Plasma catecholamine concentrations in infants at birth and during the first 48 hours of life

Preoperative Management of Neonates With Congenital Heart Disease

Clinicians caring for neonates with congenital heart disease encounter challenges in clinical care as these infants await surgery or are evaluated for further potential interventions. The newborn with heart disease can present with significant pathophysiologic heterogeneity and therefore requires a personalized therapeutic management plan. However, this complex field of neonatal-cardiac hemodynamics can be simplified. We explore some of these clinical quandaries and include specific sections reviewing the anatomic challenges in these patients. We propose this to serve as a primer focusing on the hemodynamics and therapeutic strategies for the preoperative neonate with systolic dysfunction, diastolic dysfunction, excessive pulmonary blood flow, obstructed pulmonary blood flow, obstructed systemic blood flow, transposition physiology, and single ventricle physiology.

Neonatal comorbidities and gasotransmitters

Hydrogen sulfide, nitric oxide, and carbon monoxide are endogenously produced gases that regulate various signaling pathways. The role of these transmitters is complex as constitutive production of these molecules may have anti-inflammatory, anti-microbial, and/or vasodilatory effects whereas induced production or formation of secondary metabolites may lead to cellular death. Given this fine line between friend and foe, therapeutic attenuation of these molecules' production has involved both inhibition of endogenous formation and therapeutic supplementation. All three gases have been implicated as regulators of critical aspects of neonatal physiology, and in turn, comorbidities including necrotizing enterocolitis, hypoxic ischemic encephalopathy, and pulmonary hypertension. In this review, we present current perspectives on these associations, highlight areas where insights remain sparse, and identify areas for potential for future investigations.

Attenuation of sympathoadrenal function during delivery in the fetus of a diabetic mother

Objective: We compared the association between cord arterial catecholamine levels and fetal oxygenation in newborns of mothers with diabetes mellitus to those of nondiabetic pregnancies.Methods: Cord blood obtained at delivery in 25 term appropriate-for-gestational age newborns of women with diabetes and 27 nondiabetic controls were assayed for norepinephrine, epinephrine, insulin, glucose, and blood gases.Results: There was no statistical difference in parity, birth weight, gestational age, delivery mode, use of epidural analgesia, or frequency of low 1-min Apgar scores between the groups. The pO₂ and frequency of cord arterial pH < 7.20 were also similar. Diabetic pregnancies had somewhat higher fetal glucose and substantially higher insulin levels than controls. Regression analysis using cord arterial pH to reflect oxygenation revealed significant inverse relationships between cord artery pH and ln norepinephrine (Prob > F = .001) and ln epinephrine (Prob > F = .019) in controls. In newborns of women with diabetes, however, neither relationship was significant.Conclusion: The expected surge in catecholamines associated with diminished oxygenation was attenuated in fetuses of diabetic mothers. This suggests the possibility that fetal exposure to hyperglycemia or other metabolic derangements in pregnant diabetics might compromise the fetal ability to adapt to changes in oxygenation, and might thereby contribute to the risk of fetal death.

Inotropes for preterm babies during the transition period after birth: friend or foe?

During the transition to extrauterine life, preterm infants are at high risk of developing circulatory failure. Currently, hypotension is used as major diagnostic criteria for starting treatments such as fluid boluses, inotropes or steroids. Most of these treatment options have not been studied in large randomised controlled trials for efficacy and safety and are under discussions. A wide variety in their use is reported in the literature and clear evidence about which inotrope or other treatment should be preferred is lacking. In addition, there is ongoing debate about the appropriate threshold values for blood pressure. Other diagnostic measures for poor circulation are functional echocardiography, near-infrared spectroscopy, capillary refill time, base excess and serum lactate. Large randomised controlled trials for the use of dopamine and dobutamine in preterm infants <32 weeks gestation are under way to fill the knowledge gaps on the assessment of circulatory compromise and on efficacy and safety of the studied age-appropriate drug formulations.

Arterio-venous differences in cord levels of catecholamines, glucose, lactate and blood gases

BACKGROUND

Norepinephrine (NE) and epinephrine (EPI) levels are higher in cord arterial blood relative to venous blood, consistent with active mechanisms of placental-maternal clearance. There are no contemporary studies of cord arteriovenous blood levels of sulfated and non-sulfated catechols.

AIM

To assess the arteriovenous differences in cord blood levels of dopamine (DA), the sulfated catecholamines and their sulfated and non-sulfated metabolites. To correlate levels of oxygen, H+/CO2, and glucose with cord catecholamine levels.

METHODS

Fifty-seven term infants, delivered by elective cesarean section, were recruited. Cord arterial and venous blood was sampled; levels of glucose, lactate, blood gases, six catechols and their sulfated conjugates were measured.

RESULTS

With one exception (DOPA sulfate), mean cord arterial levels of sulfated and non-sulfated catechols were significantly higher than venous levels. Arterial lactate and glucose levels were independently associated with NE levels, but only lactate was associated with levels of EPI and DA.

CONCLUSION

This study establishes that in vivo metabolic parameters of hypoxia, respiratory and metabolic acidosis are associated with catecholamine levels, a key relationship for perinatal adaptation and homeostasis, and findings that are consistent with in vitro studies of the regulators of catecholamine secretion.

Low epinephrine levels and selective deficiency of β2-adrenoceptor vasodilation at birth

AIMS

Epinephrine is unique among biogenic catecholamines as a potent agonist of β2-adrenoceptors. The β2-adrenoceptor mediated effects during development might be linked to the increase of epinephrine synthesis. Our purpose was to characterize β-adrenoceptor-mediated relaxation in the aorta of newborn and young rabbits (3 to 4months old), and to relate those responses with the epinephrine content of the adrenal gland.

MAIN METHODS

The epinephrine levels and the tyrosine hydroxylase activity were determined in adrenal glands of newborn and young rabbits. Also, concentration-response curves to phenylephrine (selective α1-adrenoceptor agonist), dobutamine (selective β1-adrenoceptor agonist), terbutaline (selective β2-adrenoceptor agonist), and CL 316243 (selective β3-adrenoceptor agonist) were determined in isolated aortic rings obtained from both groups.

KEY FINDINGS

The adrenal gland content and the plasma concentrations of epinephrine were lower in newborn than in young rabbits. In contrast, the tyrosine hydroxylase activity was higher in newborn than in young rabbits. On the other hand, the maximal response to phenylephrine was lower in newborn than in young rabbits. Terbutaline at concentrations selective for β2-adrenoceptors had no relaxing effects in neonates, in contrast to young rabbits. The potency and the maximal response of neither dobutamine nor CL 316243 were significantly different between the two groups.

