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PubMedDate not supplied

Effect of pineal gland on testosterone release in vitro.

We studied the effect of hCG, aminoglutethimide and pineal effluent on the basal testosterone secretion by superfused adult rat interstitial cells. The period used to determine the mean rates of release was 120-240 min. after the start of superfusion i.e. when basal secretory rate was stable. A 2 h administration of hCG (10 mUI/ml) induced a rapid increase in testosterone output while aminoglutethimide (100 microM) decreased it. Basal testosterone release was not modified when interstitial cells were superfused with effluent of a chamber containing 1, 2 or 4 pineal glands. These results suggest that pineal secretory products exert no direct acute action on testosterone biosynthesis by rat interstitial cells.

Aminoglutethimide↗
PubMed1994

Short-term feeding of a diet enriched in phospholipids increases bile formation and the bile acid transport maximum in rats.

Earlier studies suggested that the secretory rate maximum (SRm) of bile acid and the cholestasis which occurs after the SRm is reached may be determined by the hepatic or extrahepatic biliary phospholipid pool. We therefore investigated whether bile formation and the bile acid SRm could be influenced by feeding a diet enriched in phospholipids. Male rats were fed phospholipid (PLD) or triacylglycerol (TgD)-enriched diet for 3 days, and bile formation as well as biliary lipid output were measured on the 4th day. In other similarly fed groups, cholic acid was infused in stepwise increasing doses to determine the effect of PLD on the SRm of cholic acid. The plasma lipid levels were significantly lower in PLD and TgD diets compared to basal diet. But, while the levels of total cholesterol (CH), HDL-CH, and phospholipid (PH) were not significantly altered by PLD compared to TgD, the triacylglycerol levels were markedly increased by PLD. In the liver of PLD fed rats, triacylglycerol and CH ester contents decreased by 39 and 62%, respectively, while free CH and PH contents were not significantly changed. The PLD significantly augmented spontaneous bile flow, bile acid, PH and CH secretion rates compared to TgD diet (65, 124, 164 and 654%, respectively). The enhanced biliary secretory function was associated with an increase in pericanalicular vacuoles and diverticuli in centrilobular hepatocytes. Compared to TgD fed rats, PLD rats showed a 2-fold decrease in the ratio of cholic acid/chenodeoxycholic acid in bile and a significant decrease in the % contribution of taurine conjugated BA. The PH fatty acids in bile were similar in both groups except that in PLD group the % contribution of C18:2 was higher than in TgD group. No differences were found in plasma membrane CH/PH content or total fatty acid composition. During bile acid infusion, the SRm and the total cholic acid secreted were significantly higher in the PLD than in the TgD rats. Moreover, the cholestatic response observed after high bile acid dose was markedly reduced by PLD. The results show that short-term feeding of PLD induces changes in CH and bile acid metabolism which result in enhanced biliary output of CH and PH. The enhanced pool of biliary lipid may protect plasma membranes from the deleterious effects of high bile acid concentrations.

Animals↗
PubMed1981

[The secretion of adenosin 3',5'-monophosphate after hydrokinetic and ecbolic stimulation in the canine pancreas (author's transl)].

The secretion of cAMP is studied in vivo and in the isolated perfused canine pancreas after administration of secretin and CCK or caerulein in comparison with hydrokinetic or ecbolic secretory events as well as with the magnitude and time course of changes in tissue cAMP. 1) The total output of cAMP and pancreatic juice shows a significant and positive correlation after stimulation with secretin. The linear correspondence between cAMP concentration and secretory rates of pancreatic juice beyond 3 ml/5 min and their non-linear, reciprocal correlation at lower rates of fluid secretion point to an active as well as to a passive secretory mechanism for cAMP. 2) CCK and caerulein increase secretion of cAMP too. The output of cAMP however neither corresponds to the time course of protein secretion nor correlates quantitatively with the latter. 3) The behaviour of cAMP secretion and concentration in the pancreatic juice after administration of secretin and CCK or caerulein as well as differs from the changes in tissue cAMP levels. The respective maximum of cAMP output after addition of secretin or ecbolic secretagogues during the greatest decrease in cellular cAMP levels yields on the average about 1% of the estimated reduction in total tissue cAMP content. The results indicate a functional coherence in secretion of pancreatic juice and cAMP but oppose the assumption, that essential amounts of cAMP are released during exocytosis of zymogen granules. The secretion of cAMP may be possibly influenced by cytoplasmatic cAMP levels, but neither reflects the present changes in cellular cAMP nor seems to be of a regulatory importance for the latter.

