Antidiuretic action of angiotensin II in the river lamprey Lampetra fluviatilis: evidence for endocrine control of kidney function in cyclostomes.

Intravenous infusion of angiotensin II ([Asn¹ Val5]-Ang II) at 10⁻9 mol min⁻¹ kg⁻¹ body mass produced a significant antidiuresis in river lamprey Lampetra fluviatilis, captured during upstream migration and maintained in fresh water. Although the renin-angiotensin hormonal system (RAS) is now recognized in jawless fishes, until this study, the role of homologous Ang II in L. fluviatilis kidney function had not been examined. This study provides the first evidence for an antidiuretic action of Ang II in cyclostomes and, in evolutionary terms, suggests a renal function for the RAS in early vertebrates.

Binding and movement of silver in the intestinal epithelium of a marine teleost fish, the European flounder (Platichthys flesus).

The intestine has been indicated as a site of waterborne silver toxicity in marine fish and chronic effects at the intestine have been observed at concentrations far below acutely toxic level. Thus, models of silver toxicity to marine fish need to consider the intestine as a biotic ligand. The present study characterises binding of silver to the intestine of the European flounder (Platichthys flesus). Everted intestinal sacks were prepared and submersed in a solution mimicking the intestinal fluid of the fish at the acclimation salinity (21 per thousand). Silver was added as (110m)AgNO(3) or (110m)AgNO(3)/AgNO(3) mixtures at concentrations ranging from 1.6 to 950 nM total silver. Appearance of (110m)Ag was analysed in mucosal scrapings, muscle layers, and in the plasma saline on the serosal side of the intestine. The latter represented uptake into blood and other extra-intestinal compartments. Mucosal scrapings consisted of both epithelial cells and mucus and, thus contained adsorbed as well as absorbed silver. Most of the silver in mucosal scrapings was bound to mucus. There was no difference in silver binding between the anterior, mid, and posterior regions of the intestine. Concentration-dependency of silver binding was sigmoidal and saturated above 100 nM total silver. The saturable appearance of (110m)Ag in the plasma saline suggest that silver passage across the intestine is transcellular and carrier mediated. Mucus likely influences uptake of silver by altering its speciation from that in the lumen and by serving as physical barrier for silver binding to the brushborder membrane. A biotic ligand model for marine fish to silver may have to consider these interactions.

Intestinal iron uptake in the European flounder (Platichthys flesus).

Iron is an essential element because it is a key constituent of the metalloproteins involved in cellular respiration and oxygen transport. There is no known regulated excretory mechanism for iron, and homeostasis is tightly controlled via its uptake from the diet. This study assessed in vivo intestinal iron uptake and in vitro iron absorption in a marine teleost, the European flounder Platichthys flesus. Ferric iron, in the form (59)FeCl(3), was reduced to Fe(2+) by ascorbate, and the bioavailability of Fe(3+) and Fe(2+) were compared. In vivo Fe(2+) uptake was significantly greater than Fe(3+) uptake and was reduced by the iron chelator desferrioxamine. Fe(2+) was also more bioavailable than Fe(3+) in in vitro studies that assessed the temporal pattern and concentration-dependency of iron absorption. The posterior region, when compared with the anterior and mid regions of the intestine, was the preferential site for Fe(2+) uptake in vivo. In vitro iron absorption was upregulated in the posterior intestine in response to prior haemoglobin depletion of the fish, and the transport showed a Q(10) value of 1.94. Iron absorption in the other segments of the intestine did not correlate with haematocrit, and Q(10) values were lower. Manipulation of the luminal pH had no effect on in vitro iron absorption. The present study demonstrates that a marine teleost absorbs Fe(2+) preferentially in the posterior intestine. This occurs in spite of extremely high luminal bicarbonate concentrations recorded in vivo, which may be expected to reduce the bioavailability of divalent cations as a result of the precipitation as carbonates (e.g. FeCO(3)).

Fish as model in pharmacological and biological research.

