Читать книгу Bovine Reproduction - Группа авторов - Страница 43

The physiological role of relaxin has been intensively studied in many species over the years, including domestic ruminants, with most of the emphasis on the role in pregnancy. Experimental evidence suggests that a number of species in the Bovidae family, both domestic and non‐domestic species, do synthesize relaxin, but apparently respond to it in a physiological manner [102–104]. Specific studies performed by Bagna et al. [102] and Musah et al. [105] explored the efficacy of purified porcine relaxin on parturition in beef and dairy cattle, indicating the possible presence of relaxin RXFP receptors in the bovid female. Observing the experimental evidence suggesting that cattle may not synthesize relaxin, but appear capable of responding to the hormone physiologically, Malone et al. [106] undertook an investigation to characterize the genomic locus of the relaxin gene (RLN1) in Laurasiatherian mammals to understand how cattle may have lost the ability to synthesize this peptide hormone. The outcome of these studies revealed that both domestic and wild ruminant species, including the cow, giraffe, Tibetan antelope, sheep, and goat, lack a functional RLN1 gene. Moreover, the study documented the progressive loss of RLN1 in the evolutionary lineage leading to cattle (Figure 2.3) and that the cow genome has lost all trace of the gene [106]. Interestingly, the same study confirmed that all bovids examined possess copies of the relaxin receptors, RXFP1 and RXFP2, which may explain why in some studies, dairy and beef cattle respond to relaxin despite the inability to synthesize the hormone [106].

Figure 2.3 Genomic context of the relaxin gene in selected mammals. The cluster containing the RLN, INSL4, and INSL6 genes is flanked by the PLGRKT gene on one side and the JAK2 on the other side. Note that the cow has completely lost the RLN gene, while it has remained as a truncated pseudogene in sheep, goat, and antelope.

Source:[106].

The importance of relaxin is less well studied in male mammals. The presence of relaxin‐binding activity has yet to be clearly demonstrated in the male bovid, but with the advent of new technologies this may be possible [107]. However, Kohsaka et al. [108, 109] have demonstrated, utilizing immunohistochemical studies, the binding of relaxin to spermatozoa and suggested that this activity may impart physiological effects on sperm motility and fertility. Moreover, these authors suggested that relaxin activity in its relationship to sperm motility in domestic species may serve as a possible index for predicting the fertilizing ability of sires. Subsequent studies have demonstrated that relaxin improves sperm motility in a number of species, including the human male [110], boar [111], and bull [112]. Furthermore, others have demonstrated that use of relaxin treatment of seminal plasma induces sperm capacitation and acrosome reaction in boar [113] and domestic bull [114] spermatozoa. Other studies have shown that relaxin treatment improved the fertilizing capabilities of fresh boar spermatozoa [115] and fresh or frozen–thawed spermatozoa of the buffalo bull [116, 117] and stallion [118]. Thus, it is evident from these studies that relaxin may play an important role in sperm motility and function. While the RLN1 gene may be lost in the bovid, the physiological benefits of relaxin lie in its potential use as a semen supplement when using either fresh or frozen–thawed bull spermatozoa to facilitate sperm motility and enhance fertilizing capacity during artificial insemination.