15alpha-hydroxytestosterone induction by GnRH I and GnRH III in Atlantic and Great Lakes sea lamprey (Petromyzon marinus L.).

The sea lamprey (Petromyzon marinus L.) represents one of the two most ancient classes of vertebrates and possesses a functional hypothalamus-pituitary-gonadal axis. However, the presence and functionality of androgens in the sea lamprey remain elusive. Recently, 15alpha-hydroxytestosterone (15alpha-T) has been found in sea lamprey gonads and blood plasma. In this study we examined changes of circulatory concentrations of 15alpha-T in response to gonadotropin releasing hormone (GnRH) treatments. Plasma concentrations of 15alpha-T in sea lamprey increased 2-5 times for all GnRH-injected sea lamprey compared to controls (P < 0.001). However, there were no differences among responses: (1) to the two forms of GnRH (lamprey GnRH I or lamprey GnRH III), (2) to the doses delivered (50, 100, or 200 microg/kg), or (3) between post-injection sample intervals (8 or 24 h). Between lampreys from the Atlantic Ocean and Great Lakes sites, two of seven GnRH form and dosage comparisons showed between-site differences, but were not believed to represent an overall between-site difference. These are the first data to show a response of a C19 steroid to GnRH stimulation in sea lamprey.