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PubMed2003

Regulation of water absorption in the frog skins by two vasotocin-dependent water-channel aquaporins, AQP-h2 and AQP-h3.

A new frog aquaporin (AQP) cDNA was cloned from a cDNA library constructed from the ventral skin of the tree frog Hyla japonica. This AQP (Hyla AQP-h2) consisted of 268 amino acid residues with a high homology to mammalian AQP2. The predicted amino acid sequence contained the two conserved Asn-Pro-Ala motifs found in all the major intrinsic protein family members and the putative six transmembrane domains. The sequence also contained a mercurial compound: cysteine, one potential N-glycosylation site at Asn-124, and a putative phosphorylation site recognized by protein kinase A at Ser-262. In a swelling assay using Xenopus oocytes, AQP-h2 facilitated water permeability, especially in response to cAMP. Expression of AQP-h2 mRNA was restricted to several tissues including the ventral skin, kidney, and urinary bladder; but with immunofluorescence staining using an antipeptide antibody (ST-140) against the AQP-h2 protein, immunopositive cells were found only in the ventral skin and urinary bladder. In the ventral pelvic skin, the label for AQP-h2 was localized in the entire plasma membrane of the granular cells beneath the outmost layer of the skin and in the basolateral membrane of the granular cells in this layer. In response to vasotocin, however, the label for AQP-h2 became more intense in the apical membrane in the granular cells of the outermost layer, similar to the case for the earlier studied AQP-h3, which was specifically expressed in the ventral skin. Taken together, these findings suggest that not only AQP-h3, but also AQP-h2 acts as a regulator of the water balance in this frog.

Amino Acid Sequence↗

PubMed1977

Chromatographic evidence for vasotocin biosynthesis by cultured pineal ependymal cells from rat fetuses.

Cultured pineal ependymal cells from rat fetuses aged 17 to 19 days post-coitum release into their media a substance that has hydroosmotic, antidiuretic and rat uterine activities. Paper chromatography of concentrates from culture media demonstrates that the substance possessing all the above activities was eluted from a slow moving region (Rf 0.15-0.35) with a peak at 0.20-0.30. This region is not significantly different from the Rf of synthetic arginine vasotocin (AVT) used as standard. Neither hydroosmotic nor rat uterine activities could be detected in the chromatographic eluates from the fast moving region corresponding to the Rf of synthetic oxytocin (0.55-0.65) used as standard. The chromatographic mobility of biological activities from culture media, the ratio of the activities as well as their susceptibility to tryptic digestion, demonstrates the presence of a basic peptide indistinguishable from synthetic AVT. The total amount of AVT released into the medium during 43 days of incubation is about 40 times greater than the amount contained in non-incubated pineal glands of the same age, strongly suggesting de novo synthesis of AVT.

Animals↗

PubMed1979

The effect of subcutaneous injections of melatonin, arginine vasotocin, and related peptides on pituitary and plasma levels of luteinizing hormone, follicle-stimulating hormone, and prolactin in castrated adult male rats.

A sc injection of 2 micrograms arginine vasotocin (AVT) administered every 2 h for a 25-h period starting 1 h after castration of adult male rats caused a 43% reduction (P less than 0.05) in plasma levels of LH compared to diluent-treated castrated controls. In Exp 2, a sc injection of 5 micrograms AVT or diluent was administered to intact or acutely castrated male rats every 3 h for 48 h. After AVT administration, both plasma LH (P less than 0.001) and FSH (P less than 0.05) were significantly reduced, with a concomitant increase in pituitary levels of these gonadotropins. Using the same injection regimen in Exp 3, 250 micrograms melatonin had no effect on plasma or pituitary levels of LH in castrated male rats. In the fourth experiment, neither 1 IU arginine vasopressin nor 1 IU oxytocin had an effect on plasma or pituitary levels of LH, whereas 1 IU of AVT significantly lowered plasma levels of LH (P less than 0.05) and prevented the fall in the pituitary level of this gonadotropin (P less than 0.01) when compared to diluent-treated castrated control rats. Oxytocin (1 IU) significantly inhibited (P less than 0.01) plasma levels of FSH and raised plasma levels of PRL (P less than 0.01) in castrated male rats. No effect on plasma titers of PRL were observed after treatment of castrated rats with AVT in Exp 2 or 4. It is concluded that in acutely castrated male rats, AVT could possibly act either on the hypothalamus and/or the pituitary to affect pituitary and plasma levels of gonadotropins.

