Conscious Pekin Ducks Research Articles

Lipopolysaccharide-induced fever in Pekin ducks is mediated by prostaglandins and nitric oxide and modulated by adrenocortical hormones

Information on avian fever is limited, and, in particular, very little is known about the mediators and modulators of the febrile response in birds. Therefore, in this study, the possible mediatory roles of nitric oxide (NO) and prostaglandins (PGs), together with a potential modulatory role for adrenocortical hormones in the generation of fever was investigated in conscious Pekin ducks. Their body temperatures were continuously measured by abdominally implanted temperature-sensitive data loggers. The febrile response induced by intramuscular injection of LPS at a dose of 100 microg/kg was compared with and without inhibition of NO production by N-nitro-L-arginine methyl ester (L-NAME), inhibition of PG synthesis (by diclofenac), and elevation of circulating concentrations of dexamethasone and corticosterone (by exogenous administration). LPS administration induced a marked, monophasic fever with a rise in temperature of more than 1 degrees C after 3-4 h. In the presence of L-NAME, diclofenac, and adrenocorticoids at doses that had no effect upon normal body temperature in afebrile ducks, there was a significant inhibition of the LPS-induced fever. In addition, during the febrile response, the blood concentration of corticosterone was significantly elevated (from a basal level of 73.6 +/- 9.8 ng/ml to a peak level of 132.6 +/- 16.5 ng/ml). The results strongly suggest that the synthesis of both NO and PGs is a vital step in the generation of fever in birds and that the magnitude of the response is subject to modulation by adrenocorticoids.

Urinary clearance of angiotensin II in Pekin ducks.

To quantify the renal excretion of angiotensin II (AII) in birds, synthetic AII was intravenously infused into conscious Pekin ducks at rates of 5, 15 and 45 ng/kg/min for 30 min and the relationships between plasma and urine AII concentrations were monitored by radioimmunoassay. The infusions of AII produced dose-dependent elevations in the plasma concentrations of the hormone, however, urinary concentrations and excretion rates did not change significantly from the basal values of 11.6 +/- 1.2 pg/ml and 4.3 +/- 1.0 pg/min, respectively. The metabolic clearance rate of AII remained constant at each infusion dose (approximately 120 ml/min/kg). The urinary clearance rates (< 0.3 ml/min/kg) indicated that the fraction of AII cleared from the blood via the urine was less than 0.2%. Clearly, excretion of intact AII via this route is not a quantitatively important means of elimination for this hormone in birds.

Urinary clearance of atrial natriuretic peptide in Pekin ducks.

To quantify the renal excretion of atrial natriuretic peptide (ANP) in birds, synthetic ANP was infused intravenously into conscious Pekin ducks at rates of 10, 30 and 90 ng/kg per min for 30 min and the relationships between plasma and urine ANP concentrations were monitored by RIA. The infusions of ANP produced dose-dependent elevations in the plasma concentrations of the hormone; however, urinary concentrations and excretion rates did not change significantly from the basal values of 142.2 +/- 21.5 pg/ml and 26.4 +/- 4.5 pg/min per kg respectively. The metabolic clearance rate of ANP remained constant at each infusion dose (approximately 200 ml/min per kg). The urinary clearance rates (< 0.3 ml/min per kg) indicated that the fraction of ANP cleared from the blood via the urine was less than 0.2%. Clearly, excretion of intact ANP via this route is not a quantitatively important means of elimination for this hormone in birds.

Urinary Clearance of Arginine Vasotocin in Pekin Ducks

To quantify the renal excretion of arginine vasotocin (AVT) in birds, synthetic AVT was infused into conscious Pekin ducks at rates of 0.03, 0.10, and 0.30 ng/kg/min for 30 min and the relationships between plasma and urine AVT concentrations were monitored by radioimmunoassay. As plasma AVT concentrations increased (from a basal value of 7.8 ± 1.1 pg/ml to levels of 11.5 ± 1.9, 17.6 ± 2.2, and 24.2 ± 2.5 pg/ml, respectively) the urinary concentrations and excretion rates increased linearly from basal levels of 26.0 ± 3.1 pg/ml and 14.9 ± 1.8 pg/min to 215.6 ± 36.6 pg/ml and 39.2 ± 3.7 pg/min, respectively. The metabolic clearance rate of AVT (approximately 23 ml/min/kg) and urinary clearance (approximately 0.91 ml/min/kg) remained constant at each infusion dose and were therefore independent of plasma AVT levels. Over the range of plasma AVT concentrations tested, a constant fraction of about 5% of the AVT cleared from the blood was excreted intact in the urine.

