Cortisol regulates eel (Anguilla anguilla) aquaporin 3 (AQP3) mRNA expression levels in gill

Previous studies in eel (Anguilla anguilla) gill have shown that the expression of the aquaporin 3 (AQP3) water and small solute channel is dramatically decreased (mRNA abundance decreased by up to 97%) when these euryhaline fish are acclimated from freshwater (FW) to seawater (SW). However, AQP3 mRNA expression levels in the intestine following SW-acclimation do not change. The SW-acclimating corticosteroid hormone, cortisol has previously been shown to regulate the expression of aquaporins (particularly AQP1) in eel osmoregulatory tissues in a tissue-specific and isoform-specific fashion. AQP1 is up-regulated in intestine and oesophagus, but down-regulated in kidney, following SW-acclimation in these fish. This study extends knowledge of the regulation of aquaporin expression by cortisol in the eel and shows that elevated levels of this hormone down-regulate AQP3 mRNA expression in the gill in a similar manner to SW-acclimation. However, the smaller magnitude of the changes in branchial AQP3 expression induced by cortisol-infusion (around a 60% decrease), in comparison to those occurring following SW-acclimation, suggest that other factors must also contribute to AQP3 down-regulation. In a similar fashion to the regulation of AQP1 by cortisol, changes in AQP3 expression following hormone infusion appear to be tissue-specific, as little effect was seen on the level of AQP3 expression in the intestine. Again the apparent lack of change in intestinal AQP3 expression following cortisol-infusion mimicked the invariant level of intestinal AQP3 mRNA abundance following SW-acclimation.

Salinity adaptation and gene profiling analysis in the European eel (Anguilla anguilla) using microarray technology

The life cycle of the European eel (Anguilla anguilla) includes two long migratory periods, when the newly hatched leptocephali larvae drift on ocean currents from the Sargasso Sea to the shores of Western Europe and then again up to 30 years later when adult eels swim back to their place of birth for reproductive purposes. Prior to the migration from fresh water (FW) to sea water (SW) adult yellow eels undergo various anatomical and physiological adaptations (silvering) which promote sexual development and aid the transition to increased environmental salinities. The aim of this study was to identify and characterise changes in gene expression within the major osmoregulatory tissues of the eel which enable these fish to make the physiological adaptations required for transfer to SW environments. In particular, changes in the expression of the FW-adapting hormone prolactin were correlated with differential expression of known osmoregulatory important genes within the gill, intestine and kidney following the acclimation of eels to SW. Various tissues were sampled from individual fish at selected intervals over a 5-month period following FW/SW transfer and RNA was isolated. Suppressive subtractive hybridization (SSH) was used for enrichment of differentially expressed genes. Microarrays comprising 6144 cDNAs spotted in triplicate, from brain, gill, intestine and kidney libraries (1536 randomly selected clones per tissue library), were hybridized with appropriate targets and analysed. Microarray results were validated using known genes implicated in osmoregulation, such as prolactin, growth hormone, Na, K-ATPase and some unknown genes, the role of which in osmoregulation needs to be elucidated.

Maternal effects due to male attractiveness affect offspring development in the zebra finch

Maternal effects occur when offspring phenotype is influenced by environmental factors experienced by the mother. Mothers are predicted to invest differentially in offspring in ways that will maximize offspring fitness depending on the environment she expects them to encounter. Here, we test for maternal effects in response to mate attractiveness on offspring developmental traits in the zebra finch Taeniopygia guttata. We controlled for parental genetic quality by manipulating male attractiveness using coloured leg rings and by randomly assigning mating pairs. The potential confounding effect of differential nestling care was controlled for by cross-fostering clutches and by allowing for variance due to foster father attractiveness in general linear models. We found a difference in egg mass investment between attractiveness groups and, importantly, we found that all of the offspring traits we measured varied with the attractiveness of the father. This provides strong evidence for maternal effects in response to mate attractiveness. Furthermore, due to the experiment design, we can conclude that these effects were mediated by differential investment of egg resources and not due to genetic differences or differences in nestling care.

Osmotic and volaemic effects on drinking rate in elasmobranch fish

An increase in drinking rate of two species of marine elasmobranch fish, Scyliorhinus canicula and Triakis scyllia, acclimated to 80% sea water was observed following the introduction of 100 % sea water to experimental tanks. The drinking response in both species was found to be maximal within 6 h, and a significant increase was sustained for up to 24 h in T. scyllia. Plasma osmolality was significantly increased within 6 h following introduction of 100 % sea water, and this increase was principally due to elevated plasma Na+ and Cl- concentrations. Administration of 2 mol l-1 mannitol, 75 % sucrose and vehicle(elasmobranch Ringer) did not induce a significant increase or decrease in the drinking rate of S. canicula. However, injection of 20 % NaCl was found to decrease drinking rate significantly in S. canicula 60 min after administration. Controlled haemorrhage of approximately 5.7 % of total blood volume in S. canicula induced a rapid 36-fold increase in drinking over basal levels. The present study demonstrates a physiological dipsogenesis in response to hypovolaemia in marine elasmobranch fish as part of their overall iso/hyperosmoregulatory strategy.

The effects of dietary sodium loading on the activity and expression of Na, K-ATPase in the rectal gland of the European dogfish (Scyliorhinus canicula)

cDNA fragments of both the alpha- and beta-subunits of the Na, K-ATPase and a cDNA fragment of the secretory form of Na-K-Cl cotransporter from the European dogfish (Scyliorhinus canicula) were amplified and cloned using degenerate primers in RT-PCR. These clones were used along with a sCFTR cDNA from the related dogfish shark, Squalus acanthias to characterise the expression of mRNAs for these ion transporters in the dogfish rectal gland subsequent to an acute feeding episode. Following a single feeding event where starved dogfish were fed squid portions (20 g squid/kg fish), there was a delayed and transient 40-fold increase in the activity of Na, K-ATPase in crude rectal gland homogenates. Increases in enzyme activity were apparent 3 h after the feeding event and peaked at 9 h before returning to control values within 24 h. These increases in activity were accompanied by small and transient decreases in plasma sodium and chloride concentrations lasting up to 3 days. Significant increases in the expression of mRNAs for alpha- and beta-subunits of the Na, K-ATPase, the Na-K-Cl cotransporter and CFTR chloride channel were detected but not until 1-2 days after the feeding event. It is concluded that the transient increase in Na, K-ATPase activity is not attributable to increases in the abundance of alpha- and beta-subunit mRNAs but must be associated with some, as yet unknown, post-transcriptional activation mechanism.

