Lack of biologic activity or specific binding of amino-terminal pro-ANP segments in the rat

Abstract

In addition to atrial natriuretic peptide (ANP 99–126) itself, linear peptide fragments from its N-terminal prohormone segment (pro-ANP) have been reported to have biological activity. In vivo, diuresis and natriuresis, as well as hypotension have been observed. In vitro, sodium uptake into medullary collecting duct cells was inhibited, and tone of vascular smooth muscle was reduced, associated with activation of guanylate cyclase. Such previous studies have used heterologous peptides and species, e.g., human pro-ANP 1–30 or pro-ANP 31–67, tested in rat, pig, or dog. The present experiments were designed to test whether rat pro-ANP 1–30 or pro-ANP 31–67 were natriuretic and hypotensive in rats, whether the two peptides showed specific binding to plasma membranes from rat kidney cortex or aorta, and whether they affected particulate guanylate cyclase activity in rat glomerular membranes. To extend in vitro results from the literature, the effect of human pro-ANP 31–67 on transport in the rat medullary collecting duct in vivo was also tested. Although rat ANP 99–126, as expected, increased diuresis and natriuresis, associated with inhibition of transport in the medullary collecting duct, in identically treated rats human pro-ANP 31–67 was without effect. Similarly, only the ANP 99–126 infusion resulted in reduction of arterial blood pressure. Furthermore, no diuretic, natriuretic, or hypotensive responses were observed in rats infused with either rat pro-ANP 31–67 or pro-ANP 1–30. In plasma membranes from rat kidney cortex or aorta, neither of the rat prosegments showed specific binding, or interference with ANP 99–126 receptors. Finally, in contrast to ANP 99–126, neither of the prosegments was able to increase basal guanylate cyclase activity in rat glomerular membranes. Therefore, under our experimental conditions we were unable to replicate the earlier results. This study thus does not support a regulatory role for pro-ANP fragments in blood volume or blood pressure homeostasis.