Publication Abstract

15a-Hydroxyprogesterone in Male Sea Lamprey, Petromyzon marinus L.

M. B. Bryan, A. P. Scott, I. Cerný, B. A. Young and W. Li

There is growing evidence that sea lampreys, Petromyzon marinus L., produce gonadal steroids differing from those of other vertebrates by possessing an additional hydroxyl group at the C15 position. Here we demonstrate that sea lamprey testes produce 15α-hydroxyprogesterone (15α-P) in vitro when incubated with tritiated progesterone, that 15α-P is present in the plasma of sea lampreys, and that plasma concentrations of immunoreactive (ir) 15α-P rise dramatically in response to injections of gonadotropin-releasing hormone (GnRH). The identity of the tritiated 15α-P produced in vitro was confirmed by co-elution with standard 15α-P on high performance liquid chromatography, co-elution with standard and acetylated 15α-P on thin layer chromatography, and specific binding to antibodies raised against standard 15α-P. The in vitro conversion was used to produce tritiated 15α-P label for a radioimmunoassay (RIA), which is able to detect 15α-P in amounts as low as 2 pg per tube. The RIA has been used to measure the plasma concentrations of 15α-P in males given two serial injections, 24 h apart, of either lamprey GnRH I or GnRH III (50, 100, or 200 µg/kg) or saline control, with plasma being sampled 8 and 24 h after the second injection. Plasma concentrations of ir-15α-P rose from <1 to 36 ng/ml (mean of all treatments) 8 h after injection and declined within 24 h. This is the first time that an RIA has detected such high steroid concentrations in lampreys. This finding is suggestive of a role for 15α-P in control of reproduction in the sea lamprey.

Reference:

M. B. Bryan, A. P. Scott, I. Cerný, B. A. Young and W. Li (2004) 15a-Hydroxyprogesterone in Male Sea Lamprey, Petromyzon marinus L. Steroids 69, 473-481