SIGNIFICANCE

In rabbits, as well as in humans, β2-adrenoceptor-mediated responses and epinephrine synthesis are both immature at birth. On the other hand, the β1 and β3-adrenoceptor-mediated responses are fully developed. We conclude that epinephrine may influence the development of the β2-adrenoceptor-mediated responses at birth and the rabbit is an excellent model to study these issues.

Arginine Vasopressin and Copeptin in Perinatology

Arginine vasopressin (AVP) plays a major role in the homeostasis of fluid balance, vascular tonus, and the regulation of the endocrine stress response. The measurement of AVP levels is difficult due to its short half-life and laborious method of detection. Copeptin is a more stable peptide derived from the same precursor molecule, is released in an equimolar ratio to AVP, and has a very similar response to osmotic, hemodynamic, and stress-related stimuli. In fact, copeptin has been propagated as surrogate marker to indirectly determine circulating AVP concentrations in various conditions. Here, we present an overview of the current knowledge on AVP and copeptin in perinatology with a particular focus on the baby's transition from placenta to lung breathing. We performed a systematic review of the literature on fetal stress hormone levels, including norepinephrine, cortisol, AVP, and copeptin, in regard to birth stress. Finally, diagnostic and therapeutic options for copeptin measurement and AVP functions are discussed.

Attenuated aortic vasodilation and sympathetic prejunctional facilitation in epinephrine-deficient mice: selective impairment of β2-adrenoceptor responses

It has been suggested that there is a link between epinephrine synthesis and the development of β2-adrenoceptor-mediated effects, but it remains to be determined whether this development is triggered by epinephrine. The aim of this study was to characterize β-adrenoceptor-mediated relaxation and facilitation of norepinephrine release in the aorta of phenylethanolamine-N-methyltransferase-knockout (Pnmt-KO) mice. Catecholamines were quantified by reverse-phase high-performance liquid chromatography-electrochemical detection. Aortic rings were mounted in a myograph to determine concentration-response curves to selective β1- or β2-adrenoceptor agonists in the absence or presence of selective β1- or β2-adrenoceptor antagonists. Aortic rings were also preincubated with [(3)H]norepinephrine to measure tritium overflow elicited by electrical stimulation in the presence of increasing concentrations of nonselective β- or selective β2-adrenoceptor agonists. β2-Adrenoceptor protein density was evaluated by Western blotting and β2-adrenoceptor localization by immunohistochemistry. Epinephrine is absent in Pnmt-KO mice. The potency and the maximal effect of the β2-adrenoceptor agonist terbutaline were lower in Pnmt-KO than in wild-type (WT) mice. The selective β2-adrenoceptor antagonist ICI 118,551 [(±)-erythro-(S*,S*)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride] antagonized the relaxation caused by terbutaline in WT but not in Pnmt-KO mice. Isoproterenol and terbutaline induced concentration-dependent increases in tritium overflow in WT mice only. β2-Adrenoceptor protein density was decreased in membrane aorta homogenates of Pnmt-KO mice, and this finding was supported by immunofluorescence confocal microscopy. In conclusion, epinephrine is crucial for β2-adrenoceptor-mediated vasodilation and facilitation of norepinephrine release. In the absence of epinephrine, β2-adrenoceptor protein density was decreased in aorta cell membranes, thus potentially hindering its functional activity.

Changes in cerebral oxygenation during early postnatal adaptation in newborns delivered by vacuum extraction measured by near-infrared spectroscopy

Background

Newborns delivered by vacuum extraction quite often show clinical signs of a hemodynamic compromise, which is difficult to assess in terms of severity. The conventional means to measure the hemodynamic status are not sensitive enough to appreciate the severity of general, and more specifically of cerebral circulatory imbalance. The aim was to study cerebral tissue oxygenation during postnatal adaptation in these infants using near-infrared spectroscopy.

Methods

The tissue hemoglobin index (THI), tissue oxygenation index (TOI), arterial oxygen saturation (pre-ductal SaO₂) and heart rate (HR) were recorded immediately after birth, and again after 12–24 hours of life in 15 newborns delivered by vacuum extraction due to fetal distress. A comparison with 19 healthy newborns delivered by elective cesarean section was performed.

Results

Newborns delivered by vacuum extraction had significantly higher THI 10 to 15 minutes after birth. TOI and HR were significantly higher in the first 5 min and SaO₂ in the first 10 minutes but then did not differ from those after cesarean section.

Conclusion

Infants delivered by vacuum extraction following fetal distress show transient deviations in cerebral oxygenation and perfusion after birth which were not detectable after 24 hours.

Adrenal Epinephrine and the Regulation of Pulmonary Surfactant Release in Neonatal Rabbits

Adrenergic mechanisms influence surfactant metabolism; however the nature and importance of catechol-mediated regulation is unclear. We designed experiments to assess the role of endogenous adrenal epinephrine (E) synthesis in neonatal alveolar surfactant release. We administered the experimental adrenal epinephrine synthesis inhibitor SKF 29661 to pregnant rabbits to reduce fetal adrenal E content. Surfactant release was measured as total alveolar phosphatidylcholine (PC) content recovered by a thorough alveolar wash performed on animals sacrificed at birth and at 1 h of age. At a maternal dose of 100 mg/kg/day, SKF 29661 caused a 57% reduction in fetal adrenal E content (p less than .01), which was associated with a 40% reduction in alveolar PC at birth and a 23% reduction in alveolar PC at 1 h of age (p less than .01). Moreover, adrenal E correlated positively with total alveolar PC content (p less than .001). These results suggest that in the neonatal period, the ability of the fetal adrenal gland to synthesize E for secretion plays a role in the regulation of pulmonary surfactant release.

Ontogenesis of mRNA levels and binding sites of hepatic alpha-adrenoceptors in young cattle

Catecholamines affect hepatic glucose production through (alpha- and beta2-) adrenoceptors (AR). We studied mRNA abundance and binding of hepatic alpha-AR in pre-term (P0) calves and in full-term calves at day 0 (F0), day 5 (F5) and day 159 (F159) to test the hypothesis that gene expression and numbers of hepatic alpha-AR in calves are influenced by age and associated with beta2-AR and selected traits of glucose metabolism. mRNA levels of alpha1- and alpha2-AR were measured by real time RT-PCR. alpha1- and alpha2-AR numbers (maximal binding, Bmax) were determined by saturation binding of (3H)-prazosin and (3H)-RX821002, respectively. alpha1- and alpha2-AR subtypes were evaluated by competitive binding. alpha1A-AR mRNA levels were lower in P0 than in F0, F5 and F159 and alpha(2AD)-AR mRNA levels were lower in F159 than in P0, F0 and F5, while alpha2C-AR mRNA levels increased from P0 and F0 to F5 and F159. Bmax of alpha1-AR increased from P0 to F5, then decreased in F159. Bmax of alpha2-AR decreased from F0 to F159. Bmax of alpha1-AR was positively associated with mRNA levels of alpha1A-AR (r = 0.7), Bmax of beta2-AR (r = 0.5) and negatively with hepatic glycogen content (r = -0.6). Bmax of alpha2-AR was negatively associated with Bmax of beta2-AR (r = -0.4). In conclusion, mRNA levels and binding sites of alpha1- and alpha2-AR in calves exhibited developmental changes and were negatively associated with hepatic glycogen content.

