Splenic contraction, catecholamine release, and blood volume redistribution during diving in the Weddell seal.

The spleen of the Weddell seal (Leptonychotes weddelli) may contract and inject red blood cells (RBCs) into the peripheral circulation during diving, but evidence for this hypothesis is indirect. Accordingly, we measured splenic dimensions by ultrasonography, plasma catecholamine concentrations, hemoglobin concentration, and hematocrit in five Weddell seals before and after intravenous epinephrine during halothane anesthesia and while awake at the surface after voluntary dives. Spleen size was reduced immediately after epinephrine injection or after the seal surfaced. Within the first 2 min after the seal surfaced, cephalocaudal splenic length was 71 +/- 2% (mean +/- SD; P < 0.05) and splenic thickness was 71 +/- 4% (P < 0.05) of the maximal resting values. Splenic size increased (half-time = 6-9 min) after the seal surfaced and was inversely correlated with plasma epinephrine and norepinephrine concentrations. Hemoglobin concentration increased from 17.5 +/- 5.3 g/dl (measured during general anesthesia) to 21.9 +/- 3.7 g/dl (measured in the first 2 min after surfacing). At these same times, the hematocrit increased from 44 +/- 12 to 55 +/- 8%. These values decreased (half-time = 12-16 min) after the seal surfaced. We estimate 20.1 liters of RBCs were sequestered at rest, presumably in the spleen, and released either on epinephrine injection or during diving. Catecholamine release and splenic contraction appear to be an integral part of the voluntary diving response of Weddell seals.

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 recovery periods in McMurdo Sound, Antarctica. Depth and duration of diving, swim speed, and dive pattern were routinely monitored. An indwelling venous catheter was used to collect plasma samples at various time periods before and following diving episodes, so that changes in plasma concentrations of hormones and of metabolites could be measured. Adrenergic and nitroxidergic regulatory effects were assessed indirectly by measuring concentration changes in catecholamine and cyclic guanosine monophosphate (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 decreased during recovery (with a half time of about 10 min), (ii) that the changes in catecholamine concentrations correlated with splenic contraction and an increase in circulating red blood cell mass (hematocrit), (iii) that the changes in catecholamines, especially [epinephrine], were inversely related to insulin/glucagon ratios, which mediated a postdiving 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 concentrations. These diving-catecholamine relationships during voluntary diving at sea were similar to those observed during enforced submergence (simulated 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 to correlate with accelerated nitric oxide production, indirectly indicated by increased plasma cGMP concentrations. Taken together, the data led to the hypothesis of important adrenergic regulation of the diving response in seals, with rapid reversal at the end of diving and during recovery being regulated by nitroxidergic mechanisms.

Myoglobin saturation in free-diving Weddell seals.

Although the consumption of myoglobin-bound O2 (MbO2) stores in seal muscles has been demonstrated in seal muscles during laboratory simulations of diving, this may not be a feature of normal field diving in which measurements of heart rate and lactate production show marked differences from the profound diving response induced by forced immersion. To evaluate the consumption of muscle MbO2 stores during unrestrained diving, we developed a submersible dual-wavelength laser near-infrared spectrophotometer capable of measuring MbO2 saturation in swimming muscle. The probe was implanted on the surface of the latissimus dorsi of five subadult male Weddell seals (Leptonychotes weddelli) released into a captive breathing hole near Ross Island, Antarctica. Four seals had a monotonic decline of muscle O2 saturation during free diving to depths up to 300 m with median slopes of -5.12 +/- 4.37 and -2.54 +/- 1.95%/min for dives lasting < 17 and > 17 min, respectively. There was no correlation between the power consumed by swimming and the desaturation rate. Two seals had occasional partial muscle resaturations late in dives, indicating transfer of O2 from circulating blood to muscle myoglobin. Weddell seals partially consume their MbO2 stores during unrestrained free diving.

Three members of the nitric oxide synthase II gene family (NOS2A, NOS2B, and NOS2C) colocalize to human chromosome 17.

Nitric oxide synthases (NOSs) are a family of enzymes responsible for the synthesis of nitric oxide from L-arginine and molecular oxygen. Three human NOS enzymes (I, II, and III) with differing cellular distribution and regulatory mechanisms have been identified. To determine whether additional NOSs are encoded in the human genome, a bovine NOS II-related cDNA was used to screen two human genomic libraries. Clones containing three independent genes were isolated. One clone encoded the previously identified NOS II gene (NOS2A). The two other genes specified amino acids homologous, but not identical, to human NOS II (NOS2B and NOS2C). Southern blot hybridization demonstrated that all three genes are present in the human genome. DNA from human-mouse somatic cell hybrids were used to determine the chromosomal location of the NOS II-related genes. All three NOS II-related genes colocalized to human chromosome 17 between bands p13.1 and q25. These observations suggest that there is more than one NOS II-related gene in the human genome. This finding may have important implications for the design of NOS isoform-specific inhibitors.