ANP--a cardiac hormone and a putative central neurotransmitter.

Isolation, purification and determination of the amino acid sequences of biologically active peptides were performed in 1983-84 by several groups. By that time the existence of such a humoral diuretic/natriuretic factor had been proposed for many years. The main, and perhaps the only, circulating form of atrial natriuretic peptide (ANP) is a 28 amino acid peptide structure with a disulphide bridge. This peptide is distributed mainly peripherally in the right and left cardiac atria. Smaller amounts are found in neonatal cardiac ventricles as well as in autonomic ganglia. In the central nervous system, high concentrations are found in hypothalamus, while lower concentrations are found in midbrain and brain stem regions. The amino acid sequence of ANP in the brain may be shorter than the form originating from cardiac atria. A 1 126 amino acid prohormone is present in granulae of atrial myocytes. After atrial distention the circulating 28 amino acid form is cleaved off. The main actions of this hormone include a diuretic/natriuretic effect, relaxation of vascular smooth muscle, and inhibition of basal or stimulated aldosterone secretion from the adrenal cortex. In the central nervous system, ANP has antidipsogenic actions, decreases salt appetite and lowers blood pressure. ANP may be of pathophysiological importance in several cardiovascular disorders such as congestive heart failure, paroxysmal supraventricular tachycardia and possibly also arterial hypertension. ANP seems to be a circulating hormone as well as putative neurotransmitter with important regulatory actions on salt and water homeostasis as well as blood pressure regulation.