CONTRIBUTION OF PH, DIPROTONATED PHOSPHATE AND POTASSIUM FOR THE REFLEX INCREASE IN BLOOD-PRESSURE DURING HANDGRIP

The relative importance of pH, diprotonated phosphate (H2PO4-) and pot assium (K+) for the reflex increase in mean arterial pressure (MAP) du ring exercise was evaluated in seven subjects during rhythmic handgrip at 15 and 30% maximal voluntary contraction (MVC), followed by post-e xercise muscle ischaemia (PEMI). During 15% MVC. MAP rose from 92 +/- 1 to 103 +/- 2 mmHg. [K+] from 4.1 +/- 0.1 to 5.1 +/- 0.1 mmol L-1, wh ile the intracellular (7.00 +/- 0.01 to 6.80 +/- 0.06) and venous pH f ell (7.39 +/- 0.01 to 7.30 +/- 0.01) (P < 0.05). The intracellular [H2 PO4-] increased 8.4 +/- 2 mmol kg(-1) and the venous [H2PO4-] from 0.1 4 +/- 0.01 to 0.16 +/- 0.01 mmol L-1 (P < 0.05). During PEMI, MAP rema ined elevated along with the intracellular [H2PO4-] as well as a low i ntracellular and venous pH. However, venous [K+] and [H2PO4-] returned to the level at rest. During 30% MVC handgrip. MAP rose to 130 +/- 3 mmHg. [K+] to 5.8 +/- 0.2 mmol L-1, the intracellular and extracellula r [H2PO4-] by 20 +/- 5 mmol kg(-1) and to 0.20 +/- 0.02 mmol L-1, resp ectively, while the intracellular (6.33 +/- 0.06) and venous pH fell ( 7.23 +/- 0.02) (P < 0.05). During post-exercise muscle ischaemia all v ariables remained close to the exercise levels. Analysis of each varia ble as a predictor of blood pressure indicated that only the intracell ular pH and diprotonated phosphate were linked to the reflex elevation of blood pressure during handgrip.