Renal response to dietary protein in the house sparrow Passer domesticus.

Many birds switch seasonally or during ontogeny between diets of varying protein content. In mammals, high-protein diets induce hypertrophy of the kidney in general and of the thick ascending limbs (TAL) in particular, along with increases in glomerular filtration rate (GFR) and urine flow. A hypothesis to explain these phenomena is that the TAL become increasingly sensitive to peptide hormones (glucagon and antidiuretic hormone [ADH]) released in response to protein feeding; the consequent enhancement of ion reabsorption dilutes urine reaching the macula densa, thereby suppressing tubulo-glomerular feedback (TGF) and causing a rise in GFR. Avian kidneys possess most of the elements involved in this mechanism, including loops of Henle with TAL, sensitivity of TAL to ADH (arginine vasotocin [AVT] in birds), and the elements of TGF. We therefore hypothesized that switching from a low-protein to a high-protein diet would induce responses in birds similar to those found in mammals. We tested this hypothesis by feeding house sparrows, Passer domesticus, isocaloric diets containing either 8% or 30% protein. Birds on high-protein food had larger renal medullae, both in mass and in TAL diameter, but no increase in whole-kidney mass. Urine flow was approximately doubled on high-protein food, but there was no change in GFR. We were not able to detect an increased sensitivity of AVT-induced adenylyl cyclase activity in TAL from high-protein animals, and responsiveness to glucagon was higher in TAL from birds eating low-protein food. We are unable to conclude that a suppression of TGF is responsible for the rise in urine flow in birds eating high-protein foods, and the mechanisms behind the medullary hypertrophy and the diuresis remain to be fully explored.

Second messenger production in avian medullary nephron segments in response to peptide hormones.

We examined the sites of peptide hormone activation within medullary nephron segments of the house sparrow (Passer domesticus) kidney by measuring rates of hormone-induced generation of cyclic nucleotide second messenger. Thin descending limbs, thick ascending limbs, and collecting ducts had baseline activity of adenylyl cyclase that resulted in cAMP accumulation of 207 +/- 56, 147 +/- 31, and 151 +/- 41 fmol. mm-1. 30 min-1, respectively. In all segments, this activity increased 10- to 20-fold in response to forskolin. Activity of adenylyl cyclase in the thin descending limb was stimulated approximately twofold by parathyroid hormone (PTH) but not by any of the other hormones tested [arginine vasotocin (AVT), glucagon, atrial natriuretic peptide (ANP), or isoproterenol, each at 10(-6) M]. Thick ascending limb was stimulated two- to threefold by both AVT and PTH; however, glucagon and isoproterenol had no effect, and ANP stimulated neither cAMP nor cGMP accumulation. Adenylyl cyclase activity in the collecting duct was stimulated fourfold by AVT but not by the other hormones; likewise, ANP did not stimulate cGMP accumulation in this segment. These data support a tubular action of AVT and PTH in the avian renal medulla.

Regulation of water and sodium balance in the field by Australian honeyeaters (Aves: Meliphagidae).

We evaluated the use of water and sodium by free-living individuals of several species of Australian honeyeaters (Acanthorhynchos superciliosus, Phylidonyris novaehollandiae, Phylidonyris nigra, Manorina flavigula, and Anthochaera carunculata). Water and Na fluxes were highly variable between species, largely reflecting differences in diet. Water fluxes ranged from approximately 300% of total body water per day in 10-g, nectarivorous A. superciliosus to approximately 45% of total body water per day, typical of a desert species, in M. flavigula, a 50-g, insectivorous, arid-zone bird. Similarly, Na fluxes ranged from nearly 60% of Na pool per day in A. superciliosus to about 25% per day in M. flavigula. Despite these different fluxes, values of regulated osmoregulatory variables, including plasma osmolality, hematocrit, plasma concentrations of Na+ and K+, and exchangeable Na pool, were relatively invariant both between species and within species at different seasons. In contrast, values of variables reflecting the operation of regulatory systems did differ between species and seasons. Urine concentrations were highest in M. flavigula and, in A. carunculata, varied seasonally (higher in summer than winter). Plasma concentrations of aldosterone were lowest in A. carunculata (5-25 pg/mL), highest in P. novaehollandiae (70-200 pg/mL), and in the latter species were higher in winter than summer. Concentrations of arginine vasotocin ranged from 5 pg/mL in A. carunculata to greater than 30 pg/mL in M. flavigula. Our data demonstrate that within the family Meliphagidae, there exists substantial variation in the fluxes of water and Na and that these relate in part to body size variation but more importantly to diet. The different fluxes between species are reflected in the values of numerous osmoregulatory variables.