Animals↗

PubMed1983

A seasonal variation in arginine vasotocin immunoactivity in rat pineal glands.

Groups of male and female laboratory rats, 28-30 days of age, were killed each week from July 1980 to September 1981. Pineal glands were collected, pooled, and extracted. Arginine vasotocin (AVT) activity in the extracts was measured by RIA. For most of the calendar year, pineal AVT immunoactivity ranged between 1.8-7.7 pg/gland. The average (+/- SE) basal AVT activity level was 4.1 +/- 0.3 pg/gland (n = 48). Both years in early August, pineal AVT activity increased several hundred fold. Values of 1720 and 1170 pg/gland were measured in mid-August of 2 successive years. The signal for this dramatic yearly rhythm, and its physiological consequences, are as yet unknown.

Animals↗

PubMed1984

An osmometric method for the bioassay of vasotocin and related peptides in the toad bladder.

This study describes a new method for quantitating the antidiuretic activity of 8-arginine vasotocin (AVT) and related peptides on the isolated toad urinary bladder. The method is based on measuring changes in the osmolality of the surface fluid film of bladders that have been filled with a dilute solution and suspended in humidified air. Eight microliters of Ringer's fluid containing a known concentration of hormone are applied to small paper discs (0.7 cm in diameter), and the discs are then placed with fine forceps onto the outer surface of the bladder to which they adhere. The hormone increases the permeability to water of the epithelium that is underneath the area of the disc, and as water moves from the interior of the bladder along its osmotic gradient to the outer surface of the bladder, the Ringer's fluid in the disc becomes diluted. The magnitude of this dilution is quantitated by removing the discs to a vapor pressure osmometer at timed intervals. A supramaximal dose of AVT reduced disc fluid osmolality by 188 mosmol/kg H2O within 15 min. Similar maximal responses were observed with 8-arginine vasopressin (AVP), oxytocin, and 8-lysine vasopressin, although the potencies of these hormones diminished in the order listed above. AVT was 112-fold more potent than AVP, and AVP, in turn, was 329-fold more potent than 8-lysine vasopressin. The lower limit at which AVT was detected in this assay was 0.25 pg/disc (3 X 10(-11) M). The intra- and interassay variabilities for AVT were 14% and 28% (+/- SD), respectively. This assay is suitable for measuring the biological activity of hormone analogs lacking vasopressor activity, such as desmopressin, which was found to have a hydroosmotic activity of 8.3 +/- 2.4 U/mg. After osmotic stimulation, AVT was detected in toad plasma at a concentration of 1.4 X 10(-10) M. Therefore, this method has the requisite sensitivity for measuring this hormone in biological fluids of amphibia, reptiles, fish, and birds.

Animals↗

PubMed1985

Pineal ultrastructure and indole profiles spanning the summer rise in arginine vasotocin immunoactivity.

