Gland Fluid Secretion Research Articles

Vasoactive intestinal peptide stimulates a cAMP-mediated Cl − current in avian salt gland cells

VIP plays an integral role in both protein and fluid secretion in many exocrine glands. By employing the perforated patch-clamp whole-cell recording technique we investigated the effects of VIP on membrane potential and transmembrane currents in avian exocrine salt gland cells. Prior to application of VIP, salt gland cells had a resting membrane potential close to −45 mV. When challenged with VIP (1–100 nM) a sustained depolarization to E Cl − was induced which was mimicked by the application of cell-permeable cAMP analogues or forskolin (1 μM). By employing the voltage-clamp recording configuration a sustained increase in current was observed with a reversal potential which approximated E Cl − . Ionic substitution experiments confirmed that the current was a Cl − conductance which was inhibited by the Cl − channel blockers flufenamic acid and niflumic acid and by the inhibitory cAMP isomer, adenosine-3′,5′-cyclic monophosphothioate, Rp-isomer. Based on this, and the fact that the kinetic properties of the Cl − current activated by VIP are similar to those activated by cAMP, we propose that VIP-receptor interaction results in the activation of a cAMP-dependent Cl − current.

Ivermectin is not an agonist at a GABA receptor in tick salivary glands.

The avermectins, broad-spectrum anti-parasitic agents which are effective against ticks, act principally by stimulating gamma-aminobutyric acid (GABA) receptors directly or indirectly. GABA is known to potentiate dopamine-induced fluid secretion in the salivary glands of female ixodid ticks. We thus tested whether 10 microM ivermectin would have an effect similar to GABA in the isolated salivary gland preparation of Dermacentor andersoni. Ivermectin was not an agonist at this GABA receptor.

Vasoactive Intestinal Peptide Interacts with Alpha-adrenergic-, Cholinergic-, and Substance-P-mediated Responses in Rat Parotid and Submandibular Glands

Secretory dose-response curves were obtained with both acetylcholine and phenylephrine treatment in rat parotid and submandibular glands. Vasoactive intestinal peptide (VIP), which produced relatively low volumes of protein-rich saliva in rat salivary glands, also enhanced acetylcholine-, phenylephrine-, and substance-P-mediated fluid and protein secretion when administered in combination with these agents. The specific mechanisms involved in the synergistic actions of VIP with substances such as acetylcholine, phenylephrine, and substance P, which are primarily linked to the production of fluid secretion in rat salivary glands, have yet to be determined.

Relationship between saliva production and oropharyngeal swallow in healthy, different-aged adults.

We have evaluated the possible relationship between major salivary gland fluid secretion rate and characteristics of the oral phase of swallowing in 35 different-aged, healthy men and women. All subjects displayed normal function of the parotid and submandibular glands and oral swallow patterns on ultrasound evaluation that were comparable to previous reports. In this study group we found no significant relationships between salivary flow rates (unstimulated, stimulated) and any oral swallow measure. Evidence of a subtle, age-related oral motor change (multiple hyoid and tongue gestures) was seen but swallow duration times did not show a linear relationship to age. This study demonstrates that healthy individuals, despite a wide range in their salivary gland fluid secretory capacity, are generally similar in the characteristics of their oropharyngeal swallow.

Salivary gland fluid secretion during aging.

Salivary gland function is generally well-preserved in healthy older persons. Similar results are observed in the laboratory rat. Older people are, however, more likely to experience salivary disorders due to disease or its treatment. For many patients with remaining salivary gland parenchymal tissue, improved function may result from pharmacological therapy.

