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1. The extent to which renin release is affected by simultaneous changes in body Na and body fluid volume was studied in six sheep. 2. The animals' water intake was restricted for 10‐17 days after which they were offered solutions containing varying amounts of NaCl. 3. Plasma renin concentration (PRC) of water restricted sheep was 2‐3 times normal. 4. The changes in PRC following drinking were inversely related to the amount of sodium consumed, Na excretion and plasma Na concentration. There was no correlation between the changes of PRC and of plasma volume in so far as the latter is reflected by alterations in plasma protein concentration. 5. We conclude that changes in renin release were related to the animals' handling of NA, and not to alterations in body fluid volume. 6. These findings are compatible with the proposition that renin release was mediated by a macula densa mechanism.

1. The effects of the carbonic anhydrase inhibitors, acetazolamide, ethoxzolamide and benzolamide on the ionic composition of parotid saliva were studied in anaesthetized sheep with access to the parotid blood vessels. 2. The inhibitors were infused directly into the arterial blood supply to the gland to give blood concentrations in the range 10(‐5) to 10(‐2) M. 3. Mean anionic concentrations at basal flow rate before inhibitor infusion were, bicarbonate 98 m‐mole/l., phosphate 15 m‐mole/l. and chloride 26 m‐mole/l. In the presence of inhibitors, bicarbonate concentration fell by 11 m‐mole/ml. and phosphate and chloride concentrations rose. Secreto‐motor nerve stimulation increased bicarbonate concentration by 13 m‐mole/l. before infusion of inhibitors and the concentrations of the other anions fell. The bicarbonate rise was abolished by the inhibitors and the fall in phosphate concentration was balanced by a rise in chloride concentration. 4. These effects show that only a small component of the bicarbonate ion transfer system in the sheep parotid gland is sensitive to these inhibitors. 5. The relationship of these findings to a new enzyme with carbonic anhydrase action isolated from the sheep's parotid gland is discussed.

Several experimental investigators have reported that stimulation of gustatory and alimentary afferents may rapidly influence metabolic and endocrine processes. Changes may precede absorption of materials ingested and anticipate the physiological consequences. A colony of sheep with autotransplanted adrenal glands and a permanent unilateral parotid fistula, have been studied over a perior of 12 years. The effect on corticosteroid secretion of rapid satiation of salt appetite after 24–72 h of sodium depletion has been observed. The animals drank 300–900 mmol of NaHCO3solution in 5–20 min. Rapid voluntary intake of NaHCO3caused large evanescent reduction of aldosterone hypersecretion for the 15–36 min following satiation. Aldosterone secretion rebounded by 1 h towards control pre-drinking level. It then fell over 2–5 h to the Na+replete range as a result of absorption from the gut of the sodium ingested. The satiation inhibition was seen in the majority, but not all sheep who had had a parotid fistula for several years. The effect was reproducible in the one animal over as long as six years.Analysis of the mechanism showed that it was not due to change of the four factors currently known to be implicated in control of aldosterone secretion viz. plasma [Na], [K], angiotension II and ACTH. The data indicates the action of an unidentified factor in the control of aldosterone secretion - possibly an inhibitor substance originating in the brain.

Infusion of bovine parathyroid hormone (bPTH) preparations into the arterial blood supply of the vascularly isolated parotid gland in anaesthetized sheep increases salivary phosphate concentration and gland blood flow rate with rapid onset and offset of action. These responses have been used as a bioassay for PTH and PTH analogues and for assessing the properties of an in-vitro inhibitory analogue [Nle-8, Nle-18, Tyr-34]bPTH-(3–34)amide. [Nle-8, Nle-18, Tyr-34]bPTH-(1–34)amide at 10− 9to 10 −8mol/l was four to five times more potent than bPTH(1–34) on both salivary phosphate and blood flow assays. Human PTH(1–34) was not significantly more potent than bPTH(1–34). The [Nle-8, Nle-18, Tyr-34]bPTH-(3–34)amide analogue had very slight agonist activity at 3 × 10−7mol/l and at a 100:1 ratio of analogue to PTH it completely inhibited the action of bPTH(1–34) on phosphate secretion and gland blood flow. It caused partial inhibition at 10:1 and had no evident effect at 1:1. These results differ from previous in-vitro results and indicate that the preparation may be valuable for evaluation of agonist and antagonist analogues of PTH. The vascularly isolated parotid gland of the sheep permits repeated random testing of analogues in a control–test–control sequence and the results indicate high sensitivity to PTH in a rapidly reactive invivo system with two responding parameters.J. Endocr.(1984) 102, 375–379

