scholarly journals Stimulus-secretion coupling in the neurohypophysis of the jerboa Jaculus orientalis.

1994 ◽  
Vol 195 (1) ◽  
pp. 19-34
Author(s):  
A Raji ◽  
J J Nordmann
Keyword(s):  
Time Course ◽  
Physiological State ◽  
Nerve Endings ◽  
Neurosecretory System ◽  
Channel Blockers ◽  
Vasopressin Release ◽  
Oxytocin Release ◽  
Stimulus Secretion Coupling ◽  
Stimulation Of

1. In many mammals, severe dehydration is known to cause exhaustion of the vasopressin content of the neural lobe. Here, we have examined the physiological state of the neurohypophysis of the jerboa Jaculus orientalis, a rodent inhabitant of a semi-desert climate. 2. Isolated neurohypophyses and neurosecretory nerve endings were perfused in vitro and vasopressin and oxytocin release were determined by radioimmunoassay. 3. Electrical stimulation of the neurohypophysis with bursts of pulses mimicking the activity of hypersecreting neuroendocrine neurones induced similar increases of secretion in both control animals and animals dehydrated for up to 2 months. Neurohormone release was greatly potentiated when the bursts of pulses were separated by silent intervals. 4. Prolonged stimulation of neurohypophyses from both control and dehydrated animals induced a sustained increase of vasopressin release; in contrast, oxytocin release under similar conditions showed a biphasic secretory pattern consisting of a transient increase that subsequently decreased to a steady level whose amplitude was similar to that for vasopressin. 5. K(+)-induced secretion was largely inhibited by the Ca2+ channel blockers nicardipine and omega-conotoxin, suggesting that in this neurosecretory system both L- and N-type calcium channels play a major role in stimulus-secretion coupling. Depolarization of isolated nerve endings using a fast-flow perifusion system showed that there was no difference in the amplitude and the time course of the secretory response in dehydrated and hydrated animals. 6. The results demonstrate that, despite the climatic conditions in which the jerboas live, their neural lobes retain the capacity to release, upon depolarization of the plasma membrane of the nerve endings, large amounts of neurohormone. It is concluded that the neurohypophyseal peptidergic release system in the dehydrated jerboa functions adequately even under extreme environmental stress.

Excretion in the house cricket: stimulation of rectal reabsorption by homogenates of the corpus cardiacum

1993 ◽  
Vol 185 (1) ◽  
pp. 305-323 ◽  
Author(s):  
J. H. Spring ◽  
S. A. Albarwani
Keyword(s):  
Time Course ◽  
Chloride Transport ◽  
Malpighian Tubule ◽  
Acheta Domesticus ◽  
Rectal Absorption ◽  
K Uptake ◽  
House Cricket ◽  
Tubule Fluid ◽  
Stimulation Of

1. We describe an in vitro perfused preparation of Acheta domesticus rectum which allows direct comparison of Malpighian tubule secretion and rectal absorption under identical conditions. Rectal absorption is stimulated four- to sixfold by corpora cardiaca (CC) homogenates and the stimulated rate is sufficiently rapid to account for all the fluid secreted by the tubules. 2. The time course for increased fluid absorption is similar to that required to stimulate electrogenic chloride transport in locusts and grasshoppers. Chloride is rapidly absorbed by the rectum under all conditions, along with lesser amounts of Na+ and K+. Unlike the situation in locusts, K+ uptake is unaffected by CC homogenates and the stimulated absorbate is NaCl-rich, similar in composition to the NaCl-rich tubule fluid produced under stimulated conditions. The absorbate is always slightly hypo-osmotic to the perfusate, reaching a maximum differential of approximately 15 mosmol l-1 following CC stimulation. 3. The antidiuretic factor that reduces tubule secretion does not promote fluid reabsorption by the rectum.

Possible role of cyclic GMP in stimulus-secretion coupling by salt gland of the duck

1979 ◽  
Vol 237 (5) ◽  
pp. C200-C204 ◽  
Author(s):  
D. J. Stewart ◽  
J. Sax ◽  
R. Funk ◽  
A. K. Sen
Keyword(s):  
Cyclic Amp ◽  
Guanylate Cyclase ◽  
Cyclic Gmp ◽  
Salt Gland ◽  
Domestic Ducks ◽  
Stimulus Secretion Coupling ◽  
Stimulation Of

Stimulation of salt galnd secretion in domestic ducks in vivo increased the cyclic GMP concentration of the tissue, but had no effect on cyclic AMP levels. Methacholine, which is known to stimulate sodium transport by the glands both in vivo and in vitro, stimulated ouabain-sensitive respiration in salt gland slices. Cyclic GMP stimulated ouabain-sensitive respiration to the same extent as methacholine. Guanylate cyclase stimulators, hydroxylamine and sodium azide, also stimulated ouabain-sensitive respiration. The stimulation of ouabain-sensitive respiration by methacholine was blocked either by atropine or by removal of calcium from the incubation medium. The stimulation of ouabain-sensitive respiration by cyclic GMP still occurred in the absence of calcium. The above observations seem to indicate that cyclic GMP acts as a tertiary link in the process of stimulus-secretion coupling in the tissue.