Animals↗
PubMed1995

[Cholecystokinin in regulation of gastric secretion in healthy probands and duodenal ulcer patients].

Unlike the stimulation of gastric acid secretion, which clearly involves the release of gastrin, the mechanisms of inhibition of this secretory process are poorly defined although recent studies in animals with the use of highly selective cholecystokinin (CCK) antagonists indicate that CCK may play a crucial role in this inhibition. Duodenal ulcer patients (DU) differ from healthy controls by higher total acid secretory rates and diminished inhibition of acid secretion. Several possible pathomechanisms of the abnormal gastric secretory function in DU patients were previously proposed. The deficiency of CCK-induced gastric inhibition in DU patients together with the somatostatin hypothesis appear to be attractive, particularly so the suggestion that a deficiency of somatostatin activity exists in DU patients.

Animals↗
PubMed1975

Renal proximal tubular buffer-(glycodiazine) transport. Inhomogeneity of local transport rate, dependence on sodium, effect of inhibitors and chronic adaptation.

Using the stop flow microperfusion technique with simultaneous capillary perfusion the secretory rate of H+ ions in the proximal tubule was evaluated by measuring the level flow reabsorption as well as the static head concentration difference of 3H labeled glycodiazine. At ambient glycodiazine concentration of 21 mmol/l the level flow reabsorption is in the same range as that of bicarbonate. In the early proximal loops the reabsorption is 20% greater than in the late proximal loops. The carbonic anhydrase inhibitors acetazolamide and 3,4-methylene-dioxyphenyl-sulfonamide (both 10(-4) M) as well as furosemide (10 (-3) M) inhibit the glycodiazine reabsorption 43%, 27% and 22% respectively. Thiocyanate (2-10(-2) M), however, exerted only an insignificant inhibition (12%). When Na+ in the ambient perfusion solutions was replaced by Li+ or choline+ the glycodiazine transport was strongly reduced. Ouabain (5-10(-2) M) inhibited too, but amiloride (10(-3) M) had no effect on glycodiazine transport. The glycodiazine transport was 28% reduced in metabolic alkalosis and to a smaller although significant extent (17%) in metabolic acidosis; it was unchanged in chronic hypercapnia. In chronic K+ depletion the glycodiazine reabsorption was accelerated by 12% only in the early proximal loops. Chronic parathyroidectomy as well as acute substitution with parathyroid hormone had no effect on the glycodiazine absorption. The main conclusions are: Proximal H+ transport proceeds with suitable buffers. Although independent of HCO3- and carbonic anhydrase, it could be partially inhibited by CA inhibitors. H+ transport is supposed to proceed as countertransport with Na+ ions. In chronic alkalosis the H+ transport is reduced.

Acid-Base Equilibrium↗
PubMed1980

Exocytosis in mammalian cells. VI. Temperature dependence of pancreatic exocrine secretion.

The effects of temperature on amylase secretion in vitro have been measured under stimulated and nonstimulated conditions. In both cases a very rapid decrease of secretory rate was observed between 37 and 25 degrees C (60-70%). The decrease is less pronounced between 25 an 15 degrees C. Between 15 and 13 degrees C a drop of secretory activity (10%) was observed under stimulation whereas an increase was measured in absence of stimulus. At lower temperatures the rate of secretion falls again abruptly. These results show that the secretory pattern of amylase from pancreas in vitro as a function of temperature is very different under stimulated and nonstimulated conditions. We suggest that the abrupt change of secretory activity between 15 and 13 degrees C could correspond to a change of physical state of the membranes involved in the exocytosis process.

