Impairment of adrenergic-induced proopiomelanocortin-related peptide release in heroin addicts

The effects of iv stimulation with clonidine on plasma levels of beta-lipotropin (beta-LPH), beta-endorphin (beta-EP), cortisol, growth hormone (GH) and adrenocorticotrophic hormone (ACTH) were tested in a group of 10 healthy volunteers and in 8 heroin abusers. Hormones were measured either by direct radioimmunoassay (RIA) (GH, cortisol) or after plasma extraction and Sephadex G-75 column chromatography (beta-LPH and beta-EP) or by immunoradiometric assay (IRMA) (ACTH). Plasma levels of GH increased in a similar fashion in the two groups. In the controls, clonidine induced release of beta-LPH and beta-EP after 30 min (from 8.9 +/- 1.0 to 19.1 +/- 4.6 fmol/ml, P less than 0.01 and from 8.1 +/- 0.6 to 17.9 +/- 4.6, P less than 0.01) and of ACTH after 60 min (from 12.1 +/- 1.8 to 18.1 +/- 1.8, P less than 0.05) while in addicts beta-EP but not beta-LPH showed a significant increase (from 8.5 +/- 0.7 to 19.8 +/- 4.2, P less than 0.05), 90 min after the injection. In heroin addicts, plasma cortisol levels decreased continuously after clonidine stimulation while in controls they showed a biphasic pattern, decreasing until the 60th min (from 135.2 +/- 30.4 ng/ml to 74.0 +/- 13.3, P less than 0.05) and regaining basal levels 1 h later (122.0 +/- 24.8, P less than 0.05 vs 60th min value). These data demonstrate the existence in human beings of noradrenergic control of proopiomelanocortin (POMC)-related peptides and indicate that chronic opiate abuse greatly interferes with this control. Clonidine-induced release of plasma beta-EP may be of importance with regard to its therapeutic effects in detoxification.     

THE EFFECT OF KETANSERIN, A SPECIFIC SEROTONIN ANTAGONIST ON THE PRL, GH, ACTH AND CORTISOL RESPONSES TO HYPOGLYCAEMIA IN NORMAL SUBJECTS

The role of serotonin in the prolactin, growth hormone, ACTH and cortisol responses to hypoglycaemia has been investigated in normal subjects using a selective serotonin (5HT2) receptor antagonist, ketanserin. Circulating concentrations of these hormones were measured after administration of insulin (0.1 units/kg body weight iv) to eight normal male subjects with and without simultaneous iv ketanserin (10 mg). Plasma glucose fell to less than 2.0 mmol/1 in all subjects and was unaffected by ketanserin. Ketanserin induced a 50% decrease in the serum prolactin response to hypoglycaemia, 45 and 60 min after administration of insulin (increase in serum prolactin at 60 min: 1145 +/- 295 mU/l without ketanserin; 558 +/- 176 mU/l with ketanserin, P less than 0.05). The peak ACTH response was reduced by 30% (95.3 +/- 33.6 ng/l without ketanserin; 60.0 +/- 22.9 ng/l with ketanserin, P less than 0.05) but the plasma cortisol response was not significantly altered. The serum growth hormone response was unaffected by serotonin blockade. These findings suggest that serotonin, probably acting through 5HT2 receptors, is involved in the stimulation of prolactin and ACTH release but not in the release of growth hormone, during insulin induced hypoglycaemia.     

Diurnal rhythms in plasma melatonin concentrations in the fetal sheep and pregnant ewe during late gestation

We have measured plasma melatonin (MT) concentrations in the pregnant ewe and fetal sheep during 24-h periods between 114 and 142 days gestation. There was a clear diurnal rhythm in the plasma MT concentrations in both the ewe and fetus from 114 days gestation. Blood samples were also collected from the pregnant ewe and fetus during the day every 2-3 days from 112 days gestation to term. There was no gestational age trend in maternal or fetal day time plasma MT concentrations during late pregnancy. To establish whether there was transplacental transfer of MT, pregnant ewes were injected with [3H]MT, and total radioactivity (disintegrations per min) was measured in maternal and fetal arterial plasma and in amniotic fluid collected before and for 1 h after the [3H]MT injection. Two minutes after [3H]MT injection, radioactivity was detected in both maternal and fetal sheep plasma. Extraction of fetal plasma with chloroform indicated that [3H]MT accounted for 48.0 +/- 7.2 (SE) % of total radioactivity at 2 min after the injection. In one pregnant ewe infused with unlabeled MT (0.3 microgram/ml saline.min for 20 min) maternal and fetal plasma MT concentrations increased within 6 min after the start of the MT infusion. We conclude that there is a diurnal rhythm in the plasma concentrations of MT in the fetal lamb and pregnant ewe between 114 and 142 days gestation, and that MT crosses the ovine placenta from the maternal to the fetal circulation. Therefore, the MT present in the fetal sheep circulation may be solely of maternal origin or it may be derived from both fetal and maternal sources.     

