The effect of acetazolamide, amiloride, bumetanide and SITS on secretion of fluid and electrolytes by the parotid gland of common wombats, Vombatus ursinus.

Mechanisms of saliva formation by wombat parotid glands were investigated in anaesthetized wombats at two levels of cholinergically-stimulated flow viz. mid-range (30-40% maximum flow) and maximum flow using ion-transport and carbonic-anhydrase inhibitors. Bumetanide (0.005-0.1 mmol l-1 carotid plasma) progressively reduced mid-range flow by 52 ± 3.4% (mean ± SEM). Concurrently, saliva [Cl] decreased, [Na] and [HCO3] increased but HCO3 excretion was unaltered. Salivary flow during high-rate cholinergic stimulation was 31 ± 1.1% of the pre-bumetanide maximum. During mid-range stimulation, SITS (0.075 mmol l-1) was without effect whereas 0.75 mmol l-1 stimulated transient increases in fluid output. The higher SITS concentration caused no alterations to flow or electrolyte concentrations during maximal stimulation. Carotid plasma [amiloride] (0.05 mmol l-1) caused immediate falls in flow rate of 20-30% followed by progressive recovery over 25 min to levels above pre-amiloride flow rates despite plasma [amiloride] increasing tenfold. Concurrently, salivary [Na] and [Cl] rose to equal plasma concentrations and [K] fell by 50% indicating blockade of acinar Na/H exchangers and luminal Na channels in the ducts. Increased salivary osmolarity caused the flow recovery. Saliva flow during maximum cholinergic stimulation was reduced by 38-46%. The depression of flow was interpreted as resulting from competition between amiloride and acetylcholine for access to the muscarinic receptors. Plasma [acetazolamide] (0.35-2.5 mmol l-1) did not alter saliva outflow during mid-range or maximum flow regimes whereas salivary [Cl] increased and [HCO3] decreased consistent with reduced anion exchange resulting from inhibition of carbonic anhydrase. Combined with bumetanide, acetazolamide (1.5 mmol l-1) reduced flow by an additional 18-22% relative to bumetanide alone thereby demonstrating that acinar HCO3 synthesis supported a limited proportion of saliva formation and that some HCO3 secretion was independent of carbonic anhydrase activity.

Response of the parotid gland of red kangaroos, Macropus rufus, to phenylephrine stimulation.

Intracarotid infusions of l-phenylephrine at 1.0 or 10 nmol kg(-1) min(-1) were accompanied by increases in salivary amylase activity, protein, potassium, magnesium and chloride relative to cholinergically-stimulated saliva. Intravenous infusions of phenylephrine at the same dose rates had a lesser effect on salivary composition particularly protein. Propranolol administered with phenylephrine via the carotid artery, at an antagonist/agonist ratio of 10:1, was much more effective in blocking the phenylephrine-induced changes in salivary composition than equimolar infusion of phentolamine with phenylephrine. It was concluded that alpha(1)-adrenoreceptors were not present in functionally significant numbers in the gland and that the effect of phenylephrine on the kangaroo parotid was mediated by beta-adrenoreceptors. As the phenylephrine dose rates in the kangaroos were comparable with those used to determine alpha-adrenergic responses of eutherian salivary glands and as phentolamine appeared to have minor beta-sympathomimetic activity, at least one subtype of beta-adrenoreceptors in macropods may not be identical to its eutherian counterpart.

Effect of adrenergic antagonists during phenylephrine stimulation of the mandibular gland of red kangaroos, Macropus rufus.

Intracarotid infusions of l-phenylephrine at 1.0 nmol.kg(-1).min(-1) or(.)10 nmol.kg(-1).min(-1) were accompanied by increases in salivary protein, urea, magnesium and bicarbonate, and by decreases in osmolality, hydrogen ion activity, sodium, potassium and chloride relative to cholinergically stimulated saliva. Intravenous infusions of phenylephrine at the same dose rates had much less effect on salivary composition with the differences between the routes of administration being greatest for the higher dose rate. Propranolol administered with phenylephrine via the carotid artery, at an antagonist:agonist ratio of 10:1, was much more effective in blocking the phenylephrine-induced changes in salivary composition than equimolar infusion of phentolamine with phenylephrine. Simultaneous intracarotid infusions of either a beta(1)-antagonist (CGP20712A) or a beta(2)-antagonist (ICI118551) with phenylephrine showed that ICI118551 was more potent than CGP20712A at preventing the changes in salivary composition associated with phenylephrine administration. It was concluded that alpha(1)-adrenoreceptors were not present in functionally significant numbers in the gland and that the effect of phenylephrine on the kangaroo mandibular was mediated by beta-adrenoreceptors predominantly of the beta(2)-subtype. As the phenylephrine dose rates in the kangaroos were comparable with those used to determine alpha-adrenergic responses of eutherian salivary glands and as both propranolol and phentolamine appeared to have minor beta-sympathomimetic activity, at least one subtype of beta-adrenoreceptors in macropods may not be identical to its eutherian counterpart.