Atrial Natriuretic Peptide Suppresses Osmotically Stimulated Plasma Arginine Vasotocin Levels in the Pekin Duck

Plasma arginine vasotocin (AVT) concentrations were measured at 15-min intervals in conscious Pekin ducks intravenously infused with 1 M saline at a rate of 0.5 ml/min for 1 hr. The responses were compared in eight birds, each given in random order a polyclonal antiserum against atrial natriuretic peptide (anti-ANP) or normal rabbit serum (control). The elevations in plasma osmolalities and sodium concentrations and the reductions in hematocrit values caused by the hypertonic saline were similar in both conditions. Plasma ANP in the control animals was elevated threefold during the saline infusion (from 66.8 ± 8.8 pg/ml to a peak of 193.3 pg/ml), whereas in the same birds treated with specific antiserum, circulating ANP concentrations fell to less than 10 pg/ml and remained at this level for the duration of the experiment. Plasma AVT concentrations rose steadily and significantly from basal levels of 5.8 ± 0.5 and 5.8 ± 0.8 pg/ml in the control and anti-ANP groups, respectively; however, the concentrations measured in the birds with low plasma ANP were consistently higher ( P < 0.02) than those under the control condition. Furthermore, the sensitivity of AVT release for the control birds (0.35 pg/ml per mOsm/kg) was significantly lower ( P < 0.001) than that in the anti-ANP animals (0.86 pg/ml per mOsm/kg). Elevated plasma ANP may suppress osmotically stimulated AVT release during states of vascular volume expansion.

Modulation of kidney function in conscious Pekin ducks by atrial natriuretic factor.

The influence of avian atrial natriuretic factor (ANF) on renal function was examined in conscious saltwater-acclimated Pekin ducks undergoing a steady state diuresis maintained by iv infused isotonic avian Krebs-Ringer solution at a rate of 1.0 ml/min. Synthetic chicken ANF (chANF) was applied iv at doses of 10, 50, and 90 ng/min.kg BW for 10 min and caused dose-dependent transient increases in urine flow, osmolal excretion, glomerular filtration rate, effective renal plasma flow, and fractional water clearance at decreased urinary osmolality. Using receptor autoradiography, binding sites for [125I]Bolton-Hunter-labeled chANF [( 125I]BH-chANF) were localized in both the reptilian-type glomeruli and the collecting duct system throughout the duck kidney. A RRA for [125I]BH-chANF, established using an enriched kidney membrane fraction, indicated that unlabeled chANF and human ANF competitively displaced [125I]BH-chANF with comparable potencies. ANF-induced modulation of renal salt and water elimination via glomerular and tubular receptor interactions is consistent with the concept that this hormone has a physiological role in avian volume homeostasis.

Modulation of kidney function in conscious Pekin ducks by atrial natriuretic factor

Modulation of kidney function in conscious Pekin ducks by atrial natriuretic factor

Plasma Atrial Natriurcetic Factor Responses to Blood Volume Changes in the Pekin Duck

A RIA was developed for the measurement of immunoreactive atrial natriuretic factor (irANF) in avian plasma and was used to investigate the relationship between vascular volume and plasma irANF concentrations in conscious Pekin ducks. In normally hydrated birds, the mean plasma irANF concentration was 78.5 +/- 6.8 pg/ml. Blood volume expansion by iv infusion of isotonic saline at 1 ml/min elevated irANF concentrations by 132% after 1 h and by 233% after 2 h. Reduction of the vascular volume by nonhypotensive hemorrhage of 10% and then 20% of the total blood volume reduced irANF levels by 16% and 42%, respectively, 5 min after blood removal was completed. Similarly, in birds deprived of water for 24 h and with blood volume reduced by 4.8%, plasma irANF concentrations were 50% lower than in the same euhydrated animals. The observed correlation between plasma irANF concentrations and vascular volume is consistent with the concept that ANF has a physiological role in avian volume homeostasis.

