Biomedical subjects

S S McIntyre

Publications and source records attributed to S S McIntyre.

3 recordsLinked to original sources

PubMed2001

Decrease in beta-cell mass leads to impaired pulsatile insulin secretion, reduced postprandial hepatic insulin clearance, and relative hyperglucagonemia in the minipig.

Most insulin is secreted in discrete pulses at an interval of approximately 6 min. Increased insulin secretion after meal ingestion is achieved through the mechanism of amplification of the burst mass. Conversely, in type 2 diabetes, insulin secretion is impaired as a consequence of decreased insulin pulse mass. beta-cell mass is reported to be deficient in type 2 diabetes. We tested the hypothesis that decreased beta-cell mass leads to decreased insulin pulse mass. Insulin secretion was examined before and after an approximately 60% decrease in beta-cell mass achieved by a single injection of alloxan in a porcine model. Alloxan injection resulted in stable diabetes (fasting plasma glucose 7.4 +/- 1.1 vs. 4.4 +/- 0.1 mmol/l; P < 0.01) with impaired insulin secretion in the fasting and fed states and during a hyperglycemic clamp (decreased by 54, 80, and 90%, respectively). Deconvolution analysis revealed a selective decrease in insulin pulse mass (by 54, 60, and 90%) with no change in pulse frequency. Rhythm analysis revealed no change in the periodicity of regular oscillations after alloxan administration in the fasting state but was unable to detect stable rhythms reliably after enteric or intravenous glucose stimulation. After alloxan administration, insulin secretion and insulin pulse mass (but not insulin pulse interval) decreased in relation to beta-cell mass. However, the decreased pulse mass (and pulse amplitude delivered to the liver) was associated with a decrease in hepatic insulin clearance, which partially offset the decreased insulin secretion. Despite hyperglycemia, postprandial glucagon concentrations were increased after alloxan administration (103.4 +/- 6.3 vs. 92.2 +/- 2.5 pg/ml; P < 0.01). We conclude that an alloxan-induced selective decrease in beta-cell mass leads to deficient insulin secretion by attenuating insulin pulse mass, and that the latter is associated with decreased hepatic insulin clearance and relative hyperglucagonemia, thereby emulating the pattern of islet dysfunction observed in type 2 diabetes.

Animals↗

PubMed2000

Direct measurement of pulsatile insulin secretion from the portal vein in human subjects.

Insulin is secreted in a high frequency pulsatile manner. These pulses are delivered directly into the portal vein and then undergo extraction and dilution before delivery into the systemic circulation. The reported frequency of these insulin pulses estimated in peripheral blood varies from an interpulse interval of 4-20 min. We postulated that this discrepancy is due to the attenuation of the pulse signal in the systemic circulation vs. the portal circulation. In the present study we measured pulsatile insulin release directly in the portal circulation of human subjects who had indwelling transjugular intrahepatic portasystemic stent shunts (TIPSS) to decompress portal hypertension. We quantitated pulsatile insulin secretion in both the overnight fasted state (fasting) and during a hyperglycemic clamp (8 mmol/L). Direct portal vein sampling established that pulsatile insulin secretion in humans has an interval (periodicity) of approximately 5 min. The amplitude (and mass) of the insulin concentration oscillations observed in the portal vein was approximately 5-fold greater than that observed in the arterialized vein and was similar to that observed in the dog. Increased insulin release during hyperglycemia was achieved through amplification of the insulin pulse mass. In conclusion, direct portal vein sampling in humans revealed that the interpulse interval of insulin pulses in humans is about 5 min, and this frequency is also observed when sampling from the systemic circulation using a highly specific insulin assay and 1-min sampling, but is about 4-fold greater than the frequency observed at this site using single site RIAs. We confirm that enhanced insulin release in response to hyperglycemia is achieved by amplification of these high frequency pulses.

Adult↗

PubMed1996

Disturbed development of the preimplantation embryo in the insulin-dependent diabetic BB/E rat.

Although improved regulation of maternal IDDM during pregnancy has resulted in a major fall in the stillbirth rate, the rates for other problems, such as spontaneous preterm labor, fetuses small for gestational age, congenital malformation, and the incidence of large placentas, remain raised. This has suggested the possibility that the damaging effect of conventionally treated but poorly regulated IDDM may operate primarily at the earliest stages of gestation, even before the diagnosis of pregnancy has been made. This study shows that spontaneous autoimmune IDDM in the Bio Breeding/Edinburgh (BB/E) rat is associated with severe disturbance in the development of the preimplantation embryo in a majority of pregnancies, as indicated by a fivefold increase in the incidence of degenerate fragmented embryos and a 33% reduction in the number of expanded blastocysts and in those blastocysts that reach the expanded stage a 20% cellular deficit in the inner-cell mass without any change in trophectoderm cell number. In addition, we find that blastocysts removed from diabetic rats and cultured in vitro for 24 h show no sign of "catch-up" growth of the inner-cell mass, although under these conditions, the trophectoderm exhibits a 25% cellular accretion. It is tempting to speculate that these phenomena are a presage of the characteristic combination of fetal growth retardation and large placentas, which are a feature of both BB/E rat and human IDDM pregnancy.

Animals↗