A correlative radioimmunological-biochemical-ultrastructural study of the rat pineal gland was undertaken during the summer months when pineal arginine vasotocin (AVT) immunoactivity increases up to 200-fold. RIA confirmed a rapid rise in AVT activity during mid-August regardless of the time of day sampled. Pineal indoles were separated by HPLC and measured using electrochemical detection. Serotonin (5-HT) and 5-hydroxyindoleacetic acid levels were consistently elevated in daytime samples, and there was a significant trend for increased day and nighttime levels of 5-HT from July to September. Mid-dark levels of melatonin also exhibited a significant increase over the sample period. Nighttime levels of N-acetylserotonin mirrored fluctuations in 5-HT in the preceding photoperiod. Ultrastructural components implicated in peptide/protein and/or indole biosynthesis were quantified by stereological morphometry. The greatest amounts of rough endoplasmic reticulum stacks, lipid droplets, and annulate lamellae-like bodies coincided with peak AVT activity. Dense-cored vesicles and synaptic ribbons were consistently more frequent during the dark period. The number of dense-cored vesicles and nucleolar size tended to be greatest before and after the peak in AVT immunoactivity. These observations are consistent with the hypotheses that endoplasmic reticulum and lipid are functionally related to the synthesis and/or storage of peptide/protein factors and that numerical changes in synaptic ribbons and dense-cored vesicles are more closely related to day/night differences in indole metabolism.

5-Hydroxytryptophan↗

PubMed1986

Changes in steady state plasma arginine vasotocin levels affect ovine fetal renal and cardiovascular function.

The neuropeptides arginine vasopressin (AVP) and arginine vasotocin (AVT) are present in ovine fetal plasma in similar concentrations. Although AVP appears to be an important factor in the regulation of fetal water metabolism, the significance of AVT in the fetus is not clear. In the present study we assessed the effects of changes in steady plasma AVT levels on renal and cardiovascular function of fetal lambs (mean gestation, 128 days) maintained with vascular and bladder catheters. Successive 1-h infusions of synthetic AVT (n = 8) at rates of 1.0 and 2.0 ng/min X kg resulted in steady state plasma AVT levels of 30 +/- 7 and 59 +/- 12 pg/ml, respectively. The AVT infusions increased both urinary AVT concentrations and urinary AVT excretion. Plasma and urinary AVT clearance rates (45 +/- 8.4 ml/min X kg and 0.38 +/- 0.13 ml/min, respectively) remained constant over the observed range of plasma AVT levels. Urinary AVT clearance accounted for less than 1% of the total plasma AVT clearance and was nonsaturable. Increases in plasma AVT augmented urinary osmolar excretion and osmolar clearance, and evoked a significant natriuresis. AVT at either 1 or 2 ng/min X kg decreased fetal heart rate and tended to increase blood pressure. These results suggest that AVT, like AVP, may be important in modulating ovine fetal electrolyte homeostasis.

Animals↗

PubMed1975

Reversal by vasotocin of pinealectomy and constant light effects on the pituitary melanocyte-stimulating hormone (MSH) content in the mouse.

A single injection of 1 pg synthetic arginine vasotocin (AVT) into the third ventricle of the mouse completely prevented the pituitary MSH increase which occurs seven days after pinealectomy or 24 h after exposure to constant light. The same concentration of AVT injected into the third ventricle of normal mice markedly decreased the pituitary MSH content at 20 min following the injection. The present results suggest that AVT injected into the third ventricle of the mouse inhibits synthesis and/or release of MSH-release inhibiting factor (MIF).

Animals↗

PubMed1976

Dose-dependent prolactin releasing activity of arginine vasotocin in intact and pinealectomized estrogen-progesterone treated adult male rats.

Estrogen-progesterone (EP) treated adult male rats were injected intravenously (iv) with 0.1, 1 or 10 mug arginine vasotocin (AVT) or Ringers lactate solution. A significant dose-related rise in plasma prolactin was evident 10 min after injection with AVT. In a second experiment, sham-operated or pinealectomized EP-treated male rats were injected iv with 0.1 or 1 mug AVT or diluent. Plasma prolactin was significantly elevated in both sham-operated and pinealectomized groups at both 10 and 20 min post-injection of 1 mug AVT. These results indicate that AVT has prolactin-releasing activity and that this activity is not dependent upon the presence of an intact pineal gland.

