Increased nitric oxide release and expression of endothelial and inducible nitric oxide synthases in mildly changed porcine mitral valve leaflets.

BACKGROUND AND AIM OF THE STUDY: Little is known of the local role of nitric oxide (NO) in heart valves in relation to heart valve diseases. The study aim was to examine NO release and the expression of both endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) in relation to early local changes in porcine mitral valves. METHODS: A histological evaluation of mitral valve leaflets from slaughter pigs and sows was made, and the expression of eNOS and iNOS protein measured using immunohistochemistry. Furthermore, mRNA levels of eNOS and iNOS were measured using real-time RT-PCR. A calibrated NO-specific electrode was used to measure local NO release in specific regions of the anterior mitral leaflet from slaughter pigs and sows interchordally at the tip of the leaflet (region A), at the chordal insertion (region B), and at the center of the leaflet (region C). RESULTS: Leaflets from sows had an increased accumulation of mucopolysaccharides (MPS) compared to those from slaughter pigs. Furthermore, mRNA levels of eNOS and iNOS were significantly increased in region C due to very high levels of expression in some sow leaflets. NO release in the sow mitral valve leaflet was increased in regions B and C compared to that in region A. CONCLUSION: The relative distribution of NO release is increased in regions of porcine mitral valve leaflets with deposition of MPS and defraction of the valve structure, which may reflect changes in both eNOS and iNOS expression.

Dogs with heart diseases causing turbulent high-velocity blood flow have changes in platelet function and von Willebrand factor multimer distribution.

The purpose of this prospective study was to investigate platelet function using in vitro tests based on both high and low shear rates and von Willebrand factor (vWf) multimeric composition in dogs with cardiac disease and turbulent high-velocity blood flow. Client-owned asymptomatic, untreated dogs were divided into 4 groups: 14 Cavalier King Charles Spaniels (Cavaliers) with mitral valve prolapse (MVP) and no or minimal mitral regurgitation (MR), 17 Cavaliers with MVP and moderate to severe MR, 14 control dogs, and 10 dogs with subaortic stenosis (SAS). Clinical examinations and echocardiography were performed in all dogs. PFA100 closure times (the ability of platelets to occlude a hole in a membrane at high shear rates), platelet activation markers (plasma thromboxane B2 concentration, platelet surface P-selectin expression), platelet aggregation (in whole blood and platelet-rich plasma with 3 different agonists), and vWf multimers were analyzed. Cavaliers with moderate to severe MR and dogs with SAS had longer closure times and a lower percentage of the largest vWf multimers than did controls. Maximal aggregation responses were unchanged in dogs with SAS but enhanced in Cavaliers with MVP (regardless of MR status) compared with control dogs. No significant difference in platelet activation markers was found among groups. The data suggest that a form of platelet dysfunction detected at high shear rates was present in dogs with MR and SAS, possibly associated with a qualitative vWf defect. Aggregation results suggest increased platelet reactivity in Cavaliers, but the platelets did not appear to circulate in a preactivated state in either disease.