Insulin Administration In Rats Research Articles

Pharmacokinetic\u2013pharmacodynamic modelling of the hypoglycaemic effect of pulsatile administration of human insulin in rats

The relationship between the plasma insulin (INS) concentration–time course and plasma glucose concentration–time course during and after pulsatile INS administration to rats was characterized using a pharmacokinetic–pharmacodynamic (PK–PD) model. A total INS dose of 0.5 IU/kg was intravenously injected in 2 to 20 pulses over a 2-h period. Compared with the single bolus administration, the area under the effect-time curve (AUE) increased depending on the number of pulses, and the AUEs for more than four pulses plateaued at a significantly larger value, which was similar to that after the infusion of a total of 0.5 IU/kg of INS over 2 h. No increase in plasma INS concentration occurred after pulsatile administration. Two indirect response models primarily reflecting the receptor-binding process (IR model) or glucose transporter 4 (GLUT4) translocation (GT model) were applied to describe the PK–PD relationship after single intravenous bolus administration of INS. These models could not explain the observed data after pulsatile administration. However, the IR-GT model, which was a combination of the IR and GT models, successfully explained the effects of pulsatile administration and intravenous infusion. These results indicate that the receptor-binding process and GLUT4 translocation are responsible for the change in AUE after pulsatile administration.

Methazolamide Is a New Hepatic Insulin Sensitizer That Lowers Blood Glucose In Vivo

We previously used Gene Expression Signature technology to identify methazolamide (MTZ) and related compounds with insulin sensitizing activity in vitro. The effects of these compounds were investigated in diabetic db/db mice, insulin-resistant diet-induced obese (DIO) mice, and rats with streptozotocin (STZ)-induced diabetes. MTZ reduced fasting blood glucose and HbA1c levels in db/db mice, improved glucose tolerance in DIO mice, and enhanced the glucose-lowering effects of exogenous insulin administration in rats with STZ-induced diabetes. Hyperinsulinemic-euglycemic clamps in DIO mice revealed that MTZ increased glucose infusion rate and suppressed endogenous glucose production. Whole-body or cellular oxygen consumption rate was not altered, suggesting MTZ may inhibit glucose production by different mechanism(s) to metformin. In support of this, MTZ enhanced the glucose-lowering effects of metformin in db/db mice. MTZ is known to be a carbonic anhydrase inhibitor (CAI); however, CAIs acetazolamide, ethoxyzolamide, dichlorphenamide, chlorthalidone, and furosemide were not effective in vivo. Our results demonstrate that MTZ acts as an insulin sensitizer that suppresses hepatic glucose production in vivo. The antidiabetic effect of MTZ does not appear to be a function of its known activity as a CAI. The additive glucose-lowering effect of MTZ together with metformin highlights the potential utility for the management of type 2 diabetes.

Effect of chronic intracerebroventricular insulin administration in rats on the peripheral glucose metabolism and synaptic plasticity of CA1 hippocampal neurons

In this study we examined the effects of sustained intracerebroventricular insulin infusion on hippocampal synaptic plasticity in rats. Insulin was infused intracerebroventricularly in male Wistar rats (n=12) for 3months using osmotic minipumps. A control group (n=12) received a sham operation. Insulin infusion led to an initial reduction in food intake and body weight gain, but these differences attenuated over 12weeks. Insulin infusion did not affect fasting or non-fasting blood glucose levels. Field synaptic potentials recording from the hippocampus demonstrated a defect in the expression of long-term potentiation. Sharp electrode current-clamp recording showed that CA1 pyramidal cells fire action potentials in response to prolonged depolarizing current injection and those action potentials showed progressive broadening. The action potential broadening in the insulin-perfused animals were significantly longer than the control. The amplitude of slow after hyperpolarization (sAHP) was measured after manually “clamping” the cells at −65mV and injecting currents to evoke a train of four APs. The sAHP amplitude was significantly longer than in the control animals. We conclude that local insulin infusion into the brain of rats had significant effects on synaptic plasticity in the absence of marked effects on systemic glucose levels. These results indicate that long-term elevation of insulin levels can have adverse effects directly on the brain.

