Many authors have studied the hemodynamics of the dental pulp; however, there are scarcely any data regarding the involvement of the L-arginine/nitric oxide pathway in the regulatory mechanism. Thus, we have examined the physiological effects of (1) NG-nitro-L-arginine as an inhibitor of nitric oxide synthesis and (2) the nitric oxide donor 3-morpholinosydnonimine on blood flow and vascular resistance in the canines of anesthetized cats to study the potential involvement of nitric oxide in the regulation of dental vascular homeostasis. Mean arterial blood pressure, heart rate, blood gases, pH, cardiac output, and tissue blood flow were determined prior to and 15 min after i.v. administration of either NG-nitro-L-arginine (30 mg/kg, n = 9) or 3-morpholinosydnonimine (1 mg/kg, n = 7). Blood flow was measured by radioactive-labeled microspheres. There were no significant differences in baseline parameters between the two groups of cats. The dental pulp blood flow decreased to 53 ± 13% (p < 0.01) of the control level after NG-nitro-L-arginine administration, while it decreased only slightly (to 82 ± 12%) after 3-morpholinosydnonimine administration. The dental pulp's vascular resistance increased to 367 ± 69% (p < 0.01) of the control level after NG-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 regulation of pulpal blood circulation. A nitric-oxide-dependent basal vasodilator tone exists in the dental pulp; furthermore, since the dental pulp circulation is sensitive to exogenous nitric oxide, the stimulated release of endogenous nitric oxide may also be involved in the control of the dental pulp vascular tone.
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