Lacrimal fluid and electrolyte secretion: A review

Lacrimal gland fluid is an important component of the precorneal tear film. The rate of lacrimal gland fluid secretion is controlled primarily by parasympathetic innervation, and it is, apparently, modulated by sympathetic innervation. Lacrimal gland fluid is produced in two stages, secretion of a primary fluid which resembles an isotonic ultrafiltrate of plasma in the acinus-early intercalated duct region, and secretion of a KCl-rich fluid in subsequent ductal elements. Little is known about the electrolyte transport mechanisms of the ductal epithelia. Recent work using a variety of techniques, including tracer flux measurements, intracellular electrical recording, intracellular ion activity measurements, patch clamping, and analytical subcellular fractionation, supports a model for transcellular Cl-secretion in the acinus which involves Cl--selective channels in the apical plasma membrane and an array of Na+/H+ antiporters, Cl-/HCO3-antiporters, K+ channels, and Na,K-ATPase in the basal-lateral plasma membrane.

Signal transduction and control of lacrimal gland protein secretion: A review

Proteins in lacrimal gland fluid are secreted primarily by the acinar cells. Secretory proteins are synthesized in the endoplasmic reticulum, modified in the Golgi apparatus, stored in secretory granules, and released upon a change in the cellular level of second messenger. The second messenger level is controlled by a process termed signal transduction. Agonists, primarily neurotransmitters in the lacrimal gland, bind to receptors in the basolateral membrane of secretory cells. This interaction activates enzymes in the membrane that cause production of second messengers. It has been hypothesized that second messengers stimulate secretion by activating specific protein kinases to phosphorylate proteins important for secretion. In the lacrimal gland, cholinergic agonists stimulate protein secretion. They act by activating phospholipase C to break down phosphatidylinositol bisphosphate into 1,4,5-inositol trisphosphate (1,4,5-IP3) and diacylglycerol (DAG). 1,4,5-IP3 causes release of Ca2+ from intracellular stores. This Ca2+, perhaps in conjunction with calmodulin, activates specific protein kinases that may be involved in secretion. DAG activates protein kinase C which stimulates protein secretion. alpha 1-Adrenergic agonists also stimulate lacrimal gland protein secretion. These agonists use a pathway that is separate from that utilized by cholinergic agonists and vasoactive intestinal peptide (VIP). The specific pathway has not been identified but may be DAG and protein kinase C. VIP, beta-adrenergic agonists, alpha-melanocyte stimulating hormone, and adrenocorticotropic hormone are lacrimal gland secretagogues. They activate adenylate cyclase to produce cAMP. cAMP stimulates protein kinase A, which perhaps causes protein secretion. Thus, three separate cellular pathways stimulate lacrimal gland protein secretion. Cholinergic agonists and VIP also stimulate lacrimal gland fluid secretion, and the same signal transduction pathways utilized by these agonists to stimulate protein secretion are most likely used for electrolyte and water secretion.

Evaluation of submandibular salivary flow rate in different age groups.

The production of unstimulated and citrate-stimulated submandibular saliva was examined in 90 male and female adults, aged 26-93 years. None was taking prescription medications for treatment of systemic disease. There was no diminution in submandibular gland fluid output, at rest or during stimulation, with increasing age. Similar findings, previously reported for the parotid glands, were also confirmed. These results demonstrate that major gland fluid secretion capacity is maintained in healthy older individuals.

Regulation of calcium handling by rat parotid acinar cells.

Salivary gland fluid secretion following neurotransmitter stimulation is Ca2+-dependent. We have studied the control of cellular Ca2+ following secretory stimuli in rat parotid gland acinar cells. After muscarinic-cholinergic receptor activation, cytosolic Ca2+ is elevated 4-5 fold, due to both intracellular Ca2+ pool mobilization and extracellular Ca2+ entry. Fluid movement ensues due to the Ca2+-activated enhancement of membrane permeability to K+ and Cl-. Basal cytosolic Ca2+ levels are tightly controlled at approximately 150-200 nM through the action of high affinity and high capacity ATP-dependent Ca2+ transporters in the basolateral and endoplasmic reticulum membranes. Activity of these Ca2+ transporters can be modulated to facilitate rapid responsiveness and a sustained fluid secretory response necessary for alimentary function.

