Haemodynamic, hormonal and renal actions of osteocrin in normal sheep.

Osteocrin (OSTN) is an endogenous protein sharing structural similarities with the natriuretic peptides [NPs; atrial (ANP), B‐type (BNP) and C‐type (CNP) NP], which are hormones known for their crucial role in maintaining pressure/volume homeostasis. Osteocrin competes with the NPs for binding to the receptor involved in their clearance (NPR‐C). In the present study, having identified, for the first time, the major circulating form of OSTN in human and ovine plasma, we examined the integrated haemodynamic, endocrine and renal effects of vehicle‐controlled incremental infusions of ovine proOSTN (83–133) and its metabolism in eight conscious normal sheep. Incremental i.v. doses of OSTN produced stepwise increases in circulating concentrations of the peptide, and its metabolic clearance rate was inversely proportional to the dose. Osteocrin increased plasma levels of ANP, BNP and CNP in a dose‐dependent manner, together with concentrations of their intracellular second messenger, cGMP. Increases in plasma cGMP were associated with progressive reductions in arterial pressure and central venous pressure. Plasma cAMP, renin and aldosterone were unchanged. Despite significant increases in urinary cGMP levels, OSTN administration was not associated with natriuresis or diuresis in normal sheep. These results support OSTN as an endogenous ligand for NPR‐C in regulating plasma concentrations of NPs and associated cGMP‐mediated bioactivity. Collectively, our findings support a role for OSTN in maintaining cardiovascular homeostasis. What is the central question of this study?What role does osteocrin (OSTN) have in integrated cardiovascular, renal and neurohumoral function in normal health?What is the main finding and its importance?Osteocrin is structurally similar to natriuretic peptides (NPs) that play a crucial role in cardiovascular homeostasis and binds to the NP receptor‐C (NPR‐C). Stepped doses of OSTN raised plasma atrial NP, B‐type NP, C‐type NP and cGMP and reduced arterial and venous pressures. Collectively, these findings provide strong evidence that increased NP levels result from competitive displacement from NPR‐C, not from increased NP secretion, suggesting that OSTN might play a role in maintaining cardiovascular homeostasis. [ABSTRACT FROM AUTHOR]