Profiles of intermediary metabolites in insulin-dependent pregnant diabetic women with or without endogenous insulin production

The levels of glucose, free fatty acids (FFA), glycerol, 3-hydroxybutyrate (3-HB), cyclic AMP, and C-peptide immunoreactivity (CPR) were determined in venous plasma samples taken every half hour during an 8-h period under standardized conditions in 10 insulin-dependent pregnant women. The metabolic profiles were determined in each trimester of pregnancy. The women were divided into two groups, one with (group I: 3B, 1C, and 1D according to White's classification) and one without (group II: 1B, 3C, and 1D) measurable plasma CPR levels. Plasma glucose values were significantly higher (P less than 0.01) with greater variability in group II than in group I in the first and second trimesters, while no such difference was found in the third trimester of pregnancy. FFA, glycerol, 3-HB, and cyclic AMP levels were not different between the groups in any trimester of pregnancy. Amniotic fluid CPR was higher and skinfold thickness of the newborn greater in group II than in group I. Neonatal complications occurred only in infants of group II mothers. It is concluded that determination of plasma CPR in diabetic women in early pregnancy could give additional prognostic information to that obtained by the White classification.

Adenosine receptors mediating cyclic AMP production in the rat hippocampus

In the transversely cut rat hippocampus, adenosine caused a dose-dependent increase in the accumulation of [3H]cyclic AMP from [3H]ATP. Adenosine breakdown products were inactive. AMP was somewhat less effective than adenosine, and its effect could be partially, but not completely, abolished by alpha, beta-methylene-ADP and GMP, which inhibited its metabolism by 5'-nucleotidase. The effect of adenosine was unaffected by inhibitors of adenosine deaminase, but enhanced by several inhibitors of adenosine uptake. Some analogues of adenosine, including N6-phenylisopropyladenosine (PIA), 2-chloroadenosine and adenosine 5'-ethylcarboxamide (NECA), were more active than adenosine, whereas others such as 2-deoxyadenosine and 9-(tetrahydro-2-furyl)adenine (SQ 22536) actually inhibited the response. The effect of PIA was highly stereospecific. The action of adenosine was inhibited by several alkylxanthines, the most potent of which was 8-phenyltheophylline. [3H]Cyclohexyladenosine (CHA) bound specifically to cell membranes from the rat hippocampus. The extent of binding was similar to that found in other cortical areas. The relative potency of some adenosine analogues and alkylxanthines to displace labelled CHA was essentially similar to their potency as effectors of the cyclic AMP system. Adenosine contributed to the cyclic AMP-elevating effect of alpha-adrenoceptor-stimulating drugs and several amino acids, but not to that seen with isoprenaline. The cyclic AMP increase seen following depolarization was only partially adenosine-dependent. The present results demonstrate that the rat hippocampus contains adenosine receptors mediating cyclic AMP accumulation and that these receptors have similar characteristics to those mediating pyramidal cell depression. Adenosine-induced cyclic AMP accumulation may be used as a biochemical correlate to electrophysiology and as a convenient parameter to assess the influence of drugs on adenosine mechanisms in the rat hippocampus.

Adenosine actions and adenosine receptors after 1 week treatment with caffeine

After one week treatment with caffeine (20 mg/kg i.p.) the number of adenosine receptors, as determined by specific binding of (3H)-L-PIA, in rat cerebral cortical membranes was increased by about 25%. Cyclic AMP accumulation induced by adenosine analogues in slices of rat hippocampus was unaffected by caffeine treatment. The inhibition of lipolysis in rat fat cells by 2-chloro-adenosine was similarly unaffected. The potency of caffeine as an antagonist of these adenosine-receptor mediated effects was not altered by caffeine treatment. It is concluded that at least some adenosine receptors are up-regulated as a consequence of prolonged caffeine treatment, but that the increase in receptor number is not related to changes in at least two effects of adenosine and caffeine.