Salivary secretion during selective beta-adrenoreceptor stimulation and blockade in the parotid gland of red kangaroos, Macropus rufus.

Intracarotid infusions of noradrenaline (0.3 nmol.kg(-1) x min(-1)) stimulated salivary fluid secretion and caused increases in salivary concentrations of protein, potassium. magnesium. chloride and phosphate, and decreases in bicarbonate. These effects of intracarotid noradrenaline were not reduced by simultaneous intracarotid infusion of phentolamine (3.0 nmol.kg(-1) x min(-1)) but were significantly greater than the responses accompanying intravenous noradrenaline infusion. Concomitant administration of the beta-antagonist, CGP20712A, were much more effective in blocking the noradrenaline-induced changes in salivary composition than equimolar infusions of the beta2-antagonist, ICI118551, thereby confirming the presence of beta1-adrenoreceptors. Intracarotid infusion of salbutamol at 0.6 nmol x kg(-1) x min(-1) and 6.0 nmol x kg(-1) x min(-1) caused increasing but qualitatively similar changes in salivary composition to intracarotid noradrenaline but was less effective than noradrenaline in augmenting salivary protein release. Equimolar intravenous infusions of salbutamol and noradrenaline were equally potent in altering salivary electrolyte concentrations but salbutamol by this route had less effect on protein release and fluid secretion. Concurrent intravenous and intracarotid infusions of beta1-(CGP) and beta2-(ICI) antagonists with intracarotid salbutamol showed that the beta2-antagonist was more potent than the beta1-antagonist by the intracarotid route thereby demonstrating the presence of glandular beta2-receptors and eliminating the possibility that the response to salbutamol was due totally by reflex increases in general sympathetic tone triggered by lowered blood pressure. It was concluded that the kangaroo parotid has functional beta1- and beta2-adrenoreceptor subtypes in endpieces whereas the data provide little support for either adrenoreceptor subtype being present in the excurrent duct system.

Blockade of isoprenaline-induced fluid and protein secretion by the mandibular glands of the red kangaroo, Macropus rufus, with selective antagonists.

Selective and non-selective beta-adrenoceptor antagonists were used to block the increases in fluid and protein secretion caused by sympathomimetic stimulation of the mandibular gland of red kangaroos during intracarotid infusion of isoprenaline. Atenolol or ICI118551 at antagonist:agonist ratios up to 300:1 caused increasing but incomplete blockade of fluid secretion and protein release. Both selective antagonists had equal potency and both antagonists were more effective at blocking protein release than at blocking fluid secretion. Consequently, the mechanisms underpinning fluid secretion are more sensitive to beta-sympathomimetic stimulation than those causing protein release. Propranolol at antagonist:agonist ratios of 300:1 was more potent than the selective antagonists, almost totally blocking the increases in fluid secretion and protein release. The data are consistent with the acini of the kangaroo mandibular gland having both beta(1)- and beta(2)-adrenoceptors and with the increased fluid secretion and protein release by isoprenaline being mediated by both receptor subtypes.

Effect of beta-antagonists on isoprenaline-induced secretion of fluid, amylase and protein by the parotid gland of the red kangaroo, Macropus rufus.

