Relaxin in the male reproductive system

ABSTRACT

xin (RLN) belong s to a family of hormones structurally related to insulin and presents a broad spectrum of actions. H umans have three forms of RLN , encoded by three different genes ( RLN1 , RLN2 and RLN3 ) , but nonprimate vertebrate s have only two forms of relaxin (RLN1 and RLN3) . RLN1 of these animals is encoded by Rln1 , orthologous to the h uman RLN 2 gene , and both genes , Rln1 and human RLN2 , encode the major form of relaxin found in the male reproductive system . In the reproductive tract of human male s , RLN is mainly produced by the prostate and secreted into the seminal fluid, where it seems to play a role in sperm function. R LN may also play a role in prostate cancer progression. A lack of RLN in animal models impairs male fertili ty , and RLN knockout mice display decreased sperm maturation . T he precise role of RLN in the male reproductive system , however , is still far from clear. RLN actio n is due to its interaction with the G - protein coupled receptor RXFP1. Studies from our labora tory have shown that RLN and RXFP1 are e x pressed in rat Sertoli cells, and e x ogenous RLN stimulates Sertoli cell proliferation. RLN receptors can also be detected in rat germ cells at different stages of development, suggesting that RLN may play a direct r ole in spermatogenesis. The distribution of RLN/RXFP1 , however , appears to be species - dependent, because i n the boar testis RLN production seems restricted to the Leydig cells, whereas RXFP1 is found in Leydig, Sertoli and germ cells. The co - expression of RLN and RXFP1 in several regions of the male reproductive system suggest s that the peptide may act in an autocrine/paracrine fashion.