Plasma catecholamines and the counterregulatory responses to hypoglycemia in infants: a critical role for epinephrine and cortisol

The purpose of this study was to define plasma catecholamine responses as part of the counterregulatory hormonal reaction to hypoglycemia in infants after a regular 3- to 4-h feed was omitted. Hormone levels were assessed once, at the end of the fast or at hypoglycemia. The 121 infants were subdivided into three groups for analysis: normoglycemia (n = 94, 78%); transient hypoglycemia (n = 11, 9%); or severe and persistent hypoglycemia (n = 16, 13%). The severe and persistent hypoglycemic group had significantly higher levels of cortisol and epinephrine than the normoglycemic group. Norepinephrine and glucagon levels did not differ between the groups. Human GH levels were higher in the transiently hypoglycemic group but not in the severe and persistent hypoglycemic group. Prefeed blood lactate levels differed significantly among the groups and were highest in the severe and persistent groups. Multiple regression analysis showed that cortisol levels were significantly higher in infants who had severe and persistent hypoglycemia. The counterregulatory hormonal response in infants to severe and persistent hypoglycemia was limited to elevations in only cortisol and epinephrine levels but did not involve glucagon or human GH. This limited hormonal response may also contribute to the frequent occurrence of hypoglycemia in these infants.

gAd-globular head domain of adiponectin increases fatty acid oxidation in newborn rabbit hearts

Adiponectin is an adipocyte-derived hormone that has a number of metabolic effects in the body, including the control of both glucose and fatty acid metabolism. The globular head domain of adiponectin, gAd, has also been shown to increase fatty acid oxidation in skeletal muscle. Within days after birth, a rapid increase in fatty acid oxidation occurs in the heart. We examined whether adiponectin or gAd plays a role in this maturation of cardiac fatty acid oxidation. Plasma adiponectin increased in newborn rabbits following birth: 1.2 +/- 0.3 microg/ml in 1-day-old, 6.8 +/- 1.8 microg/ml in 7-day-old, and 45 +/- 5 microg/ml in 6-week-old rabbits. Because plasma insulin levels decrease and remain low throughout the suckling period, and because this decrease may contribute to the maturation of fatty acid oxidation, we examined the effects of adiponectin and gAd on fatty acid oxidation in isolated perfused 1-day-old rabbit hearts in the presence or absence of 100 microunits/ml insulin. Adiponectin (10 microg/ml) did not alter fatty acid oxidation in the presence of insulin. In the absence of insulin, the addition of recombinant gAd (1.5 microg/ml) increased fatty acid oxidation compared with control (129 +/- 18 versus 66 +/- 11 nmol.g dry weight(-1).min(-1), respectively (p < 0.05). In 7-day-old hearts, where fatty acid oxidation rates were 5-fold higher than 1-day-old hearts, gAd did not alter fatty acid oxidation rates. The increase in fatty acid oxidation in 1-day-old hearts occurred independently of changes in 5'-AMP-activated protein kinase, acetyl-CoA carboxylase, or malonyl-CoA. The effect of gAd on fatty acid oxidation was reversed in the presence of 100 microunits/ml insulin. These results suggest that a decrease in plasma insulin and increase in gAd are involved in the increase of cardiac fatty acid oxidation in the immediate newborn period.

Maternal antihypertensive therapy with beta-blockers associated with poor outcome in very-low birthweight infants

The progress of 36 very-low birthweight (less than or equal to 1500 g) infants born to mothers with pregnancy-induced hypertonia or pre-eclampsia was studied. During the first year of life, 7 out of 19 infants died when the mothers' antihypertensive regimen included beta-blockers. Four of the deaths occurred within 15 days. There were no deaths in 16 infants whose mothers were treated with other antihypertensive treatment (P = 0.006). These results suggest that maternal beta-blocker therapy may have adverse effects on the very-low birthweight infants.

Maternal intravaginal prostaglandin E2 gel before elective caesarean section at term to induce catecholamine surge in cord blood: randomised, placebo controlled study

OBJECTIVE

To test the hypothesis that the application of intravaginal prostaglandin E(2) gel before elective caesarean section (ECS) will induce a catecholamine surge in umbilical arterial blood.

DESIGN

Randomised, double blind, placebo controlled trial.

SETTING

A regional perinatal referral centre.

PATIENTS

Mothers booked for ECS at or above 38 weeks gestation.

INTERVENTIONS

Thirty six consenting mothers were randomly allocated to receive either 2 mg intravaginal prostaglandin E(2) gel (study group; n = 18) or an equal volume of K-Y jelly as a placebo (control group; n = 18) 60 minutes before the ECS. Computer generated random numbers contained in coded, sealed envelopes were used for allocation. The obstetric and neonatal teams were blinded to the randomisation status of enrolled mothers.

MAIN OUTCOME MEASURES

Catecholamine concentrations in the umbilical arterial blood samples collected at delivery.

RESULTS

The median (interquartile range) neonatal gestation and birth weight were 271 (269-274) days and 3605 (3072-3970) g for the study group and 271 (270-273) days and 3340 (3000-3622) g for the control group. Median (interquartile range) noradrenaline (norepinephrine) concentrations in the umbilical arterial blood were significantly higher in the study group than the control group (15.9 (9.8-28.92) v 4.6 (1.65-14.4) ng/l, p = 0.03). Adrenaline (epinephrine) concentrations did not differ significantly between the two groups (1.6 (< 0.5-3.1) v 1.4 (< 0.5-2.75) ng/l, p = 0.6). No treatment related complications occurred.

CONCLUSION

A labour related catecholamine surge could be simulated by intravaginal prostaglandin E(2) gel.

Neonatal clinical outcome after elective cesarean section before the onset of labor at the 37th and 38th week of gestation

BACKGROUND

Although elective cesarean sections are often performed after the 37th week of gestation without any complicating factor that may influence the timing of delivery,there is a possibility that infants born in the 37th week of gestation,especially early in the 37th week of gestation, do not obtain a satisfactory clinical outcome due to premature birth.