Osmoregulatory actions of angiotensin II are independent of adrenergic receptor mechanisms in the duck, Anas platyrhynchos

1. Intravenous infusion of a physiological dose of fowl angiotensin II (ANG II) in salt-loaded ducks raised systemic arterial blood pressure, inhibited nasal salt gland fluid and solute secretion, and stimulated renal-cloacal urine production. 2. Beta-adrenergic receptor blockade by propranolol lowered arterial pressure but did not prevent the effects of ANG II on salt and water excretion. 3. Alpha-adrenergic receptor blockade by prazosin decreased both arterial pressure and plasma glucose levels, but it did not impair the osmoregulatory actions of ANG II. 4. These observations indicate that redistribution by ANG II of salt and water excretion is independent of adrenergic receptor mechanisms and therefore does not depend on the sympathomirnetic activity of the hormone.

Potentiation of salivary fluid secretion in ixodid ticks: a new receptor system for gamma-aminobutyric acid.

gamma-Aminobutyric acid (GABA), having minimal intrinsic activity, potentiates dopamine-induced fluid secretion in salivary glands of female ixodid ticks. Because the effect of GABA was similar to that of spiperone, we tested whether these two drugs act at a common recognition site. Potentiation was not augmented when salivary glands were exposed to supramaximal concentrations of spiperone (1 microM) plus GABA (100 microM). (+/-)-Sulpiride (100 microM), a spiperone antagonist in this system, also blocked GABA-induced potentiation. Picrotoxin (100 microM) and (-)-bicuculline (100 microM), two GABA antagonists, blocked GABA-induced and spiperone-induced potentiation. Inhibition of GABA by picrotoxin and (-)-bicuculline was noncompetitive. Muscimol (an agonist at GABAA receptors) also potentiated dopamine-induced secretion. Baclofen (an agonist at GABAB receptors) did not elicit potentiation. We suggest that GABA may function as a neuromodulator for dopamine-induced fluid secretion in tick salivary glands.

Effects of acidosis and carbonic anhydrase inhibition in the elasmobranch rectal gland.

We studied the effects of acidosis and carbonic anhydrase inhibition on rectal gland fluid secretion. In the anesthetized dogfish shark, Squalus acanthias, volume expanded by a constant infusion of Ringer solution, fluid formation was halved by severe systemic metabolic and respiratory acidosis (pH approximately 7.10) and carbonic anhydrase inhibition. Mild respiratory acidosis (pH approximately 7.6) equivalent to the measured systemic pH during carbonic anhydrase inhibition was without effect. Inhibition of rectal gland enzyme produced severe glandular acidosis, which is indicated by an increase in gland fluid PCO2 (from 7 to 26 mmHg) and HCO3- (from 1.2 to 2.4 mM) and a decrease in pH (from 6.7 to 6.4). Gland tissue total CO2 dropped from 18 to 11 mmol/kg. These changes occurred despite nearly 50% reduction in fluid formation, O2 consumption, and CO2 output. We propose that carbonic anhydrase facilitates CO2 transfer from sites of metabolism to capillary blood by its conversion to HCO3-. This maintains a tolerable intracellular acid-base milieu during stimulated fluid secretion.

Evidence for multiple receptors mediating fluid secretion in salivary glands of ticks

Using isolated salivary glands of the ixodid tick Amblyomma hebraeum Koch, we tested the effectiveness of butaclamol and sulpiride in blocking fluid secretion stimulated by a number of agonists. (+)-Butaclamol was a potent inhibitor of dopamine, N-methyldopamine and noradrenaline (K i ≅ 30–60 nM), but was less effective on ergometrine (K i ≅ 310 nM). Tranylcypromine-stimulated fluid secretion in the absence and presence of (+)-butaclamol and (±)-sulpiride suggested that tranylcypromine's action is mediated through two receptors. (±)-Sulpiride, though a rather weak antagonist of ergometrine (K i ≅ 6150 nM), was ineffectual as a dopamine blocker, indicating distinct receptor sites on this epithelium for dopamine and ergometrine. Both (+)-butaclamol and sulpiride reversed the autoinhibition associated with supramaximal levels of dopamine. Sulpiride also abolished spiperone's potentiation of dopamine. Butaclamol, on the other hand, had no such effect on spiperone's potentiation of dopamine. Finally, although the CNS of ticks contains both dopamine and noradrenaline in quantity (≅650 and ≅370 ng · g −1 respectively), the salivary glands contain far more dopamine than noradrenaline (≅85 and ≅6 ng · g −1 respectively). The data support the hypothesis that dopamine is a natural transmitter substance in the tick salivary gland, and that there are distinct receptor sites in the epithelium mediating the actions of catecholamines, ergot alkaloids and butyrophenones. The physiological significance of the ergot alkaloid and butyrophenone sites is not clear.

