Ian W. Henderson

Angiotensin(1-7) is an antagonist at the type 1 angiotensin II receptor

Objective The present study investigated the antagonism of the amino-terminal heptapeptide fragment of angiotensin II {[des-Phe8]-angiotensin II; Ang(1–7)} to angiotensin II (Ang II) both in vitro in rabbit aortae and in vivo in rats. Methods and results In rabbit isolated endothelium intact aortic rings Ang(1–7) caused a concentration-related rightward displacement of the Ang II curve and depressed the maximum response to Ang II. By applying the data to a Schild plot an apparent pA2 of 5.5 was calculated. This depression of maximum response could be reversed by co-incubation of Ang(1–7) with the competitive angiotensin antagonist losartan. Ang(1–7) had no effect on the contractile responses of several other agonists. Intravenous infusion of 10 or 100 μg/kg per min Ang(1–7) had no effect on the resting blood pressure in the anaesthetized rat but inhibited Ang II-induced pressor responses. Conclusion The present results show that Ang(1–7) is a specific non-competitive antagonist of Ang II at type 1 angiotensin II receptors.

6 – The Adrenocortical Steroids, Adrenocorticotropin and the Corpuscles of Stannius

This chapter discusses the role of the adrenocortical secretions in the physiology of fishes. In studying the endocrinology of fishes, it is examined that aquatic environment does not exhibit the extreme vagaries encountered in the terrestrial existence. The first attempts to isolate adrenocortical secretions from the blood of fish were performed by Phillips and Chester Jones and Bondy. The principal hormones identified in teleost plasma were cortisol, cortisone, and corticosterone. The chapter presents a table showing a summary of the data in the literature on the level of adrenocorticosteroids in fish blood. Metabolic and endocrine mechanisms to accommodate engorgement in the cases of fishes and the slow planktonic continuous feeding of others, and even the periodic cessation of feeding in others have also been discussed in the chapter.

Somatostatin-related and glucagon-related peptides with unusual structural features from the European eel (Anguilla anguilla)

Peptides derived from prosomatostatins I and II and from two distinct proglucagons have been isolated from the pancreas of a teleost fish, the European eel (Anguilla anguilla). The product of prosomatostatin I processing, somatostatin-14, is identical to mammalian somatostatin-14. A 25-amino-acid-residue peptide (Ser-Val-Asp-Asn-Gln5-Gln-Gly-Arg-Glu-Arg10-Lys-Ala-Gly-Cys- Lys15-Asn-Phe-Tyr- Trp-Lys20-Gly-Pro-Thr-Ser-Cys25) is derived from prosomatostatin II. Compared with the corresponding peptides from other teleost fish, the eel somatostatin-25 contains the unusual substitution Pro for Phe at position 22. This peptide was also isolated in a form containing a hydroxylsyl residue at position 20. A 29-amino-acid-residue eel glucagon contains four substitutions relative to human glucagon Asn for Ser8, Glu for Asp15, Thr for Ser16, and Ser for Thr29). In common with mammalian and avian glucagons but unlike most other fish glucagons, the eel peptide possesses a glutamine residue at position 3. A peptide derived from a second proglucagon comprises 36 amino acid residues. A 7-residue C-terminal extension to the glucagon sequence shows structural similarity to the corresponding extension in ratfish (Hydrolagus colliei) glucagon and mammalian oxyntomodulin.

Sodium exchanges in goldfish (Carassius auratus L.) adapted to a hypertonic saline solution

Abstract 1. 1. Goldfish were adapted to diluted sea water (190 m-equiv./1 of Na) which was hyperosmotic to plasma from fresh-water-adapted fish. Fish survive well in this medium but plasma Na levels rise to equal those of the environment and exchangeable Na increases by 74 per cent. 2. 2. Fish in this hyperosmotic medium increase Na outflux about twenty times. They also increase their Na influx and drinking rates and decrease free-water excretion. 3. 3. Despite such adjustments, goldfish do not osmoregulate effectively. The goldfish appears to be stenohaline chiefly because it lacks the ability to excrete enough Na actively across the gills to balance the increased Na intake from the hyperosmotic environment.

Influence of environmental salinity on renal and adrenocortical function in the toad, Bufo marinus.

Abstract 1. Renal and adrenocortical function have been studied in toads, Bufo marinus , adapted for a period of 3 wk to distilled water (DW) or to hyperosmotic sodium chloride (S) solutions. 2. In saline plasma osmolarity (300 mOsm/liter) was maintained marginally above that of the environment (285 mOsm/liter); in DW toads plasma osmolarity averaged 209 mOsm/liter. Little difference was seen in plasma potassium concentration, but S animals were considerably hypernatraemic compared with those in DW. The hypersomolarity of plasma in S toads partly resulted from a degree of uraemia. 3. An almost 20-fold difference in urinary osmolarity occurred when the two types of toad were compared, and this seemed to result largely from alterations in sodium excretion. 4. DW toads prepared a copious dilute urine; rates of glomerular filtration and urine flow were considerably greater in DW conditions than in S. Solute excretion was elevated in the S-adapted toads, and this was achieved partly by dramatically altered rates of tubular rejection. 5. In mixed renoadrenocortical (postcaval) blood aldosterone and corticosterone concentrations and secretory rates were much greater in distilled water adapted toads than in saline adapted ones. 6. Arterial blood pressure was marginally elevated in S toads. No changes in plasma renin were noted.

