Adaptive strategies for post-renal handling of urine in birds

Unique Transcriptional Programs Identify Subtypes of AKI

Two metrics, a rise in serum creatinine concentration and a decrease in urine output, are considered tantamount to the injury of the kidney tubule and the epithelial cells thereof (AKI). Yet neither criterion emphasizes the etiology or the pathogenetic heterogeneity of acute decreases in kidney excretory function. In fact, whether decreased excretory function due to contraction of the extracellular fluid volume (vAKI) or due to intrinsic kidney injury (iAKI) actually share pathogenesis and should be aggregated in the same diagnostic group remains an open question. To examine this possibility, we created mouse models of iAKI and vAKI that induced a similar increase in serum creatinine concentration. Using laser microdissection to isolate specific domains of the kidney, followed by RNA sequencing, we found that thousands of genes responded specifically to iAKI or to vAKI, but very few responded to both stimuli. In fact, the activated gene sets comprised different, functionally unrelated signal transduction pathways and were expressed in different regions of the kidney. Moreover, we identified distinctive gene expression patterns in human urine as potential biomarkers of either iAKI or vAKI, but not both. Hence, iAKI and vAKI are biologically unrelated, suggesting that molecular analysis should clarify our current definitions of acute changes in kidney excretory function.

Incubation relative humidity induces renal morphological and physiological remodeling in the embryo of the chicken (Gallus gallus domesticus)

The metanephric kidneys of the chicken embryo, along with the chorioallantoic membrane, process water and ions to maintain osmoregulatory homeostasis. We hypothesized that changes in relative humidity (RH) and thus osmotic conditions during embryogenesis would alter the developmental trajectory of embryonic kidney function. White leghorn chicken eggs were incubated at one of 25-30% relative humidity, 55-60% relative humidity, and 85-90% relative humidity. Embryos were sampled at days 10, 12, 14, 16, and 18 to examine embryo and kidney mass, glomerular characteristics, body fluid osmolalities, hematological properties, and whole embryo oxygen consumption. Low and especially high RH elevated mortality, which was reflected in a 10-20% lower embryo mass on D18. Low RH altered several glomerular characteristics by day 18, including increased numbers of glomeruli per kidney, increased glomerular perfusion, and increased total glomerular volume, all indicating potentially increased functional kidney capacity. Hematological variables and plasma and amniotic fluid osmolalities remained within normal physiological values. However, the allantoic, amniotic and cloacal fluids had a significant increase in osmolality at most developmental points sampled. Embryonic oxygen consumption increased relative to control at both low and high relative humidities on Day 18, reflecting the increased metabolic costs of osmotic stress. Major differences in both renal structure and performance associated with changes in incubation humidity occurred after establishment of the metanephric kidney and persisted into late development, and likely into the postnatal period. These data indicate that the avian embryo deserves to be further investigated as a promising model for fetal programming of osmoregulatory function, and renal remodeling during osmotic stress.

The evolution of blood pressure and the rise of mankind

Why is it that only human beings continuously perform acts of heroism? Looking back at our evolutionary history can offer us some potentially useful insight. This review highlights some of the major steps in our evolution-more specifically, the evolution of high blood pressure. When we were fish, the first kidney was developed to create a standardized internal 'milieu' preserving the primordial sea within us. When we conquered land as amphibians, the evolution of the lung required a low systemic blood pressure, which explains why early land vertebrates (amphibians, reptiles) are such low performers. Gaining independence from water required the evolution of an impermeable skin and a water-retaining kidney. The latter was accomplished twice with two different solutions in the two major branches of vertebrate evolution: mammals excrete nitrogenous waste products as urea, which can be utilized by the kidney as an osmotic agent to produce more concentrated urine. Dinosaurs and birds have a distinct nitrogen metabolism and excrete nitrogen as water-insoluble uric acid-therefore, their kidneys cannot use urea to concentrate as well. Instead, some birds have developed the capability to reabsorb water from their cloacae. The convergent development of a separate small circulation of the lung in mammals and birds allowed for the evolution of 'high blood-pressure animals' with better capillarization of the peripheral tissues allowing high endurance performance. Finally, we investigate why mankind outperforms any other mammal on earth and why, to this day, we continue to perform acts of heroism on our eternal quest for personal bliss.

Perspectives on the convergent evolution of tetrapod salt glands

Since their discovery in 1958, the function of specialized salt-secreting glands in tetrapods has been studied in great detail, and such studies continue to contribute to a general understanding of transport mechanisms of epithelial water and ions. Interestingly, during that same time period, there have been only few attempts to understand the convergent evolution of this tissue, likely as a result of the paucity of taxonomic, embryological, and molecular data available. In this review, we synthesize the available data regarding the distribution of salt glands across extant and extinct tetrapod lineages and the anatomical position of the salt gland in each taxon. Further, we use these data to develop hypotheses about the various factors that have influenced the convergent evolution of salt glands across taxa with special focus on the variation in the anatomical position of the glands and on the molecular mechanisms that may have facilitated the development of a salt gland by co-option of a nonsalt-secreting ancestral gland. It is our hope that this review will stimulate renewed interest in the topic of the convergent evolution of salt glands and inspire future empirical studies aimed at evaluating the hypotheses we lay out herein.

Plasma osmolality reference values in African grey parrots (Psittacus erithacus erithacus), Hispaniolan Amazon parrots (Amazona ventralis), and red-fronted macaws (Ara rubrogenys)

Birds are routinely presented to veterinarians for dehydration. Success with these cases ultimately depends on providing replacement fluids and re-establishing fluid homeostasis. Few studies have been done to determine reference ranges for plasma osmolality in birds. The goals of this study were to determine reference values for plasma osmolality in 3 species of parrots and to provide recommendations on fluid selection for replacement therapy in these species. Blood samples were collected from 21 adult Hispaniolan Amazon parrots (Amazona ventralis), 21 Congo African grey parrots (Psittacus erithacus erithacus), and 9 red-fronted macaws (Ara rubrogenys), and were placed into lithium heparin containers. Plasma osmolality was measured in duplicate with a freezing point depression osmometer. Summary statistics were computed from the average values. Reference ranges, calculated by using the robust method, were 288-324, 308-345, and 223-369 mOsm/kg in African grey parrots, Hispaniolan Amazon parrots, and red-fronted macaws, respectively. The mean +/- SD values were 306 +/- 7, 327 +/- 7, and 304 +/- 18 mOsm/kg in African grey parrots, Hispaniolan Amazon parrots, and red-fronted macaws, respectively. Comparisons with osmolality values in mammals and values previously reported for psittacine bird species suggest that plasma osmolality is slightly higher in parrots than in mammals, species-specific differences exist, and differences between reported values occur. Overall, fluids with an osmolarity close to 300-320 mOsm/L, such as Normosol-R, Plasmalyte-R, Plasmalyte-A, and NaCl 0.9%, can be recommended in parrots for fluid replacement therapy when isotonic fluids are required.

Avian renal system: clinical implications

The avian renal system differs anatomically and physiologically from the mammalian renal system. However, it is affected by similar disease categories such as infectious, nutritional, degenerative, congenital, metabolic, and neoplastic conditions. The diagnosis of renal disease in birds can be challenging and, in many cases, diagnosis is made on postmortem examination. Successful treatment of avian renal disease requires early recognition of clinical signs and correct interpretation of diagnostic tools.