Renal glomerular and tubular effects of antidiuretic hormone and two antidiuretic hormone analogues in house sparrows (Passer domesticus).

We infused arginine vasotocin, the natural avian antidiuretic hormone, and two antidiuretic hormone analogues into house sparrows (Passer domesticus) to evaluate the vascular and tubular components of antidiuresis in a small (25-g) bird. During control infusion of 25 mmol L-1 NaCl (0.6 mL h-1), urine flow rate was 0.73 mL h-1, glomerular filtration rate was 10.0 mL h-1, the ratio of polyethylene glycol (PEG) in the urine relative to that in the plasma was 16.4, and urine osmolality was 279 mOsmol kg-1. Infusion of arginine vasotocin (0.4 ng kg-1 min-1) decreased urine flow rate by 50% and glomerular filtration rate by 27%, while urine osmolality and the ratio of urine PEG to plasma PEG rose to 150% and 140% of control values, respectively. A higher dose of arginine vasotocin (1.6 ng kg-1 min-1) accentuated these changes. Infusion of the antidiuretic hormone analogue dPTyr(Me)AVT, designed as an antagonist to the V1 (mammalian vascular) receptors for arginine vasopressin, by itself (4.0 ng kg-1 min-1) had no effect on any measured variable (P > or = 0.1). Infusion of the analogue along with arginine vasotocin (0.4 ng kg-1 min-1) abolished the effect of arginine vasotocin on glomerular filtration rate, which suggests that this analogue blocked vascular receptors for arginine vasotocin in house sparrows. Under these circumstances, changes in urine flow rate, the ratio of urine PEG to plasma PEG, and urine osmolality were reduced to nonsignificance. The analogue d(CH2)5[D-Ile2,Ile4,Ala-MH2]AVP, designed as an antagonist to the effects of arginine vasopressin at V2 (mammalian renal tubular) receptors, also was without effect by itself. However, in the presence of this analogue, the effects of arginine vasotocin on urine flow rate and the ratio of urine PEG to plasma PEG were significantly enhanced, and this occurred without any enhanced diminution of glomerular filtration rate. Thus, this analogue appeared to activate a tubular mechanism of antidiuresis. Overall, the data suggest that action of arginine vasotocin at renal vascular receptors plays an important role in effecting antidiuresis in house sparrows. Blockade of renal vascular actions of arginine vasotocin by a V1 antagonist suggest that these receptors may be similar to the mammalian vascular (V1) receptor. The data also suggest a separate action of arginine vasotocin at the renal tubules, but the receptors there apparently differ from the mammalian tubular (V2) receptor.

Transactional patterns of child, mother, and father adjustment in insulin-dependent diabetes mellitus: a prospective study.

Utilized both interview and self-report methods to examine transactional patterns of child, mother, and father adjustment in a sample of children and adolescents with insulin-dependent diabetes mellitus (IDDM). Overall, levels of child and parental adjustment were relatively stable over the 1-year study period. Regression analyses revealed that increases in fathers', but not mothers', distress over time contributed significant incremental variance to poorer subsequent children's adjustment, after controlling for demographic (age, gender, and SES) and disease parameters (illness duration and metabolic control). Decline in fathers' adjustment was a significant predictor of better mothers' adjustment at follow-up; child adjustment was not significantly associated with mothers' adjustment. Variations in both children's and mothers' adjustment made significant, independent contributions to predicting subsequent fathers' adjustment. Findings illustrate the transactional nature of relationships that exist in families of children with IDDM and underscore the importance of family systems or biobehavioral family treatment approaches in the clinical management of children with chronic illnesses.

