The secretion of newly synthesized insulin <i>in vitro</i>

Howell, S. L.; Taylor, K. W.

doi:10.1042/bj1020922

Cited by 75 publications

(20 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The total time from synthesis of proinsulin until its final conversion to insulin was slightly less than one hour. The time from synthesis of proinsulin until radioactive insulin appeared in the media was also about one hour, a value that corresponds to that previously reported (28).…”

Section: Discussionsupporting

confidence: 69%

Subcellular Localization of Proinsulin to Insulin Conversion in Isolated Rat Islets

1970

View full text Add to dashboard Cite

By pulse labeling isolated rat islets with tritiated leucine, it was possible to follow the synthesis of proinsulin and the subsequent conversion of the proinsulin into an intermediate product and insulin. Examination of the islets fractionated at various times indicated synthesis of proinsulin in the microsomal fraction and transfer of the proinsulin to the secretion granule fraction. The secretion, granule fraction was the most important fraction in converting proinsulin to the intermediate product and insulin. The developing secretion granules are implicated in this conversion process. During incubation, insulin was secreted in a bimodal fashion. Insulin precursors were also released into the incubation media. (Endocrinology 86: 88, 1970) AVAILABLE evidence concerning insulin J\. synthesis, storage and secretion suggests that a conventional RNA-directed mechanism is concerned in the biosynthesis of proinsulin by the rough-surfaced fraction of microsomes. Following synthesis, the insulin molecule is stored in the secretion granule, with the Golgi apparatus probably involved in this process. When the beta cell is appropriately challenged, secretion of insulin occurs. Bauer et al.(1) studied insulin biosynthesis in isolated islet tissue of the goosefish. Synthesis was followed by using tracer amino acids; the subcellular site was characterized by isolating nuclear, mitochondrial and secretion granule, microsomal, and supernatant fractions at various times after an addition of labeled amino acids to the incubation media. The results of these studies support the hypothesis that insulin is synthesized in the endoplasmic reticulum and subsequently packaged in the secretion granule.Current evidence suggests that a single polypeptide chain precursor is the most

show abstract

Section: Discussionsupporting

confidence: 69%

Subcellular Localization of Proinsulin to Insulin Conversion in Isolated Rat Islets

1970

View full text Add to dashboard Cite

show abstract

“…Early in vitro studies following radioactive labelled insulin in pancreatic islets in response to high glucose concentration demonstrated an increase in radioactive insulin release after more than 1 h delay [17, 18]. Moreover, we had to consider both leucine and glucose absorption in the gut.…”

Section: Discussionmentioning

confidence: 99%

“…This period is used for calculation of A ; and thirdly the period of disappearance of stable isotope 13 C leucine and decrease in precursor enrichment. Regarding these events, FSR calculation was based on a fixed model: this model is based on earlier in vitro literature regarding biphasic responses, with a period of secretion time for de novo synthesis within OGTT estimated as 0–90 min post-glucose load [19]; period of de novo synthesis was estimated as 90–210 min, and we assumed this time period based on (1) previous literature where in vitro isolated rodent islet cells exposed to high glucose concentrations produced de novo insulin after 60 min [17, 18] and (2) taking into account both leucine and glucose absorption in our gut; period of disappearance of stable isotope is not taken into consideration in this model.…”

Section: Methodsmentioning

confidence: 99%

“…A ‘readily releasable pool’ (RRP) of granules near the plasma membrane is responsible for the rapid first-phase release (via the triggering pathway), and the translocation of a more distal ‘storage granule pool’ (SGP) serves as replenishment of the RRP and results in the more sustained second phase [15, 16]. After an in vitro glucose stimulus, rat pancreatic islets have a biphasic insulin response and synthesize de novo proinsulin, which is stored in newly synthesized granules and subsequently secreted after 1 h [17, 18]. However, the dynamics of newly synthesized insulin and granular secretion of (de novo) insulin have not yet been investigated in humans in vivo.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A stable isotope method for in vivo assessment of human insulin synthesis and secretion

