The role of vasopressin and angiotensin II in the hemodynamic response to dynamic exercise

Regulation of Coronary Blood Flow

The heart is uniquely responsible for providing its own blood supply through the coronary circulation. Regulation of coronary blood flow is quite complex and, after over 100 years of dedicated research, is understood to be dictated through multiple mechanisms that include extravascular compressive forces (tissue pressure), coronary perfusion pressure, myogenic, local metabolic, endothelial as well as neural and hormonal influences. While each of these determinants can have profound influence over myocardial perfusion, largely through effects on end-effector ion channels, these mechanisms collectively modulate coronary vascular resistance and act to ensure that the myocardial requirements for oxygen and substrates are adequately provided by the coronary circulation. The purpose of this series of Comprehensive Physiology is to highlight current knowledge regarding the physiologic regulation of coronary blood flow, with emphasis on functional anatomy and the interplay between the physical and biological determinants of myocardial oxygen delivery. © 2017 American Physiological Society. Compr Physiol 7:321-382, 2017.

Prior exercise alters responses to hemorrhage

Traumatic injuries often occur to individuals while exercising. The author sought to determine whether exercise before injury resulting in hemorrhage would alter cardiovascular, metabolic, and neuroendocrine responses. Fifteen chronically instrumented splenectomized immature female swine were trained to run on a treadmill at 70% of maximum heart rate for 60 min. In six swine, responses to exercise were evaluated and found to return to baseline after 60 min of recovery. Swine were then randomly assigned to exercise (n = 7) or rest (n = 8) followed by hemorrhage of 25 mL/kg for 60 min then observed for an additional 60 min. The decrease in mean arterial pressure (MAP) was less after exercise, 26 +/- 9 mmHg compared with 49 +/- 2 mmHg with rest, with the difference sustained during the posthemorrhage period. Cardiac output decreased similarly in both groups. Posthemorrhage lactate and glucose concentrations were lower in exercise. The increase in plasma epinephrine was reduced in exercise, with significantly lower levels in epinephrine and norepinephrine noted posthemorrhage. Vasopressin levels and plasma renin activity were not different. In response to hemorrhage after exercise, blood pressure is better maintained although catecholamine levels were reduced, suggesting increased adrenoreceptor sensitivity. In addition, indices of increased glucose utilization and correction of lactate acidosis support a metabolic shift after exercise. Prior exercise alters responses to hemorrhage that mask the extent of hypovolemia and should be considered in the initial evaluation of a patient with hemorrhage caused by traumatic injuries.

Central blockade of vasopressin V(1) receptors attenuates postexercise hypotension

We tested the hypothesis that central arginine vasopressin (AVP) mediates postexercise reductions in arterial pressure (AP) and heart rate (HR). To test this hypothesis, nine spontaneously hypertensive rats (SHR) were instrumented with a 22-gauge stainless steel guide cannula in the right lateral cerebral ventricle and with a carotid arterial catheter. After the rats recovered, AP and HR were assessed before and after a single bout of dynamic exercise with the central administration of vehicle or the selective AVP V(1)-receptor antagonist d(CH(3))(5) Tyr(Me)-AVP (AVP-X). AP and HR were significantly decreased below preexercise values with central administration of vehicle [P < 0.05, change (Delta)-21 +/- 4 mmHg and Delta-20 +/- 6 beats/min, respectively]. In sharp contrast, after exercise with central administration of AVP-X, both AP (Delta+8 +/- 5 mmHg) and HR (Delta+24 +/- 9 beats/min) were not significantly different from preexercise values (P > 0.05). Furthermore, AVP-X at rest did not significantly alter AP (181 +/- 11 vs. 178 +/- 11 mmHg, P > 0.05) or HR (328 +/- 24 vs. 331 +/- 22 beats/min, P > 0.05). Thus central blockade of AVP V(1) receptors prevented postexercise reductions in AP and HR. These data suggest that AVP, acting within the central nervous system, mediates postexercise reductions in AP and HR in the SHR.