Comparisons of aldosterone responses to [des-Asp1]-angiotensin II and angiotensin II, often at single dose levels, have shown a wide range of potency ratios. Therefore four-point dose–response comparisons were performed in sodium-replete sheep, using i.v. infusion rates of angiotension II and angiotensin II amide that reproduced the physiological range of blood concentration of angiotensin II for sheep. Angiotensin III was infused i.v. at the same rates. Effects on arterial blood pressure, cortisol secretion rate, adrenal blood flow and plasma levels of Na+and K+were also compared. The potency ratio, angiotensin III: angiotensin II amide, was 0·87 for actual aldosterone secretion rate and 0·90 for the calculated increase in aldosterone secretion. For angiotensin III: angiotensin II the ratios were 0·80 and 0·91 respectively. These ratios were not significantly different from 1·00 but the tendency for angiotensin II to be slightly more potent was probably due to a contribution from derived angiotensin III during infusion of angiotensin II. Angiotensin II or angiotensin II amide was ∼ four times as potent as angiotensin III in raising arterial blood pressure. Cortisol secretion rate was slightly but significantly increased by all peptides at the higher infusion rates. Infusions had no effect on adrenal blood flow or plasma levels of Na +but raised plasma levels of K +slightly. These results confirm the conclusion from adrenal arterial infusion experiments that angiotensin II and III are almost equipotent in stimulating aldosterone secretion in sheep.

Plasma renin activity (PRA) and blood aldosterone and deoxycorticosterone levels were measured in Australian lungfish. Plasma renin activity was depressed after intravenous infusions of iso-osmotic (0·6%) NaCl but not after hypo-osmotic (0·3%) infusions. The presence of PRA in this fish is consistent with prior reports of renal renin activity in other sarcopterygian fishes. The results of the infusion experiments suggest that a fall in plasma osmolality or electrolyte concentrations may oppose the reduction in renin release in response to volume expansion.Aldosterone and deoxycorticosterone were identified in the blood of Neoceratodus. The concentrations of both appeared higher in females than in males. Infusions of [5-valine]-angiotensin II amide for 2–4 h at rates known to increase blood pressure in this species did not alter blood aldosterone concentrations. This negative finding may suggest that the renin/angiotensin system is not involved in aldosterone regulation in Neoceratodusor that angiotensin receptors involved in regulation of steroidogenesis have a greater specificity for endogenous angiotensin than do vascular receptors.

1. Intravenous infusion of angiotensin II increased plasma angiotensinogen concentration in five anaesthetized dogs. 2. This increase was not a consequence of haemoconcentration but was associated with an increase in peripheral corticosteroid concentration. 3. Infusion of angiotensin II did not increase plasma angiotensinogen concentration in five adrenalectomized dogs.

1. The effect of restricted water intake followed by voluntary rehydration with water or 10 mM‐KCl was studied in four conscious sheep with respect to plasma concentrations of renin, antidiuretic hormone (ADH), protein and electrolytes, and urine flow rate, osmolality and osmolal excretion. 2. Water restriction increased the plasma renin concentration and the plasma ADH concentration. 3. Rehydration with water caused a further rise in plasma renin, but plasma ADH returned to basal levels in less than 2 hr. 4. Rehydration with 10 mM‐KCl in order to stabilize plasma K concentration greatly attenuated the post‐drinking rise in plasma renin concentration, while plasma ADH levels fell as before. 5. Urine flow rates after rehydration with water and 10 mM‐KCl remained low for at least 6 hr in most experiments despite low plasma ADH levels. The effect on urine osmolality ranged from no change to a large drop. 6. The post‐drinking antidiuresis was associated with a reduction in solute excretion rate. However, free water clearance usually remained negative. 7. These experiments do not support the existence of a direct nexus between plasma ADH levels and plasma renin concentration.