Na+ dependence of in vitro pancreatic amylase release

1975 ◽  
Vol 229 (4) ◽  
pp. 1023-1026 ◽  
Author(s):  
JA Williams
Keyword(s):  
Pancreatic Enzyme ◽  
In Vitro Release ◽  
Ionophore A23187 ◽  
Enzyme Release ◽  
Pancreatic Amylase ◽  
Amylase Release ◽  
Stimulus Secretion Coupling ◽  
Vitro Release ◽  
Stimulation Of

The effects of Na+ on the in vitro release of amylase from mouse pancreas were studied. Replacement of Na+ in the medium by Tris, choline, or sucrose blocked the stimulation of amylase release by bethanechol and caerulein, whereas replacement by Li+ was without effect. The inhibiton was rapid and reversible, with stimulated amylase release linearly related to the log of the medium Na+ concentration over the range of 20-100 mM Na+. In contrast to the inhibition of amylase release stimulated by physiological secretagogues, enzyme release stimulated by the Ca2+ ionophore A23187 was unaffected by removal of Na+ from the medium. Tissue and intracellular Na+ and K+ contents were unchanged after stimulation of secretion by physiological stimulants. It is concluded that Na+ may be important in the early steps of stimulus-secretion coupling leading to the putative rise in intracellular Ca2+ that triggers pancreatic enzyme release.

Reversible effects of phenothiazines on frog gastric stimulation

1984 ◽  
Vol 247 (4) ◽  
pp. G366-G376
Author(s):  
N. Raphael ◽  
E. B. Ekblad ◽  
T. E. Machen
Keyword(s):  
Adenylate Cyclase ◽  
Time Course ◽  
Phosphodiesterase Inhibitor ◽  
Secretory Activity ◽  
Gastric Stimulation ◽  
Camp Content ◽  
Oxyntic Cell ◽  
Camp Generation ◽  
Stimulus Secretion Coupling

The calmodulin inhibitors trifluoperazine (TFP), chlorpromazine (CPZ), and promethazine (PZ) were tested for effects on stimulus-secretion coupling in in vitro bullfrog gastric mucosa. When added to histamine-stimulated tissues, the drugs caused H+ secretion to decrease and transepithelial resistance to increase over a 2-h time course. The potency sequence was TFP (IC50 = 40 microM) greater than CPZ (IC50 = 72 microM) congruent to PZ (IC50 = 72 microM). Anesthetics and other phenothiazines with weak anticalmodulin activity had no effect on secretory parameters. In the presence of histamine, further addition of isobutylmethylxanthine (IBMX, a phosphodiesterase inhibitor) plus dibutyryl cAMP (DBcAMP), IBMX alone, or forskolin (a specific activator of adenylate cyclase) to phenothiazine-inhibited tissues caused full resumption of secretory activity. If TFP (50 microM) was added before stimulation with histamine, the normal increases in tissue cAMP content (which occurs primarily in oxyntic cells), oxyntic cell apical membrane elaboration (morphometric analysis of electron micrographs), and H+ secretion were all blocked. Subsequent addition of IBMX or IBMX plus DBcAMP completely reversed the TFP effect. These results indicate that the histamine-sensitive adenylate cyclase may be the site of TFP inhibition and Ca2+-calmodulin regulation; since these drugs inhibited stimulation by DBcAMP plus IBMX, they may also be exerting additional effects distal to cAMP generation.

Excitation of cutaneous sensory nerve endings in the rat by 4-aminopyridine and tetraethylammonium

1992 ◽  
Vol 67 (1) ◽  
pp. 125-131 ◽  
Author(s):  
C. Kirchhoff ◽  
J. D. Leah ◽  
S. Jung ◽  
P. W. Reeh
Keyword(s):  
Potassium Channel ◽  
Sensory Nerve ◽  
Low Frequency ◽  
Threshold Concentration ◽  
Nerve Endings ◽  
Channel Blockers ◽  
C Fibers ◽  
Sensory Nerve Endings ◽  
Potassium Channel Blockers