PLASMA IMMUNOREACTIVE β-ENDORPHIN IS ELEVATED IN URAEMIA

Plasma immunoreactive-(IR) beta-endorphin (beta-EP) and beta-lipotrophin (beta-LPH) levels were measured in 15 adult uraemic patients on chronic haemodialysis. The presence of immunoreactivity eluting in the position of beta-EP was demonstrated following submission of pooled extracts of uraemic plasma to gel permeation chromatography on Sephadex G-50. To separate beta-EP from beta-LPH, pre-dialysis plasma extracts from six individual patients, and three pools of three patients each, were submitted to sequential immune-affinity chromatography and levels were measured by radioimmunoassay. In all cases, plasma IR beta-EP concentrations were markedly increased compared with normal subjects (m +/- SEM fmol/ml; 64.4 +/- 13.7 vs. 2.3 +/- 0.2). IR beta-LPH concentrations were also increased (m +/- SEM fmol/ml; 55.7 +/- 13.2 vs. normal 6.1 +/- 0.8). In addition, post-dialysis concentrations of plasma IR beta-EP and beta-LPH were lower than pre-dialysis levels (n = 4).     

Placental corticotropin-releasing hormone and pituitary-adrenal function during pregnancy.

The placenta secretes large amounts of the hypothalamic releasing hormone, corticotropin-releasing hormone (CRH), into both the maternal and fetal circulation during pregnancy. We characterized the relationship between maternal plasma CRH and products of the pituitary and adrenal in order to investigate the physiologic role of placental CRH in modulating maternal pituitary-adrenal function. Plasma was obtained from 8 women at biweekly intervals between 21 and 40 weeks of full-term pregnancy for CRH, adrenocorticotropin (ACTH), alpha-melanocyte-stimulating hormone (alpha MSH), cortisol, and dehydroepiandrosterone sulfate (DHEAS) measurements by radioimmunoassay. Eighteen women were also studied once at 22-34 weeks of pregnancy with plasma CRH and 24-hour urinary free cortisol measurement. Eight nonpregnant women served as control subjects. Plasma CRH was undetectable in the nonpregnant subjects and rose over the time period studied in the pregnant women. Concentrations of afternoon ACTH and cortisol also rose during pregnancy while DHEAS levels declined in the pregnant women. The alpha-MSH levels were beneath the level of detection (< 20 pg/ml) in both the pregnant and nonpregnant subjects. The overall mean afternoon ACTH concentration was higher in the pregnant than in the nonpregnant women (11.4 +/- 1.8 vs. 5.9 +/- 1.8 pg/ml; p < 0.05), although the ACTH levels in both groups remained within the normal range. The mean plasma cortisol concentrations were higher in the pregnant women, while the mean DHEAS levels were lower in the pregnant women when compared to the nonpregnant subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise-induced hypoglycaemia and subcutaneous insulin infusion