Fish represent the oldest and most diverse classes of vertebrates, comprising around the 48% of the known member species in the subphylum Vertebrata. There are many scientific fields that use fish as models in research, including respiratory and cardiovascular research, cell culture, ecotoxicology, ageing, pharmacological and genetic studies.

Circulating angiotensins in the river lamprey, Lampetra fluviatilis, acclimated to freshwater and seawater: possible involvement in the regulation of drinking.

Plasma angiotensin levels were measured for the first time in a cyclostome, the river lamprey. With the demonstration that angiotensins are present in the circulation, the possibility of a physiological role in the regulation of drinking was re-examined. Angiotensin II and III concentrations and plasma osmolalities were significantly higher in lampreys acclimated to 28 ppt seawater than in those acclimated to freshwater. No changes were found in angiotensin II and III levels 4 h after transfer from freshwater to 50% seawater, although plasma osmolality had started to rise by this time. There was a suggestion that plasma angiotensin II levels might be related to osmolality in the transfer experiment. Injection of Asp(1)Val(5)- or Asn(1)Val(5)-angiotensin II (40-169 microg/kg body wt.) did not stimulate drinking in freshwater-acclimated lampreys, even when they were still capable of drinking. The angiotensin-converting enzyme inhibitor captopril and the smooth muscle relaxant papaverine both reduced drinking rate in 50% seawater-acclimated lampreys. The data do not provide direct evidence for the involvement of the renin-angiotensin system in the control of drinking behaviour in the lamprey. Indirect evidence from the captopril effect is suggestive, but could have other explanations.

Gills of antarctic fish.

We review the literature on the way the structure of icefish gills relates the physiology of these haemoglobin-less fishes. Vascular casting confirmed earlier reports that the only special feature of the gills is the large size of the blood vessels, especially the prominent and continuous marginal channels Isolated perfused gill arches were used to study the effects of changes in afferent and efferent pressure on gill resistance and tritiated water influx in Chionobathyscus dewitti. Increasing perfusion rate did not change gill resistance, but there were moderate proportional increases in water influx. Reducing efferent pressure increased gill resistance but did not affect water influx. In both C. dewitti and Cryodraco antarcticus gills perfused at constant flow rate, noradrenaline produced concentration-dependent decreases in gill resistance and, with high concentrations, increases in water influx. Fixation while perfusion continued was used to compare blood space dimensions in control, noradrenaline-treated and unperfused gills. Noradrenaline caused large increases in the thickness of the lamellar blood space and increased lamellar height, despite a greatly reduced afferent pressure. This suggests that modulation of pillar cell active tension might be involved in control of lamellar perfusion. The possible relationship between gill water fluxes and lamellar recruitment is discussed.

A radioimmunoassay for the determination of arginine vasotocin (AVT): plasma and pituitary concentrations in fresh- and seawater fish.

A specific radioimmunoassay was developed and characterized for the measurement of arginine vasotocin (AVT) in teleost fish. Specificity of the antibody for AVT was demonstrated by parallelism of a series of AVT standards with serially diluted pituitary and plasma extracts. Crossreactivity of the antibody with the other teleost neurohypophysial peptide, isotocin, was less than 1% and the sensitivity of the assay was 0.24 fmol/assay tube. AVT was extracted from plasma by reverse-phase liquid chromatography [efficiency of 87.6 +/- 9.3% (n = 5)] and demonstrated as an effective procedure for plasma volumes ranging from 0.4 to 1.2 ml. Plasma AVT concentrations measured in a range of euryhaline and stenohaline teleost fish were between 10(-12) and 2 x 10(-11) M (1-20 pg/ml). There were no consistent differences between plasma AVT levels in euryhaline fish (flounder, trout, and eel) adapted to fresh water (FW) and sea water (SW). In flounder, pituitary AVT levels in FW- and SW-adapted fish were also similar.

The effects of neurohypophysial hormones on the vascular resistance of the isolated perfused gill of the European eel, Anguilla anguilla L.

