HORMONAL REGULATORY ADJUSTMENTS DURING VOLUNTARY DIVING IN WEDDELL SEALS

Subadult male Weddell seals were instrumented with microcomputer-based backpacks and were then monitored during voluntary diving and recover y periods in McMurdo Sound, Antarctica. Depth and duration of diving, swim speed, and dive pattern were routinely monitored, An indwelling v enous catheter was used to collect plasma samples at various time peri ods before and following diving episodes, so that changes in plasma co ncentrations of hormones and of metabolites could be measured, Adrener gic and nitroxidergic regulatory effects were assessed indirectly by m easuring concentration changes in catecholamine and cyclic guanosine m onophosphate (cGMP), respectively, The studies found that (i), except for dives of less than several minutes, epinephrine and norepinephrine both increased as a function of diving duration, then rapidly decreas ed during recovery (with a half time of about 10 min), (ii) that the c hanges in catecholamine concentrations correlated with splenic contrac tion and an increase in circulating red blood cell mass (hematocrit), (iii) that the changes in catecholamines, especially [epinephrine], we re inversely related to insulin/glucagon ratios, which mediated a post diving hyperglycemia, and (iv) that in long dives (but not short ones) the changes in catecholamines correlated with increasing reliance on anaerobic metabolism, indicated by increased plasma lactate concentrat ions, These diving-catecholamine relationships during voluntary diving at sea were similar to those observed during enforced submergence (si mulated diving) under controlled laboratory conditions, At the end of diving, even while catecholamine concentrations were still high, many of the above effects were rapidly reversed and the reversal appeared t o correlate with accelerated nitric oxide production, indirectly indic ated by increased plasma cGMP concentrations, Taken together, the data led to the hypothesis of important adrenergic regulation of the divin g response in seals, with rapid reversal at the end of diving and duri ng recovery being regulated by nitroxidergic mechanisms.