The control of drinking in elasmobranch fish with special reference to the renin-angiotensin system

In summary, it is evident that teleost and elasmobranch fish respond to extra-cellular dehydration by increasing drinking rate mediated by an increase in circulating levels of ANG II. However, although the primary stimulus for drinking may be the same, clearly the mechanisms involved in regulating ion and water balance are entirely different. In order to maintain ion and water balance in the face of cellular and extra-cellular dehydration, the integration and hormonal control of renal and extra-renal function in elasmobranchs has developed in a very different manner to that described for teleost fish.

The dipsogenic effect of the renin-angiotensin system in elasmobranch fish

This study investigated the control of drinking in elasmobranch fish through manipulation of the homologous renin-angiotensin system (RAS). The smooth muscle relaxant papaverine was found to increase basal drinking levels in the European lesser-spotted dogfish, Scyliorhinus canicula, almost 20-fold. However, this response was significantly reduced with the coadministration of the angiotensin-converting enzyme inhibitor captopril which had no effect when administered alone. Captopril was also found to block a 7-fold increase in drinking rate following administration of homologous angiotensin I in S. canicula. Finally, administration of homologous angiotensin II produced a dose-dependent response in drinking rate in two species of elasmobranchs, S. canicula and the Japanese dogfish, Triakis scyllia. These results demonstrate a central role of the RAS in the control of drinking in elasmobranch fish.

Angiotensin II binding sites in the heart of Scyliorhinus canicula: an autoradiographic study

Dogfish (125)I [Asn(1), Pro(3), Ile(5)] angiotensin II ((125)I dfANG II) was used to establish the specific binding patterns of the different cardiac regions of the elasmobranch Scyliorhinus canicula by in vitro autoradiography. In the ventricular myocardium Scatchard analysis of saturation and displacement binding data revealed two classes of high- and low-affinity dfANG II binding sites (K(d) = 53 +/- 10 and 1300 +/- 900 pM). Two classes of dfANG II binding sites were also detected in the atrium (K(d) = 47 +/- 13 and 4690 +/- 930 pM) and in the outer layer of the conus arteriosus (K(d) = 16 +/- 9 and 398 +/- 83 pM). Conversely, the ventricular endocardium and the inner conal layer were characterized by a single class of dfANG II binding sites with affinity values of 48 +/- 11 and 106 +/- 3.3 pM, respectively. Competition experiments with either cold dfANG II or CV11974 or CGP42112 (specific ligands for mammalian AT(1) and AT(2) receptors, respectively) demonstrated a prevalence of CGP42112-selective dfANG II binding sites in both the inner and the outer conal layers. In the atrium, the ventricular myocardium, and the outer conal layer, dfANG II high-affinity binding sites poorly discriminated among the cold ligands. These results suggest that the dogfish heart may be a target organ of ANG II with distinct ANG II receptor subtype distributions.

Angiotensin and angiotensin receptors in cartilaginous fishes

In mammals, a principal bioactive component of the renin-angiotensin system (RAS), angiotensin II (ANG II), is known to be vasopressor, dipsogenic, a stimulant of adrenocortical secretion and to control glomerular and renal tubular function. Historically, a RAS analogous to that found in mammals was thought to have first evolved in the bony fishes. Recent research has identified the unusually structured elasmobranch [Asp(1)-Pro(3)-Ile(5)] ANG II. Physiological studies have demonstrated that ANG II in elasmobranchs is vasopressor, and stimulates interrenal gland production of the elasmobranch corticosteroid 1alpha-hydroxycorticosterone. The specific binding of ANG II in elasmobranchs has been reported in gills, heart, interrenal gland, gut and rectal gland. The precise osmoregulatory role ANG II plays in cartilaginous fishes is not yet known; however, putative evidence is emerging for a role in the control of drinking rate, rectal gland secretion, and kidney function.

Expression of a duplicate Na,K-ATPase beta(1)-isoform in the European eel (Anguilla anguilla)

Recent studies on teleost fish have suggested that their genomes have undergone ancient polyploidization events resulting in the duplication of the genome. A duplicate copy of the Na,K-ATPase beta(1)-isoform (called beta(233)) has been identified in the European eel (Anguilla anguilla). The beta(233)-isoform shares high levels of nucleotide (74.8%) and amino acid (69.9%) homology with the eel beta(1)-subunit as well as other vertebrate beta(1)-sequences. Compared with the widely expressed beta(1)-isoform, expression of beta(233)-mRNA is mainly restricted to epithelial tissues. Seawater acclimation induced increases in beta(233)-mRNA levels in kidney, gill, and intestine of migratory "silver" but not the nonmigratory "yellow" adult eels, suggesting that the factors responsible for this upregulation are themselves developmentally regulated. Expression of a variably glycosylated 40- to 52-kDa beta(233)-protein in both gill "chloride" and intestinal epithelial cells suggests that the beta(233)-isoform of Na,K-ATPase may play an important functional role in the major osmoregulatory tissues of euryhaline fish such as the eel.

Male attractiveness and differential testosterone investment in zebra finch eggs

Good-genes hypotheses of sexual selection predict that offspring fathered by preferred males should have increased viability resulting from superior genetic quality. Several studies of birds have reported findings consistent with this prediction, but maternal effects are an important confounding variable. Those studies that have attempted to control for maternal effects have only considered differential maternal investment after egg laying. However, female birds differentially deposit testosterone in the eggs, and this influences the development of the chick. This study shows that female birds deposit higher amounts of testosterone and 5alpha-dihydrotestosterone in their eggs when mated to more attractive males.

