The association of physical activity on homocysteine in pregnant women

INTRODUCTION

Women with high levels of physical activity have improved pregnancy, labor, and delivery outcomes related to cardiovascular health. Hyperhomocysteinemia, which predicts cardiovascular disease risk, is associated with maternal vascular complications during pregnancy, such as placental abruption and preeclampsia. However, studies are lacking on whether physical activity impacts homocysteine in pregnant women, pointing to a potential mechanism behind the improved cardiovascular health in women who exercise during pregnancy. The purpose of this study was to examine if women with high levels of physical activity have lower levels of homocysteine compared to women with low levels of physical activity.

METHODS

This study was a secondary analysis using data from the 2003 to 2006 National Health and Nutrition Examination Survey. A total of 257 pregnant women were included. Physical activity was assessed objectively over seven days with accelerometers. High and low groups based on moderate-to-vigorous physical activity (MVPA) and steps/day were defined. Homocysteine and related laboratory biomarkers (vitamin B12, folate, pyridoxal 5'-phosphate) were assessed through blood draws. Data assembly was performed using SAS and analysis via SPSS Complex Samples.

RESULTS

Only an estimated 17.7 ± 4.7% of women met guidelines to achieve at least 150 min per week of MVPA. Plasma homocysteine was not different between pregnant women with high and low levels of moderate-to-vigorous physical activity (4.39 ± 0.21 and 4.44 ± 0.17 µmol/L; p > .05) or between those with high and low levels of steps (3.95 ± 0.26 and 4.62 ± 0.27 µmol/L; p > .05) when the data was split into two quantiles by the median. These results were similar when using log-transformed values for homocysteine to normalize the distribution of data. Pregnant women in the group of the high steps tended to have higher vitamin B12, folate, and pyridoxal 5'-phosphate than those in the group of the low steps. Sensitivity analyses revealed that homocysteine was not different between the upper 25% (4.04 ± 0.22 µmol/L) and lower 25% (4.17 ± 0.26 µmol/L) MVPA (p = .716) but that it was statistically higher in the low (<5000 steps/day) (4.99 ± 0.20 µmol/L) steps/day group compared to high (>7500 steps/day) steps/day (3.99 ± 0.23 µmol/L) (p = .003) after excluding individuals with hypertension and thyroid/kidney issues.

CONCLUSION

Maternal steps/day, but not MVPA, appear to be associated with homocysteine (albeit weakly) in the present study after excluding potential factors which impact homocysteine. The volume of physical activity appears to be an important indicator as this difference was not revealed until the physical activity was more distinctly separated.

Vaccine against peanut allergy based on engineered virus-like particles displaying single major peanut allergens

BACKGROUND

Peanut allergy is a severe and increasingly frequent disease with high medical, psychosocial, and economic burden for affected patients and wider society. A causal, safe, and effective therapy is not yet available.

OBJECTIVE

We sought to develop an immunogenic, protective, and nonreactogenic vaccine candidate against peanut allergy based on virus-like particles (VLPs) coupled to single peanut allergens.

METHODS

To generate vaccine candidates, extracts of roasted peanut (Ara R) or the single allergens Ara h 1 or Ara h 2 were coupled to immunologically optimized Cucumber Mosaic Virus-derived VLPs (CuMVtt). BALB/c mice were sensitized intraperitoneally with peanut extract absorbed to alum. Immunotherapy consisted of a single subcutaneous injection of CuMVtt coupled to Ara R, Ara h 1, or Ara h 2.

RESULTS

The vaccines CuMVtt-Ara R, CuMVtt-Ara h 1, and CuMVtt-Ara h 2 protected peanut-sensitized mice against anaphylaxis after intravenous challenge with the whole peanut extract. Vaccines did not cause allergic reactions in sensitized mice. CuMVtt-Ara h 1 was able to induce specific IgG antibodies, diminished local reactions after skin prick tests, and reduced the infiltration of the gastrointestinal tract by eosinophils and mast cells after oral challenge with peanut. The ability of CuMVtt-Ara h 1 to protect against challenge with the whole extract was mediated by IgG, as shown via passive IgG transfer. FcγRIIb was required for protection, indicating that immune complexes with single allergens were able to block the allergic response against the whole extract, consisting of a complex allergen mixture.