Amylases↗
PubMed1977

Steady state aldosterone dose-response relationships.

The steady state effects of different infusion rates of aldosterone on plasma concentrations of sodium and potassium, plasma renin activity, sodium space, and mean arterial pressure were determined. Measured amounts of aldosterone were infused continuously into adrenalectomized dogs for 13 weeks. Four rates of aldosterone administration were used: 16 +/- 1 mug/day, 48 +/- 3 mug/day (approximately the normal secretory rate for 22-kg dogs on a daily sodium intake of 27 mEq, potassium intake of 27 mEq), 91 +/- 4 mug/day, and 219 +/- 10 mug/day. Each rate of infusion was continued until the dogs were in sodium and potassium balance and measured variables were steady. Decreasing the rate of aldosterone administration below normal led to sharp decreases in plasma sodium concentration and sodium space, while raising the rate above normal had little effect. Plasma potassium concentration varied inversely and significantly with changes in aldosterone administration over the entire range of rates. Plasma renin activity rose extremely rapidly as the level of aldosterone fell below normal and went to zero at aldosterone infusion rates slightly above normal. Arterial pressure increased as aldosterone rose above normal but did not fall below normal at subnormal aldosterone levels, probably because of the pressor effects of simultaneously generated angiotensin II.

Adrenalectomy↗
PubMed1981

Impaired clearance of beta-lipotropin in uremia.

Immunoreactive ACTH and beta-lipotropin (beta-LPH) plasma concentrations are elevated in clinically stable chronic renal failure patients on hemodialysis (LPH: patients, 271.8 +/- 35.7 fmol ml-1; normal subjects; 6.6 +/- 0.5; ACTH: patients, 56.4 +/- 15.3; normal subjects, 19.4 +/- 1.7). To begin to study the etiology of such elevated levels, the MCR, apparent volume of distribution, and fractional rate of disappearance of synthetic human ACTH and highly purified human beta-LPH were determined in two clinically stable chronic renal failure patients on hemodialysis, after bolus simultaneous injection of both peptides. Biphasic disappearance curves were obtained for beta-LPH; triphasic for ACTH. The MCR of ACTH was within the range seen in normal subjects, whereas the MCR of beta-LPH was less than one half the normal rate. The data indicate that a decrease in MCR (rather than an increase in pituitary secretory rate) may account for the higher plasma levels of beta-LPH in uremic patients.

Adolescent↗
PubMed1980

Mode of action of clonidine upon islet function: dissociated effects upon the time course and magnitude of insulin release.

Clonidine (0.08 to 80.0 ng/ml) caused a dose-related inhibition of glucose-stimulated insulin release, but failed to affect glucose oxidation, glucose-stimulated 45Ca net uptake, and adenylate cyclase activity in isolated rat islets. Phentolamine antagonized the effect of clonidine upon insulin release. Despite profound inhibition of insulin secretion, the drug failed to affect the time course for the changes evoked by glucose in either 45Ca fractional outflow rate from perfused islets or insulin release from the isolated perfused pancreas. The latter changes were multiphasic, revealing an initial secretory peak, a period of low secretory activity, and a second secretory elevation before establishing a period characterized by a steadily and slowly increasing insulin output. In the clonidine-treated islets, the secretory rate was not significantly different from the basal value during the period after the initial secretory response. Thus, despite continuous stimulation with glucose, insulin release appears as a discontinuous phenomenon, even when little insulin is secreted during the initial phase of stimulation.

Adenylyl Cyclases↗
PubMed1990

Nature of gonadotropin-releasing hormone self-priming of luteinizing hormone secretion during the normal menstrual cycle.