Renin-angiotensin system in elasmobranch fish: A review

The renin-angiotensin system (RAS) has been identified recently in elasmobranch fish, and the structure of angiotensin II (ANG II) is unusual ([Asp(1),Pro(3),Ile(5)]-ANG II) compared to other vertebrates. Receptors for ANG II have been identified in blood vessels and in a variety of osmoregulatory tissues including the gill, kidney and rectal gland. In addition, there is considerable binding to the interrenal gland and the stimulation of 1alpha-hydroxycorticosterone production in vitro suggests a physiological role in corticosteroidogenesis. ANG II is a potent vasoconstrictor and this effect does not appear to be mediated by sympathetic activation or catecholamine release. Although the RAS may not be involved in maintaining basal blood pressure, it may be important in situations in which blood pressure is reduced. Understanding of the role of ANG II as an osmoregulatory hormone is only just emerging with putative roles in the control of gill, rectal gland and perhaps, drinking. In addition, the stimulation of corticosteroid secretion may provide another means of controlling osmoregulation. J. Exp. Zool. 284:526-534, 1999.

A radioimmunoassay for the determination of angiotensin II in elasmobranch fish

A homologous radioimmunoassay was developed to determine the concentration of angiotensin II (Asn1, Pro3, Ile5)-Ang II) in elasmobranchs. Cross-reactivity with elasmobranch angiotensin I and other heterologous angiotensins was high and therefore all potentially cross-reacting angiotensins were separated by high performance liquid chromatography after prior extraction with Sep-Pak C18 cartridges. The validity of the assay for the determination of elasmobranch Ang II was demonstrated by parallelism with a series of Ang II standards with serially diluted elasmobranch plasma extracts. Overall recovery of elasmobranch Ang II added to a plasma pool was 75.1 +/- 5.2%. Plasma Ang II concentrations measured by our RIA were similar in fish adapted to 70, 100, or 120% SW at 139 +/- 20.1, 109 +/- 15.3, and 119 +/- 16.3 fmol . ml-1, respectively.

Direct vasoconstrictor action of homologous angiotensin II on isolated arterial ring preparations in an elasmobranch fish

Arterial rings were prepared from the branchial artery, coeliac artery and ventral aorta of the Japanese dogfish Triakis scyllia and used to determine arterial contraction in a myograph. Noradrenaline caused a dose-dependent contraction (10(-9)-3 x 10(-6) M) that was completely inhibited by pre-treatment with 10(-7) M phentolamine. Homologous dogfish angiotensin II (ANG II) ([Asn1, Pro3, Ile5]-ANG II) also caused dose-dependent contraction (10(-9)-3 x 10(-6) M), but phentolamine had no effect on this response. Administration of dogfish angiotensin I (ANG-I) ([Asn1, Pro3, Ile5, Gln9]-ANG I) resulted in a contraction similar to that produced by ANG II and the effect could be blocked with 10(-7) M captopril. The mammalian ANG II receptor antagonists [Sar1, Ile8]-ANG II and [Sar1, Ala8]-ANG II caused dose-dependent contractions of coeliac artery rings, but were less potent than homologous ANG I and ANG II. These results show that the contractile effect of [Asn1, Pro3, Ile5]-ANG II is not mediated by the alpha-adrenergic system and contractions of arterial rings by noradrenaline and elasmobranch ANG II are mediated by separate vascular receptors. The elasmobranch ANG II vascular receptor may have co-evolved with the unusual structure of this peptide.

Cardiovascular actions of dogfish urotensin I in the dogfish, Scyliorhinus canicula

A synthetic replicate of dogfish urotensin 1 (U-I), a 41-amino-acid residue peptide isolated from an extract of the caudal spinal cord region of the European spotted dogfish Scyliorhinus canicula was prepared in order to study its cardiovascular actions in the species of origin. Bolus intraarterial injections of dogfish U-I (0.3-30 nmol/kg body wt) into the celiac artery of unanesthetized dogfish produced a transient fall in arterial blood pressure (P < 0.05 in the dose range 1-3 nmol/kg) followed by a sustained and dose-dependent rise in pressure (P < 0.05 in the dose range 1-30 nmol/kg). The maximum depressor response (to 3 nmol/kg) was 0.25 +/- 0.08 kPa and the maximum pressor response (to 30 nmol/kg) was 1.08 +/- 0.09 kPa. There was no significant effect on heart rate at any dose tested. Pretreatment of the animals with the alpha-adrenergic receptor antagonist phentolamine significantly (P < 0.05) attenuated the pressor response to injections of dogfish U-I (1 nmol/kg and 10 mol/kg), demonstrating that the effects of the peptide are mediated, at least in part, through release of catecholamines. The data suggest that U-I, released together with potent pressor peptide urotensin II from the caudal neurosecretory system, may play a physiological role in cardiovascular regulation in elasmobranchs.

The presence of angiotensin II receptors in elasmobranchs

The presence of specific Ang II receptors in membrane fractions was investigated using 125I-labeled homologous Ang II ([Asn1, Pro3, Ile5]Ang II; df Ang II) in Triakis scyllia. Specific binding sites occurred in a variety of tissues, with highest binding in interrenal tissue (17.11 +/- 2.45 fmol Ang II/mg protein) and gill (6.26 +/- 0. 69 fmol Ang II/mg protein) and possible Ang II receptors in rectal gland and other tissues. 125I-[Asn1, Pro3, Ile5]Ang II (10(-10)M) binding to branchial cell membrane fraction (25 microg protein) in 5 mM MgCl2, 125 mM NaCl, 50 mM Tris-HCl, 0.2% bovine serum albumin at 28 degrees (1) is rapid and saturable; (2) increases as a function of membrane concentration and time; and (3) optimally fits to a two-site (high-and low-affinity) model. The equilibrium dissociation constant (0.11 +/- 0.01 nM) and binding site concentration (35.00 +/- 1.16 fmol/mg protein) are similar to those of mammalian and avian vascular Ang II receptors. Bound labeled ligand was not competitively displaced by dogfish Ang I, dogfish C-type natriuretic peptide, bradykinin, or the AT1 receptor antagonist, CV 11974. The AT2 receptor antagonist, CGP 42112, was much less potent at displacing the labeled ligand compared to the unlabeled ligand.

