Natriuretic peptides stimulate cyclic guanosine monophosphate production in human saphenous vein and internal mammary artery

Direct comparison of relaxation and cGMP production in human coronary by-pass grafts in response to stimulation with natriuretic peptides and a nitric oxide donor

In the present study, we investigated the vasodilator properties of A-type, B-type and C-type natriuretic peptides (ANP, BNP and CNP respectively) and the NO (nitric oxide) donor sin-1 (3-morpholino-sydnonimine) in human by-pass grafts. In contrast with previous studies, the same vessel was used to demonstrate a direct link between cGMP production and functional relaxation. Remnants of the IMA (internal mammary artery) and SV (saphenous vein) were obtained from 82 patients undergoing coronary artery by-pass grafting. The responses to cumulative concentrations of ANP, BNP, CNP and sin-1 in vessel rings pre-contracted with a thromboxane A2 agonist (U46619) were measured in an organ bath. Additionally, intracellular cGMP production after single submaximal dose application of these drugs to vessel rings was determined by a RIA. ANP (P=0.001) and sin-1 (P<0.001) caused significant concentration-dependent relaxation of the IMA. In the SV, only sin-1 (P<0.001) induced marked concentration-dependent relaxation. At a single submaximal concentration, significant relaxation as well as intracellular cGMP production were found in response to ANP, BNP and sin-1 in the IMA. In contrast, in the SV, only sin-1 significantly induced cGMP production and relaxation. There was a moderate, but significant, correlation between intracellular cGMP net production and net relaxation in the IMA. In conclusion, ANP, as the most powerful relaxant of all the natriuretic peptides tested on the IMA, may be a possible alternative vasorelaxant to overcome peri-operative vasospasm in this artery. In contrast with sin-1, ANP and BNP were not effective vasorelaxants of the SV. Net relaxation in response to natriuretic peptides correlated with cGMP net concentrations in the IMA.

Role of natriuretic peptides in regulation of conduit artery distensibility

Arterial distensibility, assessed by the pulse-wave velocity (PWV), is an independent predictor of cardiovascular risk. We investigated whether natriuretic peptides, acting locally, modify conduit artery distensibility in vivo. All studies were conducted in anesthetized sheep ( n = 18) by using a validated ovine hindlimb model. In brief, the PWV was calculated, with the use of the foot-to-foot methodology, from two pressure waveforms recorded simultaneously with a high-fidelity dual pressure-sensing catheter placed in the common iliac artery. Drugs were infused either proximally, via the catheter to perfuse the segment of artery under study, or distally, via the sheath to control for any reflex changes in flow or sympathetic activation. First, the effects of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and c-type natriuretic peptide (CNP) were studied. Second, the role of endogenous ANP was investigated by infusing the natriuretic peptide receptor type A (NPRA)-selective receptor antagonist A71915. Third, A71915 was coinfused with ANP. Fourth, the NPRC-selective agonist cANF was infused. Infusion of CNP or des-[Gln18Ser19Gly20Leu21Gly22]-ANF-(4-23)-NH2 (cANF) had no effect on iliac PWV. However, infusion of ANP, and to a lesser degree BNP, resulted in a reduction in PWV (−9%; P < 0.01 and −6%; P < 0.05, respectively). A71915 increased iliac PWV from 2.97 ± 0.13 to 3.06 ± 0.13 m/s; P < 0.01. Coinfusion of A71915 with ANP completely abolished the effects of ANP ( P < 0.01). Importantly, ANP-BNP infusion via the sheath did not alter PWV. In conclusion, ANP, and to a lesser extent BNP, modify large artery distensibility via the NPRA receptor. Neither CNP nor cANF altered PWV, suggesting that the NPRB and NPRC receptors do not acutely influence distensibility in vivo.