CONCLUSIONS

Our data suggest that vaccination using single peanut allergens displayed on CuMVtt may represent a novel therapy against peanut allergy with a favorable safety profile.

Uncomplicated Pregnancies and Ultrasounds for Fetal Growth Restriction: A Pilot Randomized Clinical Trial

Objective The purpose of this multicenter pilot study was to determine the feasibility of randomizing uncomplicated pregnancies (UPs) to have third trimester ultrasonographic exams (USE) versus routine prenatal care (RPNC) to improve the detection of small for gestational age (SGA; birth weight < 10% for GA). Material and Methods At three referral centers, 50 UPs were randomized after gestational diabetes was ruled out. Women needed to screen, consenting, and loss to follow-up was ascertained, as was the detection rate of SGA in the two groups. Results During the study period at the three centers, there were 7,680 births, of which 64% were uncomplicated. Of the 234 women approached for randomization, 36% declined. We recruited 149 women and had follow-up delivery data on 97%. The antenatal detection rate of SGA in the intervention group was 67% (95% confidence intervals 31-91%) and 9% (0.5-43%) in control. Conclusion The pilot study provides feasibility data for a multicenter randomized clinical trial to determine if third trimester USE, compared with RPNC, improves the detection of SGA and composite neonatal morbidity.

Cardiac axis shift within the cardiac cycle of normal fetuses and fetuses with congenital heart defect

OBJECTIVES

To investigate changes in the cardiac axis (CAx) within the cardiac cycle of normal fetuses and fetuses with congenital heart defects (CHD).

METHODS

This was a retrospective case-control study in which stored videoclips of four-chamber views from 527 prenatal ultrasound examinations performed at 18 + 0 to 36 + 6 weeks of gestation were reviewed. Among the ultrasound scans included, 287 were of normal fetuses (controls) and 240 were of fetuses with CHD. In each case, the CAx was measured at end systole (just before the atrioventricular (AV) valve opened) and at end diastole (just before the AV valve closed). CAx measurements of fetuses with CHD were compared to those of controls.

RESULTS

The mean CAx in the control group was 45.9 ± 8.5° at end systole and 38.3 ± 8.4° at end diastole (P < 0.001), resulting in an average difference of 7.6 ± 3.2°. The mean CAx in fetuses with CHD was 53.4 ± 17.8° at end systole and 47.5 ± 17.3° at end diastole (P < 0.001), resulting in an average difference of 5.9 ± 6.3°. However, in some forms of CHD, such as hypoplastic left heart syndrome and L-transposition of the great arteries, the CAx was greater at end diastole than at end systole, with a difference of more than 5°. In 21.3% of control fetuses, there was a CAx shift within the cardiac cycle of ≥ 10°. Abnormal CAx measured at end systole was strongly associated with CHD.

CONCLUSIONS

Measurement of the CAx at end systole provides values that differ from those when measured at end diastole, in both normal fetuses and those with CHD. We recommend that the CAx be measured at end systole as a greater proportion of fetuses with CHD and fewer normal fetuses have an abnormal CAx at this stage compared to at end diastole. The occurrence of an abnormal CAx and the CAx shift within the fetal cardiac cycle depend on the type of CHD.