The role of the renin-angiotensin system in the control of blood pressure and drinking in the European eel, Anguilla anguilla

The role of the renin-angiotensin system (RAS) in the control of blood pressure and drinking was investigated in fresh water (FW)- and seawater (SW)-adapted eels, Anguilla anguilla, by comparing the effects of pharmacological manipulation through the use of papaverine (stimulator) and captopril (inhibitor) on the endogenous system. In SW eels basal blood pressure levels were lower (23.3 +/- 0.8 mm Hg) with correspondingly higher basal drinking rates (0.51 +/- 0.07 ml/kg/hr) and plasma AII concentrations (32.89 +/- 4.19 fmol/ml) compared to FW eels (33.8 +/- 1.3 mm Hg, 0.06 +/- 0.02 ml/kg/hr, 9.72 +/- 0.60 fmol/ml, respectively). In FW eels papaverine caused immediate hypotension with full recovery, decrease in plasma osmolality, and increase in drinking rate and plasma AII concentration, but in SW eels, hypotension with full recovery and an increase in plasma osmolality, drinking rate, and plasma AII concentration occurred. In FW eels captopril had no effect on the parameters measured, but in SW eels it caused a sustained decrease in blood pressure and a decline in the basal drinking rate and plasma AII concentration. Papaverine was also administered 15 min after captopril. In FW eels this manipulation caused hypotension only after the papaverine injection, followed by a partial recovery. Osmolality was unaffected, the previously observed papaverine-induced dipsogenic response was blocked, and the rise in plasma AII concentrations was smaller than with papaverine only. In SW eels there was an immediate hypotension after captopril administration with full recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

Primary sequence, tissue specificity and mRNA expression of the Na(+),K (+) -ATPase β1 subunit in the European eel (Anguilla anguilla)

The entire amino acid coding sequence of the Na(+),K(+)-ATPase β1 isoform was cloned from the gill of the European eel (Anguilla anguilla) by a PCR based method. The amino acid sequence translated from the nucleotide sequence shared 61.4 and 56.2% homology respectively with previously published Na(+),K(+)-ATPase β1 isoform sequences from the clawed toad (Xenopus laevis) and the ray (Torpedo californica) an elasmobranch fish. The size of the Na(+),K(+)-ATPase β1 mRNA transcript in eel tissues was demonstrated to be 2.35 Kb. Detectable levels of Na(+),K(+)-ATPase β1 mRNA were found at some level in all tissues except liver and cardiac muscle. The level of branchial Na(+),K(+)-ATPase β1 mRNA was observed to increase after the adaptation of fresh water eels to normal or double concentration sea water.

A peptide from the caudal neurosecretory system of the dogfish Scyliorhinus canicula that is structurally related to urotensin I

Using reversed-phase HPLC in combination with a radioimmunoassay for ovine corticotropin-releasing hormone (CRH), a peptide with CRH-like immunoreactivity was isolated in pure form from an extract of the caudal spinal cord region of the spotted dogfish, Scyliorhinus canicula. The primary structure of the peptide was established as Pro-Ala-Glu-Thr-Pro-Asn-Ser-Leu10-Asp-Leu-Thr-Phe-His-Leu-Leu-Arg- Glu-Met-Ile- Glu20-Ile-Ala-Lys-His-Glu-Asn-Gln-Gln-Met-Gln30-Ala-Asp-Ser- Asn-Arg-Arg-Ile-Met - Asp-Thr40-Ile.NH2. This amino acid sequence shows moderate structural similarity to Catostomus urotensin I (51%) and to human CRH (56%). The data provide, therefore, chemical evidence to support the conclusions of earlier immunohistochemical studies that the diffuse caudal neurosecretory system of elasmobranchs produces a peptide that is immunochemically related to teleost urotensin I peptides. However, the primary structure of urotensin I has been poorly conserved during evolution.

Primary sequence, tissue specificity and expression of the Na+,K(+)-ATPase alpha 1 subunit in the European eel (Anguilla anguilla)

The entire cDNA nucleotide sequence of the Na+,K(+)-ATPase alpha 1 isoform was cloned from the gills of the European eel (Anguilla anguilla) by a PCR based method. The amino acid sequence translated from the sequence shared 89.4 and 85.6% homology respectively with previously published Na+,K(+)-ATPase alpha subunit sequences from elasmobranch (Torpedo californica) and teleost (Catostomus commersoni) fish. The size of Na+,K(+)-ATPase alpha 1 mRNA transcripts in eel tissues was demonstrated to be 3.5 kb, except in the ovary where a 3.7 kb transcript existed. Na+,K(+)-ATPase alpha 1 mRNA was present at some level in all tissues investigated with the exception of cardiac and skeletal muscle where no Na+,K(+)-ATPase alpha 1 mRNA was detectable. The level of branchial Na+,K(+)-ATPase alpha 1 mRNA increased after the adaptation of freshwater eels to normal or double concentration seawater.

Characterization of the endogenous intestinal peptide that stimulates the rectal gland of Scyliorhinus canicula

It has been postulated that gut peptides play a major role in the regulation of rectal gland secretion in elasmobranchs. An isolated perfused rectal gland secretion in elasmobranchs. An isolated perfused rectal gland preparation was developed for Scyliorhinus canicula that responded to dibutyryl 3',5'-cyclic monophosphate plus 3-isobutyl-1-methylxanthine, increasing chloride clearance rates threefold over basal levels. Activity was stimulated by an endogenous peptide, isolated in pur form by reverse-phase high-performance liquid chromatography from the intestine of S. canicula. The primary structure was established as Ser-Pro-Ser-Asn-Ser-Lys-Cys-Pro-Asp-Gly-Pro-Asp-Cys-Phe-Val-Gly-Leu-Met- NH2. This is a sequence identical to that of the tachykinin scyliorhinin II. Perfusion of synthetic scyliorhinin II increased secretion rate in the rectal gland of S. canicula in a dose-dependent manner with a maximal response at 10(-6) M, whereas vasoactive intestinal peptide, a stimulator in the spiny dogfish, Squalus acanthias, had no effect. We propose that scyliorhinin II is the uncharacterized peptide rectin, previously identified from the intestine of S. canicula.

Immunodetection of parathyroid hormone-related protein in plasma and tissues of an elasmobranch (Scyliorhinus canicula)

We have used antiserum to human parathyroid hormone-related protein (PTHrP) (1-16) to examine tissues and plasma of the dogfish (Scyliorhinus canicula) for the presence of immunoreactive PTHrP (irPTHrP). The plasma contained high concentrations of irPTHrP (9.34 +/- 0.37 pM), comparable to levels in humans with hypercalcaemia of malignancy. Other tissues with irPTHrP included brain neurones; epithelial cells of the saccus vasculosus, kidney, rectal gland and choroid plexus; and cells of the pituitary pars distalis. PTHrP was not detected in gut, skin, oviduct, and gill epithelia, nor in branchial cartilage. The principal source(s) of plasma PTHrP is not known.

