Plasma levels of eggshell zr‐proteins, estradiol‐17β, and gonadotropins during an annual reproductive cycle of Atlantic salmon ( Salmo salar)

• Published in: Journal of Experimental Zoology
• Main Authors: Oppen‐Berntsen, D. O., Olsen, S. O., Rong, C. J., Taranger, G. L., Swanson, P., Walther, B. T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1994
• Subjects: Berntsen; Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1002/jez.1402680108; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjez.1402680108; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jez.1402680108

Abstract Eggshell zona radiata proteins (zr‐proteins) were found to occur normally in plasma of sexually mature female (but not male) Atlantic salmon ( Salmon salar ). In order to ascertain the physiological relevance of these findings, we developed a specific enzyme‐linked immunoassay for zr‐proteins and screened plasma from sexually maturing Atlantic salmon females throughout an annual reproductive cycle. While zr‐proteins were detectable at low levels in female adult salmon plasma prior to sexual maturation, zr‐protein levels increased dramatically as sexual maturation proceeded. The strong correlation between gonado‐somatic index (GSI) and plasma zr‐proteins indicates a reproductive role for blood borne zr‐proteins. During the vitellogenic phase, levels of plasma zr‐proteins were positively correlated with GSI and with plasma levels of gonadotropin I (GtH I) and estradiol‐17β, as determined by radioimmuno‐assays. However, during final sexual maturation, only the plasma level of gonadotropin II (GtH II) was positively correlated to GSI. In contrast, zr‐proteins and estradiol‐17β were both negatively correlated to plasma level of GtH II during this period. In view of estradiol‐17β‐induced hepatic synthesis and secretion of zr‐proteins (Oppen‐Berntsen et al.: Journal of Endocrinology 135:293–302, 1992a) and the established role of gonadotropins in regulating ovarian estradiol synthesis, we interpret the observed correlations among plasma levels of GtH I, estradiol‐17β and zr‐proteins in Atlantic salmon to signify that GtH I regulates ovarian estradiol‐17β synthesis, which in turn regulates hepatic synthesis and secretion of both vitellogenin and zr‐proteins during oogenesis. © 1994 Wiley‐Liss, Inc.