DISTRIBUTION AND CONCENTRATION OF UROCORTIN, AND EFFECT OF ADRENALECTOMY ON ITS CONTENT IN RAT HYPOTHALAMUS

We developed a specific and sensitive radioimmunoassay (RIA) for rat u rocortin (rUcn) and investigated the tissue distribution and concentra tion of immunoreactive (IR-)Ucn in rats. Antiserum was obtained by imm unizing rabbits with synthetic rUcn21-35 coupled with bovine thyroglob ulin. I-125-[Tyr]18-rUcn19-37 was used as the tracer. The RIA detected synthetic rUcn1-40 as low as 0.4 fmol/tube, and did not cross-react w ith other corticotropin-releasing factor-related peptides. IR-Ucn was widely distributed in central nervous system, endocrine organs, and di gestive system. Its concentration was highest in pituitary (11.0 +/- 1 .36 pmol/g.w.w., mean +/- SEM, n=4). Reverse-phase HPLC revealed that hypothalamic IR-Ucn had similar chromatographic mobility to synthetic rUcn1-40. However, bilateral adrenalectomy did not influence the hypot halamic IR-Ucn content. Our results suggest that Ucn may play importan t roles in various tissues in normal rats, but not behave as a hypotha lamic hypophysiotropic factor in mediating adrenocorticotropin secreti on in adrenalectomized rats.