Long-Term Gestational Hypoxia Modulates Expression of Key Genes Governing Mitochondrial Function in the Perirenal Adipose of the Late Gestation Sheep Fetus

We previously reported that long-term hypoxia (LTH) increases expression of brown adipose tissue (BAT) genes in the perirenal adipose in the ovine fetus. The mechanisms with which hypoxia mediates the enhanced BAT phenotype are unresolved. This study was designed to examine the effects of LTH on (1) the expression of endothelial cell nitric oxide synthase (eNOS) and (2) indicators of mitochondrial biogenesis (transcription factors mitochondrial transcription factor A (mtTFA), nuclear respiratory factor (NRF) 1, and NRF-2; cytochrome c oxidase (COX) I, II, and IV and mitochondrial DNA content). Pregnant ewes were maintained at high altitude (3820 m) from ∼40 to 137 to 140 days of gestation and perirenal adipose was collected from normoxic control and LTH fetuses. There was no effect of LTH on fetal body weight or perirenal adipose mass. Long-term hypoxia increased (P < .05) perirenal eNOS and phospho-eNOS, messenger RNA (mRNA) for NRF1, NRF-2, mtTFA as well as COX-I, COX-II, and COX-IV mRNA. In contrast, mRNA for 2 markers for cellular proliferation (Ki67 and proliferating cell nuclear antigen [PCNA]) was lower in perirenal adipose from LTH fetuses compared to controls (P < .05), while mitochondrial to nuclear DNA ratio did not differ between groups. In conclusion, nitric oxide may function as a mechanism via which LTH enhances the BAT phenotype in fetal sheep prior to birth. Although there is an apparent increase in genes supporting mitochondrial function and adaptive thermogenesis in response to LTH, there does not appear to be an increased mitochondrial biogenesis per se. Such adaptive changes may provide a mechanism for the prominence of the BAT phenotype observed in the late gestation LTH fetus.

Long-term hypoxia enhances ACTH response to arginine vasopressin but not corticotropin-releasing hormone in the near-term ovine fetus

This study tested the hypothesis that long-term hypoxia (LTH) results in enhanced fetal corticotrope sensitivity to the ACTH secretagogues, corticotropin-releasing hormone (CRH), and AVP. Ewes were maintained at high altitude (3,820 m) from 40 to 130-131 days of gestation. Upon return to the laboratory, hypoxia was maintained by maternal nitrogen infusion. Vascular catheters were placed in both LTH (n = 4) and normoxic controls (n = 4). Each fetus received a 15-min infusion of either saline, 100 ng/kg of ovine CRH, or 20 ng/kg of AVP/min over 3 consecutive days in a randomized order. Fetal blood samples were collected at 0, 15, 30, 60, and 90 min after the start of infusion and analyzed for ACTH(1-39), ACTH precursors, and cortisol. Anterior pituitaries were collected from additional noninstrumented fetuses for analysis of vasopressin receptor 1b (V1b) mRNA and protein. Basal plasma concentrations of both ACTH(1-39) and ACTH precursors were higher in LTH fetuses and were not altered by saline infusion. In response to CRH, ACTH(1-39) increased in both groups and was higher in the LTH group compared with control (P < 0.05). When analyzed as sum of ACTH(1-39) released (Delta0-90 min) above basal, CRH released equal amounts of ACTH(1-39) in both groups. In LTH fetuses, AVP evoked a greater ACTH(1-39) release (P < 0.05) when analyzed as an increased sum of ACTH(1-39) (Delta0-90 min) above basal. Both CRH and AVP elicited a release of ACTH precursors with no differences observed between LTH and control. AVP and CRH elicited significant increases in cortisol, which were higher in response to AVP than CRH. V1b mRNA and protein were elevated in the anterior pituitary of LTH fetuses compared with control. LTH significantly increases pituitary sensitivity to AVP. This enhanced sensitivity may be a mechanism of our previously observed enhanced corticotrope function.

