Immunochemical characterization of neurotensin-like peptides in chicken

Using radioimmunoassay and 3 region specific antisera toward bovine neurotensin (NT), the NT-like peptides in chicken have been shown to differ from NT but to strongly resemble its COOH-terminal region. Three substances were identified, one of which resembled NT biologically and appeared to share 7 or 8 of its COOH-terminal residues. The two other peptides were smaller than NT but seemed to possess 4–6 residue homologies with it. Tissue distribution studies indicated that the chicken pancreas and thymus had unusually high levels of this material (>200 fold that in rat) and that the 3 substances were distributed differently in tissues. Chromatographic studies showed that the peptides obtained from brain, intestine, thymus, and pancreas were similar. These results, demonstrating evolutionary conservation of the COOH-terminal region of NT, are in keeping with the known importance of this region for biological activity. These findings also suggest the existence of an NT-family of peptides serving multiple biological roles.     

Circadian rhythm of corticotropin releasing factor-like immunoreactivity in rat hypothalamus

Levels of hypothalamic corticotropin releasing factor-like immunoreactivity (CRF-LI) were measured by radioimmunuoassay (RIA) over a 24 hour light-dark cycle and found to exhibit two peaks. One peak was detected at 1100 hr and a secondary smaller peak was found at 2000 hr. The trough between the two peaks was detected at 1700 hr which coincided with the peak in plasma corticosterone levels. The results are consistent with a decreased level of hypothalamic CRF-LI at 1700 hr reflecting an increased release of peptide followed successively by the release of ACTH and corticosterone.     

Purification of [125I]-vasoactive intestinal peptide by reverse-phase HPLC

VIP was labeled with sodium ¹²⁵iodide, and ¹²⁵I-VIP was purified by reverse-phase high performance liquid chromatography. Optimal separations of ¹²⁵I-VIP and unlabeled VIP were obtained using two C₁₈-Novapak columns in series and a gradient of acetonitrile in triethylamine phosphate for elution. The specific activity of the ¹²⁵I-VIP was 1.99±0.21 Ci/μmole, approaching the maximum specific activity of monoiodinated VIP (2.26 Ci/μmole). Radioimmunoassay and radioreceptorassay for VIP were more sensitive (2.6-fold, and 2.5-fold, respectively) using ¹²⁵I-VIP purified by HPLC compared to ¹²⁵I-VIP obtained from an open-end cellulose column. These results demonstrate the advantage of preparing purified ¹²⁵I-VIP by HPLC for the accurate assay of VIP and VIP-receptors in tissues and biological fluids.     

Intracellular acetylation of desacetyl alpha MSH in the Xenopus laevis neurointermediate lobe

High performance liquid chromatography (HPLC) followed by radioimmunoassay (RIA) of the chromatographic fractions were used to separate and quantify, respectively, the alpha MSH-like peptides stored in the neurointermediate lobe (NIL) of the Xenopus laevis (X. laevis) pituitary gland and released from the X. laevis NIL, in vitro. Immunoreactive (IR) material eluting with a similar HPLC retention time as desacetyl alpha MSH was the major IR peptide in the NIL. Material with a retention time similar to alpha MSH and immunological properties equivalent to alpha MSH was also present in the NIL. However, the retention times of the X. laevis and mammalian alpha MSH-like peptides were not identical, suggesting species difference in these peptides. Following incubation of NILs in the presence of [3H]-acetyl CoA, the X. laevis variant of alpha MSH was the major [3H]-labeled, immunoprecipitable material present. Following an incubation of NILs in the presence of [3H]-amino acids for 21 hours, immunoprecipitable [3H]-alpha MSH was detected in the NILs and the ratio of [3H]-desacetyl alpha MSH to [3H]-alpha MSH was similar to the ratio of IR-desacetyl alpha MSH to IR-alpha MSH. The X. laevis variant of alpha MSH was the major alpha MSH-like peptide released from the NILs into the incubation medium. Dopamine (50 microM) significantly inhibited the release of IR-alpha MSH but not IR-desacetyl alpha MSH. No net increase in total alpha MSH (sum of release and NIL content) was observed in the actively secreting (control) NIL group versus the dopamine-treated group. These results indicate that acetylation of desacetyl alpha MSH occurs intracellularly.