Arginine vasotocin (AVT) and oxytocin (OXY), in the dose range of 2 X 10(-13)-2 X 10(-8) mol, were found to be potent vasoconstrictors of the arterioarterial pathway of isolated perfused eel gills. AVT was significantly (P less than 0.05) more potent than OXY, as indicated by the results of both dose- and concentration-response curves. Isotocin (IT) and arginine vasopressin (AVP) were unable to elicit a vascular response at doses of up to 2 X 10(-8) mol. The arteriovenous component of branchial flow was not affected by these four peptides. Results from constant-pressure head and constant-flow preparations yielded similar results.

Dynamics of glomerular filtration in the river lamprey, Lampetra fluviatilis L.

Hydrostatic pressures decreased in the dorsal aorta (from 21.6 +/- 2.0 to 18.7 +/- 0.2 mmHg), proximal (from 19.5 +/- 1.6 to 16.2 +/- 1.7 mmHg) and distal (from 16.7 +/- 0.7 to 13.2 +/- 0.9 mmHg) renal arteries, and glomerular capillaries (from 16.1 +/- 1.1 to 12.3 +/- 0.6 mmHg) of anesthetized lampreys transferred from freshwater to isosmotic 20-30% seawater. Maximal vascular resistance appeared to be in the efferent arteriole; there was a 67% decrease in pressure between glomerular and peritubular capillaries. Plasma oncotic pressure was unchanged. The calculated afferent effective filtration pressure decreased by 87% after transfer and showed a good correlation with single nephron filtration rate. Effective renal plasma flow was high but variable in freshwater lampreys and decreased by 84% after transfer, but glomerular filtration rate did not decrease proportionately and there was a nonsignificant increase in mean filtration fraction from 0.045 +/- 0.022 to 0.080 +/- 0.021. Calculation of glomerular efferent oncotic pressure indicated that filtration equilibrium did not exist in freshwater lampreys but was attained after transfer. The mean coefficient of filtration of freshwater lampreys was 0.028 +/- 0.002 nl X s-1 X mmHg-1.

Renal excretion of magnesium in a freshwater teleost, Salmo gairdneri.

Infusion of magnesium salts into the body cavity of freshwater-adapted rainbow trout led to elevated plasma magnesium concentrations and to stimulation of renal tubular secretion of magnesium. The majority of the infused load was excreted renally, no net branchial excretion being detected. Magnesium sulphate infusion led to increased tubular secretion of sulphate. Magnesium chloride infusion led to reduced tubular reabsorption of chloride. Magnesium could either be reabsorbed or secreted in control freshwater-adapted trout, apparently as a function of nutritional status. Fish could switch from reabsorption to secretion in response to magnesium loading. It is suggested that freshwater fish eliminate excess dietary magnesium renally.

Identification of beta-adrenergic receptors in teleost red blood cells.

Beta-adrenoceptors have been identified in eel erythrocyte membranes using [3H]dihydroalprenolol binding. These receptors exhibit a mean dissociation constant (KD) of 1.36 nM and a mean maximum number of binding sites (Bmax) of 315 fmol/mg protein. These receptors do not appear to belong to the beta 1-subtype.

A micropuncture study of kidney function in the river lamprey Lampetra fluviatilis adapted to sea water.

Micropuncture techniques have been used to investigate kidney function in lampreys adapted to hyperosmotic media. Plasma electrolyte concentrations were maintained well below corresponding concentrations in the external environment. Urine composition was variable, but generally showed high concentrations of magnesium, sulphate and chloride ions. Lampreys in 50% sea water produced urine which was hypo or iso-osmotic to plasma, whereas those in 100% sea water produced hyperosmotic urine. Urine flow rate in 50% sea water was one tenth of that in fresh water, due to a reduction in filtration rate and an increase in water reabsorption by the kidney. As in fresh water, little if any filtered water was reabsorbed by the proximal segment. Almost 90% of filtered water was reabsorbed by the kidney of 100% sea water lampreys and most of this must have occurred in the distal and collecting segments.