METHODS

The authors analyzed the clinical course during the neonatal period in 96 infants born in the 37th (n = 81)and 38th (n = 15) week of gestation by an elective cesarean section. Subjects were retrospectively divided into two groups: infants born in the first half of the 37th week of gestation (37+0-37+3)(n = 48), and infants born from the latter half of the 37th week of gestation (37+4-37+6)through the 38th week of gestation (n = 48). Twin pregnancies, pregnancy with placenta previa, and pregnancy of women who had a diversity of medical complications were excluded from the present study, because of the possibility that these conditions may have affected the infants' status. The incidence of infants who showed clinical symptoms during the neonatal period and who needed medical care was compared between the two groups.

RESULTS

Of the 96 subjects, 25 infants(26.0%) had significant clinical symptoms. The incidence of breathing difficulty was significantly higher in the infant group born in the first half of the 37th week of gestation than in the latter group.

CONCLUSIONS

An elective cesarean section before the onset of labor early in the 37th week of gestation should not be routinely undertaken.

Cardiovascular regulation and expressions of NO synthase-tyrosine hydroxylase in nucleus tractus solitarius of ovine fetus

The purpose of this study was to examine cardiovascular responses to fourth cerebral ventricle (4V) administration of nitroglycerin (NTG) or an inhibitor of nitric oxide (NO) synthase (NOS) in the near-term ovine and to determine whether, during birth, neuronal NOS (nNOS) is induced in noradrenergic A1 neurons in the medial nucleus tractus solitarius (mNTS). In chronically instrumented fetal sheep, 4V injection of NTG (1.2 nmol), an NO donor, produced an arterial blood depressor and a moderate decrease in heart rate. Arterial blood pressure is increased by 4V administration of NG-nitro-L-arginine methyl ester (10 nmnol), an inhibitor of NOS, in fetuses. Sections of the medulla from fetuses and newborn lambs were examined by using immunolabeling with tyrosine hydroxylase (TH) antibody combined with NADPH diaphorase (NADPHd) histochemistry, a marker of nNOS activity. The NADPHd-positive cells and TH-positive cells containing NADPHd reactivity were significantly increased in the mNTS of newborns compared with the fetuses. The results suggest that during birth, there is upregulation of NADPHd/nNOS in the noradrenergic neurons of mNTS resulting in a centrally mediated reduction of fetal arterial blood pressure.

Effect of maternal smoking on fetal catecholamine concentrations at birth

The aim of this study was to compare catecholamine concentrations in the fetal umbilical artery cord blood from the offspring of smokers versus the offspring of nonsmokers. Pregnant women who were self-identified as smokers (>/=10 cigarettes per day throughout pregnancy) or nonsmokers were recruited for study participation. Maternal blood was collected for cotinine concentrations. Umbilical artery cord blood was collected at delivery for arterial pH and catecholamine concentrations. Cord blood was obtained from 51 subjects, including 21 smokers and 30 nonsmokers. Median epinephrine concentrations [304 pg/mL versus 597 pg/mL (Mann-Whitney U = 170; p = 0.006)] and median norepinephrine concentrations [3148 pg/mL versus 6558 pg/mL (Mann-Whitney U = 191; p = 0.006)] were significantly lower in smokers compared with nonsmokers, respectively. After controlling for gestational age, route of delivery, and arterial pH, log-transformed epinephrine concentrations between smokers and nonsmokers were statistically significant (p = 0.03), with a similar trend for log-transformed norepinephrine concentrations (p = 0.07). Analyses of the data using cotinine <20 ng/mL to classify nonsmokers also showed differences in epinephrine concentrations between groups (p = 0.02). These results are consistent with results from animal studies showing that catecholamine concentrations may be affected by prenatal nicotine exposure. Further studies are needed to validate these findings and to examine the specific mechanism by which these differences may arise.

Neonatal respiratory morbidity following elective caesarean section in term infants. A 5-year retrospective study and a review of the literature

Respiratory morbidity is an important complication of elective caesarean section. The presence of labour preceding caesarean section reduces the risk of neonatal respiratory morbidity. Recently, it has been shown that the incidence of respiratory morbidity is lower in infants with a gestational age of at least 39(+0) weeks at elective caesarean section compared to infants with a gestational age less than 39(+0) weeks.This article describes the results of a 5-year retrospective study on the incidence of respiratory distress in term neonates delivered by elective caesarean section in relation to gestational age and provides a literature review on neonatal respiratory morbidity following elective caesarean section.

Mode of delivery and childhood blood pressure

A number of studies have shown that children born by cesarean section have lower blood pressure during the neonatal period. The aim of this study was to investigate whether mode of delivery influenced childhood blood pressure: at age 7.5 to 8 y in a cohort of 756 children born preterm, at 7 to 9 y in a pilot study of 166 children born at term in the United Kingdom, and in a cohort of 650 Tasmanian children born at term. In the preterm cohort, systolic blood pressure was significantly lower in children born by cesarean section rather than delivered vaginally (99.3+/-10.0 versus 101.4+/-9.4 mm Hg; 95% confidence interval, -0.69 to -3.46; p = 0.003), with a significant trend to having a higher pressure in those born by breech versus forceps versus spontaneous vaginal delivery versus cesarean section. These findings were not replicated in the term cohorts. This raises the hypothesis that there is a sensitive period for programming later blood pressure by factors associated with mode of delivery and that this period does not extend to full-term.

Influence of fetal to neonatal transition on nitric oxide synthase expression in the nucleus tractus solitarius in sheep

Transition from fetal to newborn life is accompanied by a marked rise in circulating norepinephrine (NE) concentrations though arterial blood pressure does not substantively change. Nitric oxide (NO) plays an important role in the central regulation of sympathetic tone in the nucleus tractus solitarius (NTS) and neuronal NO synthase (nNOS) expression is functionally regulated in the brain. The purpose of these studies was to determine the influence of transition at birth on nNOS expression in the brainstem nuclei, particularly in the NTS, associated with changes in arterial pressure and plasma NE concentration. Experiments were performed using time-dated gestational ewes with twin fetuses. Arterial blood pressure was recorded and arterial blood NE concentrations were measured in the term fetus (gestational 147-148 days) and newborn lambs (4 h of postnatal age). The fetal and newborn animals were then perfused with 4% paraformaldehyde. Sections of the medulla were examined by using both immunolabeling with a polyclonal antibody directed against nNOS and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry, a marker for expression of nNOS. Micrographs were quantified using a microscope with reticule grid to measure the number of positive cells containing color staining in the brainstem nuclei. Plasma NE concentration in the newborn was more than two-fold greater compared to fetal values but mean arterial blood pressure was similar between fetus and newborn. The nNOS positive cells and NADPHd positive cells were significantly increased in the medial NTS (mNTS) of the newborn compared to fetus. nNOS immunoreactivity and NADPHd reactivity tended to increase in the rostral ventral medulla (RVM) in newborn, but were not altered in other brainstem nuclei during the transition from fetal to newborn life. The results suggest that nNOS expression in the mNTS is predominately enhanced at 4 h of neonatal age vs. the term fetus. We conclude that elevated circulating NE is associated with up-regulation of nNOS in the mNTS which may serve a protective role in central regulation of neonatal arterial blood pressure.

