DOGFISH SHARK (SQUALUS-ACANTHIAS) TESTES CONTAIN A RELAXIN

Relaxin is a 6-kd polypeptide that exerts important hormonal effects i n many female mammals. Relaxin is produced by the ovary, placenta, or uterus in many mammalian species. The functions of relaxin in the male mammal are not yet firmly established, but there is some evidence sug gesting an exocrine effect on sperm motility and fertilizability. In t he male mammals that have been studied, relaxin is produced by the pro state gland (human) or seminal vesicles (boar). However, in the bird, the testis is the likely source of relaxin. Among the elasmobranchs, o varies obtained from dogfish sharks have been shown to contain a polyp eptide hormone that is structurally, biologically, and immunologically similar to mammalian relaxins, but the male reproductive tract of thi s species has not previously been investigated as a potential source o f relaxin. Extracts of testes obtained from mature dogfish sharks have now been tested by a specific relaxin bioassay and by a homologous po rcine radioimmunoassay for the presence of relaxin. Both crude and par tially purified testicular extracts contained unmistakable guinea pig pubic symphysis-''relaxing'' activity and relaxin-like immunoactivity. Following immunoaffinity purification, the shark testis polypeptide h ad an apparent specific activity of 88 mu g porcine relaxin equivalent s per milligram in the radioimmunoassay, which is similar to the immun oactivity of pure shark ovarian hormones. These data, therefore, stron gly support the view that in dogfish sharks, the male as well as the f emale gonad produces relaxin. Furthermore, as the dogfish shark has ex isted as a species for about 200 million years, the data suggest that testicular relaxin appeared early in vertebrate evolution.