Validation of Radioimmunoassays for Two Salmon Gonadotropins (GTH I and GTH II) and Their Plasma Concentrations Throughout the Reproductive Cycle in Male and Female Rainbow Trout (Oncorhynchus Mykiss)1

Abstract

RIAs were developed for the two salmon gonadotropins (GTH I and GTH II) and used to measure plasma GTH throughout the life of the rainbow trout, Oncorhynchus mykiss. The RIA for GTH II was specific and sensitive (< 0.001% cross-reaction with GTH I, mean sensitivity = 0.26 +/- 0.02 ng/ml). The RIA for GTH I was less specific and less sensitive than the GTH II RIA (9.7% cross-reaction with GTH II, mean sensitivity = 2.34 +/- 0.23 ng/ml). In both males and females, the levels of GTH II remained undetectable (< 0.3 ng/ml) throughout most of the reproductive cycle, until shortly preceding spermiation/ovulation, when they began to rise. Concentrations of plasma GTH II were maximal at spermiation/ovulation. In both sexes, plasma profiles of GTH I differed from those of GTH II. The plasma GTH I concentration in females was elevated during early vitellogenesis. It then fell to a basal level shortly before ovulation and finally was elevated again at ovulation. In males, increases in plasma GTH I were seen a year before spermiation and again later, during the final stages of testicular growth. These results support the contention that GTH I mediates gonadal growth, whereas GTH II regulates the final stages of maturation and ovulation/spermiation. In rainbow trout, plasma profiles of GTH I and GTH II mimic the cycles of plasma FSH and LH, respectively, in the ovulatory cycle of higher vertebrates.

A comprehensive evolutionary analysis based on nucleotide and amino acid sequences of the alpha- and beta-subunits of glycoprotein hormone gene family

“…Therefore, we conclude that bony fish GTH-I and mammalian FSH share the same evolutionary origin as do fish GTH-II and mammalian LH . This conclusion is also supported by several other studies that evaluated structural and biological relationships (Swanson 1991, Prat et al 1996. For example, Prat et al (1996) found that the seasonal patterns of GTH-I and GTH-II mimic the ovarian cycle of FSH and LH in mammals.…”

“…Furthermore, more than 15 cDNAs or genes for the -and -subunits of the fish gonadotropins, including types I and II, have been identified and characterized. GTH-I has been shown to be chemically and functionally related to mammalian FSH, and GTH-II to mammalian LH (Swanson 1991, Prat et al 1996, but their evolutionary relationship to FSH and LH has not been well established (Ishii 1990, Querat 1994, 1995, Wako & Ishii 1995. On the basis of amino acid sequence alignments for the 24 -subunits of this family and of one fish type I and six type II gonadotropins, Wako & Ishii (1995) performed a phylogenetic analysis and concluded that FSH is more related to TSH than to LH , and that fish GTH-II is probably related to LH , whereas GTH-I is unlikely to be related to FSH .…”

Changes in mRNAs encoding steroidogenic acute regulatory protein, steroidogenic enzymes and receptors for gonadotropins during spermatogenesis in rainbow trout testes

“…Later studies demonstrated that GTH I and GTH II are structurally and functionally similar to FSH and LH, and therefore GTH I and GTH II are currently recognized as FSH and LH respectively (Swanson et al 1989, Van der Kraak et al 1992, Koide et al 1993, Okada et al 1994, García-Hernández et al 1997, Weltzien et al 2003. In male rainbow trout, FSH in plasma was elevated during mid-spermatogenesis, whereas LH showed a significant increase in plasma during the spermiating stage (Prat et al 1996, Gomez et al 1999. For salmon testis in vitro, the relative potencies of FSH and LH in stimulating steroid synthesis did not change before the late spermatogenesis stage and spermiation (Planas & Swanson 1995).…”

Effects of sex steroids on gonadotropin (FSH and LH) regulation in coho salmon (Oncorhynchus kisutch)

“…Pituitary content (Suzuki et al 1988a, Nozaki et al 1990a,b, Naito et al 1991 and plasma levels of FSH and LH (Suzuki et al 1988a, Swanson et al 1989, Swanson 1991, OppenBerntsen et al 1994, Slater et al 1994, Prat et al 1996 vary differently during gametogenesis with FSH being elevated during vitellogenesis and spermatogenesis and LH increasing during final maturation. Subunit mRNA levels for FSH and LH also vary throughout gametogenesis (Weil et al 1995, Yoshiura et al 1997.…”