Muscle metaboreflex control of vasopressin and renin release

Dynamic exercise causes an increase in circulating blood levels of renin and vasopressin (AVP), yet the afferent mechanisms responsible for release of renin and AVP during exercise are poorly understood. Partial ischemia of active skeletal muscle induces a reflex pressor response, termed the muscle metaboreflex. Does muscle metaboreflex activation induce release of renin and AVP? The muscle metaboreflex was activated in conscious, chronically instrumented dogs during mild treadmill exercise (3.2 km/h, 0% grade) via graded partial occlusion of terminal aortic blood flow. Decreasing hindlimb perfusion to 40% of the control level during exercise significantly increased systemic arterial pressure (SAP) and heart rate (HR) from 103.4 +/- 2.4 to 166.7 +/- 4.2 mmHg and from 111.6 +/- 9.9 to 141.9 +/- 3.9 beats/min, respectively. However, only small nonsignificant changes in arterial plasma renin activity and AVP concentration occurred [control: renin = 0.46 +/- 0.8 ng angiotensin I (ANG I).ml-1.h-1, AVP = 0.53 +/- 0.17 pg/ml; metaboreflex activation: renin = 0.77 +/- 0.33 ng ANG I.ml-1.h-1, AVP = 1.09 +/- 0.34 pg/ml]. The experiments were repeated after ganglionic blockade (hexamethonium 10 mg/ml and atropine 0.2 mg/ml iv) to attenuate the reflex increase in SAP. In this setting, metaboreflex activation caused SAP to increase from 91.6 +/- 4.3 to only 114.7 +/- 6.8 mmHg and the reflex tachycardia was abolished (153.7 +/- 5.8 to 159.3 +/- 6.1 beats/min, P > 0.05). With the reflex pressor response markedly attenuated, AVP increased from 2.53 +/- 0.81 to 34.38 +/- 6.59 pg/ml with muscle metaboreflex activation, whereas no significant changes in renin activity occurred.(ABSTRACT TRUNCATED AT 250 WORDS)