Neonatal catecholamine content of adrenal and extra-adrenal chromaffin tissue after prenatal exposure to dexamethasone

We investigated the effects of prenatal exposure to dexamethasone on paraganglia and adrenal catecholamine stores in rabbit neonates. We compared pregnant rabbits injected with 0.01 mg x kg(-1) of dexamethasone (Dex) from day 24 to day 27 of gestation to an untreated group of unmanipulated rabbits. A group injected with 0.9% saline solution was added to evaluate the effect of injection and handling. Catecholamines were assessed by HPLC in offspring paraganglia and adrenal glands on days 0, 1, and 7 after birth. Data were analyzed by a two-factor ANOVA and Bonferroni-Dunn and t tests. Statistical significance was accepted at p < 0.05. Paraganglia catecholamine levels were significantly higher in the Dex animals than in the untreated ones at every maturational stage studied. For saline animals, the levels were lower than in the Dex group and higher than in the untreated one. In adrenal glands, the same pattern was observed for noradrenaline only. These findings suggest that such a treatment has a positive long-term effect on catecholamine levels of both structures with a more marked effect on paraganglia, an extra-adrenal structure exerting a main function during the perinatal period in providing the child with catecholamine stores.

Antenatal dexamethasone treatment decreases plasma catecholamine levels in preterm infants

Antenatal corticosteroid therapy (ACT) has many beneficial effects on preterm infants. The cellular mechanisms of action of ACT include beta-adrenergic receptor-mediated cAMP generation. This study investigated the effects of ACT on sympathoadrenal mechanisms during immediate postnatal adaptation of preterm infants. Plasma epinephrine, norepinephrine, 3,4-dihydroxyphenylglycol, and cAMP were measured within 12 h after birth in 103 preterm infants (gestational age 24-36 wk), who were divided into two groups (non-ACT and ACT group) according to whether the mother had received dexamethasone treatment. Infants in the ACT group had significantly lower concentrations of plasma catecholamines than infants in the non-ACT group; plasma epinephrine was 38% lower, and plasma norepinephrine was 20-40% lower in the ACT group, depending on gestational age (r = -0.37 in the non-ACT group and r = -0.28 in the ACT group, p < 0.05). Plasma cAMP concentrations were similar in the two groups. Antihypertensive treatment of the mother was associated with low plasma cAMP (p < 0.001), whereas tocolytic treatment was associated with high plasma cAMP (p = 0.001) of the infant. The results indicate that ACT attenuates the birth-related increase in plasma catecholamines. Still, plasma cAMP levels remain high, which suggests enhanced beta-adrenoceptor signaling after ACT.

Repetitive prenatal glucocorticoids improve lung function and decrease growth in preterm lambs

We evaluated the effects of multiple fetal exposures to glucocorticoids on postnatal lung function and growth. Ewes were randomized to receive 1 to 4 doses of 0.5 mg/kg betamethasone or saline placebo at 7 d intervals from 104 d to 118 d and at 124 d gestation. All lambs were delivered preterm at 125 d gestation, and postnatal lung function was evaluated. There were sequential improvements in compliance, ventilation efficiency, and lung volumes for two, three, and four doses of betamethasone. The maximal effect was a 150% increase in compliance and a 4-fold increase in lung volume after fetal exposure to four doses of betamethasone. However, birth weights decreased (15% after one dose, 19% after two doses, and 27% after three and four doses). There were no changes in lung to body weight ratios, lung dry to wet weight ratios, lung protein to body weight ratios, or lung hyaluronan content. Prenatal glucocorticoid exposure also altered postnatal cortisol, thyroid, and catecholamine plasma levels. Repetitive 7-d interval exposures of fetal lambs to glucocorticoids progressively enhanced postnatal lung function and resulted in growth and endocrine abnormalities.

Elevated plasma norepinephrine after in utero exposure to cocaine and marijuana

OBJECTIVE

To compare plasma catecholamine concentrations between cocaine-exposed and unexposed term newborns and to determine the relationship between plasma catecholamines and newborn behavior.

METHODS

Forty-six newborn infants participating in a prospective study of the neonatal and long-term effects of prenatal cocaine exposure were studied. Based on maternal self-report, maternal urine screening, and infant meconium analysis, 24 infants were classified as cocaine-exposed and 22 as unexposed. Between 24 and 72 hours postpartum, plasma samples for norepinephrine (NE), epinephrine, dopamine, and dihydroxyphenylalanine analysis were obtained. The Neonatal Behavioral Assessment Scale was administered at 1 to 3 days of age and at 2 weeks of age by examiners masked to the drug exposure status of the newborns.

RESULTS

The cocaine-exposed newborns had increased plasma NE concentrations when compared to the unexposed infants (geometric mean, 923 pg/mL vs 667 pg/mL). There were no significant differences in plasma epinephrine, dopamine, or dihydroxyphenylalanine concentrations. Analysis for the effect of potential confounding variables revealed that maternal marijuana use was also associated with increased plasma NE, although birth weight, gender, and maternal use of alcohol or cigarettes were not. Geometric mean plasma NE was 1164 pg/mL in those infants with in utero exposure to both cocaine and marijuana compared to 812 pg/mL in those exposed to only cocaine and 667 pg/mL in those exposed to neither. Among the cocaine-exposed infants, plasma NE concentration correlated with an increased score for the depressed cluster (r = .53) and a decreased score for the orientation cluster (r = -.43) of the Neonatal Behavioral Assessment Scale administered at 1 to 3 days of age. Adjusting for marijuana exposure had no effect on these relationships between plasma NE and the depressed and orientation clusters.

CONCLUSION

Plasma NE is increased in newborns exposed to cocaine and marijuana. Increased plasma NE is associated with selected neurobehavioral disturbances among cocaine exposed infants at 1 to 3 days of life but not at 2 weeks.

The heart and development

The perspective from which the developing heart is viewed can lead to differing conclusions about the effects of development on cardiac function. The hearts of the embryo, fetus and adult, viewed from a global perspective, sustain the circulation through the same basic mechanisms of developing pressure and ejecting blood. The failure of the embryonic heart to perform these tasks results in growth failure, edema, and embryonic death, just as in the infant and adult such failure results in premature death. Furthermore, from the viewpoint of gross anatomy, following embryonic morphogenesis, the developing and adult hearts appear in general to be structurally similar, differing only in size and mass. However, a closer view shows, in the molecular and structural makeup of the myocardium, richly complex changes that can modulate the basic physiological properties of the cardiac myocyte. This article focuses on how these changes and the effects of birth and development alter ventricular function.

