Effects of exogenous insulin on placental transfer of maternal glucose to the rat fetus.

There is controversy concerning the possible modulation of glucose transfer to the fetus by insulin acting on the maternal side of the placenta. To study this question, 20.5 day pregnant rats were infused simultaneously with (U-14C)-D-glucose (via the jugular vein) and with different doses of insulin (via the left uterine artery) so that placentas from the left uterine horn were exposed to a higher insulin concentration than those from the right uterine horn. Placentas and fetuses from each uterine side were processed separately. No differences were detected in total blood radioactivity, plasma-14C-glucose, -14-C-lactate, -glucose, or -radioimmunoassayable insulin in fetuses from the left versus the right uterine horn. Total placenta radioactivity and 14C-glycogen were also similar in the left and right uterine sides at all insulin doses studied. Infusion of insulin (66 mU/min) to the pregnant rat caused hyperinsulinaemia and hypoglycaemia, decreased blood total radioactivity and plasma 14C-glucose, and increased plasma 14C-lactate in the mother. The level of fetal plasma 14C-glucose paralleled that of the mother. It is concluded that in the rat, placental glucose uptake, its transfer to the fetus, and fetal glucose utilization are not directly affected by maternal circulating insulin. Metabolic changes occurring in fetuses of hyperinsulinaemic mothers are secondary to the decreased availability of glucose.

Short-term insulin infused through the portal vein enhances liver gluconeogenesis and glycogenesis from [3-14C]pyruvate in the starved rat.

Insulin infusion through the portal vein immediately after a pulse of [3-14C]pyruvate in 24 hr starved rats enhanced the appearance of [14C]glucose at 2, 5 and 10 min and glucose specific activity at 1, 2 and 20 min in blood collected from the cava vein at the level of the suprahepatic veins. Insulin infusion for 5 min decreased liver pyruvate concentration and enhanced both liver and plasma lactate/pyruvate ratio, and it decreased the plasma concentration of all amino acids. When insulin was infused together with glucose, [14C]glucose levels and glucose specific activity decreased in blood but there was a marked increase in liver [14C]glycogen, glycogen specific activity and glycogen concentration, and an increase in liver lactate/pyruvate ratio. The effect of insulin plus glucose infusion on plasma amino acids concentration was smaller than that found with insulin alone. It is proposed that insulin effect enhancing liver gluconeogenesis is secondary to its effect either enhancing liver glycolysis which modifies the liver's cytoplasmic oxidoreduction state to its more reduced form, increasing liver amino acids consumption or both. In the presence of glucose, products of gluconeogenesis enhanced by insulin are diverted into glycogen synthesis rather than circulating glucose. This together with results of the preceding paper (Soley et al., 1985), indicates that glucose enhances liver glycogen synthesis from C3 units in the starved rat, the process being further enhanced in the presence of insulin.

Glucose infused through the portal vein enhances liver gluconeogenesis and glycogenesis from [3-14C]pyruvate in the starved rat.

After a pulse of [3-14C]pyruvate, 24 hr starved rats were infused through the portal vein with two different doses of glucose (7.8 or 20.8 mg/min) or the medium, and blood was collected from the inferior cava vein at the level of the suprahepatic veins. The highest dose of glucose enhanced the appearance of [14C]glucose in blood from the 2nd to the 20th min after tracer delivery. It also enhanced production of [14C]glycogen and concentration of glycogen in the liver after 5 and 20 min. At 20 min of glucose infusion the appearance of [14C]glyceride glycerol in liver as well as liver lactate concentration and lactate/pyruvate ratio were increased. The low dose of glucose used enhanced liver values of [14C]glycogen, [14C]glycogen specific activity and glycogen concentration. Our results support the hypothesis that in the starved rat glucose is converted into C3 units prior to being deposited as liver glycogen and based on the liver zonation model (Jungermann et al., 1983) it is proposed that glucose stimulated gluconeogenesis by shifting the liver to the cytosolic redox state as a secondary consequence of increased glycolytic activity.

Liver glucose, glycogen and lipid synthesis in fed and 24-hour fasted rats soon after a pulse of [3-14C]pyruvate through the portal vein.

1. A pulse of [3-14C]pyruvate was given to rats through the portal vein and blood was collected at brief intervals from the inferior cava vein at the level of the suprahepatic veins. 2. In 24 hr fasted rats, the appearance of [14C]glucose in blood and blood glucose specific radioactivity were higher than in fed animals from the first minute after delivery of the tracer. At this time total radioactivity did not differ between the two groups. 3. After 5 and 20 min. liver radioactivity present in glycogen and glyceride glycerol was enhanced while in fatty acids it was reduced in fasted as compared with fed animals. 4. It is proposed that, in the fasted state, both glycogen and glyceride glycerol synthesis are predominantly gluconeogenic processes.

Method for the study of metabolite transfer from rat mother to fetus.

