Tritiated peptides. 12. Synthesis and biological activity of [4-3H-Phe8]substance P

Strategies for the Identification of Bioactive Neuropeptides in Vertebrates

Neuropeptides exert essential functions in animal physiology by controlling e.g., reproduction, development, growth, energy homeostasis, cardiovascular activity and stress response. Thus, identification of neuropeptides has been a very active field of research over the last decades. This review article presents the various methods used to discover novel bioactive peptides in vertebrates. Initially identified on the basis of their biological activity, some neuropeptides have also been discovered for their ability to bind/activate a specific receptor or based on their biochemical characteristics such as C-terminal amidation which concerns half of the known neuropeptides. More recently, sequencing of the genome of many representative species has facilitated peptidomic approaches using mass spectrometry and in silico screening of genomic libraries. Through these different approaches, more than a hundred of bioactive neuropeptides have already been identified in vertebrates. Nevertheless, researchers continue to find new neuropeptides or to identify novel functions of neuropeptides that had not been detected previously, as it was recently the case for nociceptin.

Chemical degradation of 3H-labeled substance P in tris buffer solution

Substance P (SP) is an important neuropeptide that has been implicated in several physiological processes, and it is necessary to devise an analytical procedure to measure endogenous SP with a combination of high sensitivity and maximum molecular specificity. However, the unique chemical nature of SP (polarity, chemical stability, ease of oxidation, peptide bond lability) plays a significant role in its analysis, such as in receptor assays, immunoassays, chromatography, and mass spectrometry. In this study, we evaluated in polypropylene and glass assay tubes the effects on the recovery and stability of tritiated SP ([3H]SP) of several pertinent experimental parameters such as buffer, pH, multiple freeze-thaw cycles, and incubation temperature and time. Bovine serum albumin (BSA) effectively reduced the absorption of [3H]SP to polypropylene and glass tube surfaces. Following multiple (6X) freeze-thaw cycles of solutions in BSA-precoated tubes, the recovery of radioactive [3H]SP remained high (greater than 75%) after the last cycle, whereas recovery was minimal in uncoated or siliconized glass tubes. A high level of radioactivity recovery was maintained for 14 days of storage of [3H]SP in triethylamine formate (TEAF) solution in BSA-precoated tubes at 4 and -20 degrees C, but decreased at 37 degrees C to less than 80% in only 3 h. Following storage in Tris-HCl (pH 7.4) buffer, a combination of HPLC and mass spectrometric analyses revealed that a significant amount of peptide bond cleavage occurred to produce the two peptides ArgProLys (RPK) and ArgProLysProGlnGln (RPKPQQ), with only a small amount of remaining intact SP. That decomposition was not observed in triethylamine formate TEAF (pH 3.14) buffer solutions.

3H-substance P binding to guinea-pig ileum longitudinal smooth muscle membranes

Specific binding of 3H-substance P was studied in guinea-pig ileum longitudinal smooth muscle membranes. A single population of non-interacting sites with an apparent dissociation constant of 1.8 nM was observed. The relative potencies of some structural analogues of substance P, notably eledoisin and substance P (5-11), in competing for 3H-substance P binding sites, however, had little resemblance to their potencies in contracting the intact muscle or in eliciting the breakdown of inositol phospholipids in this tissue. The results are discussed in the light of other binding studies for substance P.

Rapid degradation of [3H]-substance p in guinea-pig ileum and rat vas deferens in vitro

The degradation of [3H]-substance P was monitored in guinea-pig ileum and rat vas deferens. Substantial and rapid metabolism occurred in both tissues within the time course of the pharmacological responses; for example, after 1 min more than 50% of the extracted tritium from both tissues was present in the form of metabolites. [3H]-inulin was used to estimate the rate of equilibration of the extracellular space of guinea-pig ileum longitudinal muscle and rat vas deferens with the bath fluid; half-lives of 30 s and 5 min respectively were observed. These two factors combine to give different concentrations of substance P in the biophase of the tissues. The peak concentration of substance P reached in the guinea-pig ileum longitudinal muscle was approximately five times higher than in the rat vas deferens. An analogue of substance P, [3H]-DiMe-C7, was found to be stable in both tissues. These results are discussed in the light of the suggested existence of multiple receptors for substance P, based on agonist potency differences.

Substance P analog, DiMe-C7: evidence for stability in rat brain and prolonged central actions

A metabolically protected analog of substance P, [pGlu5-MePhe8-MeGly9]SP(5-11) (DiMe-C7), was approximately equipotent with substance P in causing increased locomotor activity after microinfusion into the ventral tegmental area of rat brain, but the effects of DiMe-C7 on behavior were considerably prolonged. There was little metabolic degradation of tritiated DiMe-C7 for up to 1 hour after infusion, whereas tritiated substance P was completely degraded within 10 minutes.