EVIDENCE FOR THE ROLE OF NITRIC-OXIDE IN THE CIRCULATION OF THE DENTAL-PULP

Many authors have studied the hemodynamics of the dental pulp; however , there are scarcely any data regarding the involvement of the L-argin ine/nitric oxide pathway in the regulatory mechanism. Thus, we have ex amined the physiological effects of (1) N-G-nitro-L-arginine as an inh ibitor of nitric oxide synthesis and (2) the nitric oxide donor 3-morp holinosydnonimine on blood flow and vascular resistance in the canines of anesthetized cats to study the potential involvement of nitric oxi de in the regulation of dental vascular homeostasis. Mean arterial blo od pressure, heart rate, blood gases, pH, cardiac output, and tissue b lood flow were determined prior to and 15 min after i.v. administratio n of either N-G-nitro-L-arginine (30 mg/kg, n = 9) or 3-morpholinosydn onimine (1 mg/kg, n = 7). Blood flow was measured by radioactive-label ed microspheres. There were no significant differences in baseline par ameters between the two groups of cats. The dental pulp blood flow dec reased to 53 +/- 13% (p < 0.01) of the control level after N-G-nitro-L -arginine administration, while it decreased only slightly (to 82 +/- 12%) after 3-morpholinosydnonimine administration. The dental pulp's v ascular resistance increased to 367 +/- 69% (p < 0.01) of the control level after N-G-nitro-L-arginine, while it decreased to 73 +/- 10% (p < 0.05) of control after 3-morpholinosydnonimine. We found that the L- arginine/nitric oxide pathway plays an important role in the regulatio n of pulpal blood circulation. A nitric-oxide-dependent basal vasodila tor tone exists in the dental pulp; furthermore, since the dental pulp circulation is sensitive to exogenous nitric oxide, the stimulated re lease of endogenous nitric oxide may also be involved in the control o f the dental pulp vascular tone.