Stress, severity of illness, and outcome in ventilated preterm infants

AIM

To determine physiological and hormonal stress responses in ventilated preterm infants.

METHODS

Physiological and hormonal stress responses were studied in 47 ventilated preterm infants who were judged clinically to require sedation. The correlation between the stress response and severity of illness was examined, and responses were compared between infants with different clinical outcomes.

RESULTS

Stress hormone concentrations were significantly correlated with severity of illness, assessed using the arterial: alveolar oxygen partial pressure ratio. Noradrenaline showed the strongest correlation, with an exponential pattern of increased secretion. Catecholamine concentrations before sedation were significantly higher among infants who subsequently died (n = 15, at a median age of 6 days) than among survivors: median noradrenaline 4.31 vs 2.16 nmol/l, median adrenaline 0.69 vs 0.31 nmol/l. The observed fall in noradrenaline with sedation was lower among those who died than survivors (median fall 2% vs 40%).

CONCLUSION

Preterm infants are capable of hormonal stress responses appropriate for the severity of their illness. Extreme catecholamine responses, in the sickest infants, are associated with the worst outcome.

Depression of cardiac function after deep hypothermic circulatory arrest in deeply anesthetized neonatal lambs

Cardiac dysfunction is common after neonatal cardiac operations. Previous in vivo studies in neonatal animal models however, have failed to demonstrate decreased left ventricular function after ischemia and reperfusion. Cardiac dysfunction may have been masked in these studies by increased endogenous catecholamine levels associated with the use of light halothane anesthesia. Currently, neonatal cardiac operations are often performed with deep opiate anesthesia, which suppresses catecholamine surges and may affect functional recovery. We therefore examined the recovery of left ventricular function after ischemia and reperfusion in neonatal lambs anesthetized with high-dose fentanyl citrate (450 micrograms/kg administered intravenously). Seven intact neonatal lambs with open-chest preparation were instrumented with left atrial and left ventricular pressure transducers, left ventricular dimension crystals, and a flow transducer. The lambs were cooled (< 18 degrees C) on cardiopulmonary bypass (22 +/- 6 minutes), exposed to deep hypothermic circulatory arrest (46 +/- 1 minutes), and rewarmed on cardiopulmonary bypass (30 +/- 10 minutes). Catecholamine levels and indexes of left ventricular function were determined before (baseline) and 30, 60, 120, 180, and 240 minutes after termination of cardiopulmonary bypass. Levels of epinephrine, norepinephrine, and dopamine were unchanged from baseline values. Left ventricular contractility (slope of end-systolic pressure-volume relationship) was depressed from baseline value (31.7 +/- 9.3 mm Hg/ml) at 30 minutes (15.7 +/- 6.4 mm Hg/ml) and 240 minutes (22.7 +/- 6.4 mm Hg/ml) but unchanged between 60 and 180 minutes. Left ventricular relaxation (time constant of isovolumic relaxation) was prolonged from baseline value (19.0 +/- 3.0 msec) at 30 minutes (31.4 +/- 10.0 msec) and 240 minutes (22.1 +/- 2.8 msec) but unchanged between 60 and 180 minutes. Afterload (left ventricular end-systolic meridional wall stress) was decreased at 30, 60, and 240 minutes. Indexes of global cardiac function (cardiac output, stroke volume), preload (end-diastolic volume), and left ventricular compliance (elastic constant of end-diastolic pressure-volume relationship) were unchanged from baseline values. In deeply anesthetized neonatal lambs exposed to ischemia and reperfusion, left ventricular contractility, relaxation, and afterload are markedly but transiently depressed early after reperfusion and mildly depressed late after reperfusion.

Granulocyte-colony stimulating factor levels in cord blood and neonatal peripheral blood

We measured the granulocyte-colony stimulating factor (G-CSF) levels in cord blood and peripheral blood obtained from full-term or pre-term infants during the first 3 days of birth. The mean G-CSF level among cord blood (17.2 pg/mL) was similar to that of peripheral blood on day 0 (18.3 pg/mL) and day 1 (13.6 pg/mL), while that of peripheral blood on day 0 was significantly higher than on day 2 (10.9 pg/mL) and day 3 (8.8 pg/mL; both P < 0.05). There was no correlation between neutrophil counts and G-CSF levels. No difference was found in neutrophil counts or G-CSF levels between infants who weighed more or less than 2500 g at birth. These results suggest that the neonatal neutrophil count depends on regulatory factors other than G-CSF.

Pharmacokinetics of cardiovascular drugs in children. Inotropes and vasopressors

Infants and children with congenital or acquired heart disease and children with systemic disease often require pharmacological support of their failing circulation. Catecholamines may serve as inotropic (enhance myocardial contractility) or vasopressor (elevate systemic vascular resistance) agents. Noncatecholamine inotropic agents, such as the cardiac glycosides or the bipyridines, may be used in place of, or in addition to, catecholamines. Developmental changes in neonates, infants and children will affect the response to inotropic or pressor therapy. Maturation of the gastrointestinal tract, liver and kidneys alters absorption, metabolism and elimination of drugs, although there are few clear examples of this among the vasoactive drugs considered in this review. Changes in body composition affect the volume of distribution (Vd) and clearance (CL) of drugs. Developmentally based pharmacodynamic differences also affect the responses to both therapeutic and toxic effects of inotropes. These pharmacodynamic differences are based in part upon developmental changes in myocardial structure, cardiac innervation and adrenergic receptor function. For example, the immature myocardium has fewer contractile elements and therefore a decreased ability to increase contractility; it also responds poorly to standard techniques of manipulating preload. Available data suggest that dopamine and dobutamine pharmacokinetics are similar to those in adults. Wide interindividual variability has been noted. A consistent relationship between CL and age has not been demonstrated, although one investigator demonstrated an almost 2-fold increase in the CL of dopamine in children under the age of 2 years. The CL of dopamine appears to be reduced in children with renal and hepatic failure. Fewer data are available regarding the pharmacokinetics of epinephrine (adrenaline), norepinephrine (noradrenaline) and isoprenaline (isoproterenol). Digoxin pharmacokinetics have been extensively evaluated in infants and children. The Vd for digoxin is increased in infants and children. Children beyond the neonatal period display increased CL of digoxin, approaching adult values during puberty. Although it was previously thought that children both needed and tolerated higher serum concentrations of digoxin than adults, more recent studies indicate that adequate clinical response can be achieved with serum concentrations similar to those aimed for in adults, with decreased toxicity. Evaluation of studies of digoxin pharmacokinetics is complicated by the presence of an endogenous substance with digoxin-like activity on radioimmunoassay. Limited studies of amrinone pharmacokinetics in infants and children indicate a dramatically larger Vd, and a decreased elimination half-life in older infants and children, compared with values observed in adults.

