizing hormone and estradiol on proestrus. In the uterus, hypothyroidism reduced Kp immunostaining on diestrus and KISS1R mRNA levels on proestrus. These changes were accompanied by reduced endometrial glands, reduced uterine proliferative activity, and reduced ERα gene and protein expression. Additionally, hypothyroidism led to reduced uterine gene expression of LIF, BMP2, WNT4, and HAND2. On the other hand, thyroid hypofunction increased uterine PR and TRα immunostaining, while it reduced PGR gene expression on diestrus. These findings demonstrate that hypothyroidism reduces the expression of Kiss1/Kiss1r system in the uterus, which is associated with disrupted uterine estrogen and progesterone signaling and reduced expression of uterine receptivity mediators across the rat estrous cycle.