Modulation of the orthostatic blood pressure response by acute nitrate consumption is dependent upon ethnic origin.

Abstract

Orthostatic stress triggers a response to maintain cerebral perfusion and prevent syncope. Given the hypotensive effects of inorganic nitrate this response to orthostasis may be altered by acute supplementation with inorganic nitrate and modified by ethnic origin. Caucasian and SE Asian (n=30 for both), were recruited and subjected to an 'active stand test' and brachial artery blood pressure (BP), digit blood flow and ECG were recorded. Following inorganic nitrate supplementation, (10mg/kg body mass) the tests were repeated. For both Caucasian and SE Asians transition to standing increased diastolic pressure (DP) and heart rate (HR) (P<0.001 for both) and by calculation increased rate-pressure product (P<0.001) and decreased pulse pressure (P<0.01 for both) indicative of decreased ventricular filling. Nitrate supplementation decreased both DP (P<0.001) and HR (P<0.001). Assessment of HR variability suggested sympathetic nerve activity, was higher throughout in Caucasians (P<0.05) coupled with higher parasympathetic tone (P<0.01). Nitrate had no effect on cardiac autonomic nerve activity, as estimated using HR variability, for supine or standing subjects. The tachycardia and hypertension associated with orthostatic stress were preserved in both Caucasian and SE Asian subjects, however, we highlight possible differences in autonomic nervous system activity between Caucasians and SE Asians. SE Asians are resistant to the hypotensive effects of inorganic nitrate supplementation suggesting the absence of a crucial mechanism for activation of the nitrate-nitrite-nitric oxide system.