To investigate further the nature of the gonadotropin-releasing hormone self-priming effect on luteinizing hormone release, we administered two submaximal doses of gonadotropin-releasing hormone 2 hours apart to women at three stages of the menstrual cycle and analyzed the resultant luteinizing hormone secretory episodes with deconvolution analysis. When the characteristics of the secretory episodes associated with the second gonadotropin-releasing hormone challenge were compared with those associated with the first, both an enhanced maximal secretory rate and mass of luteinizing hormone secreted was demonstrable at each phase of the cycle. No differences in the luteinizing hormone secretory event half-duration were detected when the responses to the first and second gonadotropin-releasing hormone doses were compared. These data confirm the gonadal hormone milieu-associated self-priming effect of gonadotropin-releasing hormone on luteinizing hormone release and indicate that it is the rate with which luteinizing hormone molecules are discharged from the pituitary gland, rather than the duration of the secretory episode itself, that provides for the self-priming effect.

Adolescent↗
PubMed1996

Mode of pulsatile follicle-stimulating hormone secretion in gonadal hormone-sufficient and -deficient women--a clinical research center study.

To test the hypothesis that FSH is secreted at least in part within discrete secretory bursts in women and that the characteristics of episodic FSH secretion are altered within differing gonadal hormone environments, we measured FSH by immunoradiometric assay every 10 min for 24 h in premenopausal women during the early follicular (EF), late follicular (LF), and midluteal (ML) phases of the menstrual cycle and in postmenopausal (PM) women (n = 8 in each group). Secretory events were evaluated using multiparameter deconvolution. FSH was secreted in an episodic manner, with the number of secretory bursts (per 24 h; mean +/- SEM) detected in LF (20 +/- 0.79) and PM (20 +/- 0.90) women being greater than that in EF (16 +/- 0.88) and ML (14 +/- 0.93) women. FSH secretory burst mass (milliinternational units per mL) was significantly higher in PM (12 +/- 1.6) than in EF (1.8 +/- 0.21), LF (3.1 +/- 1.3), or ML (0.8 +/- 0.11) women and primarily reflected a relative increase in the maximal secretory rate rather than increased burst half-duration. The estimated half-life (minutes) of endogenous FSH in LF women (155 +/- 18) was shorter than those calculated in EF (251 +/- 24), ML (277 +/- 38), and PM (231 +/- 18) women. Cross-correlation analysis showed strongly positive associations between successively paired serum FSH and LH concentrations in all four groups of women. Deconvolution of simultaneously obtained LH concentration-time series revealed statistically significant concordance (13-25%) between FSH and LH secretory episodes at a lag time of 0 min in EF, LF, and PM women and when LH secretory bursts led FSH secretory bursts by 10 min in ML phase women. However, as 75-87% of FSH and LH secretory pulses were discordant, we infer the operation of distinct control mechanisms in the generation of FSH and LH release episodes. In summary, these results suggest that FSH is secreted within discrete secretory bursts in women, that the mass and frequency of FSH secretory bursts differ in women exhibiting various gonadal hormone environments, and that FSH and LH secretory bursts occur coincidentally at a higher rate than expected on the basis of chance alone, but at such a low overall rate of concordance that distinct mechanisms probably operate to direct episodic FSH and LH secretory activity.

Adult↗
PubMed1976

Ionic pathways of secretory membrane of frog gastric mucosa in Cl--free media.

Experiments were performed to determine the return ionic pathways of the secretory membrane of frog gastric mucosa associated with the electrogenic H+ pump in Cl--free media. The replacement of a 52 mM Na2SO4 secretory solution with a 52 mM K2SO4 secretory solution led to a decrease of resistance, an increase of the H+ secretory rate, and a reversal of the PD. The replacement of 52 mM Na2SO4 with 52 mM MgSO4 led to an increase of resistance and a decrease of the H+ rate. These results provided evidence for the existence of K+ and Na+ pathways, the former having a lower resistance than the latter. Short-circuiting the mucosa in Mg2+ solutions increased the H+ rate to the value in Na+ solutions, hence ruling out the possibility that Mg2+ might interfere with the H+ pump. The fact that the Mg2+ secretory solution, without K+ or Na+, did not abolish the H+ rate suggested the presence of at least a third ionic pathway. presumably SO42-, providing that Mg2+ does not penetrate the mucosa.