Blood flow and secretion in the submaxillary gland of the rabbit during stimulation of the autonomic nerves.

The excitation of the chorda-tympani nerve caused a marked increase in the blood flow through the gland and in secretion of saliva; both phenomena had a threshold frequency of around 0.3 Hz and reached a maximum at around 20 Hz, where a 6-fold increase in the blood flow and a salivary secretion of at the most 300 microliters/min were seen. Sympathetic excitation severely retarded the blood flow, which almost ceased at frequencies as low as 3-5 Hz; mostly single shocks of sympathetic stimulation reduced the blood flow through the gland. An on-going parasympathetic activation did not alter the effects of sympathetic stimulation on the blood flow and the parasympathetically produced salivary secretion almost stopped. The experiments support previous results, which have suggested electrical excitation of the sympathetic trunk at or above 2 Hz to cause a vasoconstriction which adversely affects the fluid secretion in the rabbit salivary glands.

Receptor regulation of calcium release and calcium permeability in parotid gland cells.

The mechanism by which hormones and neurotransmitters regulate fluid secretion in exocrine glands apparently involves the regulation of transmembrane movements of electrolytes, a process for which Ca serves as a second messenger. Analysis of the kinetics of efflux of 86Rb+ (a marker for K+) indicates that the initial phase of the response to secretagogues is mediated through the release of Ca from a cellular pool inaccessible to chelating agents. By investigating the movements of 45Ca under nearly steady-state conditions, we find that this cellular pool can be filled from the extracellular space without a concomitant elevation in ionized intracellular Ca2+. This suggests that the cellular pool is probably associated with the plasma membrane. We have also investigated the possible role of phosphatidic acid in the mechanism by which receptors mobilize Ca2+. Our results suggest that phosphatidic acid, formed on receptor activation, may directly mediate Ca influx into the acinar cell.

Lacrimal gland electrolyte and water secretion in the rabbit: localization and role of (Na+ + K+)-activated ATPase.

1. The rate of acetylcholine (ACh)-induced fluid secretion was measured from the main secretory duct of rabbit lacrimal glands perfused in vivo with Krebs Henseleit bicarbonate solutions. 2. Perfusion with ouabain (10(-5) M) decreased the rate of lacrimal gland fluid secretion to 23% of the control value. 3. Perfusion with furosemide (10(-4) and 10(-3) M), which has been shown to inhibit the coupled transport of Na+ and Cl-, reversibly decreased the rate of secretion to 43 and 33% of the control value respectively. 4. (Na+ + K+)-activated ATPase was localized in slices of rabbit lacrimal gland using autoradiography with [3H]ouabain. 5. A high density of [3H]ouabain binding sites was present on ductal cells, whereas a very low density was found on acinar cells. For both types of cells the [3H]ouabain binding sites were located on the basolateral plasma membranes. 6. It is concluded that ACh-induced secretion of electrolytes and water is dependent upon (Na+ + K+)-activated ATPase. In addition, coupled transport of Na+ and Cl- appears to be involved in secretion. 7. Basolateral location of the (Na+ + K+)-activated ATPase implies that it plays an indirect role in electrolyte and water secretion. A possible role may be to energize a secondary active transport of Cl- that is mediated by a NaCl cotransport system.