2-chloroadenosine increases calcium mobilization from mouse calvaria in vitro

The effect of 2-chloroadenosine on bone resorption and on cyclic AMP formation in murine calvarial bones in vitro was investigated. 2-Chloroadenosine increased the release of 45Ca from the cultured bones, but had no effect on dead bones, indicating that the effect is cell mediated. The adenosine analogue remained in the medium for 48 h and caused a transient stimulation of the formation of cyclic AMP. The dose-response curve for the stimulatory effect on cyclic AMP accumulation was linear up to 10(-4) M. The dose-response curve for 45Ca release was liner from 3 x 10(-7) M to 3 x 10(-5) M but then showed a decline in the response. 8-Bromo cyclic AMP inhibited the release of 45Ca in 24 h cultures. The initial stimulatory effect on bone resorption by 2-chloroadenosine may therefore not depend on cyclic AMP. The level of inosine increased during culture indicating that adenosine is formed by bone tissue.

Formation of 12L-hydroxyeicosatetraenoic acid (12-HETE) by gingival tissue

Extracts of inflamed human gingival tissue converted exogenous [14C] -arachidonic acid mainly to a non-prostaglandin metabolite. This metabolite was identified as 12-hydroxyeicosatetraenoic acid (12-HETE) by gas-liquid chromatography-mass-spectometry. Endogenous arachidonic acid was also converted to 12-HETE. Significant formation of PGF2α , PGD2, PGI2, Thromboxane B, or 12-HHT could not be detected, but, in occasional experiments, significant conversion of arachidonic acid to PGE2 was found.

Origin of adenosine released from rat vas deferens by nerve stimulation

After labelling of vasa deferentia from intact rats with [3H] adenine there was a spontaneous outflow of labelled purines, mainly as adenosine inosine and hypoxanthine. There as a spontaneous outflow of endogenous adenosine and inosine amounting to 6 and 2 pmol/min from a single vas. The uptake inhibitor dipyridamole increased the rate of outflow to 27 and 28 pmol/min. respectively. Transmural nerve stimulation of vasa from intact and castrated rats increased the rate of purine release but with a different time course than for the release of [3H] noradrenaline ([3H]NA). Phentolamine (3 microM) increased [3H] NA release, suggesting the presence of presynaptic alpha-adrenoceptors in castrated vasa, but almost abolished purine release. Adenosine (1 microM) decreased [3H] NA release without affecting [14C] purine overflow. Dipyridamole (1 microM) had a opposite effect. The inhibitory effect of adenosine on noradrenaline release was similar in intact and castrated vasa. In the subcellular distribution studies ATP was detected in the small, dense-cored vesicle fraction, but the ratio ATP:NA was only 1.20-1.60. Labelling of the vesicle fraction by [3H] adenine was usually found, but the degree of labelling was small. The results indicate that endogenous adenosine is released from rat vas deferens in amounts that may be sufficient to cause pre- and postjunctional effects. In particular the amounts of ATP released together with NA are suggested to be quantitatively insignificant.

Purine levels in the intact rat brain. Studies with an implanted perfused hollow fibre

A thin dialysis tube was implanted stereotaxically under halothane anesthesia in the caudate nucleus of Sprague-Dawley rats and perfused with Ringer solution at a rate of 2 microliters/min. Initially there was a high rate of purine outflow but after 1-2 h of perfusion the rate was essentially constant (anesthetized - adenosine 0.4 +/- 0.04 microM, inosine 0.8 +/- 0.2 microM; non-anesthetized - adenosine 0.33 +/- 0.03 microM, inosine 0.21 +/- 0.07 microM). Hypoxia (9% O2) increased the levels more than 3-fold. The adenosine deaminase inhibitor erythro-2-(2-hydroxy-3-nonyl)adenine (EHNA) increased the adenosine level and decreased the inosine level. In vitro recovery of adenosine was about 30%. Therefore, we conclude that the free exchangable concentration of adenosine in the rat brain is likely to be 102 micro M. This level is high enough to potentially affect central nervous function.

