The C-terminal eight-amino acid derivative of CCK, sulfated on the tyrosine residue (CCK8S), stimulated a dose-dependent biphasic pattern of insulin secretion from isolated perifused islets in the presence of 7 mm glucose. It was without any effect if glucose were absent from the medium or maintained at 4 mm. The response to CCK8S was readily reversible and dependent on the presence of extracellular calcium. While CCK8S did not increase glucose usage rates above those noted with 7 mm glucose alone, inclusion of the metabolic inhibitor 2-deoxyglucose lowered glucose usage rates to values obtained with 3–5 mm glucose and abolished the influence of CCK8S on insulin output. Removal of the metabolic inhibitor restored the secretory response. N-Acetylglucosamine (15 mm) or glyceraldehyde (2.5 mm) substituted for glucose and permitted CCK8S to evoke secretion. The nonsulfated eight-amino acid derivative of CCK, CCK8, provoked insulin secretion in the presence of 7 mm glucose, but only at 10–100 times greater levels than CCK8S. CCK4 (1 μm) did not influence insulin output in the presence of 7 mm glucose. On an equimolar basis, CCK8S was significantly more effective than gastric inhibiting polypeptide in augmenting insulin output. The results support a role for CCK8S in the regulation of insulin levels in vivo. (Endocrinology119: 616–621, 1986)
Prior, short-term exposure of isolated perifused islets to cholecystokinin (CCK8S) sensitizes them to subsequent glucose stimulation. This sensitization effect develops quickly and persists long after the removal of CCK8S from the perifusion medium. Continued binding of CCK8S to its receptor on the β-cell and the increase in glucose metabolism noted with glucose stimulation are essential for the full expression of this response. This sensitization process may play an integral role in the postulated incretin effect of the peptide.
Prior exposure of isolated perifused rat islets to 20 mM glucose or 10 mM glyceraldehyde amplifies their subsequent insulin secretory response to 10 mM glucose. The involvement of phosphoinositide turnover in the induction of this "time-dependent potentiation" (TDP) was investigated. In islets in which inositol-containing phospholipids were prelabeled with myo-[2-3H]inositol, the addition of 20 mM glucose augments the efflux of 3H. This effect persists for approximately 50 min after the cessation of stimulation. Direct measurements of labeled inositol phosphate accumulation confirmed that this increase in 3H efflux is primarily the result of a persistent increase in phosphoinositide (PI) hydrolysis and not due to the slow efflux and/or degradation of performed [3H]inositol phosphates. The duration of the increase in 3H efflux parallels the duration of TDP. Mannoheptulose abolishes both the increase in 3H efflux evoked by 20 mM glucose and TDP. The omission of extracellular calcium plus 0.5 mM ethylene glycol-bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid also abolishes both of these effects of high glucose. D-Glyceraldehyde (10 mM) addition to 3H-inositol-prelabeled islets results in an acute efflux of 3H, a persistent efflux after removal of the D-glyceraldehyde from the perifusion medium, and the induction of TDP. Similar to the results obtained with high glucose, the return of 3H efflux rates to prestimulatory values is accompanied by the abolition of TDP. These results suggest that events associated with persistent stimulant-induced increases in phosphoinositide hydrolysis may participate in the induction and maintenance of TDP.
Prior exposure of isolated per if used rat islets to the sulfated gut hormone cholecystokinin-8 (CCK-8S) dramatically increased their insulin secretory response to 7.5 mM glucose, 10 mM arginine, and 10 mM α-ketoisocaproate. In the case of glucose, the heightened secretory response was still apparent 60–80 min after CCK-8S removal from the perifusion medium. Prior exposure of perifused islets to arginine (10 mM), tolbutamide (25 μM), or forskolin (1.0 μM) did not sensitize them to 7.5 mM glucose. CCK-8S exposure increased 3H efflux from islets prelabeled with [3H]inositol, and the increase in 3H efflux was sustained after CCK-8S removal from the perifusion medium. The duration of this increase in 3H efflux paralleled the temporal characteristics of this sensitization process and was significantly attenuated by 25 μM asperlicin, a competitive antagonist of CCK binding to its membrane receptor. Arginine, tolbutamide, or forskolin treatment of islets did not increase 3H efflux from [3H]inositol-prelabeled islets. The results suggest that the turnover of membrane phosphoinositides induced by CCK-8S is largely responsible for this heightened state of secretory responsiveness to various stimulants. Secondmessenger molecules generated during phosphoinositide turnover may be responsible for the phenomenon of sensitization displayed by islet tissue to CCK-8S addition.
Quality teaching affects the performance of learners across the disciplines. This study would like to explore the different teaching styles used by the professors that is prevalent in the Master in Physical Education (MPE) program and the effects of the teaching styles in their profession. The qualitative and quantitative design was utilized by the researchers in gathering and finding the results of the study. It was found out that the teaching style that is prevalent in the MPE program was consistent and intertwined relative to the delivery of instruction in the program used by the professors. Lastly, the use of indirect teaching using the Mosston’s Spectrums were vital to the improvement of the performance of the learners.
Asperlicin, a product derived from the fungus Aspergillus alliaceus, antagonized the multiple stimulatory effects of cholecystokinin (CCK-8S) on isolated islets. At a level of 10 microM, asperlicin completely inhibited insulin release in response to 25 nM CCK-8S. Increasing the level of CCK-8S to 100 nM partially restored a secretory response, while an even greater insulin stimulatory effect was noted with 500 nM CCK-8S. The inhibitory effect of asperlicin on CCK-8S-induced release was reversible. Asperlicin exposure had no effect on glucose or glyceraldehyde-induced secretion. Asperlicin reduced, in parallel with secretion, the increase in 3H efflux from [3H]inositol prelabeled islets usually noted with CCK-8S addition. Asperlicin did not influence the small glucose-stimulated increase in 3H efflux. The results support the notion that asperlicin is a specific and potent antagonist of the multiple stimulatory effects of CCK-8S on islet tissue.
