Investigation of the Superlattice Phases Formed in Ta72Ru28.

The Ta-Ru binary phase diagram has not been fully investigated, but shows potential for a two-phase region of A2 + B2. Given the high melting points of both Ta and Ru, such an alloy would have the potential for high temperature strength. A Ta72Ru28 alloy was arc melted and investigated in the as-cast and aged (at 1000 °C) states. The as cast alloy was composed of A2 and B2, albeit not in a superalloy-like morphology. A third phase was found in the aged alloy, which has not been reported before, and which is also a coherent superlattice phase of the Ta BCC matrix. The structure of this phase was found to be consistent with the tetragonal Cr2Al prototype structure, with lattice parameters of (a, a, 3a), where a is the Ta BCC lattice parameter.

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.

Comparison of synthesis of 15 alpha-hydroxylated steroids in males of four North American lamprey species.

Recent studies have provided evidence that 15 alpha-hydroxytestosterone (15 alpha-T) and 15 alpha-hydroxyprogesterone (15 alpha-P) are produced in vitro and in vivo in adult male sea lampreys (Petromyzon marinus), and that circulatory levels increase in response to injections with gonadotropin-releasing hormone (GnRH). We examined four species from the Petromyzontidae family including silver lampreys (Ichthyomyzon unicuspis), chestnut lampreys (I. castaneus), American brook lampreys (Lethenteron appendix), and Pacific lampreys (Entosphenus tridentatus) to determine if these unusual steroids were unique to sea lampreys or a common feature in lamprey species. In vitro production was examined through incubations of testis with tritiated precursors, and 15 alpha-T and 15 alpha-P production was confirmed in all species through co-elution with standards on both high performance liquid chromatography (HPLC) and thin layer chromatography. In vivo production was proven by demonstrating that HPLC-fractionated plasma had peaks of immunoreactive 15 alpha-T and 15 alpha-P that co-eluted with standards through using previously developed radioimmunoassays for 15 alpha-T and 15 alpha-P. The possible functionality of 15 alpha-T and 15 alpha-P was further examined in silver and Pacific lampreys by investigating the effect of injection of either type of lamprey GnRH on plasma concentrations of 15 alpha-T and 15 alpha-P. Injections with exogenous GnRH did not affect circulatory levels of either steroid in silver lampreys, and only GnRH III elicited higher levels of both steroids in Pacific lampreys. The 15 alpha-hydroxylase enzyme(s) for steroids appeared to present in adult males of all species examined, but the question of whether 15 alpha-hydroxylated steroids are functional in these lamprey species, and the significance of the 15-hydroxyl group, requires further research.

15Alpha-hydroxyprogesterone in male sea lampreys, Petromyzon marinus L.

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 15alpha-hydroxyprogesterone (15alpha-P) in vitro when incubated with tritiated progesterone, that 15alpha-P is present in the plasma of sea lampreys, and that plasma concentrations of immunoreactive (ir) 15alpha-P rise dramatically in response to injections of gonadotropin-releasing hormone (GnRH). The identity of the tritiated 15alpha-P produced in vitro was confirmed by co-elution with standard 15alpha-P on high performance liquid chromatography, co-elution with standard and acetylated 15alpha-P on thin layer chromatography, and specific binding to antibodies raised against standard 15alpha-P. The in vitro conversion was used to produce tritiated 15alpha-P label for a radioimmunoassay (RIA), which is able to detect 15alpha-P in amounts as low as 2 pg per tube. The RIA has been used to measure the plasma concentrations of 15alpha-P in males given two serial injections, 24 h apart, of either lamprey GnRH I or GnRH III (50, 100, or 200 microg/kg) or saline control, with plasma being sampled 8 and 24 h after the second injection. Plasma concentrations of ir-15alpha-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 15alpha-P in control of reproduction in the sea lamprey.

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.