Long-term hypoxia modulates expression of key genes regulating adipose function in the late-gestation ovine fetus

A major function of abdominal adipose in the newborn is nonshivering thermogenesis. Uncoupling protein (UCP) UCP1 and UCP2 play major roles in thermogenesis. The present study tested the hypothesis that long-term hypoxia (LTH) modulates expression of UCP1 and UCP2, and key genes regulating expression of these genes in the late-gestation ovine fetus. Ewes were maintained at high altitude (3,820 m) from 30 to 138 days gestation (dG); perirenal adipose tissue was collected from LTH and age-matched, normoxic control fetuses at 139-141 dG. Quantitative real-time PCR was used to analyze mRNA for UCP1, UCP2, 11beta hydroxysteroid dehydrogenase type 1 (HSD11B1) and 2 (HSD11B2), glucocorticoid receptor (GR), beta3 adrenergic receptor (beta3AR), deiodinase type 1 (DIO1) and DIO2, peroxisome proliferator activated receptor (PPAR) alpha and gamma and PPARgamma coactivator 1 (PGC1alpha). Concentrations of mRNA for UCP1, HSD11B1, PPARgamma, PGC1, DIO1, and DIO2 were significantly higher in perirenal adipose of LTH compared with control fetuses, while mRNA for HSD11B2, GR, or PPARalpha in perirenal adipose did not differ between control and LTH fetuses. The increased expression of UCP1 is likely an adaptive response to LTH, assuring adequate thermogenesis in the event of birth under oxygen-limiting conditions. Because both glucocorticoids and thyroid hormone regulate UCP1 expression, the increase in HSD11B1, DIO1, and DIO2 implicate increased adipose capacity for local synthesis of these hormones. PPARgamma and its coactivator may provide an underlying mechanism via which LTH alters development of the fetal adipocyte. These findings have important implications regarding fetal/neonatal adipose tissue function in response to LTH.

Long-term hypoxia modulates expression of key genes regulating adrenomedullary function in the late gestation ovine fetus

We previously communicated that long-term hypoxia (LTH) resulted in a selective reduction in plasma epinephrine following acute stress in fetal sheep. The present study tested the hypothesis that LTH selectively reduces adrenomedullary expression of phenylethanolamine-N-methyltransferase (PNMT), the rate-limiting enzyme for epinephrine synthesis. We also examined the effect of LTH on adrenomedullary nicotinic, muscarinic, and glucocorticoid receptor (GR) expression. Ewes were maintained at high altitude (3,820 m) from 30 to 138 days gestation (dGA); adrenomedullary tissue was collected from LTH and age-matched, normoxic control fetuses at 139-141 dGA. Contrary to our hypothesis, in addition to PNMT, adrenomedullary expression (mRNA, protein) of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) were reduced in the LTH fetus. Immunocytochemistry indicated that TH and DBH expression was lower throughout the medulla, while PNMT appeared to reflect a reduction in PNMT-expressing cells. Nicotinic receptor alpha 1, 2, 3, 5, 6, 7, beta 1, 2, and 4 subunits were expressed in the medulla of LTH and control fetuses. Messenger RNA for alpha 1 and 7 and beta 1 and 2 subunits was lower in LTH fetuses. Muscarinic receptors M1, M2, and M3 as well as the GR were also expressed, and no differences were noted between groups. In summary, LTH in fetal sheep has a profound effect on expression of key enzymes mediating adrenomedullary catecholamine synthesis. Further, LTH impacts nicotinic receptor subunit expression potentially altering cholinergic neurotransmission within the medulla. These findings have important implications regarding fetal cardiovascular and metabolic responses to stress in the LTH fetus.