Selective and non-selective beta-adrenoceptor antagonists were used to block the increases in fluid, protein and amylase secretion caused by sympathomimetic stimulation of the parotid gland of red kangaroos during intracarotid infusion of isoprenaline. ICI118551 at antagonist/agonist ratios up to 300:1 caused increasing but incomplete blockade of fluid secretion, and protein/amylase release. Atenolol at antagonist/agonist ratios up to 300:1 was only marginally more potent than ICI118551 at blocking the fluid, protein and amylase responses. Propranolol at antagonist/agonist ratios of 30:1 was as effective at blocking fluid and protein secretion as the highest ratios of either atenolol or ICI118551. Simultaneous administration of atenolol (30:1) with ICI118551 (30:1) was not as potent as propranolol (30:1). Thus, the beta-adrenoceptor/s in the acini of the kangaroo parotid gland appear to have antagonist-binding affinities atypical of those found for eutherian tissues. The data are consistent with the gland possessing either a single anomalous beta-adrenoceptor or functional beta(2)-receptors in addition to the beta(1)-receptors which are characteristic of eutherian salivary glands.

Selective stimulation and blockade of beta-adrenergic receptors in the mandibular gland of the red kangaroo, Macropus rufus.

Intracarotid infusions of noradrenaline (0.15 nmol x kg(-1) x min(-1)) either alone or accompanied by phentolamine (1.5 nmol x kg(-1) x min(-1)) caused similar-sized increases in salivary protein, magnesium and bicarbonate, and decreases in osmolality, sodium, potassium and chloride whereas intravenous noradrenaline stimulated much smaller responses. Concurrent infusions of the beta1-antagonist, CGP20712A, blocked these noradrenaline-induced changes in salivary composition more effectively than equimolar infusions of the beta2-antagonist, ICI118551, thereby confirming the presence of beta1-adrenoceptors. Intracarotid infusion of salbutamol at 0.15, 0.3 and 1.5 nmol x kg(-1) x min(-1) caused increasing but qualitatively similar changes in salivary composition, sodium excepted, to intracarotid noradrenaline with 0.3 nmol being most similar quantitatively. Intravenous infusion of salbutamol caused larger changes in salivary composition than equimolar intravenous noradrenaline thereby indicating that the response to salbutamol may, in part, be mediated by reflex increases in general sympathetic tone triggered by lowered blood pressure. Eliminating this hypotensive effect by concurrent intravenous and intracarotid infusions of beta1-(CGP or atenolol) and beta2-(ICII18551) antagonists with intracarotid salbutamol showed that IC1118551 was more potent than the beta1-antagonists thereby demonstrating the presence of beta2-receptors. It was concluded that the kangaroo mandibular has functional beta1- and beta2-adrenoceptor subtypes in both endpieces and excurrent ducts and that the duct system has two populations of cells, each expressing one receptor subtype.

Enzyme activity in parotid and mandibular saliva from red kangaroos, Macropus rufus.

Parotid and mandibular saliva was obtained from red kangaroos by concurrent acetylcholine isoprenaline stimulation. Salivary proteins were separated by horizontal electrophoresis on either cellulose acetate or starch gels and assessed by specific staining techniques for 23 enzymes commonly found in mammalian tissues and body fluids. Parotid saliva was positive for acid phosphatase, alpha-amylase, carbonic anhydrase, glucose-6-phosphate dehydrogenase, sorbitol dehydrogenase and superoxide dismutase activities. Mandibular saliva was positive for alcohol dehydrogenase in addition to the above six enzymes. The kangaroo salivas lacked activity for alkaline phosphatase, beta-galactosidase and non-specific esterase which occur in saliva from some mammalian species.

Response of the parotid gland of the brushtail possum, Trichosurus vulpecula, to adrenergic stimulation.

Adrenergic stimulation of parotid secretion was investigated in anaesthetised brushtail possums to ascertain fluid secretion rates and salivary composition. Because neither alpha- nor beta-adrenergic stimulation evoked saliva output, infusion of the adrenergic agonists was superimposed on a pre-existing bethanechol-stimulated flow. Isoprenaline infusion (2.4 nmol min-1) increased salivary amylase activity, [protein]; [HCO3]; [PO4] and [Ca], and amylase/Ca and protein/Ca ratios; reduced [Cl]; [K] and osmolality; but did not alter H+ activity; [urea]; [Na]; [Mg]; amylase/protein or saliva/plasma urea ratios. These data are consistent with isoprenaline stimulating acinar secretion of protein, Ca and PO4 but not the ion transport necessary for primary fluid formation at the endpieces and modifying transport of monovalent ions in the excurrent ducts. Consequently, the possum parotid has beta-adrenergic receptors in both the endpieces and excurrent ducts. Phenylephrine infusions at 2.4 and 24 nmol min-1 were without effect whereas phenylephrine at 240 nmol min-1 caused changes in salivary composition which paralleled those for isoprenaline administration but were generally of lesser magnitude. Thus, the possum parotid has few or no alpha-adrenergic receptors and the salivary response elicited was the result of cross-reaction of phenylephrine with beta-adrenergic receptors.

