Circulatory control in humans

The primary focus in my laboratory is studying how the peripheral circulation and autonomic reflexes adapt to physical stresses such as standing, exercise or body heating. We also study the influence of gender and age on these factors.

For the past several years we have attempted to determine the role that nitric oxide (NO) plays in neurally-mediated and locallymediated peripheral vasodilation in humans.

In many of these studies we instrument humans to measure blood flow in both forearms. We cannulate one brachial artery for the selective infusion of study drugs. As the subjects undergo a variety of physical or mental stresses, we measure the blood flow responses. Subsequently, we infuse agonist and antagonist drugs into the brachial artery catheter and compare the responses to a second bout of the stressor. Using this basic approach we have infused the NO synthase inhibitor L-NMMA into one brachial artery and demonstrated that NO contributes to the marked forearm skeletal muscle vasodilation seen during mental stress in humans.

Current studies attempt to determine whether the source of this NO release is from autonomic (nitroxidergic) nerves or from the vascular endothelium. We have also evaluated the contribution of NO to neurally-mediated cutaneous vasodilation during body heating and the proposed neurally-mediated skeletal muscle vasodilation seen during syncope in humans. In addition, we studied the role of NO in the hyperemic responses to muscle contraction and during postischemic (reactive) hyperemia.

Future studies will continue to focus on these areas. We hope to expand our use of NO synthase inhibitors to include L-NAME and other novel compounds. We intend to augment our pharmacology and physiology studies with histochemical/anatomical studies which use sophisticated biological staining techniques to identify the classes of nerves (adrenergic, cholinergic, nitroxidergic) that innervate blood vessels in the cutaneous and skeletal muscle circulations. Our laboratory's work on these issues is funded by the NIH.