Publication Abstract

Dose-response relationship of 15α-hydroxylated sex steroids to gonadotropin releasing hormones and pituitary extract in male sea lampreys (Petromyzon marinus)

Dose-response relationship of 15α-hydroxylated sex steroids to gonadotropin releasing hormones and pituitary extract in male sea lampreys (Petromyzon marinus)

B.A. Young, M.B. Bryan, J.R. Glenn, S.S. Yun, A.P. Scott and W. Li

The sea lamprey (Petromyzon marinus) is one of the earliest extant vertebrates for which the hypothalamic-pituitary-gonadal (HPG) axis has been shown to control and regulate reproduction in a similar fashion to gnathostome vertebrates. While the two forms of gonadotropin-releasing hormones in the sea lamprey (GnRH I and GnRH III) have been studied extensively, their in vivo effect on synthesis of 15α-hydroxytestosterone (15α-T) and 15α-hydroxyprogesterone (15α-P) have only been partially characterized. In the present study, plasma concentrations of 15α-T and 15α-P were measured in prespermiating sea lampreys that were given a single injection of either GnRH I or GnRH III in doses ranging from 5 to 100 μg/kg, or of pituitary extract (as a source of gonadotropin). Plasma was sampled at 1–6 h and 6–48 h post-injection, in separate experiments, in order to characterize the peak and duration of responses. 15α-T plasma concentrations increased slightly in response to all three treatments, but not in a dose-dependent manner, and the timing of peak concentrations varied between doses. However, 15α-P plasma concentrations showed a greater range of response (between 1 and 100 ng/ml) and were clearly correlated with the injection dose. Plasma concentrations of 15α-P also responded to far lower doses of GnRH I and GnRH III than any other steroid previously investigated in lampreys. The plasma concentrations of 15α-P peaked at 6 h after injection for all three treatments, and levels reached a mean of 53.1 ng/ml. In female lampreys that were injected twice with 50 μg/ml GnRH I or III, 15α-T concentrations did not exceed 0.5 ng/ml and 15α-P concentrations did not exceed 1 ng/ml. These results lend further support to the hypothesis that 15α-P plays an important role in the reproductive endocrinology of male lampreys.

Reference

B.A. Young, M.B. Bryan, J.R. Glenn, S.S. Yun, A.P. Scott and W. Li (2007) Dose-response relationship of 15α-hydroxylated sex steroids to gonadotropin releasing hormones and pituitary extract in male sea lampreys (Petromyzon marinus). General and Comparative Endocrinology, 151: 108-115

B.A. Young, M.B. Bryan, J.R. Glenn, S.S. Yun, A.P. Scott* and W. Li

General and Comparative Endocrinology, 151(1): 108-115