The effect of transport-blocking drugs on secretion of fluid and electrolytes by the mandibular gland of red kangaroos, Macropus rufus.

Mechanisms of primary fluid formation by macropodine mandibular glands were investigated in anaesthetized red kangaroos using ion-transport and carbonic anhydrase inhibitors. Bumetanide at carotid plasma concentrations of 0.005-0.1 mmol/l progressively reduced a stable, acetylcholine-evoked flow rate of 1.02 +/- 0.024 ml/min to 0.16 +/- 0.016 ml/min (mean +/- SEM). Concurrently, saliva [Na], [Cl] and osmolality decreased, [K] and [HCO3] increased and HCO3 excretion was unaffected. High-rate cholinergic stimulation was unable to increase salivary flow above 12 +/- 1.5% of that for equivalent pre-bumetanide stimulation. Furosemide (1.0 mmol/l) and ethacrynate (0.5 mmol/l) caused depression of salivary flow and qualitatively similar effects on ion concentrations to those of bumetanide. Amiloride (up to 0.5 mmol/l) caused no reduction in salivary flow rates or [Na] but decreased [K] and [Cl] and increased [HCO3]. When compared with bumetanide alone, amiloride combined with bumetanide further augmented [K] and [HCO3] and lowered [Cl], but had no additional effects on Na or flow. At the higher level, 4-acetamido-4'- isothiocyanatostilbene-2,2'disulphonic acid (SITS) (0.05 and 0.5 mmol/l) stimulated fluid output, increased [HCO3] and [protein], and depressed [Na], [K] and [Cl]. Relative to bumetanide alone, SITS given with bumetanide had no additional effects on salivary flow or electrolytes. Methazolamide (0.5 mmol/l) in combination with bumetanide curtailed the decrease in [Cl] and the increases in [K] and [HCO3] associated with bumetanide. The residual methazolamide-resistant HCO3 excretion was sufficient to support 2-6% of primary fluid secretion. It was concluded that secretion of primary fluid by the kangaroo mandibular gland is initiated mainly (> 90%) by Cl transport resulting from Na-K-2Cl symport activity. A small proportion of the fluid secretion (up to 6%) appears to be supported by HCO3 secretion. No evidence was found for fluid secretion being dependent on Cl transport involving Na/H and Cl/HCO3 antiports or on HCO3 synthesis involving carbonic anhydrase.

Mechanisms of fluid and ion secretion by the parotid gland of the kangaroo, Macropus rufus, assessed by administration of transport-inhibiting drugs.

Possible mechanisms of primary fluid formation by macropodine parotid glands were investigated in anaesthetized red kangaroos using ion transport inhibitors. Carotid plasma amiloride concentrations of 0.05-0.5 mmol.l-1 progressively reduced a stable acetylcholine-evoked half-maximal flow rate of 2.0 +/- 0.04 to 0.22 +/- 0.024 ml.min-1 (mean +/- SEM). Concurrently, saliva bicarbonate concentration and secretion fell (135 +/- 1.6 to 67 +/- 1.7 mmol.l-1 and 272 +/- 7.6 to 15 +/- 2.6 mumol.min-1, respectively); [phosphate], [chloride] and [sodium] rose and [potassium] and osmolality were unaltered. High-rate cholinergic stimulation did not increase saliva flow beyond 11 +/- 1.0% of that for equivalent pre-amiloride stimulation. Equipotent levels of amiloride and methazolamide given concurrently were no more effective at blocking flow and bicarbonate secretion than when given separately. Furosemide (up to 2 mmol.l-1), bumetanide (up to 0.2 mmol.l-1) and ethacrynate (1 mmol.l-1) in carotid plasma had no effect on salivary flow or ion concentrations. During methazolamide blockade, furosemide did not curtail the concurrent increase in salivary [chloride]. Chlorothiazide at 0.25-1.0 mmol.l-1 caused progressive depression of saliva flow and [bicarbonate], and elevation of [chloride]. 4-acetamido-4'-isothiocyanatostilbene-2,2'disulphonic acid at 0.1 mmol.l-1 was without effect, whereas at 0.5 mmol.l-1 it stimulated fluid secretion and increased saliva [protein], [sodium], [potassium], [bicarbonate] and osmolality. Concurrently, mean arterial blood pressure and pulse pressure fell and heart rate, haematocrit and carotid artery plasma flow rose. These responses were absent if saliva flow was kept constant by reduction in cholinergic stimulation during 4-acetamido-4-isothiocyanatostilbene-2,2'disulphonic acid administration. It is concluded that secretion of primary fluid by the kangaroo parotid is initiated mainly (> 90%) by secretion of bicarbonate which is formed in the endpiece cells from CO2 delivered by the circulation. No evidence was found for initiation of fluid secretion by chloride transport involving basolateral Na(+)-K(+)-2Cl- symports, Na(+)-Cl- symports or Cl-/HCO3- antiports.