Evaluation of Snail Mucin Motifs as Rectal Absorption Enhancer for Insulin in Non-Diabetic Rat Models

The use of snail mucin motifs as rectal absorption enhancer for insulin has been evaluated. The mucin motifs were extracted from the giant African snail Archachatina marginata by differential precipitation with acetone. The mucin motifs were found to have a molecular weight of 5780 Da and an isoelectric point of 3.4. At the concentrations evaluated, the mucin exhibited rectal absorption enhancing property for the administration of insulin in rats. The % basal blood glucose level of the rats that received the batch of suppositories containing no mucin were consistently above 100% except at the ninetieth minute when it came down slightly to 97.2%. Rats dosed with the batch containing 7%w/w suppositories showed the greatest blood glucose reduction with mean % basal blood glucose concentration of 61.2%. Batches of the suppository containing 5% and 7% mucin showed more marked and consistent lowering in blood glucose concentration than the other batches containing lower amounts of the rectal absorption enhancer. The batch with 7% mucin reduced the basal glucose level to 44% within 2 h of administration of the glycero-gelatin suppository loaded mucin.

Dipalmitoylphosphatidylcholine liposomes with soybean-derived sterols and cholesterol as a carrier for the oral administration of insulin in rats.

Dipalmitoylphosphatidylcholine (DPPC) liposomes with a soybean-derived sterol mixture (SS) or cholesterol (Ch) were examined as a carrier for the oral administration of insulin in rats. Four kinds of liposomes were prepared: liposomes containing SS or Ch (molar ratio of DPPC/X = 7:2 or 7:4, X = SS or Ch), respectively. The pharmacological availability was greater and the lag time for the glucose reduction was later in the order of DPPC/SS (7:4) > DPPC/SS (7:2) > DPPC/Ch (7:4) > > DPPC/Ch (7:2)-liposomes. This order appears to correspond well with that of the rigidity of the liposomal membrane. In particular, DPPC/SS (7:4)-liposomes reduced blood glucose levels for up to 21 h in rats after oral administration. The highest absolute pharmacological availability was 31.6% at a dose of 20.0 IU/kg of DPPC/SS (7:4)-liposomes among the liposomes in comparison to intravenous administration.

Effect of polymers and microspheres on the nasal absorption of insulin in rats

Dextran microspheres and polymer solutions have been evaluated as potential vehicles for nasal administration of insulin in rats. The polymer solutions were either viscous (polyacrylic acid and sodium hyaluronate) or showed thermal gelation (poly-N-iso-propylacrylamide and ethyl(hydroxyethyl)cellulose). The spheres were epichlorohydrin cross-linked dextran, Sephadex and DEAE-Sephadex. Administration of insulin at 1 IU/kg caused a significant decrease in plasma glucose level with two of the investigated polymer systems, polyacrylic acid and ethyl(hydroxyethyl)cellulose, and with the Sephadex spheres. Sodium hyaluronate and poly-N-isopropylacrylamide exerted a significant influence on the plasma glucose level when used as vehicle for an insulin dose of 5 IU/kg. Insulin in DEAE-Sephadex had no effect at all on the plasma glucose level. A larger reduction in plasma glucose level was observed with insulin carried in the particle system than in the polymer systems. Powder formulations which take up water and swell appear to be more efficient in promoting absorption of insulin than the polymer systems.

Verapamil prevents insulin antinatriuresis in euglycemic rats

To determine whether calcium entry is necessary for insulin antinatriuresis, urinary sodium excretion was determined before and during euglycemic insulin administration in rats receiving verapamil (10 micrograms.kg-1.min-1) or vehicle. In vehicle rats, insulin reduced sodium excretion from 2.7 +/- 0.5 to 0.98 +/- 0.2 mu eq/min (P less than 0.05) without altering arterial pressure or inulin clearance. Insulin did not reduce sodium excretion in rats receiving verapamil. Baseline mean arterial pressure was lower in verapamil rats than in vehicle rats. To exclude the possibility that lower baseline arterial pressures prevented insulin antinatriuresis, insulin's effect on sodium excretion was determined in rats receiving captopril at a dose that reduced arterial pressure to the level observed in verapamil rats, and in verapamil rats with angiotensin II levels fixed to maintain arterial pressure equivalent to vehicle rats. In captopril rats, insulin reduced (P less than 0.05) sodium excretion from 1.07 +/- 0.3 to 0.3 +/- 0.01 mu eq/min, even though arterial pressure was not different from that in verapamil rats. Insulin failed to reduce sodium excretion in verapamil rats receiving angiotensin II. Thus verapamil prevents insulin antinatriuresis by renal mechanisms related to inhibition of calcium entry. Additionally, insulin antinatriuresis is independent of angiotensin II.