Interaction of atrial natriuretic factor and osmoregulatory hormones in the Pekin duck

This study examined the influence of plasma atrial natriuretic factor (ANF) on the osmoregulatory hormones arginine vasotocin (AVT), angiotensin II (AII), aldosterone, and corticosterone in the blood of conscious Pekin ducks. Synthetic chicken ANF was iv infused at a nonhypotensive, natriuretic, and diuretic dose of 100 ng · kg −1 · min −1 in normally hydrated ducks and birds in which the circulating levels of AVT, AII, aldosterone, and corticosterone were elevated by 24-hr dehydration. In normally hydrated animals the effect of ANF was limited to a reduction ( P < 0.05) in the basal concentration of aldosterone; in dehydrated birds both AII and aldosterone levels were reduced ( P < 0.05). ANF infusion was consistently without effect on plasma AVT or corticosterone concentrations. The iv infusions of AII with or without simultaneous infusion of ANF showed that ANF inhibited ( P < 0.05) the aldosterone response to AII. Autoradiographic and membrane binding techniques indicated that there were both AII and ANF receptors in the subcapsular zone of the duck adrenal gland and that ANF had no affinity for the AII binding sites. The results demonstrate that ANF is capable of modulating the duck angiotensin-aldosterone system and suggest a role for this peptide in avian salt and fluid homeostasis.

Atrial Natriuretic Factor Controls Salt Gland Secretion in the Pekin Duck (Anas platyrhynchos) through Interaction with High Affinity Receptors

Marine birds possess supraorbital salt-secreting glands in addition to the kidneys as osmoregulatory organs to excrete a strongly hypertonic salt solution of mainly NaCl. Atrial natriuretic factor (ANF)-like peptides could be demonstrated immunocytochemically in duck atria, but not in the salt glands. To elucidate the putative role of bird-specific ANF (cANF) in the control of salt gland function, conscious saltwater-acclimated Pekin ducks received 15 pmol/min.kg BW cANF for 10 min at two states of salt gland activity. During steady state diuresis and salt gland secretion induced by systemic infusion of 1.0 ml/min isotonic Krebs-Ringer solution, cANF applied iv enhanced the secretion rate from 0.20 to 0.29 ml/min and the osmolality of secretion from 870 to 920 mosmol/kg. At threshold conditions of salt gland activity, cANF infused intracarotideally stimulated the secretion rate from 0.07 to 0.15 ml/min at elevated osmolality of 760 compared to 480 mosmol/kg. Mean arterial pressure and heart rate remained unchanged. Receptor autoradiography with [125I]Bolton-Hunter-cANF as ligand demonstrated specific binding sites throughout the salt gland tissue of both freshwater and saltwater ducks. Scatchard analysis using an enriched membrane fraction revealed high affinity (Kd = 0.9 nM) binding sites of 270 fmol/mg protein density. Displacement studies with unlabeled cANF and human ANF showed comparable Ki values for both peptides in freshwater and saltwater ducks. The combined results indicate an important role for cANF in the control of avian salt gland function.

Vasoactive intestinal peptide stimulates blood flow and secretion of avian salt glands.

The neuromodulatory role of vasoactive intestinal peptide (VIP) in avian salt gland secretion and blood flow was investigated in conscious saltwater-acclimated Pekin ducks. Glandular blood flow was measured by laser-Doppler flowmetry or the radioactive microspheres technique. Osmolal excretion was closely related to salt gland blood flow during salt loading. At threshold conditions of salt gland secretion, VIP infused intracarotidally induced both osmolal excretion and arteriolar vasodilation dose dependently (30-240 pmol.min-1.kg body wt-1). The VIPergic effect on the secretory process for NaCl was enhanced by simultaneous intracarotid application of acetylcholine (5 nmol.min-1.kg body wt-1), whereas the intrinsic vasodilatory potency of acetylcholine appeared to be nonadditive in coinfusion experiments. Ongoing secretion induced by systemic infusion of hypertonic saline could be suppressed by muscarinic antagonists, with salt gland blood flow being sustained at the reduced level of atropine-resistant vasodilation. Subsequent intracarotid infusion of VIP stimulated glandular blood perfusion and also, to a minor extent, osmolal excretion, suggesting an independent, functional VIP system in efferent salt gland control.

Dehydration and arginine vasotocin and angiotensin II in CSF and plasma of pekin ducks.

Osmolalities and, by radioimmunoassay, the contents of arginine vasotocin (AVT) and angiotensin II (ANG II) in simultaneously collected cisternal cerebrospinal fluid (CSF) and plasma samples were determined in chronically prepared conscious Pekin ducks (Anas platyrhynchos) adapted to either freshwater (FW ducks) or salt water (2% saline, SW ducks) for drinking. In FW ducks the AVT in CSF was approximately 10-fold higher than in plasma; ANG II concentration in CSF was about two-thirds of that in plasma. In SW ducks concentrations of AVT were increased approximately threefold and of ANG II fourfold in both CSF and plasma. Dehydration in FW ducks (24-48 h) increased AVT and ANG II in both CSF and plasma, the relative rise being greater in plasma. Within 150 min after rehydration plasma AVT fell at unchanged CSF AVT, whereas CSF ANG II fell at unchanged plasma ANG II. Hydration of SW ducks with freshwater had similar effects. The results indicate separate avenues of release of central and systemic AVT and ANG II and support the idea of an independent control of central ANG II as a mediator in osmoregulation, with CSF AVT reflecting the state of osmoregulatory activity of the hypothalamopituitary vasotocinergic system.