Catecholamine response to ultrasonographically guided percutaneous blood sampling in fetal sheep

OBJECTIVE

The purpose of this study was to investigate the fetal catecholamine and arterial blood gas responses to ultrasonographically guided percutaneous needle aspiration of blood from a fetal cardiac ventricle.

STUDY DESIGN

A crossover trial design was used. Nine pregnant sheep of 120 to 130 days' gestation were stratified to either percutaneous fetal blood sampling or a sham experiment performed on the first day, and the alternative study on the following day. Arterial blood samples were withdrawn from chronically implanted catheters.

RESULTS

Percutaneous fetal blood sampling caused small but statistically significant increases in mean plasma epinephrine and norepinephrine levels 5 seconds after the procedure. Levels thereafter were similar to baseline values. Arterial pH and PCO2 values were unaltered except in one fetus, where blood sampling was followed by bradycardia with acidosis and elevated catecholamine levels.

CONCLUSIONS

Ultrasonographically guided percutaneous fetal blood sampling from a cardiac ventricle in sheep produces a rise in catecholamine levels that return to baseline values within 5 minutes. This technique provides an alternative to chronic catheterization for some experiments in which blood sampling or drug injection is required. The results also indicate that needle insertion produces only a modest and transient stress response in the fetus.

Fetal endocrine and renal responses to in utero ventilation and umbilical cord occlusion

OBJECTIVE

Fetal to neonatal transition involves a myriad of endocrine and renal adaptive changes triggered by multiple simultaneous stimuli. We examined the extent to which ventilation and umbilical cord occlusion have an impact on the many endocrine and renal function changes in fetal sheep at 133 +/- 1 day of gestation.

STUDY DESIGN

Nine fetuses were chronically prepared with an endotracheal tube, vascular and bladder catheters, and an inflatable umbilical cord occluder. After a 2-hour control period fetuses were treated with commercially prepared surfactant and ventilated with 100% oxygen. One hour after the onset of stable ventilation the umbilical cord was occluded and the animals were monitored for 3-hours.

RESULTS

In response to ventilation fetal arterial PO2 increased (18 +/- 1 to 86 +/- 29 mm Hg) and remained significantly above control values after cord occlusion. Fetal arterial pH, hematocrit, and mean arterial pressure and heart rate did not change during the study. Ventilation alone evoked significant increases in epinephrine and norepinephrine concentrations. Renal responses to ventilation included significant decreases in urine flow rate, fractional sodium excretion, and fractional water excretion. Neither ventilation nor cord occlusion resulted in significant changes in plasma concentrations of atrial natriuretic factor, arginine vasopressin, and angiotensin II or in glomerular filtration rate, urine osmolality, free water, and osmolar clearances.

CONCLUSIONS

(1) Mechanical ventilation and oxygenation alone increase circulating fetal catecholamine levels. (2) The addition of umbilical cord ligation has minimal impact on fetal endocrine and renal adaptive responses.

Plasma catecholamine levels in children

While blood norepinephrine and epinephrine levels are well established in adults, literature data concerning concentrations in young children are conflicting. This situation prompted us to assay plasma catecholamines in 86 healthy subjects aged two days to fifteen years using a sensitive high-performance liquid chromatography technique with electrochemical detection. Norepinephrine and epinephrine concentrations remained elevated up until 24 months of age, then dropped progressively to adult levels between 24 and 36 months, with fluctuations. These fluctuations, which reflect the sensitivity of children to environmental factors, prevented demonstration of any catecholaminergic secretory abnormality by blood assays in subjects under two years of age. Urinary assays, for which established values exist, are the only applicable procedure in such patients.

Catecholamine levels and associated cardiovascular responses in infants with meconium-stained amniotic fluid

Catecholamine levels and associated cardiovascular responses were determined in 21 control and 30 term infants with meconium-stained amniotic fluid (MSAF). Cord arterial blood was obtained for determination for norepinephrine (NE) and epinephrine (EPI) levels; cardiovascular measurements included heart rate and systolic blood pressure at 30 min. Pregnancy was uncomplicated in all cases. The total length of labor 964 +/- 402 versus 555 +/- 312 min (P < 0.001) and active phase of labor 300 +/- 261 versus 135 +/- 104 min (P < 0.001) were significantly longer in MSAF infants when compared to controls. The 1 min Apgar score was < 7 (range 1-6) in 11 of 30 MSAF infants versus 0 of 21 control infants; these 11 infants required positive pressure ventilation for approximately 60 s secondary to transient respiratory depression (RD). The 5 min Apgar score was > 7 in 49 of the 51 infants. Infants with MSAF exhibited a higher PaCO2 (6.89 +/- 1.17 vs 6.24 +/- 1.17 mmHg; P < 0.02) and lower pH (7.25 +/- 0.06 vs 7.29 +/- 0.05; P < 0.02) compared to controls. Infants with transient RD demonstrated the most marked arterial blood gas differences, i.e., PCO2 7.41 +/- 1.30 mmHg (P < 0.001), pH 7.21 +/- 0.07 (P < 0.001) and base deficit -6 +/- 4 versus -3 +/- 2.8 (P < 0.001) when compared to controls. NE and EPI levels were significantly higher in MSAF versus control infants, i.e., 12600 +/- 3040 versus 3740 +/- 1000 pg/ml (SEM) (P < 0.02) and 1550 +/- 250 versus 620 +/- 130 pg/ml (P < 0.001) respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of morphine and pancuronium on the stress response in ventilated preterm infants

Ninety-five premature newborns who had hyaline membrane disease and were struggling against the ventilator were randomised to one of three treatment groups: morphine (group M), pancuronium (group P) or morphine with pancuronium (group M+P). The dose of morphine was 50 micrograms/kg per h but was increased to 100 micrograms/kg per h in group M infants if they continued to struggle. The dosage of pancuronium was 100 micrograms/kg given as required to inhibit spontaneous respiration. Plasma catecholamine levels were measured on entry and at 24 h. Blood pressure and ventilatory requirements were determined on entry and at 6 h. The clinical outcome of the infants was documented. Group M infants (n = 29) showed a significant reduction in noradrenaline levels (median change -2.2 nmols/l (range -47.2 to +7.2 nmols/l), although seven were withdrawn from this group because of failure to settle. Group P (n = 28) and group M+P (n = 38) showed no significant change in noradrenaline levels. Comparison between the groups showed that group M infants had a significant reduction in noradrenaline levels compared with group P. The immediate effects of treatment on blood pressure and ventilatory requirements were similar in the three groups. The clinical outcome did not differ for any of the measured parameters. When adequate sedation is achieved, morphine may reduce the stress of newborn intensive care.

