Despite the abundance of oxygen in atmospheric air relative to water, the initial loss of respiratory surface area and accumulation of carbon dioxide in the blood of amphibious fishes during emersion may result in hypoxemia. Given that the ability to respond to low oxygen conditions predates the vertebrate invasion of land, we hypothesized that amphibious fishes maintain O 2 uptake and transport while emersed by mounting a co-opted hypoxia response. We acclimated the amphibious fish Kryptolebias marmoratus, which are able to remain active for weeks in both air and water, for 7 days to normoxic brackish water (15‰, ~21 kPa O 2 ; control), aquatic hypoxia (~3.6 kPa), normoxic air (~21 kPa) or aerial hypoxia (~13.6 kPa). Angiogenesis in the skin and bucco-opercular chamber was pronounced in air-versus water-acclimated fish, but not in response to hypoxia. Aquatic hypoxia increased the O 2 -carrying capacity of blood via a large (40%) increase in red blood cell density and a small increase in the affinity of hemoglobin for O 2 (P 50 decreased 11%). In contrast, air exposure increased the hemoglobin O 2 affinity (decreased P 50 ) by 25% without affecting the number of red blood cells. Acclimation to aerial hypoxia both increased the O 2 -carrying capacity and decreased the hemoglobin O 2 affinity . These results suggest that O 2 transport is regulated both by O 2 availability and also, independently, by air exposure. The ability of the hematological system to respond to air exposure independent of O 2 availability may allow extant amphibious fishes, and may also have allowed primitive tetrapods to cope with the complex challenges of aerial respiration during the invasion of land.KEY WORDS: Hemoglobin, Oxygen-carrying capacity, Hemoglobin-oxygen affinity, Air-breathing organ, Air-breathing fish, Mangrove rivulus INTRODUCTIONThe transition from aquatic to terrestrial life represents a major step in vertebrate evolution because the physical conditions between these environments are dramatically different. Oxygen solubility is relatively low in water and even well-oxygenated aquatic environments contain only about 3% of the O 2 available in atmospheric air (Dejours, 1988). Low concentrations of aquatic O 2 , particularly in hypoxic habitats, have often been hypothesized to be one of the driving forces behind the evolution of amphibious or terrestrial life histories because invasion of land would allow animals to exploit the O 2 -rich aerial environment (Graham, 1997). RESEARCH ARTICLEDepartment of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.*Author for correspondence (aturko@uoguelph.ca) Received 4 July 2014; Accepted 15 September 2014Taking advantage of aerial O 2 presents several challenges for fishes. Water-breathing fishes exchange respiratory gases across the gills but during emersion the gill lamellae typically collapse and coalesce, reducing the surface area available for respiration. Accumulation of CO 2 in the blood of emersed fishes, resulting from the low solubility of CO 2 in...

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Since there is no direct evidence that the fetal kidney is responsive to arginine vasopressin (AVP), the effects of AVP infusion (600 uU/min/kg) were studied in 13 chronic fetal lamb preparations (106-142 days gestation). During infusion, AVP increased from a mean of 1.18t0.35 to 25.97'2.58 uU1ml (p<0.001), free water excretion (CH20) decreased, and both osmolality (Uos mOsm/KgH20 and sodium excretion (UN~V) ueq/min increased. There was no change in GFR ml/min nor total renal blood flow when measured by microspheres. A significant decrease in plasma renin activity (PRA) n~/ml/hr was also observed during AVP infusion. I Looking at factors modulating the fetal AVP response, a positive correlation was found between Uosm and fetal age (r=0.85, p<0.001) during AVP infusion. Significant negative correlations were shown between AVP metabolic clearance rate (AVP-MCR) and both fetal age (r=-0.88, p<0.005) and Uosm (r=-0.85, p<0.01). These observations suggest the presence of functioning vasopressin receptors in fetal kidneys and that fetal AVP-MCR may moduUniv. of Iowa Hosp., Dept. of Peds., Iowa City, Iowa. Maturation of the glucose reabsorptive process by the fetal kidney was studied in 9 chronic fetal lamb preparations (0.66 to 3.72 kg) and values compared to data obtained from 4 nonpregnant ewes. Blood and urine control values showed a close relationship between fetal glomerular filtration rate (GFR ml/min) and fetal body weight (r=0.78, p<0.02). The mean value for blood glucose observed at threshold was higher in fetuses (200t13.3 mg/100 ml) than in adult ewes (177'2.8 mg/100 ml). Fetal glucose threshold was correlated to fetal body weight (r=0.71, pC0.05) and fetal GFR (r=0.74, p<0.025). The maximum amount of glucose reabsorbed expressed per unit of GFR (m/GFR) was reached in only 1 fetus and was 4.73. In all other fetuses, TmG was not reached since metabolic acidosis developed during the course of glucose infusion. However, in those fetuses, the highest amount of glucose reabsorbed, expressed per unit of GFR (TGIGFR), before glucose infusion was stopped, varied 2.32-3.85 with a mean of 2.83'0.26. In the adult ewes TmGIGFR varied 1.94-2.47 and the mean value (2.21+0.12) was significantly lower (p<0.05) than the mean GFR and TG/GFR values found in fetuses. These data indicate plas ma threshold values for glucose reabsorption by the fetal kidney increased with fetal GFR, suggesting a parallel development in fetal tubular and glomerular function. Moreover, the fact that fetal m / G F R and TG/GFR were higher than adult m / G F R suggests a non-functional correlate to the documented anatomical glomerular preponderance during fetal life. (HP)relative to adult animals. We studied the renal response to this relative HP in beagle puppies age 5-10 days. Animals were divided into 2 groups: phosphate loaded group (PL,n-7) received 320 mg phosphorus daily as a neutral P solution by nasogastric feeding; phosphate restricted group (PR,n=8)received aluminum hydroxide gel. After 3 days P titration studies were performed. Control p...