Animals↗

PubMed1992

Pharmacological characterization of vasotocin stimulation of phosphoinositide turnover in frog adrenal gland.

In a previous report we demonstrated the presence of a vasotocin (AVT)-like peptide in chromaffin cells of the amphibian adrenal gland and showed that synthetic AVT is a potent stimulator of corticosterone and aldosterone secretion by frog adrenocortical cells. In the present study we evaluated the relative potency of various AVT analogs and investigated the mechanism of action of AVT on frog interrenal (adrenal) tissue. Several AVT agonists, including hydrin 2, oxytocin (OXT), arginine vasopressin (AVP), Lys-conopressin G, and mesotocin (MT), were able to mimic the stimulatory effect of AVT on steroid secretion, but AVT was by far the most potent stimulator of steroidogenesis. In the series of analogs studied, the order of potency was: AVT greater than hydrin 2 greater than OXT greater than AVP greater than Lys-conopressin G greater than MT greater than [deamino-Cys1,D-Arg8]AVP greater than [d(CH2)5,Tyr(OMe)2] AVP. The effect of AVT (5 x 10(-10) M) was totally blocked by both the antidiuretic V2 antagonist [d(CH2)5,D-Phe2,Ile4,Ala9-NH2]AVP (10(-6) M) and the oxytocinergic antagonist [d(CH2)5,Tyr(OMe)2,Orn8]AVT (10(-6) M); the V2 antagonist was approximately twice as potent as the OXT antagonist. In contrast, the V1 antagonist 1-(1-mercapto-4-phenylcyclohexaneacetic acid)-AVP (10(-6) M) did not affect the response of the interrenal tissue to AVT. Indomethacin (5 microM), a cyclooxygenase inhibitor, induced a dramatic decrease in the spontaneous secretion of corticosteroids, but did not impair the stimulatory effect of AVT (5 x 10(-9) M) on corticosterone and aldosterone secretion. In addition, AVT did not stimulate the production of prostaglandin E2, suggesting that prostaglandins are not involved in the mechanism of action of AVT. Concurrently, AVT did not modify cAMP production by frog adrenal slices. In contrast, AVT induced both an increase in inositolphosphate production and a reduction of membrane phospholipid content. We conclude that in the frog adrenal gland, the stimulatory effect of AVT on steroid secretion is mediated through activation of receptors related to the mammalian V2 and/or OXT receptors, which are positively coupled to phosphoinositide-specific phospholipase C.

Adrenal Cortex Hormones↗

PubMed1992

Effect of vasotocin on cytosolic free calcium concentrations in frog adrenocortical cells in primary culture.

In a previous report we have shown that vasotocin (AVT), the amphibian counterpart of vasopressin, is a potent stimulator of corticosterone and aldosterone secretion by frog adrenocortical cells. We have also observed that the stimulatory effect of AVT on corticosteroid secretion is mediated through activation of receptors positively coupled to phospholipase-C. In the present study we examined the effect of AVT on cytosolic Ca2+ concentrations ([Ca2+]i). Since the interrenal (adrenal) gland of the frog is composed of a mixed population of chromaffin and adrenocortical cells, cytochemical identification of cultured cells was performed by immunofluorescence, using antibodies to AVT or 11 beta-hydroxylase as markers of chromaffin cells or steroid-producing cells, respectively. Cultured interrenal cells were loaded with the fluorescent Ca2+ indicator indo-1, and variations in [Ca2+]i were studied using dual emission wavelength microfluorimetry. Exposure of adrenocortical cells to AVT induced elevation of [Ca2+]i. Prolonged infusion of AVT caused an immediate increase in [Ca2+]i, followed by a sustained response of adrenocortical cells. Repeated pulses of AVT resulted in a gradual decline in the [Ca2+]i increase, suggesting the existence of a desensitization phenomenon. The effect of AVT on calcium mobilization was totally blocked when the cells were incubated in the presence of the V2 antagonist [d(CH2)5,D-Phe2,Ile4,Ala9-NH2]AVP. In calcium-free medium, the AVT-evoked increase in [Ca2+]i was suppressed. In contrast, when Ca2+ was replaced by Mn2+ in the incubation medium, the early response of the cells (transient peak of [Ca2+]i) was preserved, while the plateau phase disappeared. Incubation of the cells with the dihydropyridine Ca2+ channel blocker nifedipine did not affect the AVT-induced [Ca2+]i rise. These results indicate that AVT exerts a dual action on [Ca2+]i in frog adrenocortical cells. The initial rise of [Ca2+]i can be ascribed to immediate mobilization of intracellular Ca2+ stores, probably mediated by inositol trisphosphategated channels, whereas the sustained increase in [Ca2+]i results from nifedipine-insensitive plasma membrane Ca2+ channels.