To assess whether exercise-induced hypoglycaemia could be prevented by interruption of insulin infusion (3 h) we studied diabetic patients treated with continuous subcutaneous insulin infusion (CSII). The studies were performed in 7 insulin-dependent diabetics (aged 31.4 +/- 4.8 (mean +/- SD) years, duration of diabetes 16.9 +/- 5.4 years), after an overnight fast and in the afternoon, 4 h after the last pre-meal bolus injection (exercise and control period). Bicycle exercise (45 min at 60% of maximum oxygen consumption) was started 30 min after the insulin infusion was stopped. During exercise there was a more pronounced decline in blood glucose in the afternoon (2.2 +/- 0.3 mmol/l, mean +/- SEM) than in the morning (1.4 +/- 0.4 mmol/l) (p less than 0.01). This corresponded to higher mean levels of free insulin during exercise in the afternoon (20 +/- 4.5 mU/I vs 12.0 +/- 1.0 mU/l, in the morning). Interruption of insulin delivery for 3 h resulted in a moderate increase of blood glucose, a gradual decrease of free insulin, and a moderate increase in free fatty acids and beta-hydroxybutyrate. During exercise in the afternoon 3 diabetics suffered from symptomatic hypoglycaemia (BG less than 2.8 mmol/l). In contrast with most of the other patients they showed no decline of free insulin during exercise. Thus even after interruption of basal rate insulin infusion moderate postprandial exercise may lead to hypoglycaemia if there is relative hyperinsulinism.     

Plasma Met-enkephalin and catecholamine responses to insulin-induced hypoglycaemia in greyhounds

The involvement of endogenous opioid peptides in the stress response was investigated by measuring plasma concentrations of Met-enkephalin-like immunoreactivity (MLI), adrenaline and noradrenaline during insulin-induced hypoglycaemia in conscious greyhounds. Moreover, the molecular forms of circulating MLI were characterized using gel filtration chromatography. In the first group of animals, i.v. administration of insulin (0.3 units/kg) provoked marked hypoglycaemia (blood glucose concentrations fell from 4.4 +/- 0.1 to 1.5 +/- 0.2 mmol/l; mean +/- S.E.M.) which was associated with significant (P less than 0.001) rises in plasma MLI concentrations from a basal concentration of 45 +/- 8 to a peak of 189 +/- 39 ng/l. A within-subject study comparing five different insulin doses ranging from 0.004 to 0.3 units/kg showed dose-related effects on blood glucose with nadir concentrations of 4.1 +/- 0.6 mmol/l (after the smallest dose of insulin) and 0.8 +/- 0.1 mmol/l (after the largest dose of insulin). This was associated with dose-related rises in plasma MLI with peak concentrations of 56 +/- 17 and 558 +/- 35 ng/l, plasma adrenaline with peak concentrations of 0.45 +/- 0.06 and 15.76 +/- 1.33 nmol/l and plasma noradrenaline with peak concentrations of 0.49 +/- 0.07 and 2.27 +/- 0.45 nmol/l following the smallest and largest doses of insulin respectively. These results are the first demonstration of raised plasma MLI concentrations following hypoglycaemia. Moreover, they show that the hormonal responses vary with the degree of hypoglycaemia achieved. Together with reports by other investigators these findings might suggest opioid modulation of the responses of the sympathoadrenal system to hypoglycaemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of placental proteases on maternal and fetal blood pressure in normal pregnancy and preeclampsia

Although many proteases exist in human placenta, their physiologic roles are still unknown. Our study showed that placental proteases metabolize vasoactive peptides possibly derived from the fetus.Because vasopressin and angiotensin are known to play an important role in normal and aberrant (preeclampsia) fetal-placental circulation, the clearance of these peptides in the placenta is important in controlling fetal blood pressure. Vasopressin and angiotensin act as a fetal-placental vasoconstrictor; therefore, placental proteases in human placenta are likely to work as a clearance factor for these peptides.Although human and animal pregnancy is normally associated with a refractory response to the pressor effect of exogenously infused angiotensin II, patients with preeclampsia, as well as nonpregnant women, are sensitive to the pressor effect of angiotensin II. Our study suggested that the decreased pressor responsiveness to angiotensin II in pregnancy is caused by increased inactivation of angiotensin II by angiotensinase in pregnant serum and the placenta.Although vasopressinase and angiotensinase activities increase with advancing gestation in normal pregnant sera, the activities of both enzymes in severe preeclampsia sera were clearly lower than those in normal pregnancy. Therefore, it is reasonable to speculate that the increased sensitivity to angiotensin II of preeclampsia is attributable to the decreased degradation of angiotensin II by placental angiotensinase.The negative correlations between the systolic to diastolic ratio obtained from pulsed Doppler measurement techniques and the activities of both enzymes in preeclampsia sera suggested that the systolic to diastolic ratio, which reflected constriction of placental vessels, is influenced by the concentration of vasoactive peptides in the fetal-placental circulation due to changes in the activities of placental proteases.Placental proteases play important roles in controlling fetal and maternal blood pressure through regulation of the concentration of vasoactive peptides in the interface (placenta) between fetus and mother.     