The anatomy and blood system of the kidney in the river lamprey, lampetra fluviatilis.

The anatomy and blood system of the kidney in the river lamprey, Lampetra fluviatilis, was studied after injecting microfil into nephrons or the arterial system. Renal arteries arose at irregular intervals from the dorsal aorta and gave rise to a regular arrangement of afferent arterioles supplying the network of glomerular capillaries. Nephron units were arranged in two longitudinal series on each side of the glomerular capillaries, with the capsule of each nephron closely related to the capillary network. A short neck segment lead into the convoluted proximal segment, which accounted for over half the length of each nephron and was surrounded by a network of capillaries and sinusoids supplied by efferent glomerular arterioles. The end of each proximal segment formed the descending limb of a nephron loop, which lay parallel to the ascending distal limb and the end of each collecting duct. Peritubular blood flow in this region was generally opposite the flow of tubular fluid and blood eventually drained into large thin-walled sinuses connected to the post-cardinal vein.

Uterine prostaglandin levels following stimulation of the decidual cell reaction: effects of indomethacin and tranylcypromine.

Prostaglandin E (PGE) and F (PGF) levels were measured in mouse uteri at various times after either trauma (hemostat crusing) or oil stimulation of the decidual cell reaction (DCR). The oil induced DCR led to an early increase (within 5 min) in both PGE and PGF levels. Both returned to baseline by 1 h after stimulation. A second peak in PGF levels was observed at 120 min after oil stimulation. This study demonstrates a distinct difference between the pattern of PGE and PGF changes in the uterus following oil stimulation of the DCR. Indomethacin pretreatment completely blocked the oil stimulated DCR as well as all prostaglandin increases following either stimulus. The trauma stimulated DCR was not completely blocked by indomethacin pretreatment. Pretreatment with tranylcypromine, an inhibitor of prostacyclin biosynthesis, did not block the prostaglandin E and F increases, but did block the oil stimulated DCR. These findings suggest that prostacyclin may be an early mediator of the DCR.

Measurement of single nephron filtration rate in the kidney of the river lamprey, Lampetra fluviatilis L.

1. The reliability of [3H]inulin as a reference substance for the measurement of glomerular filtration rate (GFR) in river lampreys was investigated. 2. Simultaneously measured renal clearances of [3H]inulin and [14C]-polyethylene glycol (PEG) were not significantly different. 3. Recoveries of [3H]inulin in the urine following its injection into the proximal tubule and urinary duct averaged 83.5+/-4.0% (n = 14) and 93.0+/-4.6% (n = 9) respectively. 4. No evidence was obtained to suggest penetration of the tubular wall by by [3H]inulin following its introduction into peritubular capillaries. 5. Gel-filtration of lamprey plasma and urine produced no signs of any significant degradation of the inulin to fructose. 6. [3H]inulin recoveries, though significantly below 100% (P less than 0.001), were considered adequate to justify its use after allowing for possible sources of error. 7. A mean single nephron filtration rate (SNGFR) value of 7.02+/-0.27 nl/min (n = 89) was obtained from the kidneys of anaesthetized freshwater lampreys. 8. [51 Cr]EDTA was found to be totally unsuitable for the measurement of GFR in this species.

Changes in RNA polymerase activity in isolated mouse uterine nuclei during the decidual cell reaction.

The artificially stimulated decidual cell reaction has been used as a model to study changes occurring in the uterus at the time of implantation. Activities of RNA polymerases I, II and III were measured in uterine nuclei isolated from ovariectomized non-primed mice, hormonally primed mice, and hormonally primed mice following stimulation of the decidual cell reaction. Activities of all three RNA polymerases increased following hormonal priming of ovariectomized mice. In nuclei from stimulated uterine horns, activities of RNA polymerases I and III increased 9 h after stimulation of the decidual cell reaction and remained elevated through 21 h. RNA polymerase II activity did not change following stimulation of the decidual cell reaction. These changes in RNA polymerase activities occur at the time of increased histone modifications and may result from changes in the template capacity.