Secretion of electrolytes, protein and urea by the mandibular gland of the common wombat (Vombatus ursinus).

Saliva was collected from the mandibular glands of anaesthetized common wombats (Vombatus ursinus) to ascertain maximal flow rates, salivary composition and possible adaptations, particularly PO4(3-) secretion, to assist digestion. After temporary catheterization of the main duct through its oral opening, salivary secretion was evoked at flow rates ranging from 0.02 +/- 0.002 (+/- SEM) ml.min-1 (0.7 +/- 0.07 microliter.min-1.kg body weight-1) to 0.4 +/- 0.05 ml.min-1 (14 +/- 1.9 microliters.min-1.kg body weight-1) by ipsilateral intracarotid infusion of acetylcholine. The [Na+] (15 +/- 5.1 to 58 +/- 8.6 mmol.l-1) and [HCO3-] (35 +/- 1.9 to 60 +/- 1.9 mmol.l-1) were positively correlated with salivary flow rate. The [K+] (58 +/- 5.2 to 30 +/- 2.4 mmol.l-1), [Ca2+] (10.4 +/- 1.67 to 4.1 +/- 0.44 mmol.l-1), [Mg2+] (0.94 +/- 0.137 to 0.17 +/- 0.032 mmol.l-1), [Cl-] (71 +/- 9.2 to 45 +/- 6.0 mmol.l-1), [urea] (9.3 +/- 0.79 to 5.1 +/- 0.54 mmol.l-1), H+ activity (29 +/- 1.6 to 17 +/- 1.6 nEq.l-1) and amylase activity (251 +/- 57.4 to 92 +/- 23.3 mu kat.l-1) were negatively correlated with flow. Both concentration and osmolality fell with increasing flow at the lower end of the flow range but osmolality always increased again by maximal flow whereas the relation between protein and flow was not consistent at the higher levels of flow and stimulation. Salivary [PO4(3+)] was not correlated with flow and at 3-14% of the plasma concentration was extremely low.(ABSTRACT TRUNCATED AT 250 WORDS)

Salivary proline-rich proteins in mammals: Roles in oral homeostasis and counteracting dietary tannin.

We review information on the structure of proline-rich proteins (PRPs), their various functions related to oral homeostasis and dietary tannin, and the structural basis of these functions. Consideration of the multifunctional nature of these salivary proteins helps explain both the subtle and large variations found in structure and secretion rates both within individuals and between species. We propose that the ancestral function of PRPs is in maintaining oral homeostasis and that counteracting dietary tannins by binding with them is a derived function. PRPs are effective in oral homeostasis at low secretion levels, whereas counteracting tannin depends on high secretion levels. In the dietary habits ranging from carnivores through omnivores to exclusively planteaters, the dietary nitrogen level is progressively reduced, and plant allelochemical intake, including tannins, increases. We suggest that during this evolution from meat-eater to plant-eater, there was some point in omnivory at which selective pressure from nitrogen limitations, arising from a low nitrogen/high tannin diet, became sufficiently great for the evolution of increased secretion level and diversification of PRPs for dealing with tannin. If this hypothesis is correct, carnivorous mammals should secrete low levels of PRPs for oral homeostasis, but should never secrete high levels, unless they are secondarily carnivorous. Omnivores consuming a diet of very little animal tissue but higher levels of tannin-containing foliage or fruit should generally have the capacity to produce high levels of salivary PRPs. Browsers and frugivores should also produce high levels of PRPs, but grazers may have reduced secretion rates depending on the antiquity of the dietary habit. This hypothesis is consistent with the limited information available on the abundance, type, and distribution of PRPs in mammals. Studies are suggested which would test the functional and evolutionary arguments presented.

