Читать книгу Bovine Reproduction - Группа авторов - Страница 42

Increasing evidence emerging in the literature indicate that relaxin and relaxin‐like peptides play an important role in male reproductive function. Insulin‐like peptide 3 (INSL3; formerly known as relaxin‐like factor 3) is a peptide hormone belonging to the relaxin–insulin family of peptide hormones [86–88] and binds to the RXFP2 receptor complex [89] to initiate physiological responses. It was first identified in the testes of pigs [90] and is now thought to be an important factor in regulating normal testicular decent [87], particularly during the second phase where it acts on the gubernaculum, as demonstrated using knockout mice. The peptide hormone has been identified in male and female tissues of other species, including human, marmoset monkey, sheep, goat, bovine, as well as deer, dog, and other species [88]. It is produced in large quantities by the Leydig cells of both the fetal and adult testes, and circulating INSL3 concentrations have been measured in the blood of adult male mammals including the rat (5 ng/ml) [91], mouse (2 ng/ml) [91], and human (0.8–2.5 ng/ml) [92, 93]. Although INSL3 has been successfully extracted from bovine testis [94] and found to be present in amniotic fluid from human male fetuses [95], it is only recently that Anand‐Ivell et al. [96] using new time‐resolved fluorescence immunoassay to directly detect INSL3 in the blood and body fluids of ruminants reported that mid‐gestation (day 153) cows carrying a male fetus showed significantly higher maternal blood concentrations of INSL3 compared with cows carrying a female fetus. The authors speculate that INSL3 provides the first example of a gender‐specific fetal hormone with the potential to influence both placental and maternal physiology. In a recent review, it is reported that INSL3 is a major secreted product of the interstitial Leydig cells of the mature testes in all mammalian males [97]. Moreover, current evidence points to autocrine, paracrine, and endocrine roles, acting through the G‐protein coupled relaxin family receptor 2 (RXFP2), although more research is required to characterize these functions in detail. Indeed, recent studies have provided evidence of the presence of both RXFP1 and RXFP2 receptors in porcine spermatozoa [98], which would suggest that relaxin may play an important role in sperm production motility and [99]. Disruption of the INSL3 binding to its receptor complex RXFP2 demonstrated the importance of this hormone in promoting and maintaining normal sperm production in the boar testis [100]. Pitia and colleagues [101] investigated the functional INSL3 hormone‐receptor system in the testes and spermatozoa of several domestic ruminant species including bulls, rams, and goats, and explored the potential of this hormone‐receptor to evaluate the fertility of sires. In all ruminants examined, the study identified the presence of RXFP2 in the Leydig cells, testicular germ cells, and sperm (equatorial segment) of fertile males, but in sub‐fertile bulls, the expression pattern in these tissues was significantly reduced. Moreover, the study observed a significant reduction in spermatozoa INSL3 binding in semen recovered from sub‐fertile bulls [101]. Consequently, the authors proposed that poor INSL3 binding by spermatozoa may have potential in predicting sire fertility.