Renal function and plasma levels of arginine vasotocin during free flight in pigeons.

We examined urinary water loss and plasma levels of arginine vasotocin (AVT) in free-flying, tippler pigeons trained to fly continuously for up to 5 h. First, we used [3H]polyethyleneglycol ([3H]PEG) as a glomerular filtration marker by implanting an osmotic minipump into each bird. In two flights (10 birds in winter at an ambient temperature of 13-15 degrees C and seven in summer at 23 degrees C), we measured pre-flight (hydrated, resting control birds) and post-flight [3H]PEG activity and osmolality in blood and ureteral urine. For comparison, we measured these variables in 10 birds in winter before and after controlled dehydration (24 h at 25 or 30 degrees C). Second, we measured plasma levels of AVT in 6-8 birds before and immediately after each of three different summer flights. Urine osmolality increased significantly by up to three times the control level in both post-flight and dehydrated pigeons; urine:plasma osmolality ratios did not exceed 2. Compared with controls, glomerular filtration rate (GFR) was significantly lower after flight in summer, but did not change in either post-flight or dehydrated winter pigeons. In winter, mean post-flight urine flow rate (UFR) decreased significantly to less than half the control level, while in summer, post-flight UFR did not differ from control levels. In general, mean filtered water reabsorption (FrH2O) increased from 95 % in controls to 98 % in post-flight and dehydrated birds. Plasma levels of AVT increased after flight to between three and eight times the preflight levels. The data from this first study of kidney function during flight are consistent with previous studies of dehydration in birds and exercise in mammals in which both increased FrH2O and decreased GFR contribute to renal conservation of water.

Animal model of spinal cord infarction induced by cholesterol embolization.

Though several animal models of ischemic brain infarction have been developed, no animal model of purely ischemic spinal cord infarction exists. In humans, such paralysis often occurs as a complication of aortic surgery. While working on an animal model of cholesterol embolic renal disease, the authors produced an animal model of ischemic spinal paralysis by direct intraaortic injection of cholesterol suspension. With histologic examination of spinal cords of the paralyzed rats, prominent cholesterol crystals were found obliterating the lumen of the anterior and/or posterior spinal arteries. Spinal cord infarction was seen most prominently in the lateral columns and anterior horns, though other areas also were affected. Permanent paraplegia developed in most rats, but transient paralysis developed in a few, followed by partial or full recovery. This model of spinal infarction in nonanesthetized rats can be used to study the pathophysiology and therapy of spinal infarction.

Effects of water restriction during growth and adulthood on renal function of bobwhite quail, Colinus virginianus.

Renal function and osmoregulation were studied in bobwhite quail (Colinus virginianus) raised with unrestricted water (chronically unrestricted group) or restricted water (chronically restricted group). There was no difference in urine concentrating ability between adult and juvenile (3.5 or 7.5 week-old) quail. A filtration marker (polyethylene glycol) was infused into adult quail via osmotic minipumps and responses to the following regimens studied: ad libitum water intake, short-term (4-day) water restriction, and acute (1-day) dehydration (withdrawal of all drinking water). Chronically restricted quail had higher urine-to-plasma ratios of polyethylene glycol and lower urine flow rates during short-term restriction. A greater proportion of the reduction in urine flow rate during dehydration was attributable to enhanced tubular reabsorption, rather than reduced rates of filtration, in chronically restricted than in chronically unrestricted birds. Chronically restricted birds also had higher maximum urine-to-plasma ratios of polyethylene glycol (but not higher urine osmolality). These differences occurred in the face of arginine vasotocin concentrations that were not different in the two groups of birds (approximately 15 pg.ml-1 during hydration, and 45 pg.ml-1 during water restriction or dehydration). These observations suggest that chronically restricted quail have an enhanced responsiveness of tubular reabsorption to dehydration, a finding consistent with previous observations of tubule hypertrophy and hyperplasia in these birds (Goldstein and Ellis 1991). Despite this, no difference was found in medullary cAMP levels, either basal or arginine vasotocin- or forskolin-stimulated, in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Osmoregulatory responses of glucous-winged gulls (Larus glaucescens) to dehydration and hemorrhage.