Animals↗
PubMed1977

The insulinotropic action of D-erythrose.

D-erythrose (5.0 to 20.0 mM) stimulates insulin release. This insulinotropic action of erythrose displays several features in common with that of glucose. First, erythrose (20 mM) causes a shift to the left of the sigmoidal curve relating the secretory rate to the glucose eoncentration, but fails to enhance the maximal response to glucose. Second, the secretory response to erythrose occurs as an early peak followed by a phase of sustained release. Third, erythrose increases the output of lactate from the islets. Last, erythrose inhibits the efflux of 45calcium and favours its accumulation in isolated islets. It is suggested that, whether in response to glucose or erythrose, an increase in glycolytic flux may represent the key process involved in the identification of the secretagogue, a subsequent remodeling of calcium fluxes being apparently responsible for the activation of the insulin-releasing system.

Animals↗
PubMed1987

Autoradiographic study of the production of secretory material by the subcommissural organ of frogs (Rana temporaria) after injection of several radioactive precursors, with special reference to the glycosilation and turnover rate of the secretory material.

The suitability of several radioactive precursors for studying the secretory processes in the cells of the subcommissural organ (SCO) of frogs (Rana temporaria) was tested by means of autoradiography. Special attention was paid to: the contributions made by different cellular compartments to the glycosilation of the secretory product, and the intracellular turnover rate of the secretory material. From the results it is concluded that: 3H-glucosamine excellently labels Reissner's fibre (RF) in autoradiographs, much better than any other of the radioactive precursors applied. 3H-glucosamine molecules are attached to the protein moiety of the secretory product within the peri- and subnuclear granular endoplasmic reticulum, whereas 3H-fucose and additional 3H-glucosamine molecules are added to the oligosaccharide moiety in the supranuclear Golgi apparatus, previous to apical release; consequently, the subnuclear secretory material and the material that is released into the brain ventricle are chemically different so far as the oligosaccharide moiety is concerned. The oligosaccharide portion of the apical secretory product belongs (at least partially) to the class of the N-linked complex type oligosaccharides. The intracellular half-life of the subnuclear secretory material is at least 5.5 days. The subnuclear secretory material in the ependymal SCO-cells presumably has to pass through the Golgi apparatus before it can be released; this release probably occurs at the apical cell border.

Animals↗
PubMed1991

Lipoprotein secretion by the human hepatoma cell line Hep G2: differential rates of accumulation of apolipoprotein B and lipoprotein lipids in tissue culture media in response to albumin, glucose and oleate.

Serum low-density lipoprotein (LDL) concentration is a major determinant of susceptibility to the development of atherosclerosis. A major component of the protein moiety of LDL and its precursor very-low-density lipoprotein is apolipoprotein B (apo B). The human hepatoma cell line, Hep G2, was used as a model for the investigation of mechanisms which control hepatic secretion of the apo B and lipid components of lipoproteins. Using a sensitive immunoradiometric assay for apo B developed in this laboratory, we showed that bovine serum albumin inhibited and glucose, and fatty acids enhanced the rate of accumulation of apo B in the culture medium of Hep G2 cells. However, these substances did not necessarily affect LDL lipids in the same way as apo B. This finding appeared to be due to Hep G2 cells expressing lipase activities which led to triacylglycerol and phospholipid hydrolysis and lipid reuptake. Reuptake of apo B also occurred, but its rate of accumulation in the culture medium suggested it was a closer reflection of its true secretory rate.

Apolipoproteins B↗
PubMed1988

Cellular mechanisms of renin release.