Effects of cholinergic stimulation and aldosterone administration on salivary parotid secretion in the brushtail possum, Trichosurus vulpecula.

Parotid salivation was stimulated by infusion of bethanechol chloride into anaesthetized brushtail possums to ascertain maximal flow rates, salivary composition and dietary adaptations of salivary function. Secretion rates for one gland ranged from 5.3 +/- 0.16 to 84.3 +/- 3.20 microliters/min (2.4 +/- 0.07 to 37.8 +/- 1.43 microliters/min per kg body weight). Salivary osmolality (160.8 +/- 15.39 to 248.2 +/- 8.70 mosmol/kg) and the concentrations of Na (63.1 +/- 10.93 to 124.1 +/- 5.52 mmol/l) and HCO3 (19.5 +/- 3.41 to 89.0 +/- 3.19 mmol/l) were positively correlated with flow rate. The concentrations of urea (7.8 +/- 0.64 to 4.6 +/- 0.33 mmol/l), PO4 (2.6 +/- 0.25 to 0.96 +/- 0.10 mmol/l), H+ (46.2 +/- 16.30 to 9.0 +/- 1.51 nequiv/l), K (21.4 +/- 3.73 to 13.7 +/- 2.33 mmol/l), Ca (3.7 +/- 0.53 to 2.2 +/- 0.27 mmol/l) and Mg (0.3 +/- 0.07 to 0.04 +/- 0.007 mmol/l) fell with increasing flow rate. The relations between flow rate and amylase activity (22.6 +/- 10.47 to 10.5 +/- 3.68 mu kat/l), protein concentration (2.7 +/- 0.61 to 1.3 +/- 0.28 g/l), and Cl concentration (62.1 +/- 6.88 to 50.6 +/- 6.37 mmol/l) were inconsistent between experiments. Salivary Na/K ratios were not decreased by infusion of aldosterone (2.2-22.2 nmol/h for 5 h), showing that the gland of Na-replete possums is unresponsive to short-term increases in mineralocorticoids. The low salivary amylase activity, less than that of kangaroos, presumably reflects the interaction of evolutionary history of the possum with its natural low-starch diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships between plasma composition and parotid salivary composition and secretion rates in the potoroine marsupials, Aepyprymnus rufescens and Potorous tridactylus.

Parotid salivation was investigated in two species of potoroine marsupial, Aepyprymnus rufescens and Potorous tridactylus to ascertain flow rates and composition, the buffer capacity of the saliva with respect to possible dependence of these animals on foregut fermentation, and the similarity of anion excretion patterns to those of the kangaroo parotid. Under anaesthesia neither species secreted spontaneously and secretion was stimulated by intravenous infusion of carbachol, bethanechol and isoprenaline. Under cholinergic stimulation in Aepyprymnus, the concentrations of Na, Cl, HCO3 and osmolality were positively correlated with flow rate, whereas K, Mg, PO4, H+ and urea were negatively correlated with flow. Amylase activity and the concentrations of protein and Ca showed no consistent relation to flow. Relative to Aepyprymnus, saliva of Potorous had much lower amylase activity and amylase activity per gram protein, lower concentrations of urea and Ca, and higher Na. Protein, K and HCO3 concentrations were similar in both species. The plasma of both species had similar electrolyte concentrations, but Potorous had lower protein, urea, osmolality and amylase activity. Plasma amylase activity in Aepyprymnus rose during cholinergic stimulation to levels in excess of rodent plasma. Isoprenaline infusion in Aepyprymnus increased salivary amylase activity and concentrations of protein, Ca, HCO3 and PO4, and reduced the concentrations of Cl and H+. The patterns of anion excretion in the two potoroine marsupials were dissimilar to those of the kangaroo parotid suggesting that parotid fluid secretion is not HCO3 driven to the same extent as that of Kangaroos. Buffer anion concentrations and secretion rates were similar to koalas and low relative to kangaroos, indicating that these potoroines do not rely on foregut fermentation.

