ANP(5–28) is the major molecular species in hypophysial portal blood of the rat

We have previously demonstrated that the concentrations of immunoreactive atrial natriuretic peptide (IR-ANP) are significantly higher in hypophysial portal compared with peripheral blood of the rat, and that ANP suppresses the pituitary release of ACTH and β-endorphin in vitro and in vivo. Using HPLC, we have now shown that the predominant species of IR-ANP in extracts of portal blood from adult male and female rats is ANP(5–28), whereas in peripheral blood, ANP(1–28) predominates. The ratio of ANP(5–28) in portal compared with peripheral blood was 4.2 in male and 4.8 in female animals.