Infusion medium containing a tracer was introduced through the left uterine artery to 20.5-day pregnant rats. In this way, the left uterine horn received the tracer directly while it reached the right horn after dilution in the mother's circulation. When U-14C-D-glucose or U-14C-L-alanine was infused, radioactivity in fetal blood from the left uterine horn was 3 or 8 times higher respectively than in the right horn and 2 or 6 times higher than in maternal blood. When the infusion was carried out with 125I-labelled growth hormone, which is known not to cross the placental barrier, very little radioactivity was found in fetuses compared with that in the mother's plasma and no differences were observed in blood radioactivity levels of fetuses from either horn. After infusion of U-14C-D-glucose through the maternal jugular vein instead of left uterine artery, radioactivity was the same in fetuses from the left and right horns, indicating that manipulations of the left uterine side did not greatly affect its circulation. These findings. together with the determination of specific radioactivity of the tracer used in both maternal and fetal plasma, validate the technique as a semiquantitative means to determine the direct transfer of any product through the placental barrier in the rat.

Studies on the dynamics and mechanism of glibenclamide-induced insulin secretion.

Sustained, 60-minute perfusion of glibenclamide (0.5, 1.5 and 10 mug/ml) elicits a one-phase insulin release profile, formed by a rapid secretion peak followed by a second peak with lower insulin levels than the former. Basal insulin secretion values are observed during the period comprised between 13 and 60 minutes of perfusion. Concurrent stimulation with glucose (100, 150, 200 and 300 mg%) plus glibenclamide (1 mug/ml) causes a marked rise in both phases of insulin secretion. The addition of glibenclamide does not modify the biphasic secretion pattern caused by maximal glucose concentration (400 mg%). The maximal values of both phases of secretion in the dose-response curve elicited by different glucose concentrations shift to the left when glibenclamide is added to the perfusate. The increase in insulin secretion caused by glibenclamide is not inhibited by puromycin. Both theophylline and phentolamine modify and increase the glibenclamide-induced insulin release pattern. Propranolol and imidazole inhibit glibenclamide-induced insulin release. Our results suggest that: 1. Glibenclamide increases beta cell sensitivity to glucose stimulation. 2. Glibenclamide and glucose induce secretion of insulin originating in the same compartment. 3. Modification of alpha and beta adrenergic receptors may modify glibodulate the beta cell response to glibenclamide.

Evidence for a hypophyseal factor that stimulates insulin secretion by the pancreas (insulotrophine?)

The continuous infusion of glucose (1 mg/kg/min) via the carotid artery in anesthetized dogs produced a biphasic pattern of insulin secretion. The first peak reached a maximum 3 min after glucose infusion and decreased to basal level at 7 min. As long as glucose infusion persisted a slow and maintained increase in insulin level in the pancreatico-duodenal vein was observed. The same amount of glucose infused in to the carotid arteries of hypophysectomized dogs, failed to induce any change in plasma insulin level. Plasma sample obtained from the jugular vein of dogs receiving glucose via the carotid arteries were infused into a second dog via the pancreatico-duodenal artery. One minute after the onset of infusion a rise in insulin was observed in the pancreatico-duodenal vein. The stimulating effect was not due to the high blood glucose level present in the jugular vein of dogs undergoing the cephalic glucose infusion. Infusion through the pancreatico-duodenal artery of a glucose solution at a concentration equal to the highest blood glucose level observed in the jugular vein did not evoke insulin secretion. Plasma samples obtained from the jugular vein of dogs receiving saline via the carotid arteries did not evoke insulin secretion when receiving into the pancreatico-duodenal arteries of dogs. Pancreatic infusion of plasma obtained from the jugular vein of hypophysectomized dogs infused glucose through the carotid arteries did not evoke any pancreatic response. These findings are demonstrative of the presence of a hypophyseal humoral insulin stimulating factor in the jugular vein of dogs receiving a cephalic glucose load.

[Animal experimental study on spasmolytic and analgesic activities of pramiverine, metamizole and their combination (author's transl)]. / Tierexperimentelle Untersuchungen auf spasmolytische und analgetische Wirkungen von Pramiverin, Metamizol sowie einer Kombination beider Substanzen

In two pharmacological in vivo tests a comparative study was performed on the spasmolytic and analgesic effects of 4,4-diphenyl-N-isopropyl-cyclohexylamine-hydrochloride (pramiverine, Sistalgin), metamizole and a combination of both active principles in equal dose ratio (1 : 1000). The results demonstrated that pramiverine showed a potent spasmolytic effect which was potentiated by the combination with metamizole, and that the positive analgesic effect of metamizole was fully displayed in the combination with pramiverine, but that for pramiverine alone no analgesic effect was detected.

Effect of cephalic glucose infusion on insulin secretion.

The continuous infusion of glucose (1 mg/kg/min) via the carotid artery in anesthetized dogs produces a biphasic pattern of insulin secretion. The first peak reaches a maximum 3 min after glucose infusion and drops to basal level at 7 min. As long as the glucose infusion persists a slow and mantained increase in insulin level in the pancreaticoduodenal vein can be observed. The same amount of glucose infused in the general circulation via the jugular vein provoked a different pattern of insulin secretion. Cerebral glucose infusion to vagotomized dogs also produced a two phase response to insulin secretion, but the levels reached in the first phase were lower that those observed in the normal dogs. The infusion of glucose, via the jugular vein, in vagotomized dogs, failed to induce any change in plasma insulin levels. Our data suggest that a glucose load to the brain induces pancreatic insulin secretion mediated partially by the vagus nerves. These results are also compatible with the hypothesis that a humoral factor could be involved in the pancreatic response.