Characterization of plasma beta-endorphin immunoactivity in the fetal lamb: effects of gestational age and hypoxia

To characterize the immunological forms of beta-endorphin (beta-EP) in the fetal circulation, total beta-EP immunoactivity [beta-EPi] and N-acetyl beta-EPi were measured in the plasma of chronically catheterized fetal lambs in undisturbed conditions and before, during, and after periods of controlled hypoxia. Measurements of the peptide concentrations in each plasma sample were made by RIA using an antiserum to the midportion of beta-endorphin which cross-reacts with both acetylated and unacetylated forms of the peptide as well as with beta-lipotropin, and a second antiserum which reacts only with acetylated forms of beta-EP. In 25 plasma samples from 12 fetal animals at 113-142 days gestation, total beta-EPi was 87.0 +/- 10.9 pg/ml, while N-acetyl beta-EPi was 90.8 +/- 7.7 pg/ml (mean +/- SE). When a plasma pool obtained from 3 fetuses in the basal state was extracted and chromatographed on Sephadex G-50, most of the N-acetyl beta-EPi eluted in the same position as the synthetic N-acetyl beta-EP standard. Thus, most of the beta-EPi in the plasma of the unstressed fetus could be accounted for by N-acetylated forms of the peptide. These are the major forms of beta-EP produced by the intermediate lobe of the pituitary. To examine the effects of acute hypoxia on fetal plasma peptide levels, pregnant ewes were exposed to 10% O2 in N2 for 30 min. In 15 studies at 113-142 days gestation, mean fetal PO2 decreased from 21.7 +/- 0.6 to 11.0 +/- 0.7 mm Hg (P less than 0.001). Total beta-EPi increased significantly from 93.0 +/- 17.7 to 527 +/- 146 pg/ml during hypoxia and returned toward basal values after 30 min of recovery to 372 +/- 116 pg/ml (P less than 0.02). Over the same intervals, N-acetyl beta-EPi did not change significantly, with mean levels of 88.5 +/- 10.7, 123 +/- 16.3, and 130 +/- 16.8 pg/ml. This shows that the increase in total beta-EPi with hypoxia could not be accounted for by an increase in N-acetyl beta-EPi. Our finding that most of the total beta-EPi in the circulation of the undisturbed fetus is N-acetyl beta-EPi favors an intermediate lobe origin. Since beta-EP is inactivated by N-acetylation, these data suggest that this immunoactivity has little or no biological activity. Enhanced release of total beta-EPi during hypoxia, which could not be accounted for by acetylated forms, suggests that this type of stress activates the anterior pituitary lobe and results in increased plasma concentrations of the biologically active peptide.     

Effect of restriction of placental growth on the concentrations of insulin, glucose and placental lactogen in the plasma of sheep

The effect of restricting placental growth on maternal glucose, insulin and placental lactogen was investigated in 16 ewes carrying singleton lambs. Uterine caruncles were removed from seven ewes (caruncle ewes) before pregnancy, resulting in reduced placental size and retarded intra-uterine fetal growth. The concentration of insulin in maternal plasma was similar in both control and caruncle ewes. The concentration of glucose was significantly higher in the caruncle than in the control ewes (3.26 +/- 0.15 (S.E.M.) mmol/l, number of observations (n) = 9, vs 2.75 +/- 0.1, n = 9, P less than 0.02, and 3.27 +/- 0.16, n = 7, vs 2.46 +/- 0.11, n = 12, P less than 0.001, for the carotid artery and utero-ovarian vein respectively). The concentration of ovine placental lactogen (oPL) in the utero-ovarian vein was reduced in the caruncle compared with the control ewes (283 +/- 65 micrograms/l, n = 8, and 705 +/- 106 micrograms/l, n = 18, P less than 0.02, respectively). Restriction of placental growth by removal of endometrial caruncles similarly reduced the concentrations of oPL in maternal arterial plasma (231 +/- 54 micrograms/l, n = 9, and 621 +/- 96 micrograms/l, n = 18, P less than 0.002). Production of oPL by the placenta was also reduced by limiting placental growth to 30 +/- 11 micrograms/min, n = 8, compared with 133 +/- 43 micrograms/min, n = 15, P less than 0.05, for the controls. Production of oPL per gram of placenta in the caruncle group, although only 34% of the control value, was not reduced significantly.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of insulin on glucose uptake and metabolism in the human placenta