Homeostatic disruption and memory: effect of insulin administration in rats

The present study examined the effect of insulin-induced hypoglycemia on 24-h retention of passive avoidance in rats. In the initial experiment, rats received either insulin (50 U/kg) or saline injections 30 min prior to training and testing. Impairments in retention were observed when animals were trained with insulin and tested with saline. This anterograde memory loss was attenuated, however, when insulin was administered prior to both training and testing. A subsequent experiment further explored the disruptive effect of hypoglycemia on memory. Data from this study indicated that lower doses of insulin at training (5 and 10 U/rat) yielded impairments in 24-h retention of passive avoidance. It is concluded that disruption of glucoregulation can produce state-dependent anterograde memory losses in rats. Possible implications for the effects of hypoglycemia on cognitive functioning in humans are discussed.

Activation of liver and muscle insulin receptor tyrosine kinase activity during in vivo insulin administration in rats

We have studied autophosphorylation and tyrosine kinase activity of the insulin receptor purified from liver and muscle of fasted rats before and after infusion of insulin (100 mU/h) during a 2.5 h glucose clamp. Recovery of insulin receptors and insulin binding to the solubilised receptors was unaffected by the glucose clamp. Autophosphorylation of the insulin receptor beta subunit was increased in liver receptors prepared from rats at the end of the glucose clamp compared to rats in the basal state both in the absence of insulin in vitro (109% increase, p less than 0.001) and after in vitro stimulation with 10(-7) mol/l insulin (clamped vs fasted; 96% increase, p less than 0.001). Insulin (10(-7) mol/l) stimulated autophosphorylation was also increased in muscle receptor preparations from clamped rats compared with rats in the basal state (58% increase, p less than 0.05). In both liver and muscle receptors, the clamp increased the amount of [32P]-phosphate incorporated into the beta subunit without changing the sensitivity of the insulin stimulation. HPLC analysis of the tryptic phosphopeptides derived from the beta subunit after insulin stimulated autophosphorylation of liver receptors revealed an increase of 32P in all phosphorylation sites without any change in the overall pattern. Tyrosine kinase activity of liver and muscle insulin receptors from clamped rats was also increased approximately twofold (p less than 0.05) when analysed using a synthetic substrate (poly Glu4 Tyr1). Our results support the notion that the insulin receptor exists in an active an inactive form, and that elevated plasma insulin concentrations increases the proportion of active receptors.

Caloric compensation following insulin administration in rats

Caloric intakes following injections of insulin were examined in male rats maintained on diets of different caloric densities. Following saline or insulin injections, food intake was measured every two hours for six hours or food was withheld for six hours until recovery of normo-glycemia and total intake was measured at seven and eight hours post-injection. Additionally, levels of plasma metabolic fuels, liver glycogen and stomach contents were measured following saline and insulin injections. Animals in both the continuous and delayed access conditions consumed the same number of calories following injections of insulin. Similarly, the increases in intake relative to saline baseline conditions were comparable across diet groups in both conditions although animals tested in the delayed access paradigm were less variable in their response. Changes in levels of metabolic fuels, stomach contents and liver glycogen were found to be consistent with the known effects of insulin and counter-regulatory responses to the induced hypoglycemia.

Increased carbohydrate intake as a function of insulin administration in rats

Patterns of dietary self-selection were examined in male rats following subcutaneous injections of NPH insulin. Self-selection animals received separate dietary sources of protein, carbohydrate and fat, while single diet animals received ground Purina Rodent Chow. Food intakes and body weights were measured daily. In comparison to non-injected animals, both self-selection and single-diet animals displayed similar increases in caloric intakes and body weights in response to insulin administration. In animals maintained on the self-selection regime, the increase in caloric intake was solely a function of an increase in carbohydrate intake. Neither protein intake nor fat intake varied as a function of insulin administration. While fat intake remained stable in insulin-injected animals, non-injected self-selection animals gradually increased fat consumption throughout the experiment. Termination of insulin administration for all animals led to decreases in caloric intake below the levels of non-injected animals. Again, modification in caloric intakes in selecting animals were primarily a consequence of altered carbohydrate intake. Patterns of dietary self-selection in insulin-injected animals are contrasted to patterns of selection in other forms of experimental obesity.