Thermally induced changes in neural and hormonal control of osmoregulation in a bird with salt glands (Anas platyrhynchos).

In conscious Pekin ducks adapted to hypertonic saline (1.9%) as drinking water, steady state secretion of the salt glands was established by continuous intravenous salt loading and the effects of hypothalamic thermal stimulation on salt gland activity and on the plasma concentrations of arginine vasotocin (AVT) and angiotensin II (AII) were observed. Hypothalamic cooling depressed salt gland secretion and the plasma level of AVT. Hypothalamic warming caused transient activation and subsequent inhibition of salt gland secretion without consistent changes of the plasma levels of AVT and AII. Whole body cooling by heat extraction with a colonic thermode produced moderate inhibition of salt gland activity, without changes in plasma AVT and AII, which may be explained by peripheral vasoconstriction. The results are consistent with the view that hypothalamic osmoregulation is under an influence of local temperature by combined osmo/thermo-responsiveness of hypothalamic neurons and temperature dependence of signal transmission in hypothalamic neural integration of osmoregulation.

Mammalian and avian antidiuretic hormone: Studies related to possible species variation in osmoregulatory systems

1. In two representative species of the mammalian and avian classes, the dog and Pekin duck, antidiuretic hormone (ADH) concentrations in the blood were measured by a common radioimmunoassay (RIA) making use of an antiserum raised against the mammalian ADH, arginine vasopressin (AVP) which also cross reacted with the avian ADH, arginine vasotocin (AVT), (Fig. 1). The effects of 24 h dehydration on blood osmolality and ADH concentration and the plasma clearance rates of ADH of conscious dogs and Pekin ducks were compared. 2. An AVP plasma level of 2.37±0.20 pg·ml−1 (2.18±0.18 fmol·ml−1) (mean±SE) was found in normally hydrated dogs at 298.1±1.0 mOsm· kg−1 plasma osmolality; 24 h water deprivation increased plasma AVP to 6.64±0.96 pg·ml−1 (6.12±0.88 fmol·ml−1) and osmolality to 314.2±2.3 mOsm·kg−1 (Fig. 2). In ducks, osmolality and AVT concentration increased from 297.6±1.2 mOsm·kg−1 and 5.80±0.41 pg·ml−1 (5.51±0.39 fmol·ml−1) in normally hydrated animals to 318.6±3.2 mOsm·kg−1 and 14.46±1.45 pg·ml−1 (13.75±1.38 fmol·ml−1) after 24 h water deprivation (Fig. 3). 3. In both species the correlations between plasma osmolality and ADH concentration were highly significant (2 P<0.001) and indicated similar sensitivities of the ADH system to changes in plasma osmolality: 0.24 pg·ml−1 per mOsm·kg−1 in dogs (Fig. 4) and 0.39 pg·ml−1 per mOsm·kg−1 in Pekin ducks (Fig. 5). This interspecies difference in sensitivity was found to be less than the intraspecies variations (Table 1).

Afferent connections of physiologically identified neuronal complexes in the paraventricular nucleus of conscious Pekin ducks involved in regulation of salt- and water-balance.

The afferent connections of the paraventricular nucleus (PVN) of the domestic mallard (Pekin duck), Anas platyrhynchos, were demonstrated by means of microiontophoretic injection of horseradish peroxidase (HRP). To place the HRP injection exactly into the PVN, its location was identified prior to the injection by observing antidiuretic reactions to electrostimulations within the rostral hypothalamus of conscious, hydrated animals. Antidiuresis was induced only when electrostimulation was applied to a distinct hypothalamic area. Two different patterns of antidiuresis were observed: (i) an immediate reduction in rate of production of urine, and (ii) antidiuresis preceded by a period of increase in production of urine. Repeated stimulation of the same site with the same parameters resulted in decreasing antidiuretic effects. At the site where stimulation had elicited the most pronounced antidiuresis of either response type, HRP was injected microiontophoretically.