1. The effects of the potassium channel blockers 4-aminopyridine (4-AP) and tetraethylammonium (TEA) on cutaneous sensory nerve endings have been investigated with the use of an in vitro skin-nerve preparation from the rat. 2. Direct application of these compounds to the nerve endings, but not to the axons, induced continuous discharges in most A beta, A delta, and C fibers. There was no relationship between the fibers' responsiveness or the threshold concentration required to induce discharges and either the conduction velocity or sensory properties of the fibers. 3. The rate of induced discharges increased linearly with increasing concentrations of 4-AP. At threshold concentrations of 10(-6)-10(-5) M, low-frequency, irregular discharges developed; but at the highest concentration of 10(-3) M, a characteristic doublet or bursting discharges usually emerged. 4. During and after the induced discharges there did not appear to be an alteration in the sensitivity of the sensory nerve endings to mechanical or thermal stimuli. 5. It is concluded that the induced activity arises from an action of these potassium channel blockers at or near the action potential generator region at the nerve endings.

scholarly journals DYNAMICS OF ACRIDINE ORANGE-CELL INTERACTION

1963 ◽  
Vol 18 (2) ◽  
pp. 237-250 ◽  
Author(s):  
Elliott Robbins ◽  
Philip I. Marcus
Keyword(s):  
Cell Viability ◽  
Acridine Orange ◽  
Time Course ◽  
Physiological State ◽  
Vital Staining ◽  
Cell Interaction ◽  
Extracellular Milieu ◽  
Ultimate Fate ◽  
Cell Compartmentalization

The in vitro localization of acridine orange (AO) in living cells was monitored by means of fluorescence microscopy, quantitative cell viability studies, and photofluorimetric measurements following dye-cell interaction. The parameters, pH, time, dye concentration, and the metabolic state of the cell were found to exert a profound influence on the time course and distribution of staining. The parameters studied are mutually interdependent, and intracellular dye localization may be predictably altered by their appropriate manipulation. Conditions are defined whereby two morphologically distinct but physiologically interrelated reactions, namely, acridine orange particle (AOP) formation and cytoplasmic reddening (CR) may be caused, prevented, reversed, or modified. These results are explained in terms of the facilitation or inhibition of an intracytoplasmic dye-segregating mechanism, in turn affected by the rate of dye ingress and the physiological state of the cell. Whereas the accumulation of AO in AOP is compatible with cell viability, the appearance of CR is correlated with cell death. It is pointed out that meaningful interpretation of vital staining requires precise regulation of many parameters in the extracellular milieu. A scheme of cell compartmentalization with respect to AO is proposed to satisfactorily account for the effects of environmental variations on the distribution and ultimate fate of intracellular dye. The AOP are viewed as normally present acid phosphatase-positive multivesicular bodies.

POTENTIATION BY URETHANE AND INHIBITION BY PENTOBARBITONE OF OXYTOCIN RELEASE IN VITRO

1975 ◽  
Vol 67 (3) ◽  
pp. 453-458 ◽  
Author(s):  
R. E. J. DYBALL
Keyword(s):  
Calcium Ion ◽  
Chloride Concentration ◽  
Ion Uptake ◽  
Hormone Release ◽  
Partial Explanation ◽  
Obvious Effect ◽  
Oxytocin Release ◽  
Neurotransmitter Substances ◽  
Stimulation Of

SUMMARY Isolated rat neural lobes were incubated in vitro in Locke's solution containing anaesthetic quantities of urethane, pentobarbitone or tribromoethanol. The oxytocin content of the incubation medium was estimated before, during and after stimulation of the tissue by raising the potassium chloride concentration from 5·6 to 56 mmol/l. Urethane (25 mmol/l) significantly potentiated oxytocin release (P < 0·01) whereas tribromoethanol (0·5 mmol/l) had no obvious effect and pentobarbitone (0·4 mmol/l) significantly (P < 0·01) inhibited its release. Reduction of the sodium chloride concentration in the medium potentiated the release of oxytocin in each case but did not alter its pattern. Urethane which increased secretion of oxytocin also increased calcium ion uptake by the neural lobes and pentobarbitone which decreased oxytocin release decreased calcium ion uptake. The results may explain why the blood concentration of the neurohypophysial hormones tends to be higher in rats anaesthetized with urethane than with tribromoethanol. Inhibition of hormone release by pentobarbitone suggests that this anaesthetic is unsuitable for use in studies of neurohypophysial hormone release. A partial explanation of the anaesthetic properties of urethane and pentobarbitone may also have been found if the release of neurotransmitter substances is influenced in a similar manner.

scholarly journals Stimulation of the production of unesterified fatty acids in nerve endings of guinea-pig brain in vitro by noradrenaline and 5-hydroxytryptamine