The renin-angiotensin system plays a central role in salt and water balance and in the regulation of arterial blood pressure. The level of activity of this system is determined primarily by the rate at which the granulated juxtaglomerular cells (JG cells) secrete renin into the blood. Physiologically, renin secretory rate is controlled by a number of first messengers: afferent arteriolar transmural pressure or some function of it, such as stretch (the baroreceptor mechanism); solute transport in the macula densa segment of the nephron (the macula densa mechanism); catecholamines released from the renal nerves and the adrenal medulla (the beta-adrenergic mechanism); extracellular concentrations of many organic and inorganic substances including angiotensin II, vasopressin, K, and Mg (1-3). In addition to these physiological first messengers, a number of pharmacological agents affect renin secretion (3). It is an accepted principle of cellular biology that first messengers act by affecting the intracellular concentrations of only a few second messengers. The evidence that intracellular free ionic calcium, cyclic AMP, and cyclic GMP are second messengers in renin secretion has been reviewed in detail recently (4-9). These reviews are cited extensively, since space limitations precluded citing all the original literature.

Animals↗
PubMed1997

Parotid secretion daily patterns and measurement with ultrasonic flow probes in conscious sheep.

Five sheep under halothane anesthesia were prepared with bilateral transit time ultrasonic flow probes around the parotid ducts. The ducts were fitted with non-obstructive sampling catheters through their oral ends. After probe encapsulation (8 days), salivary flows were continuously recorded (4-5 days, dual-channel ultrasonic flowmeter). For rumination, eating, resting and drinking periods, respectively, the parotid daily outputs recorded were 1.96 +/- 0.57, 0.97 +/- 0.34, 2.84 +/- 0.41 and < 0.041 and bilateral flow rates were 6.76 +/- 0.70, 5.63 +/- 1.42, 2.50 +/- 0.58 and 1.69 +/- 0.88 ml min-1. An ipsilateral secretory reflex was evident when the sheep changed chewing side during rumination (4.44 +/- 0.96 ml min-1 ipsilateral vs 2.63 +/- 0.90 ml min-1 contralateral flow, P < 0.01). Secretory patterns are described in detail during rest, eating, drinking and rumination periods. The pH of parotid saliva (8.36 +/- 0.14) and the osmolality (273.8 +/- 9.9 mosmol kg-1) were independent of secretory rates. In situ probe calibration showed high accuracy (0-9%). The main advantages of the technique are its accuracy and good tolerance, duct integrity and maintenance of nervous supply, minimal surgery, uninterrupted salivary flow, simultaneous bilateral measurements and precise flow monitoring, permitting detailed observations.

Animals↗
PubMed1996

Distinct cellular mechanisms of cholinergic and beta-adrenergic sweat secretion.

The cholinergic and beta-adrenergic sweat secretions from human sweat glands differ with respect to secretory rates and their susceptibility to cystic fibrosis (CF). Using the cultured beta-adrenergic-sensitive sweat secretory cell, we sought to determine the intracellular electrophysiological mechanisms underlying these functional differences. We found that the cholinergic agonist methacholine (10(-6) M) induced a Ca(2+)-dependent biphasic membrane potential (Vm) response: an initial hyperpolarization and a secondary depolarization. The initial hyperpolarization was independent of bath Cl- and dependent on transmembrane K+ gradient. However, the secondary depolarization of Vm was dependent on bath Cl-. In contrast, the beta-adrenergic agonist isoproterenol (10(-5) M) induced a monophasic depolarization of Vm. This depolarization was 1) dependent on bath Cl-, 2) independent of K+ conductance (GK) blocker Ba2+ (5mM), 3) unaffected by the methacholine-induced secondary depolarization of Vm, and 4) absent in cells derived from CF subjects. These results indicated that the cholinergic agonist-induced secretion mainly involves the activation of Ca(2+)-dependent GK and Cl- conductance (GCl), whereas the beta-adrenergic secretion seems to mainly depend on the activation of cystic fibrosis transmembrane conductance regulator-GCl.

Adrenergic beta-Agonists↗