THE COEXISTENCE OF INSULIN-MEDIATED DECREASED MEAN ARTERIAL-PRESSURE AND INCREASED SYMPATHETIC-NERVE ACTIVITY IS NOT MEDIATED BY THE BARORECEPTOR REFLEX AND DIFFERENTIALLY BY HYPOGLYCEMIA

In this study we measured simultaneously and sequentially the lumbar s ympathetic nerve activity (LSNA) or renal sympathetic nerve activity ( RSNA), mean arterial pressure (MAP), and heart rate (HR) in response t o insulin with co-existing hypoglycemia or with glucose replacement in normal rats. Sinoaortic denervation (SAD) was used to evaluate the in fluence of the baroreflex. LSNA, RSNA, MAP and HR were determined usin g an acquisition processor and computer software. Bolus insulin infusi on where the blood glucose was allowed to decrease resulted in an imme diate decrease in MAP. The HR decreased for approximately 15 min and s ubsequently increased. The LSNA increased immediately after insulin in fusion peaking at 25 minutes and then recovered toward baseline. Insul in infusion with glucose replacement resulted in a decrease in MAP and HR. The LSNA progressively increased and was maintained throughout th e experimental period. Insulin infusion with hypoglycemia increased RS NA and when hypoglycemia was prevented the RSNA decreased. SAD attenua ted the decrease in MAP and LSNA response to insulin. Thus, insulin ac ts to decrease MAP while simultaneously increasing HR, LSNA and RSNA w hen hypoglycemia is allowed to occur. However, insulin acts to decreas e HR and RSNA when euglycemia is maintained. The insulin-induced incre ase in LSNA is modulated by the baroreflex mechanism. We conclude that insulin has independent direct and indirect effects on LSNA, RSNA, MA P and HR that are modulated by glycemia and the baroreflex.