1972 ◽  
Vol 126 (3) ◽  
pp. 575-585 ◽  
Author(s):  
C. J. Price ◽  
C. E. Rowe
Keyword(s):  
Fatty Acids ◽  
Cerebral Cortex ◽  
Guinea Pig ◽  
Synaptic Vesicles ◽  
Nerve Endings ◽  
Synaptic Membranes ◽  
Pig Brain ◽  
Guinea Pig Brain ◽  
Stimulation Of

1. Noradrenaline (1mm) and 5-hydroxytryptamine (1mm) stimulated the production of unesterified palmitate, oleate, stearate and arachidonate in nerve endings (synaptosomes) isolated from combined guinea-pig cerebral cortex and cerebellum. 2. Iproniazid phosphate (0.36mm) increased the concentrations of the same acids in osmotically ruptured synaptosomes. Further addition of 1mm-noradrenaline or 1mm-5-hydroxytryptamine reversed this increase. 3. Noradrenaline (0.01mm) stimulated the production of unesterified fatty acids in isolated synaptic membranes. 5-Hydroxytryptamine (0.01mm) stimulated the production of unesterified fatty acids in synaptic membranes and synaptic vesicles.

Potent stimulation of glycoprotein secretion in canine trachea by substance P

1984 ◽  
Vol 57 (5) ◽  
pp. 1323-1327 ◽  
Author(s):  
S. J. Coles ◽  
K. H. Neill ◽  
L. M. Reid
Keyword(s):  
Substance P ◽  
Time Course ◽  
Collecting Duct ◽  
Regulatory Peptides ◽  
Submucosal Gland ◽  
Airway Mucosa ◽  
Glycoprotein Secretion ◽  
Median Effective Concentration ◽  
Stimulation Of

The effects have been investigated of the regulatory peptides, substance P (SP) and bombesin, on the secretion of [14C]glucosamine-labeled trichloroacetic acid-phosphotungstic acid precipitable glycoproteins by canine tracheal explants. SP (10(10) to 10(-7) M) induced a dose-dependent increase in secretion of high-molecular-weight (greater than 2 X 10(6) radiolabeled glycoproteins predominantly from the submucosal glands. On a molar basis, SP [median effective concentration (EC50) = 8.2 X 10(-10) M] was about 1,000-fold more potent than methacholine (EC50 = 6.3 X 10(-7) M). Bombesin (10(-10) to 10(-4) M) had no effect on glycoprotein secretion. The time course of SP effect was characterized by an initial stimulation of glycoprotein secretion followed by a period of inhibition, suggesting that it rapidly exhausts a pool of glycoprotein, possibly that present within the duct lumen of the submucosal gland. Consistent with this are the findings that SP-induced secretion of glycoprotein was augmented by preincubation with methacholine while methacholine-induced secretion was diminished by preincubation with SP. Our findings show that SP is a potent stimulant of airway glycoprotein secretion in vitro and suggest that it acts by increasing the rate of clearance of mucus from the ducts of the submucosal gland, possibly by induced constriction of the secretory tubules and collecting duct. A role is discussed for SP in mucus hypersecretion induced by local axonal reflexes in the airway mucosa.

Actions of somatotrophin on oxytocin and progesterone release from the microdialysed bovine corpus luteum in vitro

1994 ◽  
Vol 143 (2) ◽  
pp. 243-250 ◽  
Author(s):  
J Liebermann ◽  
D Schams
Keyword(s):  
Early Pregnancy ◽  
Oestrous Cycle ◽  
Luteal Function ◽  
Bovine Corpus Luteum ◽  
Oxytocin Release ◽  
Dose Levels ◽  
Dose Dependent ◽  
Bovine Somatotrophin ◽  
Stimulation Of

Abstract In the present investigation, the effect of recombinant (BST) and pituitary-derived (bGH) bovine somatotrophin on progesterone and oxytocin release was examined. Individual copora lutea (CL) were obtained from cows at different stages of the oestrous cycle (days 5–7, 8–12 and 15–18) and also from early pregnancy (days 60–120) and were implanted with an in vitro microdialysis system (MDS). Perfusion with BST for 60 min (005, 0·5 and 5 μmol/l) induced a dose-dependent stimulation of progesterone release. Release of oxytocin from CL was significantly stimulated by BST at all dose levels. BST (0·5 μmol/l) stimulated progesterone release most during the early and mid-luteal phases and oxytocin release especially during the early luteal stage (days 5–7) of the oestrous cycle. CL from early pregnancy (days 60–120) treated with BST showed a significant response in progesterone and oxytocin release. bGH showed comparable effects. Our results suggest that somatotrophin acts directly on the secretory function of bovine CL in the MDS, specifically during the early luteal stage (days 5–7) of the oestrous cycle and early pregnancy (days 60–120). Somatotrophin may therefore have physiologically relevant effects associated with the development and maintenance of luteal function. Journal of Endocrinology (1994) 143, 243–250

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