Long-term hypoxia increases leptin receptors and plasma leptin concentrations in the late-gestation ovine fetus

This study was designed to test the hypothesis that long-term hypoxia (LTH) increases fetal plasma leptin and fetal adipose or placental leptin expression and alters hypothalamic and adrenocortical leptin receptor (OB-R) expression. Pregnant ewes were maintained at high altitude (3,820 m) from day 30 to approximately 130 days of gestation. Reduced Po2 was maintained in the laboratory by nitrogen infusion through a maternal tracheal catheter. On day 132, normoxic control and LTH fetuses underwent surgical implantation of vascular catheters (n=6 for each group). Five days after surgery, maternal and fetal arterial blood samples were collected for leptin, insulin, and glucose analysis. Placental tissue, periadrenal fat, and fetal hypothalami and adrenal glands were collected from additional control (n=7) and LTH (n=8) fetuses for analysis of leptin mRNA by quantitative, real-time, RT-PCR (qRT-PCR). There was a significant (P<0.03) elevation in fetal plasma leptin in the LTH fetuses (3.5+/-0.7 ng/ml) vs. control (1.1+/-0.1 ng/ml). There were no differences in either glucose or insulin concentrations between the two groups. Periadrenal adipose leptin mRNA was significantly higher in the LTH group compared with control, as was placental leptin expression. The levels of leptin mRNA in adipose were approximately 70 times higher vs. placenta. LTH significantly reduced expression of OB-Ra (short-isoform) in the hypothalamus (P=0.0156), while resulting in a significant increase in adrenal OB-Rb (long-form) expression (P<0.03). Our data suggest that leptin is a hypoxia-inducible gene in the ovine fetus and OB-R expression is altered by LTH. These changes may be responsible in part, for our previously observed alterations in fetal hypothalamic-pituitary-adrenal function following LTH.

Long-term hypoxia represses the expression of key genes regulating cortisol biosynthesis in the near-term ovine fetus

Basal plasma ACTH(1-39) concentrations are elevated in long-term hypoxic (LTH) fetal sheep. This study was designed to determine whether the expression of genes regulating cortisol biosynthesis was altered after LTH. Pregnant ewes were maintained at high altitude (3,820 m) from day 30 of gestation to near term, when the animals were transported to the laboratory. Reduced PO2 was maintained by nitrogen infusion through a maternal tracheal catheter. On days 137-141, fetal adrenal glands were collected from LTH and normoxic control fetuses. Real-time PCR was used to quantify mRNA for steroidogenic acute regulatory protein, 17alpha-hydroxylase (CYP17), 21-hydroxylase (CYP21), cholesterol side-chain cleavage (CYP11A1), 3beta-hydroxysteroid dehydrogenase type II (HSD3B2), and the ACTH receptor. We analyzed mRNA by slot-blot hybridization and also quantified mRNA for transcription factors necessary for adrenocortical development by quantitative real-time PCR: steroidogenic factor 1 and dosage-sensitive sex reversal, adrenal hypoplasia congenital, critical region on the X chromosome (DAX-1). Protein was quantified by Western blot analysis. Adrenal mRNAs for CYP17, CYP11A1, and the ACTH receptor were significantly reduced in LTH fetal sheep compared with levels shown in controls. Similarly, CYP11A1 protein and CYP17 protein were reduced in the LTH group. CYP21, steroidogenic acute regulatory protein, HSD3B2, steroidogenic factor 1, and DAX-1 expressions were not altered in response to LTH. We conclude that expression of two key steroidogenic enzymes (CYP17, CYP11A1) regulating cortisol biosynthesis and the ACTH receptor is lower in response to LTH. This likely represents an adaptive response to LTH, to prevent excessive cortisol production that would restrict fetal growth and potentially induce preterm delivery.

Long-term hypoxia enhances proopiomelanocortin processing in the near-term ovine fetus