The effect of insulin on glucose uptake, transfer, and metabolism was investigated in the human placenta perfused in vitro. Insulin concentrations in maternal perfusion medium were varied from 0-1200 microU/ml, whereas the glucose concentration was kept constant in maternal and fetal perfusion media. Despite significant uptake of insulin by the perfused placenta, neither glucose uptake and transfer nor lactate release were significantly modified during a 1-h insulin perfusion. The MCR of insulin by the placenta was 0.29 +/- 0.03 (+/- SEM) ml/min X g at physiological insulin levels. These data suggest that placental glucose transport and metabolism are insensitive to maternal plasma insulin variations and that the low clearance rate of insulin by the placenta is not a major determinant of maternal insulin adjustments during pregnancy.     

Lack of effect of melatonin on myometrial electromyographic activity in the pregnant sheep at 138-142 days gestation (term = 147 days gestation)

A 24-h rhythm has been demonstrated in fetal and maternal melatonin plasma concentrations in pregnant sheep in the last third of gestation. Melatonin in the maternal circulation can cross the placenta and is the major source of melatonin in the fetal circulation. Melatonin has been postulated to act as a prostaglandin (PG) synthetase inhibitor in the uterus. PG synthetase inhibitors decrease myometrial contractility. To assess transplacental passage of melatonin and potential influences of melatonin on uterine contractility, we infused melatonin continuously into the maternal jugular vein in seven pregnant sheep at 138-142 days gestation (term in our instrumented animals is 147 days gestation) at three infusion rates for successive 1-h periods during the late morning to late afternoon. There was no change in the total time during which the myometrium was active, as indicated by myometrial electromyographic activity or the myometrial contracture frequency during the 3 h before and after melatonin infusions and for each hour of the infusions. The MCR for melatonin in the ewe was 4128 +/- 410 ml/min (mean +/- SE; n = 7; weight, 50-70 kg). The resting maternal to fetal melatonin concentration ratio was 0.8; this ratio was maintained at 2.28 during melatonin infusion to the ewe at a wide range of maternal melatonin concentrations. Melatonin concentrations in the range of 3-200 times normal had no effect on the maternal plasma PGF2 alpha metabolite concentration, but caused a 40.4% fall in fetal plasma PGE2 (P less than 0.05). We conclude that changes in maternal and fetal plasma melatonin concentrations within the physiological range observed throughout the day do not alter myometrial contractility, but do alter fetal PGs.     

In preeclampsia, the circulating factors capable of altering in vitro endothelial function precede clinical disease

The pathophysiology of preeclampsia involves the release of a circulating factor(s) from a hypoperfused placenta that activates the maternal endothelium. This study investigated the effect on in vitro endothelial function of plasma taken from women in whom preeclampsia subsequently developed. Women at increased risk for an adverse pregnancy outcome were identified using Doppler waveform analysis. Plasma samples (22 and 26 weeks) were incubated with myometrial vessels taken from women with uncomplicated pregnancies. Wire myography was used to study the effect of plasma on the endothelium-dependent vessel behavior. Incubation of vessels from normal pregnant women with plasma from women in whom preeclampsia subsequently developed (n=19) significantly reduced endothelium-dependent relaxation, compared with vessels incubated with plasma from normal pregnant women (n=48). This effect was demonstrable for plasma taken at 22 weeks (residual constriction 47.1+/-6.6% versus 32.0+/-4.4%, P=0.004 at 1-hour incubation; and 59.1+/-8.4% versus 42.3+/-5.9%, P=0.001 at 18-hour incubation) and 26 weeks (59.2+/-5.2% versus 29.1+/-5.6%, P<0.001 at 1 hour; and 63.3+/-7.6% versus 31.9 +/-7.2%, P<0.0001 at 18 hours). Endothelial-dependent relaxation was unaltered after incubation with plasma taken from women in whom normotensive intrauterine growth restriction subsequently developed (n=19). This study supports the hypothesis that plasma, from women in whom preeclampsia develops, collected weeks before diagnosis is capable of altering endothelial function.     

