The ovine hypothalamus and pituitary have markedly different distribution of C-type natriuretic peptide forms

C-type natriuretic peptide (CNP) was measured in the hypothalamus and pituitary of four sheep by radioimmunoassay after extraction. The mean concentration of CNP in the hypothalamus was 1.01 +/- 0.08 pmol/g and 45.8 +/- 12.8 pmol/g in the pituitary. Analysis of these extracts by size exclusion HPLC showed the presence of two immunoreactive CNP components that cochromatographed with porcine CNP-53 and CNP-22 standards. Similar amounts of CNP-53- and CNP-22-like IR-CNP were present in the ovine hypothalamus (ratio 0.9:1), whereas in the pituitary, the bulk of the immunoreactive CNP was in the CNP-53-like form. These results show major differences in the distribution of IR-CNP forms between the hypothalamus and pituitary, which may reflect differences in CNP prohormone processing in these two tissues.