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.

Effects of dogfish urotensin II on lipid mobilization in the fasted dogfish, Scyliorhinus canicula

Previous studies, both in vitro and in vivo, have shown that urotensin II stimulates hepatic release of nonesterified fatty acids in teleost fish, but the effects of the peptide on lipid mobilization in elasmobranchs are unknown. Infusions of synthetic dogfish urotensin II (40 pmol/min/kg for 30 min followed by 400 pmol/min/kg for 30 min) into the first afferent gill artery of the fasted, unrestrained dogfish, Scyliorhinus canicula (n = 6), produced no significant change in the circulating concentrations of acetoacetate, 3-hydroxybutyrate, and triacylglycerols. Circulating nonesterified fatty acids were undetectable (< 0.1 mmol/liter) both before and after the urotensin II infusions. There was no significant change in the circulating concentrations of glucose and lactate during either the low- or the high-dose infusions. The data support the hypothesis that lipid is converted primarily to ketone bodies in the livers of elasmobranch fish and do not indicate a role for urotensin II in regulating either lipid or glycogen mobilization.

Primary structures of peptides derived from proglucagon isolated from the pancreas of the elasmobranch fish, Scyliorhinus canicula

Three peptides derived from the posttranslational processing of proglucagon have been isolated from the pancreas of the elasmobranch fish, Scyliorhinus canicula (European common dogfish). The peptide HSEGT FTSDY SKYMD NRRAK DFVQW LMST represents the 29 amino acid residue form of glucagon previously identified in dogfish intestine. A second component with 33 amino acid residues represents glucagon extended from its COOH-terminal region by -KRNG. The peptide HAEGT YTSDV DSLSD YFKAK RFVDS LKSY represents glucagon-like peptide (GLP). The primary structures of the GLPs from mammals have strongly conserved but a comparison of the amino acid sequences of known GLPs from different classes of fish shows that the structure of the peptide has been very poorly conserved in lower vertebrates. Only three residues (Ala2, Asp9, and Leu26) are found in the same position in all fish GLPs. A similar comparison of the primary structures of glucagons from the same species shows 13 amino acid residues in common.

A novel angiotensin I isolated from an elasmobranch fish

It is believed that the renin-angiotensin system evolved initially in primitive bony fishes and is absent from elasmobranchs. We have isolated angiotensin I from the incubates of plasma and kidney extracts of an elasmobranch fish, Triakis scyllia, using eel vasopressor activity as an assay system. Its sequence was determined to be H-Asn-Arg-Pro-Tyr-Ile-His-Pro-Phe-Gln-Leu-OH. Dogfish angiotensin I is teleost-like because of an asparagine residue at position 1 but it is mammalian-like because of an isoleucine residue at position 5. The unique and most important substitution in dogfish angiotensin I is a proline residue at position 3 which may cause significant changes in its tertiary structure. A glutamine residue at position 9 is also unique among all angiotensin Is sequenced to date. Dogfish angiotensin I is more potent than rat angiotensin I in its vasopressor activity in the dogfish but the relationship is reversed in the rat. Thus angiotensin receptors as well as the hormone molecules appear to have evolved during vertebrate phylogeny. Our findings establish the elasmobranch renin-angiotensin system and support the hypothesis that the renin-angiotensin system is a phylogenetically old hormonal system which plays important roles in cardiovascular and fluid homeostasis.

Cardiovascular actions of dogfish urotensin II in the dogfish Scyliorhinus canicula

Bolus injections of synthetic dogfish urotensin II (0.1-1.0 nmol) into the celiac artery of the conscious dogfish Scyliorhinus canicula (n = 8) resulted in sustained and dose-dependent increases in arterial blood pressure and pulse pressure. A maximum rise in mean arterial pressure of 10.5 +/- 1.2 mmHg (equivalent to 38.6 +/- 4.2% over mean basal values) and a maximum increase in pulse pressure of 3.9 +/- 0.8 mmHg was elicited by injection of 0.5 nmol of peptide. In comparison, a bolus injection of epinephrine (5 nmol) elicited a rise of 24.8 +/- 3.3% in mean arterial pressure. Bolus injection of 0.5 nmol synthetic goby (Gillichthys mirabilis) urotensin II under the same conditions did not elicit a significant hypertensive response. When dogfish urotensin II (0.5 nmol) was administered 3 min after an intra-arterial injection of phentolamine, the rise in arterial blood pressure was completely abolished. Dogfish urotensin II produced a dose-dependent contraction (pD2 = 6.58 +/- 0.07; n = 8) of isolated rings of vascular muscle prepared from the first afferent branchial artery of the dogfish. A maximum contractile force of 1.3 mN was produced by 10(-5) M peptide. The urotensin II-induced contraction of the vascular rings was unaffected by pretreatment with tetrodotoxin (1 microM) or indomethacin (14 microM). It is concluded that urotensin II has potent hypertensive activity in the dogfish that is mediated, at least in part, through release of catecholamines, but the sustained nature of the pressor response suggests that the peptide may have a direct action on the heart.