The influence of L 364718 on islet responsiveness to sulfated cholecystokinin (CCK-8S) was investigated. In islets whose inositol-containing phospholipids were prelabeled during a 2-h incubation period, subsequent exposure to L 364718 (1 nM) significantly impaired the secretion of insulin usually noted in response to 200 nM CCK-8S in the simultaneous presence of 7 mM glucose. A higher level of the antagonist (10 nM) completely abolished insulin secretion. L 364718 (1-10 nM) reduced the efflux of 3H from myo-[2-3H]-inositol prelabeled islets in parallel with the reduction in secretion. L 364718 (10 nM) significantly reduced the accumulation of 3H-containing inositol phosphates usually noted with CCK-8S addition. L 364718, at levels 10- to 100-fold greater than those necessary to attenuate CCK-8S–induced insulin secretion, had no adverse effect on the insulin secretory response of freshly isolated islets to 10 mM glucose alone, 5 mM D-glyceraldehyde, 15 mM α-ketoisocaproate, or 50 ng/ml gastric inhibitory polypeptide. L 364718 (1000 nM) had no adverse influence on carbamylcholine (1 mM)–induced phosphoinositide hydrolysis. These results establish L 364718 as a potent and highly selective antagonist of cholecystokinin's stimulatory actions on βc-ells. Because of its potency, selectivity, and oral effectiveness, in vivo studies with L 364718, aimed at unraveling the pleiotropic effects of CCK-8S on glucose and insulin homeostasis, seem feasible.
The effects of sulfated cholecystokinin (CCK-8S) and glucose on insulin secretion and polyphosphoinositide (PPI) metabolism were studied in isolated rat islets. Both agonists stimulate PPI hydrolysis, inositol phosphate accumulation, 3H efflux from [3H]inositol-prelabeled tissue, and 45Ca efflux from prelabeled cells. However, the effects ofCCK-8S on PPI metabolism are considerably greater than those of glucose. Furthermore, the effectsof CCK-8S on PPI and Ca2+ metabolism are observed whether islets are incubated in either 2.75 or 7 mM glucose, but CCK-8S only stimulates insulin secretion (a biphasic response) when the higher glucose concentration is present. Addition of 1 μM forskolin to islets incubated in media containing 2.75 mM glucose does not influence basal insulin secretion but sensitizes the islets to the action of CCK-8S. In the presence of forskolin, CCK-8S induces a very marked first phase but no second phase of insulin secretion. We postulate that CCK-8S acts in this tissue via receptor-linked PPI hydrolysis, leading to an inositol trisphosphate-induced Ca2+ efflux. These receptor- mediated effects of CCK-8S are not altered either by the ambient glucose concentration or the cAMP content of the islets, but these two factors determine the responsiveness of the islets (in terms of insulin secretion) to a given CCK-8S signal.
The antihelminthic drug mebendazole (MEB) has been reported to elevate circulating insulin levels in vivo. By using isolated perifused rat islets we tested the acute effects of this drug directly on the beta cell in the absence or presence of exogenous glucose. In the absence of glucose, MEB (40 micrograms/ml) caused a delayed but sustained increase in insulin output from the islet. Release induced by this concentration of MEB was not influenced by either forskolin (10 microM), a compound that increases islet cyclic AMP levels and potentiates glucose-induced secretion, or the absence of extracellular calcium. In the presence of a submaximal stimulatory glucose concentration (8 mM), release was dramatically potentiated by the further addition of 10 to 40 micrograms/ml of MEB. The potentiating effect of the drug on glucose-induced release was readily reversible and abolished by the omission of extracellular calcium or the addition of 10 mM mannoheptulose, a compound that blocks glucose phosphorylation. Despite its positive effects on hormone secretion, MEB did not affect glucose metabolism. MEB may prove useful for investigating the factors that regulate insulin secretion.
The influence of cyclic AMP (cAMP) and extracellular calcium on phosphoinositide (PI) hydrolysis in isolated islets was assessed and related to insulin output. Three stimulants were chosen to activate the β-cell: sulfated cholecystokinin (CCK-8S, 200 nM), high-level glucose (20 mM), and the sulfonylurea tolbutamide (200 μM). The insulin secretory response to all three agonists was amplified by forskolin (which increases cAMP levels) and reduced by nitrendipine (which decreases calcium influx). All three stimulants increased the hydrolysis of inositol-containing phospholipids, an event monitored by an increase in [3H]inositol efflux from [3H]inositol-prelabeled islets and by the accumulation of labeled inositol phosphates. Forskolin, despite its positive impact on insulin secretion, reduced [3H]inositol efflux and inositol phosphate accumulation in response to all agonists. A similar inhibitory effect on these parameters was noted with nitrendipine; however, nitrendipine abolished secretion in response to all agonists. These findings support the following conclusions: 1) an increase in cellular cAMP levels reduces the quantitative impact of various agonists on these indices of PI hydrolysis; 2) despite this inhibitory effect, cAMP amplifies the insulin secretory response to these agonists; and 3) extracellular calcium is a crucial determinant of both PI hydrolysis and the ensuing insulin secretory response.