Plasma beta-endorphin and beta-lipotropin levels increase in well trained athletes after competition and non competitive exercise

Plasma beta-endorphin (beta-EP) and beta-lipotropin (beta-LPH) levels were measured in 15 healthy trained marathon runners. These hormones were evaluated in two different conditions: 1-before (1h) and after a marathon race (n = 10); 2-before, during and after a prolonged (90 min) submaximal exercise (bicycle ergometer at 50% VO2 max) (n = 5). In these latter group plasma beta-EP and beta-LPH levels were measured every 15 min for 165 min. In all the athletes, both plasma beta-EP and beta-LPH levels were significantly higher after the end of the marathon race than in basal conditions (p less than 0.01). The prolonged exercise with bicycle ergometer significantly stimulated plasma beta-EP and beta-LPH levels. Starting 60 min after the beginning of the exercise, plasma beta-EP and beta-LPH levels resulted significantly higher than basal values until the end of the exercise (p less than 0.01 at 60, 75 and 90 min). These data confirming that marathon running is a potent stress stimulus, showed that the duration and related factors but not the work load may be considered critical in stimulating beta-EP and beta-LPH release during physical exercise.     

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

Summary 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.     

Effect of a hypertonic saline load on plasma concentrations of atrial natriuretic peptide in fetal calves and their dams

Plasma concentrations of atrial natriuretic peptide (ANP) were studied in eight adult non-pregnant cows and in two groups of six chronically catheterized bovine fetuses and their mothers in the eighth month of pregnancy. The first group of fetuses was used for studying the effect of an acute i.v. sodium load (240 mmol NaCl/fetus) on fetal ANP; the second group acted as controls. The mean basal ANP levels in the third-trimester bovine fetus were three to four times higher than maternal values (39.5 +/- 5.5 and 9.4 +/- 0.6 pmol/l respectively; P less than 0.01). Basal maternal plasma ANP levels were twice as high in pregnant cows in the third trimester of pregnancy than in non-pregnant cows (9.4 +/- 0.6 and 4.3 +/- 0.7 pmol/l respectively; P less than 0.05). In response to an i.v. hypertonic saline injection, fetal plasma ANP levels increased significantly (P less than 0.01) to a maximum of 86.7 +/- 17.6 pmol/l 10 min after the injection, and returned to baseline within 60 min after the treatment; during the 20 min following the i.v. sodium load, fetal plasma ANP correlated significantly with fetal plasma sodium concentrations (r = 0.96; n = 12) and with fetal plasma osmolality (r = 0.94; n = 12). No significant changes in maternal ANP values were observed in the two groups of animals. These results suggest that ANP secretion is stimulated during pregnancy in cows, and that, in the bovine fetus, a hypertonic sodium load appears to be a potent stimulus for ANP release.     

Studies of oxytocin in the baboon during pregnancy and delivery.

Oxytocin was determined by radioimmunoassay in pregnant baboons throughout gestation, in the foetus at caesarean section, and after oxytocin infusion into the mother and foetus. Serial maternal plasma oxytocin in 6 baboons during pregnancy showed a significant correlation between the gestational age and maternal plasma oxytocin concentrations with a correlation coefficient of r = 0.3185 and P less than 0.005. Seventy-one out of 75 plasma samples (94.7%) during pregnancy had detectable levels of oxytocin. Uterine vein plasma had higher oxytocin concentrations than maternal plasma and amniotic fluid (18.6 +/- 4.6 pg/ml; mean +/0 SE) but lower than umbilical, jugular vein and cardiac blood from the foetus. Foetal pituitary gland contained 5.4--26.1 micrograms oxytocin/g. Regular uterine contractions were established with iv oxytocin of 4--20 mU/min and the plasma oxytocin measured showed a significant correlation with the uterine activity achieved (r = 0.64, P less than 0.001). The disappearance of plasma oxytocin at 179 days gestation gave an apparent half-life of 1.1 and 1.7 min in 2 baboons with a late half-life of 9.9 and 17.3 min, respectively. In one baboon at 171 days gestation, the apparent half-life of oxytocin was 9.9 min. The metabolic clearance rates were calculated to be 3.1, 3.2 and 11.7 ml/kg/min, respectively. The production rates were 97, 74, 390 pg/kg/min, respectively. Oxytocin injected into the umbilical vessel near term showed an increase in oxytocin concentration in maternal and uterine vein plasma and amniotic fluid, suggesting that oxytocin can cross the placenta from the foetal to the maternal side. Our findings indicate that in the baboon (1) oxytocin is present throughout pregnancy, (2) uterine activity can be correlated with plasma oxytocin during oxytocin infusion, (3) foetal circulation has higher oxytocin concentration than maternal blood and (4) oxytocin probably can cross the placenta from the foetus to the mother.     