Regional blood flow changes in response to thermal stimulation of the brain and spinal cord in the Pekin duck

In conscious Pekin ducks, carotid and sciatic blood flows, respiratory rate, core and skin temperatures were measured during selective thermal stimulations of the spinal cord and rostral brain stem in thermoneutral (20 °C) and warm (32 °C) ambient conditions. At thermoneutral ambient temperature selective heating of the spinal cord by 2–3 °C (to 43–44 °C) increased the carotid blood flow by 138% and the sciatic blood flow by 46%. Increase in blood flows was correlated with increased breathing rate and beak and web skin temperatures. Selective cooling of the spinal cord at warm ambient temperatures and panting reduced the blood flow in both arteries and decreased the breathing rate. Heating or cooling of the brain stem showed generally very weak but otherwise similar responses as thermal stimulation of the spinal cord. In one duck out of six there was a marked effect on regional blood flow during brain stimulation. The results show that thermal stimulation of the spinal cord exerts a marked influence on regional blood flow important in thermoregulation, whereas the lower brain stem shows only a weak thermosensitivity, and stimulation caused only small cardiovascular changes of no major consequence in thermoregulation.

Osmotic and volume control of diuresis in conscious ducks (Anas platyrhynchos)

In conscious Pekin ducks made diuretic either by infusing hyposmotic glucose solution or isosmotic saline, osmotic and volume effects on renal water excretion were investigated. As in mammals, antidiuresis mediated by enhanced release of antidiuretic hormone was induced by increasing carotid blood osmolality while a decrease augmented diuresis, indicating cerebral osmotic control of renal water excretion in birds.

Impedance of the lower respiratory system in ducks measured by forced oscillations during normal breathing

The lower respiratory system of 10 conscious Pekin ducks breathing normally was subjected to superimposed oscillations of 1.3 to 16 Hz by a small volume piston pump. Induced sinusoidal flow (V̇ O) and pressure (P O) signals were measured in late expiration, when the gas flow ventilated by the animal was minimum. The modulus of the respiratory impedance was calculated as the ratio P O/V̇. The values obtained at the various oscillatory frequencies were compared to those predicted on the basis of a series mechanical network model consisting of resistive, inertial and compliant elements (RIC) using a least squares non linear regression method. The experimental data fitted well the frequency response of a simple RIC mathematical model. After correcting for the effects of the endotracheal tube, the mean values ±SE of the optimized parameters were: resistance 4.8±0.4 cm H 2O·L −1·sec; inertance: 0.05±0.01 cm H 2O·L −1·sec 2; compliance: 7.7±0.5 ml·cm H 2O −1; natural frequency: 8.0±0.4 Hz. It is concluded that: (1) the lower respiratory system in ducks can be closely modeled by a RIC mechanical series network model; (2) the forced oscillation method can be used to investigate avian mechanics of breathing, with the birds awake and breathing spontaneously.

How are neuronal thermosensitivity and lack of thermoreception related in the duck's hypothalamus? A tentative answer

1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C T hy ( F 40), local temperature coefficients ( Δ/ ΔT) and Q 10. 2. 2.| Q 10 and either F 40 or ΔF/ ΔT were little or not related. 3. 3.|A positive correlation between F 40 and ΔF/ ΔT was observed which was particularly close ( r = 0.94 and 0.96) when the neurons were classified according to their Q 10 of <2 and >2. 4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships. 5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.

Serum arginine-vasotocin (AVT) and afferent and central control of osmoregulation in conscious Pekin ducks

In conscious Pekin ducks adapted either to fresh water or to hypertonic saline (1.9%) as drinking fluid, urinary excretion, salt gland secretion and the serum concentration of radioimmunoassayable arginine-vasotocin (AVT) were examined with regard to their afferent and central control. The experiments were carried out under conditions of water diuresis, osmotic diuresis or supraorbital salt gland secretion, which were induced by continuous infusions of appropriate solutions. Temporary bilateral vagus blockade caused rises in AVT serum concentration accompanied by antidiuresis in hydrated ducks and by inhibition of salt gland secretion in salt-stressed ducks. Rostral brainstem cooling caused decreases of AVT serum concentration and water diuresis in ducks under osmotic diuresis and reduction of AVT serum concentration and inhibition of salt gland secretion in salt-stressed ducks. Cerebral osmotic stimulation in hydrated ducks by intracarotid injection or by intracerebroventricular microinfusion of hypertonic NaCl solutions caused antidiuretic reactions associated with rises of AVT serum concentration.