Role of renal sympathetic nerves in lambs during the transition from fetal to newborn life

To determine the role of renal sympathetic nerves in influencing renal function during the transition from fetal to newborn life, studies were carried out in conscious, chronically instrumented fetal sheep with either bilateral renal denervation (n = 11) or intact renal nerves (n = 12), 3-6 d after surgery. Endocrine, renal, and cardiovascular parameters were measured before and after delivery of lambs by cesarean section. Blood pressure and heart rate were similar in intact and denervated fetuses, and increased after delivery in both groups. There was also a transient diuresis and natriuresis, in the immediate postnatal period, the response being significantly greater in denervated than intact lambs (P less than 0.05). By 24 h postnatally, fluid and electrolyte excretions were similar in both groups, and significantly less than fetal levels. In the absence of renal nerves, the normal rise in plasma renin activity at birth was attenuated. These data provide evidence that renal sympathetic nerves play an important role during the transition from fetal to newborn life, and support the premise that birth is associated with sympathetic activation.

Establishment of functional residual capacity in infants delivered vaginally and by elective cesarean section

Functional residual capacity (FRC) was measured with an open circuit N2 washout method in 20 vaginally born infants and 15 delivered by cesarean section, 30 and 120 min after birth. Umbilical artery blood was collected and analyzed for pH and catecholamine concentration. FRC was significantly higher in the cesarean section infants than in the vaginally delivered infants at 120 min of age (23.8 versus 16.8 ml/kg). The cesarean section infants also tended to have lower tidal volumes and higher respiratory frequencies than infants delivered vaginally. No significant correlation was found between catecholamine levels in umbilical artery and FRC in either group although there was a significant correlation between catecholamine level at birth and the increase of FRC from 30 to 120 min in the cesarean section group. It is suggested that the higher FRC, higher respiratory frequency and lower tidal volume in the cesarean section infants is an adaptation to a higher pulmonary water content to ensure an efficient gas exchange with the least respiratory work.

Tactile-kinesthetic stimulation effects on sympathetic and adrenocortical function in preterm infants

The purpose of our study was to investigate the neuroendocrine response in preterm infants to a pattern of tactile-kinesthetic stimulation that facilitates their growth and development. Preterm infants (mean gestational age 30 weeks, mean birth weight 1176 gm) received normal nursery care or tactile-kinesthetic stimulation for three 15-minute periods at the start of three consecutive hours each day for 10 days. On day 1 and day 10 of the study, a 24-hour urine sample was collected for norepinephrine, epinephrine, dopamine, cortisol, and creatinine assay and a blood sample was taken by heel stick for cortisol and growth hormone assay. Urine norepinephrine and epinephrine values increased significantly only in the stimulated babies. Urine dopamine and cortisol values increased in both groups, and serum growth hormone decreased in both groups. Individual differences in urine norepinephrine, epinephrine, dopamine, and cortisol values were highly stable across the 10 days despite a 10-fold range of values among the infants. The results of this study suggest that tactile-kinesthetic stimulation of preterm infants has fairly specific effects on maturation and/or activity of the sympathetic nervous system. In addition, this study has defined catecholamine and cortisol secretion across gestational age in normal preterm infants. Finally, these data suggest that highly stable individual levels of catecholamine and cortisol secretion are established by birth in humans.

Beta-adrenoceptor responsiveness in intact leukocytes from adults and newborn infants; effect of phosphodiesterase inhibitors

Intact mononuclear and polymorphonuclear leukocytes from adults and newborn infants were used to estimate the beta 2-adrenoceptor responsiveness in vitro. The accumulation of cAMP in response to receptor stimulation by isoprenaline was used as a measure of the receptor responsiveness. The relevance of the method is dependent on the activity of the cAMP phosphodiesterase inside the cells. The xanthine derivatives, theophylline (4 mmol l-1) and 3-isobutyl-l-methyl-xanthine (0.1-2.5 mmol l-1), were used to inhibit the cAMP phosphodiesterase activity. It appears that 3-isobutyl-l-methyl-xanthine at 2.5 mmol l-1 inhibits the phosphodiesterase activity almost completely. By use of this concentration no age-dependent changes in the isoprenaline-stimulated cAMP accumulation in mononuclear and polymorphonuclear leukocytes from adults and newborn infants could be demonstrated.

Plasma concentrations of free and sulfoconjugated dopamine, epinephrine, and norepinephrine in healthy infants and children

Plasma concentrations of free and sulfoconjugated catecholamines were measured in healthy infants and children under resting conditions. Free norepinephrine and epinephrine levels were up to three times higher in healthy children under 2 years than in adults, even under true resting conditions. In contrast, free dopamine concentrations of all age groups fell within the normal range for adults. The levels of sulfoconjugation were in the adult range.

Cerebral and peripheral circulatory responses to intracranial hypertension in fetal sheep

Fetal head compression during normal labor can increase intracranial pressure (ICP). We studied the cerebral and peripheral blood flow responses to ICP elevation in utero in chronically catheterized fetal sheep using the radiolabeled microsphere technique. ICP was elevated, stepwise, in increments of 6 +/- 1 mm Hg by infusion of artificial cerebrospinal fluid into a lateral ventricle. When ICP was raised to within 28 mm Hg of baseline mean arterial blood pressure (i.e., ICP above 22 mm Hg), arterial pressure began to increase. Above this ICP level, up to 41 mm Hg, mean cerebral perfusion pressure was maintained by equivalent increases in arterial pressure. Cerebral blood flow and O2 uptake at the highest ICP levels were not different from baseline values. Changes in peripheral organ blood flow were graded according to the level of ICP. At the highest level (ICP = 41 mm Hg), renal, gastrointestinal, and skin blood flow decreased by 68%, 69%, and 65%, respectively. Myocardial and adrenal blood flow doubled, whereas heart rate and cardiac output were unchanged. Placental blood flow increased in proportion to arterial pressure. Arterial plasma epinephrine, norepinephrine and arginine vasopressin increased by nearly two orders of magnitude. Therefore, as ICP approaches baseline mean arterial pressure, fetal lambs are capable of sustaining cerebral perfusion by initiating profound visceral vasoconstriction without curtailing placental blood flow. Since cerebral O2 uptake was maintained, there is no evidence that stimulation of the peripheral response requires pronounced cerebral ischemia. This highly developed Cushing response may be important for ensuring cerebral viability when the fetal head is compressed during parturition.