The effects of dehydration and hemorrhage on plasma ionic, osmotic, and antidiuretic hormone (arginine vasotocin) concentrations and of hemorrhage on salt gland secretion and glomerular filtration rate were evaluated in glaucous-winged gulls, Larus glaucescens. Dehydration for 24 h did not affect plasma ionic, osmotic or arginine vasotocin concentrations; 72 h dehydration significantly elevated plasma osmolality, plasma sodium and chloride concentrations, and plasma arginine vasotocin concentration, but did not affect plasma potassium concentration. Constant infusion of 0.8 mol.1-1 NaCl increased plasma arginine vasotocin concentration and produced salt gland secretion in seven gulls; four secreted well, while three secreted less well. Removal of 20% blood volume during saline infusion immediately reduced (P<0.001) salt gland secretion rate in all gulls. After bleeding, good secretors maintained glomerular filtration rate and urine flow rate; the poorer secretors increased glomerular filtration rate and became diuretic. Blood replacement returned salt gland secretion rate to the prebleeding level (P<0.05) without affecting salt gland secretions sodium concentration in gulls which secreted well, but did not restimulate salt gland secretion in gulls which secreted poorly. Reinfusion of blood had no effect on glomerular filtration rate. Bleeding and blood replacement did not affect plasma arginine vasotocin concentration.

Effect of water restriction during growth and adulthood on kidney morphology of bobwhite quail.

We raised bobwhite quail (Colinus virginianus) either with unrestricted water (HYD birds) or with restricted water (DEH birds). DEH quail grew more slowly and reached lower adult body mass. Despite this, kidney mass was not different in the two groups. The number of nephrons per kidney, heterogeneity of glomerular sizes, number of medullary cones per kidney, and lengths of medullary cones (equivalent to the lengths of the longest loops of Henle) did not differ between HYD and DEH quail. However, the mass of an individual medullary cone was greater in the DEH birds; this included both hypertrophy and hyperplasia of the epithelia in thick ascending limbs of Henle and hypertrophy without hyperplasia in the collecting ducts. We found no differences among groups in the sizes of tubule cross sections from cortical nephron segments (proximal tubules). Water restriction of HYD birds for 5 days as adults stimulated tubule hypertrophy but not to the same extent as the chronic regimen and with no evidence for hyperplasia. DEH quail given unrestricted water as adults maintained elevated drinking rates for the full week water was available; this rehydration had no effect on sizes of tubule epithelia.

Structure and concentrating ability in the avian kidney.

We quantified various aspects of the morphology of the kidney in seven bird species and related these measures to urinary concentrating ability (the concentration of ureteral urine in dehydrated animals) for six of the species. Kidney mass, number of glomeruli, and number of medullary cones all tended to increase with body mass. Smaller birds, with smaller kidneys, had smaller nephrons with smaller glomeruli. Lengths of medullary cones tended to increase with body mass and were exceptionally long in the macaroni penguin. The proportion of nephrons that were mammalian-type (MT, with loops of Henle) ranged from 7% (ring-necked pheasant) to 30% (zebra finch, glaucous-winged gull) and was unrelated to kidney mass. The percent of kidney mass comprised of medullary cones varied from 5 to 13%, unrelated to kidney mass. The number of reptilian-type (without loops of Henle) nephrons associated with each medullary cone tended to increase with kidney mass. Of the variables examined, length of the medullary cones, and hence of the longest loops of Henle, was most strongly correlated with urinary concentrating ability; however, this correlation was negative. Concentrating ability was also strongly negatively correlated with body mass (small birds concentrate better). No significant relation existed between concentrating ability and proportion of MT nephrons. Our data suggest that, in a broad interspecific comparison, the quantitative extent of the renal medulla is not the primary determinant of urinary concentrating ability in birds.

Absorption by the cecum of wild birds: is there interspecific variation.