et al. 2016

View full text Add to dashboard Cite

AimsIn vitro, beta cells immediately secrete stored but readily releasable insulin in response to a rise of glucose. During a prolonged insulin response, this is followed by newly synthesized insulin. Our aim was to develop an in vivo test to determine the ratio between readily available and newly synthesized insulin after a stimulus in humans by labelling newly synthesized insulin.MethodsA stable isotope tracer of 1.0 g 13C leucine with C-peptide as target peptide was administered 45 min prior to 75 g glucose load of a frequently blood sampled 210-min oral glucose tolerance test (OGTT). Our OGTT also encompassed collection of urine, which has a high content of C-peptide. Prior, the optimal conditions under which the tracer 13C leucine was administered for enrichment of (pre) proinsulin were established. Also, techniques to obtain urinary C-peptide under highly purified circumstances were set up. Our main outcome measure was the stable isotope enrichment of de novo C-peptide, which we related to early plasma insulin and glucose AUC. Twelve healthy Caucasian individuals (M4F8, age 41.8 ± 2.3, BMI 28.3 ± 1.7) with normal glucose tolerance underwent our OGTT.ResultsWe found that during a 75-g OGTT, newly synthesized insulin contributed approximately 20 % of total insulin secretion. The pattern of isotope enrichment obtained by collecting multiple urine voids was suggestive that the newly synthesized insulin contributes to the late phase of insulin secretion. De novo C-peptide correlated negatively with both early plasma insulin AUC (r = −0.629, P = 0.028) and early plasma glucose AUC (r = −0.605, P = 0.037).ConclusionsWith stable isotope technique added to OGTT, we were able to measure newly synthesized insulin in healthy individuals. This new technique holds the promise that it is feasible to develop a direct in vivo beta cell function test.Electronic supplementary materialThe online version of this article (doi:10.1007/s00592-016-0896-3) contains supplementary material, which is available to authorized users.

show abstract

“…One explanation may be that, in in vivo experiments, xylitol is rapidly metabolized in pancreatic islets and intermediate substance stimulates insulin secretion as it is metabolized in liver (Krebs et al, 1966) and adipose tissue (Mori et al, 1967), although the results of Montague and Taylor (1968) disagree. Another possibility is that the high concentrations of glucose stimulate the biosynthesis of insulin (Howell and Taylor, 1967 ;Lin and Haist, 1969) and proinsulin and newly synthethized insulin appear in the medium after 60 min of incubation (Steiner, 1967), while xylitol may not have this effect (Lin and Haist, 1969 ments. One reason may be that this experiment was done to the fasting dog, since the effect of mannoheptulose was more potent on the pancreas tissue from the fasted animal (Malaisse et al, 1967b).…”

Section: Discussionmentioning

confidence: 99%

Effects of Xylitol and Glucose on Insulin Release from Dog Pancreas Tissue <I>in vitro</I>

Tasaka¹,

Nakamura²,

So³

et al. 1971

Endocrinol Japon

View full text Add to dashboard Cite

SynopsisIn order to study the mechanism or insulin release ny xyiitoi ana glucose, in vitro experiments were done in dog pancreas tissue, using the method described by Malaisse et al. Xylitol and glucose in low concentration (60mg/100ml) did not stimulate insulin release above base line values observed in the absence of sugar. High concentration of xylitol and glucose (300mg/100ml) stimulated insulin release significantly, but the amount of insulin released by xylitol was not so much as that by the same concentration of glucose. The insulin-stimulatory effects of glucose and xylitol were inhibited by the addition of epinephrine or propranolol. 2,4-dinitrophenol blocked them, too. Mannoheptulose inhibited the release of insulin by glucose, but it had no significant effects on xylitol-induced insulin release. These results suggest that xylitol has a direct insulinstimulatory effect in dog pancreas tissue and that there may be a common path in the mechanism of insulin release by xylitol and glucose after it has been metabolized in pancreatic islets.

show abstract

The secretion of newly synthesized insulin in vitro

Cited by 75 publications

References 18 publications

Subcellular Localization of Proinsulin to Insulin Conversion in Isolated Rat Islets

Subcellular Localization of Proinsulin to Insulin Conversion in Isolated Rat Islets

A stable isotope method for in vivo assessment of human insulin synthesis and secretion

Effects of Xylitol and Glucose on Insulin Release from Dog Pancreas Tissue <I>in vitro</I>

Contact Info

Product

Resources

About