Dose-response relationship of 15alpha-hydroxylated sex steroids to gonadotropin-releasing hormones and pituitary extract in male sea lampreys (Petromyzon marinus).
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 15alpha-hydroxytestosterone (15alpha-T) and 15alpha-hydroxyprogesterone (15alpha-P) have only been partially characterized. In the present study, plasma concentrations of 15alpha-T and 15alpha-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 microg/kg, or of pituitary extract (as a source of gonadotropin). Plasma was sampled at 1-6h and 6-48 h post-injection, in separate experiments, in order to characterize the peak and duration of responses. 15alpha-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, 15alpha-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 15alpha-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 15alpha-P peaked at 6h 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 microg/ml GnRH I or III, 15alpha-T concentrations did not exceed 0.5 ng/ml and 15alpha-P concentrations did not exceed 1 ng/ml. These results lend further support to the hypothesis that 15alpha-P plays an important role in the reproductive endocrinology of male lampreys.
Young
Bradley A
BA
Department of Fisheries and Wildlife, Michigan State University, 13 Natural Resources Building, East Lansing, MI 48824, USA.
Bryan
Mara B
MB
Glenn
Jessica R
JR
Yun
Sang Seon
SS
Scott
Alexander P
AP
Li
Weiming
W
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D012739:Gonadal Steroid Hormones / Q000097:blood / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D006062:Gonadotropins / Q000008:administration & dosage / Q000494:pharmacology; D006915:Hydroxytestosterones / Q000097:blood* / Q000378:metabolism; D007798:Lampreys / Q000378:metabolism*; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects* / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism; D013997:Time Factors
D012739:Gonadal Steroid Hormones; D006062:Gonadotropins; D006915:Hydroxytestosterones; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; C035390:15-hydroxytestosterone