Acute albumin-induced plasma volume expansion and exercise in the heat: Effects on hormonal responses in men

To assess the responses of fluid regulatory and stress hormones to acute expansion of plasma volume and exercise in the heat, 50 g of albumin dissolved in 200 ml normal saline or 200 ml saline alone was administered intravenously to 7 adult, male test subjects followed by exercise (40% \(\dot V\) O₂ max) in the heat (Tdb=45‡ C, Twb=25‡ C). Blood samples were obtained after sitting in the heat for 1 h, 1 h after completion of infusion which itself required approximately 1.5 h, after standing for 30 min, and 15, 30, 45, and 60 min after commencing exercise. Plasma cortisol levels were generally unaffected by these treatments. Responses of plasma aldosterone levels to postural change and exercise in the heat were attenuated in the albumin trial, and growth hormone levels were unaffected by albumin administration. Angiotensin I levels were significantly decreased at several sampling intervals during the albumin trial, but unaffected by exercise. We concluded from these studies that plasma volume expansion by intravascular albumin administration had no effect on stress hormone responses during exercise in the heat, while regulatory hormone levels were lower in several instances during the albumin trial.