Knutson, Jean N.

Salt sensitivity is a major cardiovascular focus, but extremes of sodium (Na + ) intake can affect subject dropout rates. We analyzed dietary compliance and baseline cardiovascular indices in an ongoing genotype‐phenotype protocol in healthy young adults. Study visits followed 5 day consumption of 3 daily Na + levels: normal (150) low (10) and high (400 mmol/day). Compliance was determined by 24‐hour Na + excretion. Vital signs were obtained on each visit. Of the first 30 subjects to date, one was unable to tolerate the low Na + diet due to palatability. Mean ± SE urine Na + excretion was 113 ± 27, 25 ± 18 and 328 ±110 mmol for normal, low, and high Na + , respectively. Low Na + caused a significant weight change of −1.6 ± 2.2 kg from screen. High Na + diet decreased resting HR (−2.7 bpm) and increased 24hr urine volume 25% from the normal Na + diet. No correlation was found between urine indices and weight change in the subjects. This dietary sodium crossover study is generally well‐tolerated with high compliance. Low Na + diet appears to cause weight loss; high Na + causes an increase in urine volume and decrease in HR, but no effects on weight or blood pressure. HL 089331

Nitric oxide (NO) contributes to compensatory vasodilation in the contracting human forearm subjected to hypoperfusion during exercise. We tested the potential for adenosine/NO interaction in the compensatory dilation. Eight males (25 ± 2 yrs) performed forearm exercise (20% of max) during intra‐arterial balloon inflation. Each trial included; exercise, exercise with balloon inflation, and exercise after deflation (3 min each). Forearm blood flow (FBF; ultrasound) and brachial artery catheter pressure (BAP) were measured. Exercise was repeated during NO synthase inhibition (L‐NMMA) alone and with the combination of L‐NMMA/aminophylline (adenosine receptor blockade). Forearm vascular conductance (FVC; ml/min/100mmHg) was calculated from BF (ml/min) and BAP (mmHg). The % recovery in FVC during inflation was calculated as (steady state inflation plus exercise value – nadir)/[steady state exercise (control) value‐nadir]. FVC fell acutely with balloon inflation during all trials (P < 0.01). During the control trial, the % recovery in FVC was 111 ± 8%. The % recovery in FVC was attenuated with NOS inhibition alone (80 ± 9%; P < 0.001 vs. control) and attenuated further with combined inhibition of NO/adenosine (63 ± 9%; P < 0.05 vs. L‐NMMA). Thus, adenosine has an NO independent role in the compensatory vasodilatation during exercise with acute hypoperfusion. NIH HL46493 (MJJ), AR55819 (DPC) and RR‐024150.

We tested the hypothesis that dietary Na + intake alters the hemodynamic response to mental stress (MS) in normotensive subjects, which could be mediated by β‐adrenergic receptors (ADRB). As part of an ongoing ADRB2 phenotyping protocol, 12 subjects (age 23±5 year) completed 5 days of low (10 mmol day −1 ), normal (150) and high (400) dietary Na + intake. We measured heart rate (ECG), mean arterial pressure (MAP, Finometer), and calculated stroke volume (SV), cardiac output (CO) and systemic vascular resistance (SVR) responses to arithmetic MS, before and after administration of propranolol. The high Na + diet decreased CO (6.3±0.3 vs. 5.7±0.3 l min −1 , p<0.01) and increased SVR (1187±47 vs. 1311±68 dynes s −1 cm −1 , p<0.01) at rest, but MAP was unchanged (92±2 vs. 93±3 mmHg, p=0.37). During MS, the increase in HR, CO, and MAP was not affected by diet, nor was the decrease in SVR. However, on the high Na + diet β‐blockade increased resting MAP (93±3 vs. 97±2 mmHg, p<0.01), while the absolute MAP response to MS was unchanged, the ΔMAP was blunted (7.3 vs. 4.3 %, p=0.03) and ΔSV was decreased (1.7±3.5 vs. −5.3±2.0 %, p=0.03). In conclusion, reactivity to MS was not influenced by dietary Na + , but systemic β‐blockade after high Na + blunted the SV response during MS. This may be suggestive of augmented ADRB function or blunted non‐ADRB mechanisms of ventricular function during MS after high Na + . Support: R‐01 HL‐089331 and CTSA RR‐024150.

Key pointsCommon single nucleotide polymorphisms in the beta‐2 adrenoceptor (ADRB2) gene influence cardiovascular function, but they exist in combinations (haplotypes), so it is crucial to characterize the haplotypes to improve the functional predictive power of ADRB2 gene variation.Dietary sodium affects ADRB2 function.In a large randomized cross‐over phenotyping trial that administered low, normal and high dietary sodium, we determined the interactions between ADRB2 haplotype, receptor density on lymphocytes, cardiovascular haemodynamics during stress manoeuvres, forearm blood flow vasodilator responsiveness and dietary sodium.Healthy young adults were recruited based on the homozygous haplotypes of the ADRB2 gene: Arg16+Gln27, the rare Gly16+Gln27 and Gly16+Glu27.Independent of dietary sodium, the Gly16+Glu27 haplotype had the greatest ADRB2 density and Arg16+Gln27 had the least, suggesting that ADRB2 haplotype influences ADRB2 protein expression, yet the haemodynamic consequences appear modest in healthy humans, necessitating larger trials that explore variation in multiple candidate genes.AbstractDietary sodium affects function of the beta‐2 adrenoceptor (ADRB2). We tested the hypothesis that haplotype variation in the ADRB2 gene would influence the cardiovascular and regional vasodilator responses to sympathoexcitatory manoeuvres following low, normal and high sodium diets, and ADRB2‐mediated forearm vasodilation in the high sodium condition. Seventy‐one healthy young adults were grouped by double homozygous haplotypes: Arg16+Gln27 (n = 31), the rare Gly16+Gln27 (n = 10) and Gly16+Glu27 (n = 30). Using a randomized cross‐over design, subjects were studied following 5 days of controlled low, normal and high sodium with 1 month or longer between diets (and low hormone phase of the menstrual cycle). All three visits utilized ECG and finger plethysmography for haemodynamic measures, and the high sodium visit included a brachial arterial catheter for forearm vasodilator responses to isoprenaline with plethysmography. Lymphocytes were sampled forex vivoanalysis of ADRB2 density and binding conformation. We found a main effect of haplotype on ADRB2 density (P = 0.03) with the Gly16+Glu27 haplotype having the greatest density (low, normal, high sodium: 12.9 ± 0.9, 13.5 ± 0.9 and 13.6 ± 0.8 fmol mg−1protein, respectively) and Arg16+Gln27 having the least (9.3 ± 0.6, 10.1 ± 0.5 and 10.3 ± 0.6 fmol mg−1protein, respectively), but there were no sodium or haplotype effects on receptor binding conformation. In the mental stress trial, there was a main effect of haplotype on cardiac output (P = 0.04), as Arg16+Gln27 had the lowest responses. Handgrip and forearm vasodilation yielded no haplotype differences, and no correlations were present for ADRB2 density and haemodynamics. Our findings support cell‐based evidence that ADRB2 haplotype influences ADRB2 protein expression independent of dietary sodium, yet the haemodynamic consequences appear modest in healthy humans.