Adrenal Cortex↗

PubMed1980

Presence of relatively high concentrations of arginine vasotocin in the cerebrospinal fluid of newborns and infants.

Lumbar cerebrospinal fluid (CSF) was obtained from healthy newborns, infants, and children of both sexes between 23-777 days of age. Bioassay of the CSF revealed relatively high antidiuretic and hydroosmotic activities. Rat uterine activities could be detected only in the CSF of newborns, and these activities were increased in the presence of magnesium. The antidiuretic and hydroosmotic activities of CSF from newborns were significantly higher than the same CSF activities of infants (P less than 0.01) and children (P less than 0.001). No sex differences were observed in the above biological activities of CSF. The ratio of these activities, their susceptibility to tryptic digestion, and the increase of the rat uterine activity by magnesium demonstrate the presence in CSF of a basic peptide indistinguishable from synthetic arginine vasotocin. In contrast to the CSF of healthy newborns and infants, neither antidiuretic nor hydroosmotic activities could be detected in the CSF of a boy, aged 413 days, with a pineal tumor and precocious puberty.

Age Factors↗

PubMed1985

A novel oxytocin-like and vasotocin-like peptide in human plasma after administration of estrogen.

Using three antisera to oxytocin (OT Pitt Ab-1, OT Pitt Ab-2, and TOR OT Ab), we found comparable levels of OT in response to infant suckling and during infusion of synthetic OT, and identical standard curves with biological and synthetic standards of OT. Pitt Ab-1, but not Pitt Ab-2 or TOR OT Ab, measured increased OT in response to estrogen. Using an arginine vasotocin RIA (TOR AVT Ab), we found an increase in AVT immunoreactivity after estrogen treatment. Mean basal OT levels measured with OT Pitt Ab-2 in plasma of men [0.75 +/- 0.06 (+/- SEM) microU/ml] and women (0.8 +/- 0.09 microU/ml) were lower than OT measured with Pitt Ab-1 (1.7 +/- 0.09 microU/ml in men and 1.7 +/- 0.07 microU/al in women; P less than 0.001). Mean OT measured with Pitt Ab-2 in the plasma of women given estrogen chronically (0.8 +/- 0.04 microU/ml) and acutely (0.6 +/- 0.15 microU/ml) were not significantly different from basal levels. OT levels measured with Pitt Ab-1 in the same samples were 4.6 +/- 0.5 and 4.3 +/- 0.5 microU/ml, respectively, both significantly increased from basal levels (P less than 0.001) and significantly higher than OT measured with Pitt Ab-2 (P less than 0.001). Mean OT measured with Pitt Ab-1 in the plasma of pregnant women was 8.6 +/- 1.02 microU/ml, significantly higher than OT measured with Pitt Ab-2 (1.0 +/- 0.3 microU/ml; P less than 0.001). Men given 25 mg diethylstilbestrol had significant increases in OT measured with Pitt Ab-1 and in AVT measured with TOR AVT (P less than 0.01), but not in OT measured with Pitt Ab-2. Plasma from a man given diethylstilbestrol was prepared for high performance liquid chromatography and applied to a C18 muBondapak reverse phase column. The plasma contained two peaks of immunoreactivity detected as OT with Pitt Ab-1 and as AVT using TOR AVT Ab. The material was not detected by Pitt Ab-2 or TOR OT Ab and did not coelute with standards of OT, AVT, or AVP. Pregnancy plasma, thioglycolic acid, chymotrypsin, and trypsin reduced Pitt Ab-1, Pitt Ab-2, and TOR OT immunoreactivity of synthetic OT. The percent recovery of OT immunoreactivity was not significantly different with Pitt Ab-1 vs. Pitt Ab-2. A novel peptide, which is increased in response to administered estrogen, is present in human plasma and is detected by some antisera to OT and AVT. The observation explains the wide variability in OT levels in the estrogen-primed state and provides a new mechanism to study estrogen-related physiology and pathophysiology.