The major functions proposed for the avian cecum--energy balance and osmoregulation--involve absorption of material from the cecum, yet little is known of these absorptive processes in wild birds. The magnitude of transport of compounds from the ceca depends on the concentrations of compounds in the ceca, the presence of transport pathways for those compounds, and the size of the reabsorptive surface. Interspecific variation in size of avian ceca is well documented, but the other two determinants of absorption are much less well studied. All ceca examined contained acetic, propionic, and butyric acid; water content varies from less than 70 to greater than 90%. Most other constituents have been quantified in just one or two species. A model for cecal transport, derived from studies of mammalian ceca but consistent with observations on birds, is described. A luminal (mucosal) Na+/H+ exchanger couples the absorption of Na+ to that of volatile fatty acids, which are absorbed in their uncharged (protonated) form; these two compounds are thereby mutually stimulatory in their absorption. The cecum also absorbs water, sodium, carbon dioxide, and probably some nitrogenous compounds (e.g., ammonia). Too few data exist to analyze interspecific variation in cecal transport in birds. However, variations in the following characteristics do exist: cecal contents, cecal absorptive surface area, transport characteristics of other regions of avian intestine (e.g., rectum), cecal transport among mammalian species, and histology of avian ceca. Studies of the physiological consequences of these variation should yield insight into the function and contributions of the avian cecum.

Contributions of the kidneys and intestines to water conservation, and plasma levels of antidiuretic hormone, during dehydration in house sparrows (Passer domesticus).

The contributions of the kidneys, the small intestine and the lower intestine (rectum plus cloaca) to water conservation during dehydration in unanaesthetized, unrestrained house sparrows (Passer domesticus) were assessed. Thirty hours of acute dehydration resulted in a 12% loss in body mass and a significant increase in plasma osmolality. Glomerular filtration rate declined by 55%, from 7.7 to 3.5 ml/h, and urine flow rate delined by more than 80%, from 0.2 to 0.03 ml/h. These changes are likely attributable to a large increase in plasma levels of arginine vasotocin during dehydration, from less than 26 pg/ml in hydrated birds to greater than 200 pg/ml after 30 h dehydration. Flow of water from the ileum to the lower intestine was reduced during dehydration, primarily because of a reduced flow of dry matter (with no significant reduction in water content). The rate of water loss in the excreta declined from 0.2 ml/h in hydrated birds to 0.04 ml/h in dehydrated birds. The rate of water reabsorption in the lower intestine (equal to the rate of water loss in the excreta minus the combined rates of inflow into the lower intestine from the urine and the ileal contents) slightly exceeded the rate of water flow from the ileum in both hydrated and dehydrated birds. We suggest that much of the water reabsorbed in the lower intestine of hydrated birds derives from the urine, but that primarily water from ileal contents is reabsorbed in dehydrated birds. That is, urine undergoes significant post-renal modification in hydrated but not dehydrated house sparrows.

Lower intestinal modification of ureteral urine in hydrated house sparrows.

The ureters of birds empty into the posterior portion of the lower intestine, thereby providing the possibility for modification of ureteral urine by this latter organ. We have used in vivo perfusion to measure the transport of Na+, K+, and water across the lower intestine (colon and coprodaeum) of anesthetized house sparrows (Passer domesticus). Na+ was reabsorbed from (Vmax = approximately 22 mu eq . cm-2 . h-1, Km = approximately 69 meq/l) and K+ was secreted (at variable rates) into all saline perfusion fluids. The osmotic permeability of the intestinal epithelium was 0.39 microliter . cm-2 . h-1 . mosM-1 in the mucosal-to-serosal direction and 0.43 microliter . cm-2 . h-1 . mosM-1 in the serosal-to-mucosal direction. At isosmotic perfusion, Na+-linked water transport occurred at a rate of 1.7 microliter/mu eq Na+. In hydrated house sparrows the composition of ureteral urine (osmolarity = 351 mosM, Na+ = 86.5 meq/l, K+ = 60.5 meq/l) was significantly modified by transport in the lower intestine (voided fluid osmolarity = 344 mosM, Na+ = 60 meq/l, K+ = 90 meq/l). Interspecific comparisons of lower intestinal resorptive surface area and transport parameters at the level of the tissue, organ, and whole animal reveal no consistent pattern of adaptation related to habitat.