Effect of phosphate-regulating hormones on plasma composition, cardiovascular function, and parotid salivary phosphate secretion in red kangaroos (Macropus rufus).

The effects of administration of phosphate-regulating hormones on plasma composition, cardiovascular function, and secretion of phosphate and other electrolytes in parotid saliva were investigated in anesthetized red kangaroos. Plasma [PO4] was elevated by intravenous injections of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) at 5 or 12.5 nmol/12 hr for 72 hr but was unaltered by intravenous or intracarotid infusion of either salmon or porcine calcitonins at rates up to 3.2 IU min-1 for 60 min or by intracarotid infusions of the 1-34 amino acid fragments of rat, human, or bovine parathyroid hormones (PTH(1-34) at 350-460 pmol/min for 60 min. Plasma [Ca] fell during high-rate calcitonin infusion and rose during 1,25(OH)2D3 administration. PTH(1-34) infusion did not alter plasma [Ca] but did lower plasma [K] and arterial blood pressure and elevated heart rate and hematocrit. Salivary [PO4] and [Ca] and secretion rates were unaffected by the calcitonin infusions, by PTH(1-34) infusions, or by 1,25(OH)2D3 injection. Plasma and salivary concentrations of other ions were unaltered. These data provide evidence that kangaroo tissue can recognize and respond to all three types of phosphate-regulating hormones despite the peptides being foreign; however, the parotid gland of kangaroos, unlike the parotids of rats and sheep, did not respond and presumably lacks some component of the receptor-secretion couplings for these hormones. This independence of salivary PO4 secretion from hormonal regulation may be one of several adaptations which ensure relatively stable and adequate phosphate delivery to the foregut microorganisms despite an unreliable phosphorus intake in the natural diet.

The effect of carbonic anhydrase inhibitors on secretion by the parotid and mandibular glands of red kangaroos Macropus rufus.

The effects of carbonic anhydrase inhibitors on secretion by macropodine parotid and mandibular glands were investigated using anaesthetized red kangaroos. In the parotid gland, acetazolamide (500 mumol.l-1) reduced a stable acetylcholine-evoked, half-maximal flow rate of 2.02 +/- 0.034 to 0.27 +/- 0.023 ml.min-1 (87% reduction). Concurrently, salivary bicarbonate concentration and secretion fell (129.4 +/- 1.46 to 80.9 +/- 1.63 mmol.l-1 and 264.8 +/- 7.96 to 22.3 +/- 2.30 mumol.min-1, respectively), phosphate and chloride concentrations rose (14.0 +/- 0.79 to 27.6 +/- 0.85 mmol.l-1 and 5.6 +/- 0.25 to 27.5 +/- 1.32 mmol.l-1, respectively), sodium concentration and osmolality were unaltered, and potassium concentration fell (8.8 +/- 0.33 to 6.4 +/- 0.29 mmol.l-1). High-rate cholinergic stimulation during acetazolamide blockade was unable to increase salivary flow beyond 11 +/- 0.9% of that for equivalent unblocked control stimulation. However, superimposition of isoprenaline infusion on the acetylcholine stimulation caused a three-fold increase in the blocked flow rate. These treatments were accompanied by small increases in salivary phosphate and chloride concentrations but not bicarbonate concentration. Methazolamide infusion caused similar changes in parotid secretion. In the mandibular gland, acetazolamide infusion had no effect on salivary flow rate during either low- or high-level acetylcholine stimulation. Acetazolamide caused no alterations in salivary electrolyte secretion at low flow rates, but curtailed the rise in bicarbonate concentration associated with high-level acetylcholine stimulation. Acetazolamide administration did not affect the increase in salivary flow rate associated with isoprenaline infusion, but did block the concomitant increase in bicarbonate concentration and secretion substantially.(ABSTRACT TRUNCATED AT 250 WORDS)

Salivation in the red kangaroo (Macropus rufus) during sympathetic nerve stimulation.