Secondary stressors in long-term hypoxic (LTH) fetal sheep lead to altered function of the hypothalamic-pituitary-adrenal axis. Although ACTH is considered the primary mediator of glucocorticoid production in fetal sheep, proopiomelanocortin (POMC) and 22-kDa pro-ACTH (22-kDa ACTH) have been implicated in the regulation of cortisol production in the ovine fetus. This study was designed to determine whether POMC expression and processing are altered after LTH. Pregnant ewes were maintained at high altitude (3,820 m) from day 30 of gestation to near term, when the animals were transported to the laboratory. Reduced Po2 was maintained by nitrogen infusion through a maternal tracheal catheter. On days 139-141, fetal anterior pituitaries were collected from normoxic control and LTH fetuses. We measured POMC and corticotrophin-releasing factor type 1 receptor (CRF1-R) mRNA using quantitative real-time PCR, and we used Western blot analysis for quantitation of ACTH, ACTH precursor, and CRF1-R proteins. We measured plasma ACTH1-39 using a two-site immunoradiometric assay specific for ACTH1-39. Plasma ACTH precursors were measured by ELISA. Anterior pituitary POMC mRNA levels were not different between groups, whereas CRF1-R levels were significantly higher in the LTH anterior pituitaries compared with control (P<0.05). In contrast, protein levels of POMC, CRF1-R, 22-kDa ACTH, and ACTH1-39 were significantly lower in the LTH group. Plasma concentrations of both ACTH precursors and ACTH1-39 were significantly elevated in LTH fetuses, whereas the ratio of plasma precursors to ACTH was significantly lower. We conclude that LTH results in enhanced POMC processing and/or release to ACTH and increased hypothalamic drive.

Long-term hypoxia alters calcium regulation in near-term ovine myometrium

Previous studies showed that long-term hypoxia (LTH) during pregnancy alters myometrial contractility. The present study was designed to test the hypothesis that LTH during pregnancy suppresses myometrial contractility in sheep by affecting the calcium signaling cascade. Pregnant sheep were maintained at high altitude (3820 m) from Day 30 to Day 139 of gestation, when the animals were killed for collection of myometrial tissue. Tissue was also collected from age-matched, normoxic controls. Circular and longitudinal layers were separated, and strips from each layer were mounted in a muscle bath. After pretreatment with 10(-8) M oxytocin, the strips were exposed to increasing half- or quarter-log doses of nifedipine (L-type calcium-channel blocker), ruthenium red, ryanodine (blockers of inositol 1,4,5-trisphosphate-insensitive calcium stores), or 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC; phospholipase C inhibitor). Area under the contraction curve was analyzed, and pD(2) (log of concentration yielding 50% of maximum response) values and maximum relaxation responses were calculated. The maximum relaxation response to nifedipine was increased in both longitudinal (P < 0.01) and circular (P < 0.05) myometrial layers from LTH compared to control tissue, whereas no difference was observed in response to ruthenium red or ryanodine. The maximum relaxation response to NCDC was lower in the LTH circular layer (P < 0.05). Together, these data are indicative of an increase in the dependence of ovine uterine smooth muscle on extracellular calcium influx through the L-type, voltage-gated calcium channels following LTH. This appears to occur not through an increase in L-type calcium channels but, rather, through a possible decline in importance of the oxytocin-induced, phospholipase C-mediated pathway, resulting in a greater proportion of extracellular calcium contributing to contraction. Layer-dependent differences also exist between the circular and longitudinal myometrium in response to phospholipase C inhibition.

Long-term hypoxia changes myometrial responsiveness and oxytocin receptors in the pregnant ewe: differential effects on longitudinal versus circular smooth muscle

Previous studies from our laboratory demonstrated that long-term hypoxia (LTH) altered in vitro contractile responses to oxytocin in full-thickness myometrial strips from pregnant sheep. The present study was designed to determine, first, if the reduced contractile response to oxytocin following LTH is the result of combined effects on longitudinal and circular smooth muscle or if the effect is specific to a single muscle layer and, second, if the reduced contractile response to oxytocin following LTH is caused by changes in oxytocin-receptor protein. Pregnant ewes were maintained at high altitude (3820 m) from Day 30 to Days 137-142 of gestation, when the ewes were killed for collection of myometrial tissue. Tissue was also collected from age-matched, normoxic controls. Longitudinal and circular layers were separated, length-tension curves generated to determine optimal resting tension, and all strips exposed to increasing half-log doses of oxytocin ranging from 10-12 to 10-6.5 M. The expression of oxytocin-receptor protein was measured using Western blot analysis. We found that LTH did not affect KCl-induced contraction of either smooth muscle layer, whereas the sensitivity of both myometrial layers to oxytocin was altered. A decreased maximum contractile response of the circular layer to oxytocin was also observed. Additionally, LTH decreased expression of oxytocin-receptor protein in the circular layer and increased levels in the longitudinal layer. Results from the present study indicate that LTH alters contractile responses and oxytocin-receptor protein expression in a layer-specific manner in the pregnant sheep myometrium.