Adult↗

PubMed1985

High pressure liquid chromatographic separation of an oxytocin/arginine vasotocin-like peptide from the plasma of patients with chronic renal failure.

Levels of a novel oxytocin (OT)- and arginine vasotocin (AVT)-like peptide detected by one antiserum to OT (Pitt Ab-1) and one antiserum to AVT (Tor AVT) were recently found to rise in human plasma in response to administration of estrogen. The novel peptide rose in parallel with the estrogen-stimulated neurophysin (ESN). The mean level (+/- SEM) of ESN in plasma of 11 individuals with altered renal function (nondialyzed) was significantly higher than the level in individuals with normal renal function (4.2 +/- 0.9 vs. 1.1 +/- 0.04 ng/ml; P less than 0.01). In patients treated with hemo- or peritoneal dialysis, mean (+/- SEM) levels of ESN were 18.1 +/- 3.2 and 16.8 +/- 3.7 ng/ml, respectively. Levels of estradiol and estrone were not elevated and did not correlate with high levels of ESN. Levels of OT Pitt Ab-1, AVT, and ESN immunoreactivity were measured in plasma form nine patients undergoing hemodialysis and eight patients undergoing peritoneal dialysis. Mean (+/- SEM) levels of all three peptides were elevated (12.9 +/- 1.5 microU/ml, 32.1 +/- 6.7 pg/ml, and 13.5 +/- 4.0 ng/ml, respectively). ESN was significantly correlated with OT Pitt Ab-1 and AVT (R2 = 0.80; P less than 0.001). Plasma samples from the same patients were pooled, treated, and separated by reverse phase HPLC. The plasma contained a peak of immunoreactivity detected by Pitt Ab-1 and Tor AVT Ab. The position of the material was distinct from that of synthetic OT, AVT, or AVP and corresponded to the position of the novel OT-like peptide found in plasma of individuals given estrogen. The findings support parallel secretion of the OT-like peptide with ESN and represent the first disease state characterized by high levels of this OT- and AVT-like peptide.

Adult↗

PubMed1985

Neurohypophysial hormones in cerebrospinal fluid of adults: absence of arginine vasotocin and of a diurnal rhythm of arginine vasopressin.

