INCREASED SKIN BLOOD-FLOW AND ENHANCED SENSIBLE HEAT-LOSS IN HUMANS AFTER NICOTINIC-ACID INGESTION

1. A series of studies was conducted to characterize thermal and cardi ovascular responses to nicotinic acid (NA) ingestion (5 mg . kg(-1)) i n healthy subjects: (a) at rest, seated (T-a = 30 degrees C, RH = 23%) at 0800 h and again between 1800 and 2100 h; (b) at rest and during s eated exercise (T-a = 29 degrees C, RH = 30%); and (c) during upright exercise when wearing a protective clothing system (T-a = 28 degrees C , RH = 30%). 2. (a) NA ingestion decreased esophageal (T-es) and arter ial pressure and increased mean skin temperature ((T) over bar(sk)), s kin blood flow (SkBF), forearm blood flow (FBF), heart rate, and cutan eous vascular conductance (P < 0.05) in the morning and evening. In th e evening 2/4 subjects experienced substantial hypotension. (b) At res t, peak SkBF and peak FBF were 600% higher in NA than control while T- es was 0.6 degrees C lower and (T) over bar(sk), was 0.6 degrees C hig her after NA (P < 0.05). During seated exercise, SkBF and FBF were 30% higher and T-es was 0.3 degrees C lower after NA than control (P < 0. 05). (c) During upright exercise, NA increased SkBF in subjects clothe d in protective clothing. 3. Vascular responsiveness to NA was enhance d in the evening as shown by the increased hypotensive effect of NA in the evening. NA ingestion effectively increased sensible heat flux du ring rest, seated exercise and upright exercise. However, manipulation of SkBF by NA ingestion should be done cautiously, especially when NA will be used in novel circumstances.