The effect of dietary protein restriction on the secretory dynamics of 1 alpha-hydroxycorticosterone and urea in the dogfish, Scyliorhinus canicula: a possible role for 1 alpha-hydroxycorticosterone in sodium retention

The putative osmoregulatory role of the unique elasmobranch corticosteroid, 1 alpha-hydroxycorticosterone (1 alpha-OH-B), was investigated using dietary protein restriction as a means of limiting urea biosynthetic ability. Groups of dogfish (Scyliorhinus canicula) were adapted to either a high or a low protein diet (HPD and LPD respectively) and the secretory dynamics of urea and 1 alpha-OH-B were determined following acclimation to normal (100%), 130% and 50% sea water. In normal sea water, LPD fish showed significantly decreased blood production of urea compared with fish fed a HPD (P < 0.05), and the plasma urea concentration required to maintain iso-osmolality was achieved only by a substantial decrease in urea clearance from the plasma. Unlike HPD fish, LPD fish in 130% sea water had no apparent ability to increase plasma urea concentration. An alternative strategy adopted by these animals was the retention of high plasma concentrations of Na+ and Cl-, which increased plasma osmolality and tended to decrease osmotic water loss. Concomitant with the increased ion concentrations, plasma 1 alpha-OH-B concentration was also greatly elevated in LPD fish indicating that the steroid may be acting to minimize Na+ (and Cl-) excretion at osmoregulatory sites such as the rectal gland, kidney and gills. This and a previous study have also demonstrated that 1 alpha-OH-B concentration is elevated in 50% sea water. Decreases in plasma Na+ concentration are tolerated down to 75% sea water, whereafter Na+ is preferentially retained and further decreases in osmolality are achieved by reductions in plasma urea concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Arginine vasotocin and fish osmoregulation

Pituitary arginine vasotocin (AVT) secretion is sensitive to the osmotic challenge associated with transfer of euryhaline teleosts between sea water (SW) and fresh water (FW). Pituitary AVT content in FW-adapted flounders greatly exceeds that in SW-adapted fish. Plasma AVT concentrations are in the range 10(-12)-10(-11) M (1-100 pg/ml). In euryhaline species, like the eel, flounder and trout, there were no consistent, marked differences in plasma AVT concentrations between FW- and SW-adapted fish. In SW- but not FW-adapted flounders plasma AVT and sodium concentrations are correlated. During the initial period of acclimation from FW to SW eels, show a transitory rise in plasma AVT concentration which is associated with a transitory increase in plasma Angiotensin II. In view of the range of plasma AVT concentration observed in SW- and FW-adapted fish, it is evident that of the described dose-dependent effects of AVT on urine production, only the antidiuretic responses are likely to be of physiological significance. In addition to the presence of a V1-type vascular receptor for AVT, the nephron also possesses a V2-type receptor, coupled to adenylate cyclase. In the gill tissue AVT receptors are also present, but in this tissue receptor occupancy leads to inhibition of cAMP production rather than the stimulation observed in renal tissue. The functional significance of the gill AVT receptor remains to be established.

Mechanisms of ACTH- and angiotensin II-stimulated 1 alpha-hydroxycorticosterone secretion in the dogfish, Scyliorhinus canicula

An isolated perifused interrenal gland preparation from the lesser-spotted dogfish, Scyliorhinus canicula, was used to investigate the mechanisms of action of ACTH and angiotensin II (AII) on elasmobranch adrenocortical cells. ACTH-stimulated 1 alpha-hydroxycorticosterone secretion was unaffected by dantrolene and significantly decreased in the absence of extracellular calcium. Dibutyryl cyclic AMP produced a dose-dependent increase in 1 alpha-hydroxycorticosterone secretion. The results suggest that the mechanism of ACTH action in elasmobranchs may be similar to that reported for mammals and amphibians, involving the synergistic action of calcium with the cyclic AMP messenger system. AII-stimulated 1 alpha-hydroxycorticosterone secretion was significantly inhibited in the presence of dantrolene and in the absence of extracellular calcium, indicating that both extracellular and intracellular calcium are required for the full action of AII. These results are consistent with results in mammals and amphibians where AII stimulates phosphatidylinositol 4,5-bisphosphate hydrolysis and changes in intracellular calcium concentration, and they suggest that AII may operate via this mechanism to stimulate 1 alpha-hydroxycorticosterone secretion in elasmobranchs.

Distribution and activity of dogfish NPY and peptide YY in the cardiovascular system of the common dogfish

Neuropeptide Y is present in sympathetic nerves in the mammalian cardiovascular system. This study has investigated the distribution of neuropeptide Y in the cardiovascular and gastrointestinal systems and the effect of dogfish neuropeptide Y and related peptides on cardiovascular tissue of an elasmobranch fish, the common dogfish (Scyliorhinus canicula). Neuropeptide Y-like immunoreactivity is present in varicose nerve fibers innervating dogfish gut and cardiovascular tissue and in endocrine cells of the dogfish spiral intestine. Dogfish neuropeptide Y, dogfish peptide YY, and porcine neuropeptide Y contract the dogfish afferent branchial artery in a concentration-dependent manner. The effect is not inhibited by the presence of tetrodotoxin or by removal of the endothelium. The mammalian Y1 receptor selective agonist [Leu31Pro34]NPY but not the mammalian Y2 receptor selective agonist neuropeptide Y-(13-36) peptide has vasoconstrictor properties in this system, suggesting that the receptor mediating the vasoconstriction resembles the mammalian Y1 receptor more than the Y2 receptor.

Primary structures and biological activities of substance-P-related peptides from the brain of the dogfish, Scyliorhinus canicula

Two peptides with substance-P-like immunoreactivity were isolated in pure form from an extract of the brain of the elasmobranch fish, Scyliorhinus canicula (european common dogfish). One peptide was identical to scyliorhinin I, previously identified in dogfish intestine, and the second was the undecapeptide Lys-Pro-Arg-Pro-Gly-Gln-Phe-Phe-Gly-Leu-Met-CONH2 which is structurally similar to mammalian substance P. Scyliorhinin II or a peptide analogous to mammalian neurokinin A were not detected in the extract. Synthetic dogfish substance P ([Lys1, Arg3, Gly5]substance P) was approximately threefold more potent than mammalian substance P (Kd = 0.21 +/- 0.11 nM versus Kd = 0.74 +/- 0.17 nM; mean +/- SD; n = 6) in inhibiting the binding of 125I-labelled substance P to neurokinin (NK1) receptors in rat submandibular gland membranes. The vasodilator action of tachykinins in mammals is mediated primarily through interaction with NK1 receptors. Bolus intravenous injections of [Lys1, Arg3, Gly5]substance P (100 pmol) and scyliorhinin I (100 pmol) produced appreciable (> 4 kPa) decreases in arterial blood pressure in the rat whereas intravenous injections of up to 5 nmol of the peptides into conscious, unrestrained dogfish produced no change in arterial blood pressure, pulse amplitude or heart rate. Injections of greater amounts of the peptides (10-50 nmol) produced a slight increase (400-667 Pa) in blood pressure. The data indicate that mammalian-type NK1 tachykinin receptors are not involved in cardiovascular regulation in elasmobranch fish.

