Seadragon VI: a 7-day dry saturation dive at 31 ATA. III. Alterations in basal and circadian endocrinology.

Four male divers were exposed to an environment of 1 ATA air for 7 d, followed by 7 d of 31 ATA He-O2, and following decompression to a postdive 1 ATA air environment for 3 d. Urine and blood were collected for hormonal measurements. Divided 24-h urine collections were obtained during 3 consecutive d at predive 1 ATA conditions, and at 31 ATA conditions. Two consecutive day collections were obtained at early decompression (31-25 ATA), at late decompression (14-8 ATA), and at postdive 1 ATA. Two blood samples were obtained, at predive 1 ATA, at 31 ATA, and at postdive 1 ATA. Plasma antidiuretic hormone (ADH) concentration decreased about 45% (P less than 0.005), while plasma aldosterone concentration and urinary aldosterone excretion were doubled (P less than 0.005) after the subjects were at 31 ATA. Plasma cortisol concentration and plasma parathyroid hormone concentration were not significantly affected by hyperbaria. Urinary excretion of aldosterone was not significantly different between day (0700-1900) and night (1900-0700) at any time, and both day and night excretion rates were increased at 31 ATA through late decompression (P less than 0.005). Urinary ADH excretion was greater during daytime at predive 1 ATA (P less than 0.005), but not thereafter. Both daytime and nighttime ADH excretion rates were decreased from 31 ATA through late decompression (P less than 0.005). It is concluded that hyperbaria eliminates the circadian release pattern of ADH and that the overall reduction of ADH may contribute to the increased free water clearance observed at hyperbaria. Also, increased parathyroid hormone was not associated with the phosphaturia observed at hyperbaria, but increased aldosterone coexisted with the increased kaliuresis observed.