Carbachol potentiates the cyclic AMP-stimulating effect of VIP in cat submandibular gland

The effect of VIP and carbachol on cyclic AMP production were studied in isolated acini of the cat submandibular gland and guinea pig pancreas. VIP was almost 100 times more potent in stimulating cyclic AMP in the pancreas than in the submandibular salivary gland. Carbachol did not influence cyclic AMP in the pancreas while a 20-30% increase was seen in the submandibular gland. The addition of carbachol potentiated the cyclic AMP response to VIP in the submandibular acini while no such effect was observed in the pancreas. Atropine abolished the effect of carbachol.

On the mechanism by which theophylline inhibits histamine release from rat mast cells

Theophylline (2.5 mM) did not influence the spontaneous release of histamine but inhibited histamine release induced by antigen, compound 48/80 or phosphatidylserine. The effect on 48/80-induced histamine release could not be reversed by increasing extracellular Ca2+. Exogenous adenosine (10(-8) to 10(-4) M) did not influence spontaneous histamine release or 48/80-induced release but potentiated antigen-induced release. The adenosine potentiation was competitively inhibited by theophylline in concentrations (10(-5) to 10(-4) M) lower than those required to inhibit antigen-induced histamine release in the absence of adenosine. In order to see if endogenous adenosine levels are high enough to potentiate an anaphylactic histamine release in vivo, adenosine was determined in mast cell incubates and in plasma from 4 different strains of rat. The levels were 0.18 to 0.99 microM in plasma, which is sufficient to cause significant potentiation of histamine release, but only 3 x 10(-8) M in mast cell incubates. Theophylline (2.5 mM) increased cAMP levels about 100%, whereas adenosine (10(-5) M) had little effect on cAMP and cGMP levels. However, when incubated together, adenosine could inhibit the theophylline-induced increase in cAMP levels but not the inhibition of histamine release. It is concluded that the effect of low concentrations of theophylline could be due partly to antagonism of adenosine effects. In addition, in higher doses, theophylline appears to exert an inhibitory action that is unrelated to cyclic nucleotides, extracellular calcium and adenosine.

Metabolic and hormonal adjustments during hemorrhage in cats after interference with the sympatho-adrenal system

The relative contribution of the splanchnic sympathetic innervation and the adrenal medulla for metabolism and hormone secretion during two different levels of hemorrhagic hypotension was investigated in 3 groups of anesthetized cats, viz, intact, adrenalectomized and splanchnicotomized (adrenalectomy + cutting of splanchnic nerves). In intact cats, hemorrhage caused very marked elevations of arterial plasma glucose, adrenaline, noradrenaline, dopamine, lactate, cAMP, glycerol and glucagon concentrations whereas plasma insulin fell to only 20% of control values. Adrenalectomy attenuated the glucose, adrenaline, noradrenaline and cAMP responses whereas the normal insulin inhibition was abolished. Splanchnicotomy further reduced the hemorrhagic glucose and glycerol responses and, possibly, also that of glucagon. It is concluded that the adrenergic system as a whole is important for the adjustments of the release of glucose, cAMP, glycerol, insulin and glucagon that occur during hemorrhage in cats. The adrenal medulla seems to be of particular importance for the regulation of cAMP release.

Development of tolerance to oral salbutamol in the third trimester of pregnancy: a study of circulatory and metabolic effects