Drinking behaviour in sea water and fresh water teleosts, the role of the renin-angiotensin system

Basal drinking rate and responses to administered angiotensin were examined in 12 species of fish. The responses of representative euryhaline, stenohaline marine and fresh water species to pharmacological manipulation of endogenous renin-angiotensin system (RAS) activity were also investigated.Basal drinking rates were consistently low in stenohaline and euryhaline fresh water fish, and all species examined showed an increased imbibition in response to administered angiotensin. Marine fish drank large volumes of water, rates varying considerably between species, with euryhaline species exhibiting lower rates than stenohaline groups. The extremely high drinking rates observed in the sea scorpion were associated with a high plasma osmolality. With the exception of the sea scorpion, all other species examined in sea water showed a further rise in drinking in response to exogenous angiotensin.Although the freshwater stenohaline carp showed a dipsogenic response to angiotensin, it was apparently unable to evoke this response when fish were acclimated to brackish water. The high drinking rates of both euryhaline and stenohaline fish held in sea water appeared dependent upon an activated endogenous RAS, and were lowered following inhibition of Al to All conversion by Captopril. Drinking was further stimulated in these marine species following stimulation of endogenous RAS activity by the administration of the hypotensive agent Papaverine. The study endorses a role for the RAS in the control of adaptive drinking in euryhaline and stenohaline marine teleosts.

Renin and angiotensin converting enzyme in elasmobranchs

Renin-like activity (RLA) and angiotensin I converting enzyme-like activity (ACELA), the two key enzymes of the renin-angiotensin system (RAS), were sought in the elasmobranch Scyliorhinus canicula. Renal extracts were desalted in a G-25 and eluted in a G-100 Sephadex column (calibration 15,000-70,000). The fractions were concentrated in a vacuum device. A 48,000-MW fraction incubated with synthetic and porcine angiotensiongen generated angiotensin I estimated by RIA. This same fraction was vasopressor in rats and dogfish. ACELA was sought in gill, heart, liver, spleen, pancreas, intestine, kidney, gonads, brain, skin, and muscle of dogfish using a spectrophotometric assay. The highest level of ACELA was found in the gills followed by spleen, kidney, and brain (33.79 +/- 2.3, 29.56 +/- 1.0, 14.62 +/- 1.0, and 13.80 +/- 2.3 nmol hippurate/min/mg protein, respectively). Intestine, gonads, skin and muscle contained no measurable amounts of ACELA. Captopril inhibited enzymatic activity from all ACELA containing tissues.

A C type natriuretic peptide is a vasodilator in vivo and in vitro in the common dogfish

The effects of an elasmbranch cardiac C-type natriuretic peptide (dogfish CNP-22) on arterial blood pressure were investigated in vivo in chronically cannulated dogfish Scyliorhinus canicula and in vitro by a myographic technique using the distal part of the first branchial artery. In-vivo dogfish CNP-22 caused a dose-dependent reduction in mean arterial blood pressure which was much more potent than that of alpha-human ANP. In-vitro dogfish CNP-22 also caused a dose-dependent relaxation which was independent of the endothelium. These results are in marked contrast to those obtained in similar studies on other vertebrate species in which CNP exhibited only mild hypotensive effects compared to both atrial and brain natriuretic peptides. This study indicates the importance of using homologous peptides in determining the physiological role of natriuretic peptides in non-mammalian vertebrates.

Structural characterization of neuropeptide Y from the brain of the dogfish, Scyliorhinus canicula

A peptide of the pancreatic polypeptide (PP) family was isolated in pure form from the brain of an elasmobranch fish, Scyliorhinus canicula (European common dogfish). The primary structure of the peptide was established as: Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu10-Gly-Ala-Pro-Ala-Glu-Asp- Leu-Ala-Lys- Tyr20-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu30-Ile-Thr-Arg- Gln-Arg-Tyr-NH2. This sequence contains only two amino acid substitutions compared with pig neuropeptide Y (NPY) (Gly for Asp11 and Lys for Arg19), and two substitutions (Gly for Asp11 and Leu for Met17) compared with frog NPY. The amino acid sequence of NPY from dogfish brain is appreciably different from the neuropeptide Y-related peptide previously isolated from dogfish pancreas (five amino acid substitutions). The data indicate that evolutionary pressure to conserve the complete primary structure of neuropeptide Y has been very strong. It is suggested that the NPY-related peptide present in the pancreas of elasmobranch and teleost fish represents the piscine equivalent of mammalian peptide tyrosine tyrosine (PYY).

Purification and characterization of urotensin II and parvalbumin from an elasmobranch fish, Scyliorhinus canicula (common dogfish)

The caudal portion of the spinal cord of elasmobranch fish incorporates a diffuse neuroendocrine system. Using an antiserum raised against urotensin II from a teleost fish (goby) to facilitate purification, a peptide structurally related to urotensin II was isolated in pure form from an extract of neuroendocrine tissue from the spinal cord of the European common dogfish, Scyliorhinus canicula. The primary structure of the peptide was established as: Asn-Asn-Phe-Ser-Asp-Cys-Phe-Trp-Lys-Tyr-Cys-Val. The amino acid sequence was confirmed by chemical synthesis. A comparison of this sequence with those of the known teleost urotensin II peptides shows that the cyclic region of the molecule has been fully conserved between species and suggests that the presence of an acidic residue at position 5 and a hydrophobic residue at position 12 are important features for the biological activity of the peptide. The dogfish spinal cord extract also contained a high concentration of the calcium-binding protein, parvalbumin and the amino acid sequence at its NH2 terminus [residues (1-50)] was determined.

Biological actions of atrial natriuretic factor in flatfish

Flounder adapted to seawater were chronically cannulated and received a single i.v. injection of either saline (control) or 10 µg/kg b.w. of human ANF. Compared to controls, ANF significantly reduced (p<0.001) mean arterial blood pressure; full recovery was evident after 4 hours. Blood samples taken at intervals after saline or ANF injection showed that ANF caused a marked increase of 33.7 µg/100 ml in plasma cortisol concentration (p<0.001) 5 hours post injection. The rate of recovery of(22)Na in seawater after a single i.v. injection of 14×10(6) cpm/kg(22)NaCl was significantly increased (p<0.01) following ANF injection compared to controls suggesting that ANF stimulates Na(+) efflux. This observation was confirmed in plaice and dab. The steroidogenic action of ANF and its ability to promote Na(+) efflux are discussed in relation to its potential osmoregulatory role in teleost fish.

