Primary Aging: Thermoregulatory Sweating & Skin Blood Flow

Heat related morbidities and mortalities are disproportionately high in the aged population(=60 yr). Aging without overt illness is associated with the attenuation of heat dissipationmechanisms including cutaneous vasodilation and eccrine sweating responses. These agerelateddecrements in thermoregulatory function are well represented in literature discussingheat dissipation, yet despite attempts to investigate a potential signaling mechanismbetween sweating and skin blood flow (SkBF), a functional link has not beendemonstrated. Recent evidence supports a role of nitric oxide (NO), a potent signalingmolecule in cutaneous vasodilation, as additionally signaling the eccrine sweatingresponse. The aim of this study was to investigate the putative role of NO in eccrine sweatgland signaling in young and primary aged individuals. Prior to experimentation, pilotstudies were conducted to develop experimental drug dilutions to achieve a successful flowmatching protocol. In two subjects, three intradermal microdialysis (MD) probes wereinserted into the left ventral forearm and perfused with 1) Lactated Ringer’s solution, 2)Epoprostenol sodium (EPO) + NG-Nitro-L-arginine (L-NNA), and 3) Sodium Nitroprusside(SNP) + L-NNA. Regional sweating rates (RSR) over each MD membrane were measuredusing ventilated capsules with a laser Doppler probe housed in each capsule formeasurement of red cell flux (laser Doppler flux, LDF) and divided by mean arterial bloodpressure (Cutaneous vascular conductance (CVC) = LDF/MAP) as an index ofSkBF. Subjects completed a whole body heating protocol to a 1°C rise in sublingualtemperature. Maximal CVC values were obtained pharmacologically at the end of eachprotocols using 25 mM SNP. During whole body heating in the second pilot, the L-NNA/EPOsite displayed lower levels of CVC than the control site, implying the EPO had becomeinactive. A buffer solution was created to maintain EPO stability at physiological pH. Thenext steps are to complete pilot tests with EPO in buffer to ensure it remains active and toachieve a successful flow matching protocol before beginning the sweating study.