The relationship of phosphodiesterase and cyclic AMP to the process of fluid secretion in the salivary glands of the ixodid tickAmblyomma americanum

Phosphodiesterase (PDE) activity in the salivary glands of the female. Amblyomma americanum decreased as the tick progressed from a slow to a rapid phase of feeding, while the rate of fluid secretion increased when glands were stimulated with cyclic AMP and theophylline. Dopamine stimulated PDE activity and an 'inhibitory' factor was found in glands obtained from rapidly engorging ticks which decreased PDE activity. These findings are discussed as they relate to the process of fluid secretion by salivary glands of feeding ixodid ticks.

Electron microprobe and ion-selective microelectrode studies of fluid secretion in the salivary glands of Calliphora.

ABSTRACT The concentrations of sodium, potassium, chloride and water in the cells, secretory canaliculi and the lumen of Calliphora salivary glands have been measured by microprobe analysis of frozen-hydrated sections. Free concentrations of K+ and Cl- in all three compartments were measured with ion-selective microelectrodes. Most of the quantitative data from the two techniques are in close agreement. Microprobe values for the cytoplasm are (mm kg−1 wet weight):Na 20, K 115, Cl 33 in unstimulated glands and Na 15, K 125, Cl 23 after stimulation with 10−8 M 5-hydroxytryptamine (5-HT). The water content is 85% and 77·5% respectively. The highest concentrations are found in the canaliculi. The results indicate that the fluid in the canaliculi is 60–80 m-osmol more concentrated, thus supporting the hypothesis that canaliculi are the sites of solute-water coupling by some form of local osmosis. Both the microprobe and microelectrode measurements show that 5-HT stimulation causes a rise in the level of intracellular potassium and a fall in that of chloride. On 5-HT stimulation there is a rise in the luminal concentrations of K and Cl and little change in sodium level. In K-free medium the potassium in all tissue compartments is replaced with sodium; nearly normal rates of fluid secretion are maintained. The possible routes for the entry of K, Cl and H2O into the canaliculi are discussed.

Development of and Fluid Accumulation in Mammary Glands of Freemartins Administered Estradiol, Estrone, or Testosterone

Eighteen Holstein freemartins acquired at 1 wk of age were assigned to a control and to four treatment groups, but only two of the groups received hormone the first 50 wk. Testosterone administered for the first 50 wk appeared to inhibit teat growth whereas estrone stimulated teat and udder length. At 50 wk of age, implants releasing daily approximately 12.9μg of testosterone, 2.9μg of estrone, or 2.6μg of estradiol-17β per kg of body weight were implanted for 6 wk. One of three testosterone-treated and 9 of 11 estrogen-treated animals exhibited increased udder development associated with fluid accumulation. The 10 animals with fluid accumulation in the udders were milked once 39 days after implanting. The fluid contained 15.0% total solids, 4.1% fat, and 7.0% protein, values which are between those for normal milk and colostrum. These studies support the concept that administration of low concentrations of estrogens alone, released continuously from implants, were capable of stimulating fluid secretion in mammary glands of animals that had no detectable gonadal luteal tissue.

Control of fluid secretion by isolated salivary glands of the lone star tick

Adrenaline, noradrenaline, cyclic-AMP, and theophylline stimulated salivary fluid secretion in glands isolated from rapidly engorging females of the lone star tick, Amblyomma americanum. Cyclic-AMP and theophylline effectively initiated secretion only after the glands were pre-incubated and pre-stimulated to secrete with adrenaline. Pilocarpine nitrate, 5-hydroxytryptamine (5-HT), and glutamate did not stimulate glandular secretion, 2,4-Dinitrophenol (DNP) slowed adrenaline's ability to stimulate secretion. Results obtained after additions of harmaline and ouabain point to the possibility of a (Na ++K +)-ATPase system for helping to move fluid across the glandular epithelium. The significance of these findings to the mechanisms and control of tick salivary glandular function is discussed.