We previously reported a prominent diurnal rhythm of oxytocin (OT) in human cerebrospinal fluid (CSF) similar to the brisk CSF OT rhythm in monkeys. An OT CSF rhythm has not been found in lower species. In contrast, a pronounced arginine vasopressin (AVP) rhythm has been found in lower species, but the AVP CSF rhythm is less marked in subhuman primates. In patients (n = 7) in whom lumbar drains had been temporarily placed for treatment of CSF rhinorrhea, we obtained CSF samples every 6 h. In 6 of these 7 patients, we previously reported (1) finding a prominent CSF OT rhythm, with a peak at 1200 h, by analysis of variance of repeated measures. When the samples of CSF of these same 6 patients (plus 1 additional patient) were assayed for AVP, no AVP rhythm was found. We also measured AVP, OT, and arginine vasotocin (AVT) by RIA in single samples of CSF obtained from 23 other patients. In these single samples of CSF, mean AVP was 0.9 +/- 0.11 (+/- SEM) pg/ml, and OT was 3.7 +/- 0.5 microU/ml. CSF AVT immunoreactivity was 0.6 pg/ml or less in the 23 patients. Two pools of CSF were separated by reverse phase high pressure liquid chromatography. The peak OT and AVP, as determined by RIA, coeluted exactly with synthetic and human posterior pituitary OT and AVP, respectively. No immunoreactive AVT was found in the position of synthetic AVT in the eluates. Thus, OT and AVP are present in human adult CSF, but AVT is not. The lack of a prominent rhythm of AVP in human CSF is in marked contrast to the brisk OT rhythm. The rhythm of neurohypophysial peptides in human and subhuman primates is different from the rhythm in lower species, suggesting different functions for OT and AVP in the central nervous system of various species.

Adult↗

PubMed1987

Suppression of sensory to motor synaptic transmission and narrowing of the sensory neurone action potential by arginine vasotocin in Aplysia californica.

The vertebrate neurohypophysial peptide arginine vasotocin (AVT), which may be endogenous to the Aplysia central nervous system, was tested for its effect on sensory to motor neurone synaptic transmission. In the semi-intact preparation, superfusion of AVT (10(-6) moll-1) over the abdominal ganglion decreased the amplitude of both the gill withdrawal reflex and the short-latency excitatory postsynaptic potentials (EPSPs) evoked in gill and siphon motor neurones by single action potentials elicited in sensory neurones. AVT slowed the rate of rise of the EPSP, enhanced the rate of homosynaptic depression, and reversibly decreased the duration of the action potential of mechanosensory neurones in isolated, perfused abdominal and pleural ganglia. Frequency-dependent prolongation of action potentials of pleural sensory cells was also decreased by application of AVT. Because this peptide has been shown to modulate the gill withdrawal reflex and its subsequent habituation, the hypothesis that AVT plays a physiological role in the expression of the suppressed behavioural state is proposed. In addition, it is proposed that modulation of the reflex by AVT occurs in part by shortening the duration of the sensory neurone action potential.

Animals↗

PubMed1997

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.

Animals↗

PubMed1975

Micropuncture study of the renal responses of the urodele amphibian Necturus maculosus to injections of arginine vasotocin and an anti-aldosterone compound.

1. Necturus maculosus kidney function has been examined using standard clearance techniques and renal tubular micropuncture methodology. 2. Throughout, cyanocobalamin (vitamin B12) has been used to monitor glomerular filtration rate (GFR) and tubular water movements. It was established that this substance was handled by the Necturus kidney in a similar manner to inulin. It can be readily analysed, together with renal electrolytes, by electron microprobe techniques. 3. Profiles of transtubular gradients (TF:P ratios) along the nephron were established for osmolarity, sodium, potassium, calcium and cobalt (of cyanocobalamin). 4. Ureteral urine is always hyposmotic with respect to plasma and the site of dilution of the plasma ultrafiltrate is within the distal segment. 5. Up to 30% of the filtrate is isosmotically reabsorbed along the proximal tubule; the tubular fluid:plasma ratio for osmolarity and sodium is around 1, and the TF:P for cobalt of cyanocobalamin is about 1.4 by the end of this segment. 6. The renal effects of the neurohypophysial hormone arginine vasotocin (AVT) and an aldosterone antagonist (SC14266; Soldactone) have been examined. 7. AVT was consistently antidiuretic causing both a decreased GFR and an enhanced distal tubular reabsorption of water. 8. SC14266 also increased distal tubular reabsorption of water. Such an effect differs from that found in higher vertebrates, and may indicate a "glucocorticoid-type" of renal action for aldosterone in amphibians.

Aldosterone↗