Administration of bovine parathyroid hormone (PTH) preparations increased the phosphate concentration in the parotid saliva of sheep. Data on the site of action of PTH (1–84) were obtained by (a) equimolar infusions of PTH (1–84) and (1–34) directly into the arterial blood supply of the vascularly isolated parotid gland in anaesthetized sheep, (b) intravenous infusion of PTH (1–84) at a similar rate and (c) intra-arterial infusion of PTH (1–84) with complete drainage of the venous effluent from the gland during the infusion. Results showed substantial time– and dose–response identity of the two peptides, at 10−9to 4 × 10−9mol/l in arterial blood, in raising salivary phosphate concentration. The effect of PTH (1–84) was not due to recirculated fragments because the response was obtained when recirculation was prevented by complete venous drainage and little or no response occurred when the same infusion was given i.v.

1. The blood capillaries from the alveolar areas of the sheep's parotid gland drain into a sinusoidal portal venous system which is in close relation to the striated intralobular ducts.

1. The effect of feeding on the circulation, on renin release and on renal function has been examined in the sheep.

1. The effect of restricted water intake and rapid rehydration was studied in three conscious sheep with respect to plasma renin concentration (PRC), blood corticosteroid levels, plasma protein and electrolyte concentrations, and the renal and faecal excretion of sodium and potassium.

Conscious trained sheep with adrenal autotransplants and a unilateral parotid fistula were studied.Progressive depletion of sodium, up to 900 mEq. over 69 h, resulted in a progressive and proportional increase in aldosterone secretion rate, the peripheral blood concentration of aldosterone and angiotensin, and the plasma renin level.The same parameters were then studied following the rapid correction of sodium depletion by voluntary drinking of 2–3 1 of hypertonic NaHCO3solution (300 mEq./l). In 11 of 12 experiments, where animals rapidly drank adequate sodium solution to correct body deficit, aldosterone secretion fell close to, or into the sodium replete range within 6 h after drinking. Although plasma renin concentration and blood angiotensin levels also tended to decrease, they fell at a much slower rate than the aldosterone secretion rate. The dissociation was most apparent about two hours after drinking NaHCO3solution. On occasions, large fall of aldosterone occurred without fall of angiotensin. However, the close correlation between renin and angiotensin was unchanged. The results were indicative that, during rapid correction of sodium deficiency, aldosterone secretion rate was determined by factors other than, or additional to, the contemporary level of angiotensin in peripheral blood. The question whether changes in plasma ionic concentrations could wholly, or only partly account for this disjunction between angiotensin and aldosterone is discussed, and the existence of an aldosterone inhibitory mechanism is postulated.

Conscious trained sheep with adrenal autotransplants were allowed to become severely Na+deficient by uncompensated salivary loss via a unilateral permanent parotid fistula. Hypertonic NaHCO3was infused into the adrenal artery at concentrations and rates appropriate to locally change adrenal plasma (Na+), (K+) and (HCO3−) to Na+replete levels without significant alteration of body Na+status, or systemic ionic concentrations. After 2 hours of infusion aldosterone secretion rate was not significantly decreased; after 4–6 hours of infusion aldosterone secretion rate was significantly reduced but remained at levels appropriate for moderate to severe Na+deficiency. The direct adrenal action of plasma ionic changes then, fails to explain the fall in secretion rate to close to Na replete levels which is seen over 2–6 hours after an animal rapidly corrects body Na+deficit by drinking 2–3 1 of hypertonic NaHCO3solution (300 mEq./l) – since the adrenal arterial infusion produced the same ionic changes as occur systemically after drinking adequate NaHCO3to correct body Na+deficit.

