The effect of chemosterilization on sex steroid production in male sea lampreys

The sterile male release technique (SMRT) is currently used as part of an integrated effort to control Great Lakes populations of sea lampreys Petromyzon marinus, yet the effects of chemosterilization on the reproductive endocrinology of the sea lamprey are unknown. Male sea lampreys were chemosterilized with bisazir (P,P-bis(1-aziridinyl)-N-methylphosphinothioic amide) and given timed-release implants containing lamprey D-Arg(6)-GnRH I (where GnRH is an acronym for gonadotropin-releasing hormone) and lamprey DArg(6)-GnRH III. The effects of chemosterilization on the reproductive endocrine system were evaluated by measuring plasma concentrations of 17beta-estradiol (E2) and 15alpha-hydroxytestosterone (15alpha-T) with radioimmunoassays. The effectiveness of the implants was evaluated by measuring plasma concentrations of steroids and determining the duration of steroidal responses. The E2 and 15alpha-T response profiles showed Do difference between sterilized and untreated male sea lampreys (P = 0.53). Peak concentrations of E2 were 1.3-2.8 times greater for GnRH-treated lampreys than for controls; peak concentrations of 15alpha-T were 1.6-2.4 times greater for GnRH-treated lampreys than for controls. After 6 h, both GnRH treatments elicited higher concentrations of both sex steroids than either control treatment (P < 0.001), and after 12 h GnRH I consistently elicited higher concentrations of both sex steroids than GnRH III (P < 0.001). The GnRH-releasing implants sustained increased sex steroid responses for at least 2 d. The absence of endocrine disruption indicates that steroidogenesis continues to function normally in sterilized males and is consistent with normal function of the hypothalamus-pituitary-gonadal axis from the time of GnRH release to steroidogenesis. These findings support the continued use of the SMRT and may provide opportunities for its enhancement.