1 The purpose of the study was to investigate whether a development of tolerance does occur or not to salbutamol-induced cardiovascular and metabolic effects after oral long term treatment in pregnancy. 2 Twenty-three women in late pregnancy were given an oral dose of 4 mg salbutamol in the morning after an overnight fast. Ten of the women had not been exposed to beta-adrenoceptor agonists earlier in their pregnancy (group A). Thirteen of the women had been treated with salbutamol in a dose of 4 mg four times a day for 12 to 33 days preceding the study (group B). 3 Blood samples were collected every 30 min for 120 min and analyzed for cyclic AMP, insulin, C-peptide, glucose, lactate, glycerol, non-esterified fatty acids (NEFA) and 3-hydroxybutyrate (3-HB). Heart rate and blood pressure were recorded simultaneously. 4 In group A there was significant increase in plasma cyclic AMP and increased glycogenolysis, lipolysis and insulin secretion. In this group there were also significant cardiovascular effects, that is, an increase of heart rate and decrease of diastolic blood pressure. 5 In group B the effects of salbutamol were significantly less pronounced, indicating a development of tolerance. 6 We conclude that the metabolic side-effects are not sufficient reason to withhold beta-adrenoceptor agonists to healthy pregnant women with threatened premature labour, since tolerance rapidly develops to these actions.

Early changes in ATP and cyclic AMP levels in experimental critical skin flaps

A cranially based pedicle skin flap, 2 cm wide and 7 cm long, was prepared in the midline of the rat dorsum. The contents of ATP and cyclic AMP were determined in the proximal, middle and distal parts of the flap. The basal level of ATP was 1.3 +/- 0.1 nmol/g dry weight. Following the operation the level of ATP fell rapidly. The fall was more marked in those parts of the flap that eventually do not survive. During the first 12 h the level of cyclic AMP fell at least as rapidly. However, thereafter the cyclic AMP level remained constant or even increased while the ATP showed a further decrease. It is suggested that the rapid fall in ATP may be used to assess the eventual survival of skin flap. The results are also compatible with the opinion that a period of metabolic stimulation in the skin flap starts 12--18 h after operation, i.e. at the time when the adrenergic nerves in the flap degenerate.

Circulatory and metabolic effects of a combined alpha- and beta-adrenoceptor blocker (labetalol) in hypertension of pregnancy

1 Seven women with hypertension of pregnancy were given the combined alpha- and beta-adrenoceptor blocking drug labetalol (50 mg i.v.) in their last trimester. Acute effects were studied for 3 h after administration. 2 Systolic and diastolic blood pressures were significantly reduced from 143 +/- 4 (s.e. mean) to 127 +/- 5 mmHg and from 101 +/- 2 to 88 +/- 2 mmHg, respectively. Maternal heart rate fell significantly from 77 +/- 5 to 68 +/- 3 beats/min. The changes remained during the 3 h of observation. Foetal heart rate was not affected. No side-effects were encountered. 3 Plasma noradrenaline increased significantly from 1.54 +/- 0.16 to a peak value of 2.37 +/- 0.41 nmol/l suggesting sympathetic activation following labetalol. Plasma adrenaline levels were essentially unchanged. Plasma glucose, insulin and C-peptide showed only minor changes. No major effects on lipid metabolism were seen except a significant fall of nonesterified fatty acids at 60 min. Plasma cyclic AMP increased significantly throughout the observation period, perhaps indicating beta-adrenoceptor agonist activity of labetalol. 4 The effectiveness of labetalol as an acute hypertensive agent together with apparent absence of metabolic disturbances and other side-effects makes it an interesting drug for the treatment of hypertension during pregnancy.

The antilipolytic effect of endogenous and exogenous adenosine in canine adipose tissue in situ

The effects of adenosine, 2-Cl-adenosine, two adenosine uptake inhibitors (dipyridamole and dilazep) and the adenosine deaminase (ADA) inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) were studied on basal and stimulated lipolysis in subcutaneous adipose tissue. The basal lipolysis was unaffected by all agents. Lipolysis induced by nerve stimulation (4 Hz, 5 min) was dose-dependently antagonized (up to 100%) by close i.a. infusions of adenosine (1--40 microM in blood); if the nerve induced vasoconstriction was prevented by alpha-adrenoceptor-blockade. 2-Cl-adenosine was a more potent antilipolytic agent than adenosine. EHNA (3--10 microM in blood) did not inhibit stimulated lipolysis in vivo possibly because of the low ADA activity in fat cells. Dipyridamole (0.5--1.5 microM in blood) in combination with EHNA increased the venous plasma concentration of adenosine from 0.3 +/- 0.05 to 0.7 +/- 0.1 microM and enhanced the tissue concentration close to 3-fold. Lipolysis induced by nerve stimulation (4 Hz) was reduced by about 40% by dipyridamole + EHNA and that induced by close i.a. noradrenaline injection (20 nmol) by approximately 60%. It is concluded that adenosine is an antagonist of stimulated lipolysis in subcutaneous adipose tissue in situ in concentrations that are reached during prolonged sympathetic nerve stimulation.