Isolation of high-molecular-weight C-type natriuretic peptide from the heart of a cartilaginous fish (European dogfish, Scyliorhinus canicula)

A high-molecular-weight form of C-type natriuretic peptide (CNP) was isolated from both cardiac atria and ventricles of European dogfish, Scyliorhinus canicula, and its primary structure was determined. The peptide consists of 115 amino acid residues, in which the C-terminal 22 residues show high homology to CNPs identified to date. This is the first direct evidence for the presence of natriuretic peptide in the cartilaginous fish, and for the presence of CNP in an organ other than the brain.

Structural characterization and biological activity of a neuropeptide Y-related peptide from the dogfish, Scyliorhinus canicula

A peptide of the pancreatic polypeptide (PP) family was isolated in pure form from the pancreas of an elasmobranch fish, Scyliorhinus canicula (European common dogfish). The primary structure of the peptide was established as: Tyr-Pro-Pro-Lys-Pro-Glu-Asn-Pro-Gly-Glu10-Asp-Ala-Pro- Pro-Glu-Glu-Leu-Ala-Lys-Tyr20-Tyr-Ser-Ala-Leu-Arg-His- Tyr-Ile-Asn-Leu30-Ile-Thr-Arg-Gln-Arg-Tyr.NH2. This sequence contains 86% amino acid sequence homology with human neuropeptide Y, and the COOH-terminal region (residues 20-36) has been fully conserved. Bolus injection of a synthetic replicate of the peptide (0.5-4 nmol) into the celiac artery of conscious dogfish resulted in a significant (P less than 0.01) and dose-dependent increase in arterial blood pressure. A maximum rise in mean pressure (67 +/- 11% over mean basal values; n = 6) was elicited by an injection of 2 nmol peptide. Bolus injections of human neuropeptide Y (0.5-4 nmol) also elicited dose-dependent rises in blood pressure, and the effects produced by the dogfish and human peptides were not significantly different at any dose. The data are consistent with a physiological role for neuropeptide Y-related peptide in cardiovascular regulation in elasmobranch fish.

Effects of altered dietary sodium intake on hormonal profiles in salt-sensitive hypertensive rats

Blood pressure and selected putatively influential hormones were measured in Brattleboro rats which were without diabetes insipidus and which were subjected to various manipulations in dietary sodium intake. Rats fed a control diet from weaning to 16 weeks of age showed a slow increase in blood pressure whereas rats fed a sodium-enriched diet for the same period exhibited sustained hypertension (115 +/- 3 versus 169 +/- 5 (S.E.M.) mmHg). In animals fed a sodium-enriched diet plasma concentrations of antidiuretic hormone (ADH) were significantly increased from 55 +/- 8 to 108 +/- 5 fmol/l. Rats fed the control diet from weaning (group A) and subsequently maintained on that diet or changed to a sodium-enriched diet or sodium-deficient diet showed no differences in their blood pressure. Plasma hormone concentrations were similar in these groups, with the exception of aldosterone suppression in rats switched from control to a sodium-enriched diet (0.26 +/- 0.04 versus 0.08 +/- 0.03 nmol/l; P less than 0.001). Animals fed the sodium-enriched diet from weaning to 16 weeks of age (group b) and either maintained on that diet or changed to a control diet showed little change in their established hypertension. Transfer to the control diet was associated with increased plasma renin concentrations (PRC) (13.8 +/- 2.1 to 122.6 +/- 6.2 nmol/l) and plasma aldosterone concentrations (0.04 +/- 0.01 to 0.08 +/- 0.01 nmol/l; P less than 0.001) but corticosteroids and ADH concentrations were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretory patterns of 1 alpha-hydroxycorticosterone in the isolated perifused interrenal gland of the dogfish, Scyliorhinus canicula

An isolated in-vitro perifused interrenal gland preparation from the dogfish Scyliorhinus canicula was used to study production of quantitatively the major corticosteroid 1 alpha-hydroxycorticosterone (1 alpha-OH-B), measured by radioimmunoassay. Basal secretory rates were 877.1 +/- 145 (S.E.M.) fmol/mg per 15 min (n = 14) and the preparation remained viable for up to 22 h, as reflected in a brisk response to 10 microM cyclic AMP (cAMP) after this time. Steroid production responded in a dose-dependent manner to porcine ACTH, with 10 microM producing a maximum stimulation of 225% above the basal secretory rate. cAMP (10 microM) produced an increase of 278% above basal, while 1 microM forskolin increased basal secretory rates by 127%. [Val5]- and [Ile5]-angiotensin II (0.1 microM) increased 1 alpha-OH-B production by 120 and 372% respectively over basal secretory rates. Increasing the concentration of K+ in the perfusate from 8 mM to 12, 18, 28 and 40 mM produced a significant rise only at 28 mM. Alterations in the concentration of Na+ and osmolarity of the perifusion medium had inconsistent effects on steroid production. Increased concentrations of urea (from 360 to 720 mM) increased the basal secretory rate by 121%, whilst reducing the concentration of urea (from 360 to 90 mM) had no effect.

Circulatory and ionoregulatory effects of atrial natriuretic peptide on rainbow trout (Salmo gairdneri Richardson) fed normal or high levels of dietary salt

Rainbow trout fed a normal salt diet (1.3% NaCl) or a high salt diet (12% NaCl for at least 6 months) were chronically cannulated in the dorsal aorta and received 10 μg kg(-1) ANP (1-28 human, UBC-Bioproducts) infused over a 10 min period. This had an insignificant influence on sodium balance, blood electrolytes and branchial sodium fluxes. In fish given a normal diet, the blood pressure and heart rate were uninfluenced by ANP, but pulse pressure was reduced by on average 60% and in some cases was not evident at all. Blood pressure in the fish fed a high salt diet was significantly higher than in the control fish; this together with heart rate and pulse pressure was not affected by ANP administration.