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SUMMARY
When isolated eel gills were perfused under conditions resembling, as closely as possible, those found in vivo and under constant pressure, neurohypophysial hormones decreased and catecholamines increased the rate of flow of perfusate, the latter response being mediated by β-adrenergic receptors. When the Ringer solution was not filtered before use, flow rates rapidly declined and 10−5 m-adrenaline or noradrenaline was required to maintain constant flow. Under these conditions, 10−14 m-isotocin or 10−13 m-arginine vasotocin (AVT) produced vasoconstriction. When the Ringer solution was filtered through a 0·22 μm Millipore filter before use, constant high flow rates could be maintained in the absence of catecholamines. Noradrenaline increased the flow rate at concentrations of down to 10−9 mol/l, adrenaline being slightly less active when filtered Ringer solution was used. However, the sensitivity to neurohypophysial hormones was considerably reduced, 10−11 to 10−10 m-isotocin and 5 × 10−11 to 5 × 10−10 m-AVT being the lowest concentrations producing vasoconstriction.
No difference in sensitivity to neurohypophysial hormones or catecholamines was observed between gills from seawater adapted or freshwater adapted gills. The results are discussed in relation to the alternative pathways of blood flow through the gills.
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Low doses of arginine-vasotocin (AVT), isotocin and oxytocin (1 pg–1 ng/kg body weight) were antidiuretic in eels adapted to fresh water but not in those adapted to sea-water. High doses (more than 10 ng/kg) were always diuretic. No effects on tubular water reabsorption were observed and the glomerular filtration rate (GFR) was proportional to the maximum reabsorptive rate for glucose (T m (glucose)) in eels adapted to sea-water. Increases in urinary flow appeared therefore to result from glomerular recruitment. Infusion of AVT or isotocin at low rates reduced the GFR and urinary flow of freshwater eels to the levels found in seawater eels. Vasopressin (lysine or arginine) had no direct effect on kidney function in freshwater eels but blocked both the diuretic and antidiuretic actions of the other hormones. When infused into seawater eels it was diuretic. This effect could have been due to blockade of the actions of endogenous AVT and/or isotocin.
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SUMMARY
The major steroid products of the rat adrenal gland were studied both in vitro and in vivo. It was found that these methods gave similar results with regard both to the nature of the compounds produced and to their relative proportions. In particular, the status of 11-desoxycorticosterone as a physiologically important adrenal product is discussed, and it is concluded that this compound, as well as aldosterone, may possibly be instrumental in controlling electrolyte flux in the rat.
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SUMMARY
A method for the study of renal function and measurement of mean ventral and dorsal aortic blood pressure for the freshwater and seawater-adapted eel, and during transfer of the animal from fresh water to sea-water, is described.
Freshwater eels have higher resting blood pressure, p-aminohippuric acid (PAH) and inulin clearance rates and urine flow than seawater eels. Urine from freshwater animals has low Na, K, Ca, Mg and Cl concentrations, while the clearance rate of inorganic phosphate exceeded that of inulin. Urine from seawater animals has high Na, Ca, Mg and Cl concentrations while that of inorganic phosphate was low. Clearance rates for Ca and Mg greatly exceeded those of inulin.
During transfer from fresh water to sea-water there was an initial fluctuation in blood pressure, urine flow and PAH and inulin clearance rates which lasted about 2 hr. Thereafter these gradually declined to values observed for the seawater-adapted animal.
The significance of PAH and inulin clearance rates in the study of renal function in the eel and in teleosts in general is discussed.
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SUMMARY
Removal of the caudal neurosecretory system from freshwater eels did not affect urine flow or urinary Na excretion. There was, however, a marked initial increase in K, Ca and Mg excretion which later declined to very low levels by the 4th day after operation.
Intravenous injection of saline extracts of Mugil or Anguilla urophyses elicited a rise in urine flow and inulin clearance rates. This response was correlated with rises in blood pressure in the dorsal aorta. Urinary Na concentration also increased.
Injection of saline extracts of corpuscles of Stannius at the dose of two glands/kg. body weight generally caused an initial decline in inulin clearance rates while urine volume increased. Smaller doses caused the reduction of inulin clearance rates only.
Isotocin, amongst the neurohypophysial peptides, was the most effective in causing a diuresis and increases in p-aminohippuric acid and inulin clearance rates. There was little or no change in urinary Na concentration. Oxytocin and arginine vasotocin were effective but less potent. Arginine or lysine vasopressin had no effect even at large doses.
Angiotensin II and adrenaline induced diuresis and natriuresis followed occasionally by a transient antidiuresis.
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Search for other papers by I. W. HENDERSON in
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SUMMARY
The distribution of water, electrolyte composition (Na, K, Ca, Mg, PO4, Cl) and extracellular fluid volume of eels (Anguilla anguilla L.) were investigated under different experimental conditions.
Adrenalectomy of the freshwater eel was followed by an increase in body weight, a fall in the amount and concentration of sodium in serum and muscle and a shift of water into the cells. The concentration of serum potassium remained within the normal range. Adrenalectomy of the sea-water eel was followed by a decrease in body weight and an increase in the concentration of extra- and intracellular sodium. The concentration of serum calcium also increased, that of potassium remained within the normal range but the actual content diminished.
Removal of the corpuscles of Stannius from the freshwater eel gave some effects similar to adrenalectomy. There was, however, no significant increase in body weight but the concentrations of serum potassium and calcium rose. Removal of the corpuscles from the sea-water eel brought about changes similar to, but less pronounced than those after adrenalectomy. The results of the injection of mammalian corticotrophin, cortisol, aldosterone and anti-aldosterone compounds are given. They are discussed in the light of the possible roles of the adrenal cortex and the corpuscles of Stannius in the maintenance of homeostasis of the eel in different environments.
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SUMMARY
Extracts of corpuscles of Stannius from the silver eel have been shown to contain a substance with a powerful pressor action on intravenous injection into the rat. This material resembles mammalian renin in being non-diffusible through cellophane, heat-labile, and destroyed by acidification to pH 2. The effect in the rat differs, however, from that produced by mammalian renin in being more prolonged, and frequently biphasic.
Pressor activity has also been demonstrated in extracts of kidneys from freshwater silver eels. Incubation of kidney extract with mammalian renin-substrate produced an angiotensin-like pressor substance.
Both renal and corpuscular extracts had a prolonged pressor effect on intravenous injection into the eel. The identities of these pressor materials have not been finally established.
Removal of the corpuscles of Stannius from freshwater silver eels was followed by a drop in blood pressure to levels normally found in eels adapted to seawater.
The possible existence, in the eel, of a renin-angiotensin system analogous to that existing in mammals is discussed.