Quinacrine and release of purines from the rat hypothalamus

The acridine derivative quinacrine accumulates in certain endocrine cells and nerve endings. It has been suggested that it binds to ATP stored in granules in such cells. For this reason the uptake and release of quinacrine and the ATP-precursor adenine was studied in slices and in crude synaptosomes from the rat hypothalamus. Both quinacrine and purines were taken up and after uptake there was a spontaneous release. The rate of purine release could be stimulated by nerve stimulation, the depolarizing agent veratridine, and by omitting glucose from the medium. Veratridine-induced purine release was inhibited by dipyridamole, an inhibitor of carrier-mediated nucleoside transport, whereas release induced by glucose deprivation was not. None of the procedures caused release of labelled quinacrine. The results are not compatible with the opinion that the bulk of the purines are released from specific storage vesicles that have the capacity specifically to bind quinacrine.

Regulation of thymocyte proliferation: effects of L-alanine, adenosine and cyclic AMP in vitro

Thymocyte proliferation in culture was studied by measuring the mitotic activity at hourly intervals during two periods, 0-13 and 18-30 h after the start of incubation. In particular, we investigated the effect of increased levels of cyclic AMP which are generated during preparation of the cells due to influence of endogeneously released adenosine. This cycle AMP surge, which could be blocked by combined treatment with adenosine deaminase and theophylline, caused a transient inhibition of proliferation at a stage 4 h prior to mitosis, suggesting a cyclic AMP-sensitive step in that part of the cell cycle. The temporary rise of cyclic AMP did not trigger any resting cells to proliferate. Addition of adenosine deaminase plus theophylline stimulated mitotic activity in the 18-30 h interval, possibly by blocking the influence of continuously released adenosine. The growth of thymocytes was partly synchronous, which was independent of the early cyclic AMP peak. About half of the cycling cell population was shown to be critically alanine dependent. L-alanine deprivation inhibited these cells at a stage in the cell preparation, release of prostaglandins and changes in cell viability could not explain the synchronous growth. The selective elimination of late S- and G2-phase cells during preparation of thymocytes is offered as a possible explanation instead.

Alkylxanthines elevate hippocampal excitability. Evidence for a role of endogenous adenosine

The effects of four xanthines (theophylline, 8-phenyltheophylline, isobutylmethylxanthine (IBMX), and 7-benzyl-IBMX) were studied in the hippocampal slice in vitro. These agents increased the excitability of this preparation with 8-phenyltheophylline being the most potent, 7-benzyl-IBMX the least potent, and theophylline and IBMX having intermediate potencies. A similar rank order was observed in terms of the potencies of these xanthines in antagonizing a) electrophysiological responses to adenosine, and b) adenosine-stimulated cyclic AMP formation. These results indicate that the excitatory actions of xanthines in the vivo hippocampus can be most easily explained on the basis of their ability to block adenosine's actions; the CNS excitatory actions of these drugs in vivo may depend upon a similar mechanism of action.