The effect of sodium depletion on the conversion of corticosterone to aldosterone has been examined in vivousing the adrenal transplants of two sheep. [3H]Corticosterone was infused continuously directly into the adrenal gland via the carotid artery over a period of 30 min. and the total adrenal effluent was collected via the jugular vein in six consecutive 5-min. samples. The conversion of [3H]corticosterone to [3H]aldosterone and the endogenous output of aldosterone was measured in each sample using a double isotope derivative method and the specific activity of the aldosterone calculated. Radioactive conversion of B → aldosterone reached equilibrium within 10 min. of the start of infusion and remained constant over a period of 10–25 min. Aldosterone secretion was also constant during the first 25 min. of infusion.In the same sheep the mean percentage conversion increased as aldosterone secretion rose over a range of 2–12 μg./hr. With more severe sodium depletion, i.e. with aldosterone secretion rates of 12–16 μg./hr., conversion decreased to that found in the sodium replete state. The specific activity of the aldosterone was constant throughout the mildly deplete range (2–12 μg./hr.) but fell with severe sodium depletion. In the sodium replete range (0–2 μg./hr.) before the introduction of a parotid fistula, the specific activity was the same as in the mildly deplete state. After the introduction of a parotid fistula the specific activity increased as the secretion decreased from 2 to 0 μg.The validity of the approach and interpretation of the results in terms of the biosynthetic pathways involved are discussed.

Native Australian and introduced species of animals are adapted to severe sodium deficiency. Effects of such a deficiency are aggravated by pregnancy and lactation, and it has been shown that mechanisms controlling sodium homeostasis in wild rabbits are subject to profound stress.

Bilateral nephrectomy of an Eastern Grey kangaroo (Macropus giganteus) increased plasma renin-substrate concentration approximately tenfold when compared with intact kangaroos. A preparation made from this plasma had a renin-substrate concentration of 3000 ng/ml. A pH profile of rate of reaction with pig renin had an optimum at pH 5·39. By comparison, the pH optimum of sheep renin-substrate was pH 6·15. Estimates of plasma renin concentration for kangaroos, wombats and wallabies, using kangaroo renin-substrate or sheep renin-substrate were highly correlated. Results from incubation with sheep renin-substrate were greater and hence indicate the advantage in using this substrate for marsupial renin estimation.The consistently large difference between sheep and kangaroo renin-substrate when incubated with renin from marsupial and eutherian species appears to be due to a structural difference between the two substrates, probably near the C-terminal end of the angiotensin I molecule.

Aldosterone was infused intravenously at 30 μg/h into sodium replete adrenalectomised sheep which caused salivary [K] to rise to 14–45 mEq./l. After 4 h the animals were anaesthetised and the parotid duct cannulated. With salivary [K] at 14–45 mEq./l, stimulation of the sympathetic nerve supply to the gland caused rapid expulsion of ½-1 ml of saliva with a [K] of 4–8 mEq./l, the normal for sodium replete level. It is concluded that in the sodium replete animal, aldosterone acts on Na+– K+exchange sites in the ducts only.

A renin—angiotensin system was shown to be present in several marsupial species in plasma and homogenates of the renal cortex. Species studied were: Eastern Grey kangaroo (Macropus giganteus), Red kangaroo (Megaleia rufa), common wombat (Vombatus hirsutus), pademelon (Thylogale billardierii), Bennett's wallaby (Wallabia rufogrisea frutica), a quokka (Setonix brachyurus) and a tiger cat (Dasyurus maculatus). Renin-substrate was found in the plasma of the Eastern Grey kangaroo, the Red kangaroo and the wombat. Renin was shown to be present in the plasma of all species by incubation alone or with heterologous marsupial renin-substrate. Plasma renin concentration and renal renin content were estimated by an established method using standard sheep renin-substrate. Plasma renin concentration was high, suggesting that marsupial renins have a high affinity for sheep substrate; renal renin estimates were low relative to eutherian species, suggesting that renal storage may be small. Plasma renin concentration and renal renin levels were proportionately related. Renin levels were consistently lowest in the wombat. Bilateral nephrectomy of an Eastern Grey kangaroo reduced plasma renin concentration to zero and increased renin-substrate concentration eightfold. The angiotensin-like incubation product from Eastern Grey kangaroo renin-substrate did not cross react with antibodies to [5-Ile]-angiotensin I, suggesting that the product has a different sequence of amino acids.

Experiments were made on conscious undisturbed sheep with autotransplants of the adrenal gland. Large local increase of the aldosterone concentration of adrenal arterial blood was made for 2–6 hours in Na replete and Na deficient sheep. The results did not indicate that the secretion of aldosterone which occurs in response to concurrent lowering of Na and increase of K concentration of adrenal arterial blood in Na replete sheep, or in Na deficiency was significantly modified by the local increase of aldosterone in adrenal arterial blood.