1. Continuous electrical stimulation at low frequency (5 Hz) and short pulse duration (500 microseconds) of the cervical sympathetic trunk for periods up to 15 min caused no obvious flow from the parotid or mandibular glands of the red kangaroo. 2. Higher frequencies combined with longer pulse durations caused both glands to secrete. Flow reached maximum in less than 3 min and then declined but, on cessation of stimulation, flow increased again for a short period. This flow response may be caused by the interaction of the secretory response with myoepithelial contraction. 3. The parotid saliva had substantially higher protein, phosphate and hydrogen ion concentrations, and lower sodium concentrations than cholinergic parotid saliva. The low pH indicates bicarbonate concentrations far lower than in other sympathetic salivas. 4. The mandibular saliva had higher protein, urea and potassium, and lower chloride and hydrogen concentrations than cholinergic mandibular saliva.

The effect of beta-sympathomimetic stimulation on parotid salivation in the red kangaroo (Macropus rufus).

Salivation was stimulated by intracarotid isoprenaline infusion given alone or combined with acetylcholine. By itself, isoprenaline (0.12-1.2 nmol kg-1 min-1) stimulated flow rates of 0.037-0.233 ml min-1 (2.77-10.5 microliters/g gland per min). Salivary Na, Cl, PO4 and total solute concentrations were positively correlated with flow; K, Mg and urea were negatively correlated with flow; and Ca, H+, HCO3, protein and amylase activity were not correlated with flow. Relative to cholinergic saliva, isoprenaline-evoked saliva had higher levels of amylase activity, urea, protein, K, Mg, H+, PO4 and Cl but lower osmolality, Na, Ca and HCO3. At a steady flow (1 ml min-1), isoprenaline infusion (0.3 nmol kg-1 min-1) superimposed on a pre-existing acetylcholine infusion increased salivary amylase activity, protein, urea, K, Mg, Cl and PO4, reduced HCO3 and did not alter Na, Ca, H+ and osmolality. Superimposition of isoprenaline infusion (0.5 nmol kg-1 min-1) on a low-level acetylcholine infusion increased flow rate by 400-900%. Excretion rates of K, Mg, Cl and PO4 were higher and Ca lower than predicted for saliva secreted at equivalent flows during acetylcholine stimulation. Na, H+ and HCO3 were as predicted for the same flow rate under cholinergic stimulation. The simplest coherent interpretation of these data is that isoprenaline affects transport of protein and ions at the end organs, but has little effect on the resting transport characteristics of the striated and excretory ducts of the kangaroo parotid, in accord with the known nerve distribution of this gland.

Secretion by the mandibular gland of the red kangaroo (Macropus rufus) during isoprenaline infusion.

Intracarotid infusion of isoprenaline, either alone or in combination with acetylcholine infusion was used to stimulate salivation by the mandibular glands of anaesthetized red kangaroos. Isoprenaline alone (0.20-1.25 eta mol.kg-1.min-1) elicited flow rates ranging from 0.014 to 0.239 ml.min-1 (1.21-28.1 microliters.g gland-1.min-1). Salivary concentrations of sodium, chloride, phosphate and urea were negatively correlated with flow, whereas potassium, calcium, magnesium, hydrogen ion, bi-carbonate, protein, and osmolality were poorly correlated with flow. Relative to cholinergic saliva produced at equivalent flow rates, isoprenaline-evoked saliva had higher osmolality, saliva/plasma urea ratios and concentrations of protein, potassium, magnesium, bicarbonate, and phosphate, but lower sodium, chloride and hydrogen ion levels. At a steady salivary flow (0.5 ml.min-1), superim-position of isoprenaline infusion (0.15 eta mol.kg-1.min-1) on a pre-existing acetylcholine infusion reduced the rate of acetylcholine administration necessary to maintain flow, increased osmolality and the concentrations of protein, urea, potassium, calcium, magnesium, bicarbonate and phosphate and decreased sodium, chloride and hydrogen ion in the saliva. Salivary amylase activity was low and highly variable and the amylase activity/protein ratio fell substantially during isoprenaline stimulation. These results support the conclusion that the enzyme is of extrinsic origin. The response of the kangaroo mandibular gland to isoprenaline stimulation was very similar to that reported for rat mandibular gland, suggesting that the same ion transport phenomena underlie mandibular secretion in both species and probably in therian mammals generally.