Role of adenosine in adipose tissue circulation

The vasodilatory effect of adenosine and some related compounds were studied in subcutaneous adipose tissue in situ. The effects of three drugs that inhibit adenosine elimination; two adenosine uptake blockers, dipyridamole and dilazep, the adenosine deaminase inhibitor, EHNA, were also studied. Plasma levels of adenosine were simultaneously determined by HPLC. Adenosine was a potent vasodilator and 2- and 6-substituted analogues were even more potent. Tissue blood flow was linearly related to the venous plasma concentrations of adenosine. An elevation of adenosine in plasma from 0.25 to 0.5 Mu M enhanced blood flow by approximately 50%. A further increase to 1 mu M was associated with a doubling of adipose tissue blood flow. Adenosine also increased the vascular conductance and the capillary filtration coefficient, indicating that is is active on all sections of the vascular bed. Theophylline and caffeine (30- 100 mu M in arterial plasma) antagonized the vasodilatory effect of exogenous adenosine, abolished vasodilation due to EHNA+dipyridamole and reduced resting blood flow. The results suggest that adenosine plays a physiological role in regulating adipose tissue blood flow.

Insulin-induced hypoglycaemia in diabetic women during late pregnancy and one year post partum

Insulin (0.1 IW/kg) later followed by glucose was injected intravenously in nine diabetic women in the supine position both during pregnancy and one year post partum. C-peptide was present in five subjects, indicating some residual beta-cell function. Their mean basal C-peptide level, before insulin, was twice as high in the pregnant as inthe non-pregnant state. C-peptide decreased progressively after insulin. The mean basal plasma glucose level was lower during pregnancy (4.8 mmol/l) than after it (9.6 mmol/l), but decreased to the same level (2.2 mmol/l) after insulin. The rate of fall in glucose was thus lower during pregnancy (kt = 2.54) than after (kt = 4.08), but was unrelated to the basal glucose levels. Basal levels of free fatty acids (FFA), 3-hydroxybutyrate (3-HB), cyclic AMP, and lactate were similar, while glycerol was lower during pregnancy. Insulin-induced changes in FFA, glycerol, 3-HB, cyclic AMP, and lactate were similar during and after pregnancy. Plasma amino acid concentrations were generally lower in pregnancy, significantly so only for arginine and glycine. Amino acid levels were unaffected by insulin in pregnancy, whereas leucine, isoleucine and tyrosine decreased significantly in the non-pregnancy, whereas leucine, isoleucine and tyrosine decreased significantly in the non-pregnancy, whereas leucine, isoleucine and tyrosine decreased significantly in the non-pregnancy state. We conclude that there are differences in metabolic responses to insulin in diabetic women during and after pregnancy, indicating a decreased sensitivity to insulin during pregnancy in some tissues.

Metabolic and circulatory effects of oral salbutamol in the third trimester of pregnancy in diabetic and non-diabetic women

Metabolic and cardiovascular effects of 4 mg oral salbutamol were studied in ten non-diabetic, ten chemical diabetic and five juvenile diabetic women in late pregnancy. None of the women had been treated with beta-sympathomimetic drugs earlier in their pregnancy. Heart rate and blood pressure were recorded and blood samples for measurement of plasma cyclic AMP, insulin, C-peptide, glucose, lactate, glycerol, non-esterified fatty acids (NEFA) and 3-hydroxybutyrate (3-HB) were collected every 30 minutes for 120 minutes after salbutamol. All women underwent the same procedure at random without salbutamol. There were significant cardiovascular effects of salbutamol in all the groups but no differences in these effects between the groups. Salbutamol caused significant increases of glycogenolysis and lipolysis in all the groups, significantly larger in the juvenile diabetic than the non-diabetic and chemical diabetic women. This observation could be explained by the inability of the juvenile diabetics to secrete insulin, shown by their non-measureable plasma C-peptide levels. The metabolic responses following salbutamol in the chemical diabetics were intermediate between the non-diabetic and juvenile diabetic groups. The results show that diabetes does not alter the sensitivity of beta-receptors involved in cardiovascular regulation, while the metabolic responses to oral salbutamol are enhanced, especially in juvenile diabetics. We suggest that during treatment with beta-sympathomimetic drugs, blood glucose should be monitored in all patients showing criteria of potential diabetes.