RESPONSE OF PANCREATIC POLYPEPTIDE TO HYPOGLYCAEMIA IN INSULIN-DEPENDENT DIABETICS WITH AND WITHOUT RESIDUAL β-CELL FUNCTION

To investigate a possible association between the beta-cells and the cells secreting pancreatic polypeptide (PP), the response of PP to insulin-induced hypoglycaemia was investigated in seven insulin-dependent diabetics with and seven without residual beta-cell function, all without signs of autonomic neuropathy. The mean concentrations of PP was significantly greater from 15 to 60 min after symptoms of hypoglycaemia in patients with residual beta-cell function than in patients without (P less than 0.05) despite similar blood glucose concentrations in the two groups. Also the total integrated areas beneath the response curves as well as the incremental integrated areas were significantly greater in patients with beta-cell function (216 +/- 36 pmol/l x min and 188 +/- 34 pmol/l x min, respectively) than in patients without beta-cell function (125 +/- 26 pmol/l x min and 102 +/- 26 pmol/l x min) (P less than 0.05 for both). The mean maximal concentrations of adrenaline (1.53 +/- 0.28 ng/ml v. 1.29 +/- 0.12 ng/ml) and noradrenaline (0.56 +/- 0.16 ng/ml v. 0.45 +/- 0.04 ng/ml) were not statistically different in the two groups. No well established explanation for an association between residual insulin secretion and capacity for PP-response to hypoglycaemia in type 1 diabetics exists.     

Plasma endothelin response to acute hypoglycaemia in adults with Type 1 diabetes.

AIMS: To determine whether acute insulin-induced hypoglycaemia provokes a detectable alteration in peripheral plasma endothelin (ET) concentrations in humans with Type 1 diabetes. METHODS: Serial plasma concentrations of ET were measured in 20 patients with Type 1 diabetes during controlled hypoglycaemia induced by intravenous infusion of soluble insulin. RESULTS: A significant increase was observed in plasma ET concentrations, from 3.80 +/- 0.31 pg/ml at baseline to 6.72 +/- 1.47 pg/ml at 60 min after the onset of the hypoglycaemic reaction (P < 0.05). CONCLUSIONS: Acute insulin-induced hypoglycaemia induces a rise in plasma endothelin concentrations in people with Type 1 diabetes. This finding is consistent with a putative role for ET in the mediation of hypoglycaemia-induced vasoconstriction, and the possible precipitation of macrovascular or microvascular events.     

Differential effects of insulin-induced hypoglycaemia on the plasma branched-chain and non-branched-chain amino acid concentrations in humans.

In order to determine plasma amino acid concentrations during a prolonged but moderate insulin-induced hypoglycaemia, six healthy volunteers received a constant subcutaneous insulin infusion (15 mU.m-2.min-1) over a 12 hour period. The plasma glucose concentrations decreased from 4.72 +/- 0.11 to 2.83 +/- 0.07 mM at 600 minutes and then remained stable over the last 120 minutes. Plasma counterregulatory hormones (glucagon, epinephrine, growth hormone and cortisol) increased significantly between 120 and 180 minutes. The plasma concentration of all the amino acids paralleled the decrease in plasma glucose. The branched chain amino acids decreased to a greater extent in the first part of the study (0-360 min) in comparison to the essential non-branched chain aminoacids (p < 0.01), then increased significantly with a peak at 600 minutes (p < 0.05 vs 360 min) despite stable hyperinsulinaemia. These results suggests that during prolonged but moderate hypoglycaemia the counterregulatory hormones are able to antagonize partially the effects of insulin on protein metabolism, analogous to their well-known anti-insulin effects on glucose and fatty acid metabolism.