Influence of intracerebroventricular administration of tetanus toxin on experimental seizures and protection afforded by some antiepileptic drugs in mice

The dose to the intracerebroventricularly administered (i.c.v.) tetanus toxin (Tetx) evoking the death of 50% of experimental mice (LD50) was estimated to be 18.0 (11.5-28.2) times the minimal lethal dose (MLD). MLD is defined as the lowest does of Tetx necessary to kill a 20-g albino mouse within 96 h after intraperitoneal treatment. Tetx (0.25 and 0.5 LD50) increased the convulsive threshold of electric current from 24 to 96 and 120 h, respectively, following i.c.v. administration. Both doses of Tetx diminished convulsant potencies of pentylenetetrazole, bicuculline, aminophylline and pilocarpine 24 h after application. At the same time Tetx (0.5 LD50) increased the protection afforded by carbamazepine, valproate, phenobarbital and diazepam in maximal electroshock (MES) by approximately 36, 11, 21 and 26%, respectively, without affecting total blood plasma levels of antiepileptic drugs. No marked changes in gamma-aminobutyric acid (GABA) concentration and total activity of L-glutamic acid decarboxylase (GAD) assessed in the whole-brain homogenates resulted from Tetx treatment. Our results seem to indicate that low doses (< LD50) of i.c.v. administered Tetx may lead to a relative prevalence of inhibitory over excitatory processes in the central nervous system suggesting a complex action of Tetx at the neuronal level.

Intracerebroventricular pertussis toxin enhances sensitivity to chemical convulsants and decreases the protective efficacy of carbamazepine in mice

The effects of pretreatment with pertussis toxin on pentylenetetrazole-, bicuculline-, aminophylline- and pilocarpine-induced seizures were investigated in mice. In animals treated intracerebroventricularly with pertussis toxin (0.5 microgram animal-1 120 h prior to testing), the CD50 (convulsive dose in 50%) values were considerably decreased in comparison with the CD50 in sham-treated animals. CD50 values of pentylenetetrazole, bicuculline, pilocarpine and aminophylline were calculated to be 39.9, 2.0, 262 and 141 mg kg-1, whereas they were calculated to be 57.7, 2.7, 324 and 230 mg kg-1 in sham-treated animals. The observations suggest that the enhanced sensitivity to a number of chemical convulsants irrespective of their mode of action possibly results from a functional suppression of inhibitory transmission at receptors coupled to pertussis toxin sensitive G proteins, rather than a direct action on G protein linked excitatory neurotransmission. Pertussis toxin significantly decreased the protective action of carbamazepine, increasing its ED50 (effective dose in 50%) from 14.8 to 20.1 mg kg-1 in a maximal electroshock convulsive test. It influenced the ED50 of neither diphenylhydantoin nor diazepam. The diminution of carbamazepine's efficacy might result from a summation effect of adenosine receptor antagonist properties of the drug and a suppression of transmission at adenosine receptors coupled to G proteins sensitive to pertussis toxin. Pertussis toxin pretreatment remained without any significant influence on the total plasma levels of carbamazepine, diphenylhydantoin and diazepam. This may lead to the conclusion that the interaction between pertussis toxin and carbamazepine does not seem to be of a pharmacokinetic nature and occurs probably at neuronal level.