Metabolism of 25-hydroxycholecalciferol in a teleost fish, the rainbow trout (Salmo gairdneri)

Plasma concentrations of vitamin D3 (cholecalciferol) metabolites have been studied in rainbow trout (Salmo gairdneri) adapted to varying environmental calcium concentrations in both fresh water and artificial seawater, and in natural seawater. In vivo, intraarterial injection of tritiated 25-hydroxycholecalciferol was followed by its transformation to a number of metabolites including compounds that cochromatographed on high performance liquid chromatography (HPLC) with 1,25-dihydroxycholecalciferol and 25,26-dihydroxycholecalciferol. Hypercalcaemia and increased environmental calcium were associated with a greater transformation to the compound cochromatographing with 25,26-dihydroxycholecalciferol, while hypocalcaemia and reduced environmental calcium concentrations induced more conversion to the 1,25-dihydroxycholecalciferol-like compound. In vitro, both metabolites were produced by liver but not by kidney preparations, and the difference in conversion ratios observed in vivo associated with changes in plasma calcium were also seen in vitro. It is concluded that the metabolism of 25-hydroxycholecalciferol in the trout can be influenced by calcium status, but at present the physiological importance of this metabolism and the mechanisms and site(s) of action of the metabolites are unknown.

Single nephron filtration rates (SNGFR) in the trout,Salmo gairdneri

Abstract1.Trout kidney slices incubated in the presence of14C-sodium ferrocyanide accumulated radioactivity. Uptake by individual nephroi increased with time, stabilizing after 30 min. The greater the concentration of radioactivity the greater the uptake per mm of tubule, while reduced specific activity inhibited14C uptake.2.The renal excretory pattern of14C-sodium ferrocyanide was compared with that of3H-inulin in fresh water adapted trout. The renal clearance rates of the substances were similar and linearly related over a range or urine flows, providing plasma ferrocyanide concentrations were between 1.5 and 2.5 mM.14C-ferrocyanide is thus a reliable marker for glomerular activity in this species.3.A protocol for the determination of single nephron glomerular filtration rates (SNGFR) in trout is described. The method exploits the ability to visualize ferrocyanide as Prussian Blue within nephroi after a single pulse injection superimposed upon a constant infusion of14C-ferrocyanide. The effects of surgical procedure and extraluminal contamination are assessed.4.The SNGFR of freshwater trout, 1.31±0.2 nl/min is approximately 65% less than that observed in sea water adapted fish (3.74±1.12 nl/min). The overall, total kidney glomerular filtration rate, (GFR) is 142.6±17.4 μl/min/kg in fresh water animals and 20.1±0.9 μl/min/kg in sea water fish.5.It is concluded that whilst SNGFRs of sea water animals are higher than those of fresh water animals, filtration is distributed to nephron populations selected to meet the homeostatic demands of the organism.

Gastrin-releasing peptide from the intestine of the elasmobranch fish, Scyliorhinus canicula (common dogfish)

The concentration of gastrin-releasing peptide in the intestine of the elasmobranchian fish, Scyliorhinus canicula, measured with an antiserum directed against the COOH-terminal region of porcine gastrin-releasing peptide, was higher than the concentrations measured in mammalian intestines. The immunoreactivity was resolved by gel permeation chromatography into two peaks with the approximate elution volumes of porcine gastrin-releasing peptide and bombesin/neuromedin C. The primary structure of the larger peptide was established as Ala Pro Val Glu Asn Gln Gly Ser Phe Pro Lys Met Phe Pro Arg Ser His (Trp) Ala Val Gly (His Leu Met.NH2). Residues in parentheses are only tentatively assigned. Chromatographic evidence and the presence of the arginyl residue at position 15 in the peptide suggest that the smaller molecular form of gastrin-releasing peptide may be identical to mammalian neuromedin C. Amphibian bombesin was not identified in the dogfish gut.

The effects of vasopressin on pituitary oxytocin content and plasma renin activity in rats with hypothalamic diabetes insipidus (Brattleboro strain).

Abstract Drinking, urine flow and osmolarity, plasma renin activity (PRA), and pituitary oxytocin have been studied in male and female Brattleboro rats, homozygous [with diabetes insipidus (DI)] and heterozygous (non-DI) for the phenotype of hypothalamic diabetes insipidus. The polydipsia and polyuria as well as the extreme hypotonicity of the urine was confirmed for male and female DI rats: urine to plasma osmolar ratios averaged 0.5 in DI and 5.0 in non-DI. Under similar conditions female DI rats concentrated the urine slightly more than males. PRAs were higher in DI than in non-DI rats, a difference especially noticeable in male animals. Pituitary oxytocin content was much reduced in male and female DI rats compared with equivalent non-DIs. In male DI rats, vasopressin (1.0 U/rat/day for 7 days) produced a profound fall in PRA and an increased pituitary oxytocin content as well as inducing the formation of an hypertonic urine with renal reabsorption of osmotically free water. In female DI rats, graded does of vasopressin (0.1, 0.25, 0.5 or 1.0 U/rat/day for 8 days) all reduced the pituitary oxytocin concent to the same degree, while the reduction in fluid turnover and the marginal increases in PRA were roughly proportional to the dose employed. Female DI rats were less sensitive to vasopressin than male DI animals as judged by the urinary osmolarity achieved for a given dose of hormone.

Estrogen receptor mRNA in mineralized tissues of rainbow trout: calcium mobilization by estrogen

RT‐PCR was undertaken on total RNA extracts from bone and scales of the rainbow trout, Oncorhynchus mykiss. The rainbow trout estrogen receptor (ER)‐specific primers used amplified a single product of expected size from each tissue which, using Southern blotting, strongly hybridized with a 32P‐labelled rtER probe under stringent conditions. These data provide the first in vivo evidence of ER mRNA in bone and scale tissues of rainbow trout and suggest that the effects of estrogen observed in this study (increased bone mineral and decreased scale mineral contents, respectively) may be mediated directly through ER.