The distribution of a novel neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), was studied in the brain of the rat and man and a variety of other rat tissues using Northern blot hybridization and two radioimmunoassays for PACAP 1-38 and PACAP 1-27. The assay, using PACAP 1-38 as standard and an antibody to PACAP 21-38 and radiolabelled tracer, revealed immunoreactive PACAP in all brain regions examined, with the highest concentrations in the rat being in the hypothalamus, nucleus accumbens and substantia nigra (380±34, 310±37 and 346±30 pmol/g wet tissue, means ±S.E.M., n=5 respectively), whilst in man the highest concentrations were found in the pituitary gland (15.8±4.7 pmol/g). Immunoreactive PACAP 1-38 was also detected in the rat gastrointestinal tract, adrenal gland and testis. The assay using PACAP 1-27 as standard and label and an antibody to PACAP 1-27 detected immunoreactive PACAP only in the rat hypothalamus (12.6±1.8 pmol/g wet tissue, n=5). PACAP mRNA of approximately 2.7 kb in size was detectable in all brain regions of both rat and man, and its distribution paralleled that of the immunoreactive peptide. Gel permeation chromatography of different regions of human and rat hypothalamus, and also rat spinal cord and small intestine, showed a broad immunoreactive peak corresponding to PACAP 1-38. Fast protein liquid chromatography (FPLC) resolved this peak into two immunoreactive peaks, the majority eluting in the position of synthetic PACAP 1-38. Presence of immunoreactivity corresponding to PACAP 1-27 was also confirmed in rat hypothalamic extracts using FPLC. The presence of immunoreactive PACAP and its precursor encoding mRNA in various neural and other tissues is in accord with a role for PACAP as a neurotransmitter, neuromodulator or neurohormone.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism