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Biomedical subjects

C E Blanco

Publications and source records attributed to C E Blanco.

At least 37 records · Page 2Linked to original sources
PubMed2001

Arthroscopic decompressive medial release of the varus arthritic knee: Expanding the functional envelope.

We present the rationale and technique for treating medial knee osteoarthritis by dynamically unloading the medial compartment of the knee. Recent advances in kinematic studies indicate a dynamic linkage between differing degrees of freedom in the knee joint. Both the adduction moment and the foot progression angle are important determinants of medial compartment loading. The medially osteoarthritic knee has progressive compromise of free motion in more than 1 plane. Arthroscopic decompressive medial release unloads the medial compartment by release of the medial capsule and medial collateral ligament in the presence of intact cruciate ligaments, which may allow a decreased adduction moment and decrease of the external rotation restraint in extension found in more severely osteoarthritic knees. A case series of 38 patients with medial gonarthrosis was treated by this technique at the Hermanos Ameijeiras Hospital in Havana, Cuba. All patients had good results without postoperative valgus instability or significant complications. We feel that this technique warrants further clinical and biomechanical study for its use in isolation or in combination with high tibial osteotomy or minimally invasive selective osteotomy for the treatment of medial gonarthrosis of the knee. A minimally invasive, selective approach to biomechanical factors in osteoarthritis may be combined with other modulating techniques in efforts to forestall or prevent the need for total joint replacement.

Animals↗
PubMed2001

Combined partial arthroscopic synovectomy and radiation therapy for diffuse pigmented villonodular synovitis of the knee.

We present the results of combined partial arthroscopic synovectomy and low-dose external-beam radiation therapy (RT) in the treatment of diffuse pigmented villonodular synovitis (PVNS) of the knee. Mechanical synovectomy is an effective tool in treating PVNS of the knee, but when used alone it may be insufficient to eliminate all affected tissue. Intra-articular radiation or external-beam radiation may be added to mechanical synovectomy to treat recurrence but is not routinely done at the time of initial synovectomy. Combining intra-articular synovectomy with RT at the initial treatment for PVNS of the knee may reduce the recurrence rate. We present a prospective study of the treatment of 22 patients with clinical, ultrasonic, and histologically confirmed findings of diffuse PVNS of the knee. Characteristic clinical findings included pain, swelling, and erythema. These patients were treated by the Arthroscopic Surgery Group of the Orthopaedic Service at the Hospital "Hermanos Ameijeiras" in Havana, Cuba from 1990 to 1998. The protocol included anterior (patellofemoral, medial, and lateral) arthroscopic synovectomy and postoperative RT with a total dose of 2,600 cGy. This combination therapy was effective in reducing symptoms of pain and edema, and in improving overall function of patients. Nineteen patients (86%) had good or excellent results at an average follow-up of 33 months (range, 26 to 76 months). Three patients had residual stiffness and swelling, 2 of whom also had pain. Three had clinically and ultrasonically confirmed recurrence of disease and were treated with repeat arthroscopic synovectomy without harmful effects from RT. In all of the cases requiring repeat arthroscopic synovectomy, we observed fibrous bands secondary to reorganization of synovial inflamed tissue, meniscal retraction, and microscopic findings of fibrosis and cellular paucity. Partial arthroscopic synovectomy combined with low-dose RT in anti-inflammatory doses produced good results in the treatment of PVNS without significant complications in our patient series. Partial arthroscopic synovectomy of the knee for PVNS may be combined with RT to reduce the risk of disease recurrence. Adjuvant RT should also be considered for patients receiving a radical synovectomy to treat inaccessible or hidden disease sites. Rates of recurrence with combined partial (anterior) synovectomy and RT approach that of complete synovectomy in this series. Combining RT with radical arthroscopic synovectomy might further reduce recurrence rates.

Adult↗
PubMed2001

Extent of intestinal damage in the developing chick embryo after repetitive hypoxia under normoxic or hyperoxic conditions.

BACKGROUND: Episodes of hypoxia and reperfusion play an important role in the development of intestinal damage during perinatal development. The aim of this study was to investigate the histopathology of the intestine in the developing chick embryo after exposure to repetitive hypoxia and recovery under two different conditions: normoxic and hyperoxic (60% O2). METHODS: Chick embryos were exposed to 5 minutes of hypoxia. This was repeated six times with a recovery period of 15 minutes under normoxic conditions (21% O2) for chick embryos in test group 1 (TG1) and under hyperoxic conditions (100% O2) for chick embryos in test group 2 (TG2), from day 11 until day 20. Chick embryos that recovered under hyperoxic conditions (100% O2) were previously incubated under hyperoxic conditions (60% O2 for 24 hours). Histologic evaluation of the ileum was performed at different times after the interventions (2, 4, 8, 16, and 24 hours). RESULTS: In both test groups, only chick embryos older than 19 days showed intestinal damage. Intestinal histology on day 19 showed vasodilation of villus capillaries (10% in TG1 and 15% in TG2), necrosis in the top of the villi (29% in TG1 and 30% in TG2), and necrosis with preservation of base of the crypts (2% in TG1) and transmucosal necrosis (2% in TG2). CONCLUSIONS: Significant histologic changes, compared with the control group, were only found in chick embryos that were studied 2 hours after the interventions. Furthermore, recovery under hyperoxic conditions did not cause more intestinal damage compared with recovery under normoxic conditions.

Age Factors↗
PubMed2001

Alpha-adrenergic contribution to the cardiovascular response to acute hypoxemia in the chick embryo.

Fetal responses to acute hypoxemia include bradycardia, increase in blood pressure, and peripheral vasoconstriction. Peripheral vasoconstriction contributes to the redistribution of the cardiac output away from ancillary vascular beds toward myocardial, cerebral, and adrenal circulations. We investigated the effect of alpha-adrenergic receptor blockade on this fetal response. Fluorescent microspheres were used to measure cardiac output distribution during basal and hypoxemic conditions with and without phentolamine treatment. Phentolamine altered basal cardiac output distribution, indicating a basal alpha-adrenergic tone, but this was mainly noted at the earlier stages of incubation. During hypoxemia, phentolamine prevented vasoconstriction in the carcass. At day 19 of incubation, the percent cardiac output distributed to the carcass increased by 20% compared with a decrease in the control group by 17%. Phentolamine markedly attenuated the subsequent redistribution of the cardiac output toward the brain (from +102% in the control group to -25% in the phentolamine-treated group) and the heart (from +196% in the control group to +69% in the phentolamine-treated group). In the chick embryo, alpha-adrenergic mechanisms contribute to the maintenance of basal vascular tone and to the redistribution of the cardiac output away from the peripheral circulations toward the brain and heart during hypoxemic conditions.

Acute Disease↗
PubMed2001

Exogenous testosterone treatment decreases diaphragm neuromuscular transmission failure in male rats.

The effect of chronic exogenous testosterone (T) treatment on neuromuscular transmission in the diaphragm (Dia) muscle of adult male rats was determined. The contribution of neuromuscular transmission failure (NTF) to Dia fatigue was evaluated by superimposing intermittent direct muscle stimulation on repetitive nerve stimulation of isometric contraction in vitro. T treatment significantly reduced the contribution of NTF to Dia fatigue by approximately 20% (P < 0.001). Fiber type-specific effects on NTF were determined by measuring Dia fiber glycogen levels subsequent to repetitive nerve or muscle stimulation. T treatment had no effect on glycogen depletion in Dia type I and IIa fibers regardless of stimulation route. In the control group, type IIx fibers demonstrated significantly less glycogen depletion after nerve stimulation compared with direct muscle stimulation (P < 0.05), suggesting the presence of NTF. In contrast, T treatment increased glycogen depletion of type IIx fibers during nerve stimulation to levels similar to those after direct muscle stimulation. These data indicate that testosterone treatment substantially improves neuromuscular transmission in the Dia.

Animals↗
PubMed2001

Chronic exposure to cigarette smoke extract impairs endothelium-dependent relaxation of chicken embryo pulmonary arteries.

Maternal smoking may increase the risk for various adverse neonatal outcomes including persistent pulmonary hypertension of the newborn (PPHN). We investigated whether chronic prenatal cigarette smoke extract (CSE) exposure could produce abnormal vasoreactivity in pulmonary arteries. Daily injections of CSE (diluted in phosphate buffered saline) or vehicle were added to the air cells of fertilized eggs starting on day 5 of the 21-day incubation period of the chicken embryo. On day 19, pulmonary arteries were dissected out and their contractile properties were assessed using small vessel myography. Endothelium-dependent and endothelium-independent vasorelaxations were examined by using acetylcholine (ACh, 10(-8) to 10(-4) M) and sodium nitroprusside (SNP, 10(-8) to 10(-4) M), respectively. The drug concentration inducing 50% of the maximal relaxation was determined for each concentration-response curve and expressed as negative log molar (pD(2)). Exposure to CSE significantly decreased the sensitivity of pulmonary arteries to ACh (pD(2) control group: 7.29 +/- 0.24; pD(2) CSE-exposed group 6.24 +/- 0.12, p < 0.05). SNP elicited similar responses in vessels of both groups at all tested concentrations. In conclusion, chronic prenatal exposure to CSE impaired endothelium-dependent but not endothelium-independent vasodilation in chicken embryo pulmonary arteries. This observation suggests that cigarette smoke components may produce deleterious effects on fetal vascular endothelial vasorelaxant pathways, leading to the development of adverse outcomes such as PPHN.

Acetylcholine↗
PubMed2001

Androgen receptor immunoreactivity of male rat cervical motor neurons is increased by chronic pharmacologic testosterone treatment.

Chronic pharmacologic testosterone treatment of adult male rats decreases neuromuscular transmission failure (NTF) in the rat diaphragm muscle and increases choline acetyltransferase (ChAT) mRNA levels in cervical motor neurons. These testosterone-induced changes in NTF and ChAT mRNA levels may be mediated through the activation of the androgen receptor (AR). The purpose of this study was to determine if the AR expression of cervical motor neurons is modulated by chronic pharmacologic testosterone treatment of gonadally intact male rats with testosterone propionate (TP). Serum testosterone levels were elevated by a subcutaneous implant of capsules containing crystalline TP for 28 days. The proportion of motor neurons containing AR-I positive nuclei was increased from 14.8 +/- 10.8% among the control group to 81.7 +/- 12.6% in the TP-treated animals (p<0.05). These results imply that anabolic-androgenic steroid effects on neuromuscular function may be mediated through AR dependent regulation of gene expression in motor neurons.

Animals↗
PubMed2000

Chronic hypoxia stimulates periarterial sympathetic nerve development in chicken embryo.

BACKGROUND: Epidemiological findings suggest an association between low-for-age birth weight and the risk to develop coronary heart diseases in adulthood. During pregnancy, an imbalance between fetal demands and supply may result in permanent alterations of neuroendocrine development in the fetus. We evaluated whether chronic prenatal hypoxia increases arterial sympathetic innervation. METHODS AND RESULTS: Chicken embryos were maintained from 0.3 to 0.9 of the 21-day incubation period under normoxic (21% O(2)) or hypoxic conditions (15% O(2)). At 0.9 incubation, the degree of sympathetic innervation of the embryonic femoral artery was determined by biochemical, histological, and functional (in vitro contractile reactivity) techniques. Chronic hypoxia increased embryonic mortality (32% versus 13%), reduced body weight (21.9+/-0.4 versus 25.4+/-0.6 g), increased femoral artery norepinephrine (NE) content (78.4+/-9.4 versus 57.5+/-5.0 pg/mm vessel length), and increased the density of periarterial sympathetic nerve fibers (14.4+/-0.7 versus 12.5+/-0.6 counts/10(4) microm(2)). Arteries from hypoxic embryos were less sensitive to NE (pD(2), 5.99+/-0.04 versus 6. 21+/-0.10). In the presence of cocaine, however, differences in sensitivity were no longer present. In the embryonic heart, NE content (156.9+/-11.0 versus 108.1+/-14.7 pg/mg wet wt) was also increased after chronic hypoxia. CONCLUSIONS: In the chicken embryo, chronic moderate hypoxia leads to sympathetic hyperinnervation of the arterial system. In humans, an analogous mechanism may increase the risk for cardiovascular disease in adult life.

Arteries↗
PubMed2000

Developmental changes in plasma catecholamine concentrations during normoxia and acute hypoxia in the chick embryo.

In the mammalian fetus, the cardiovascular responses to acute hypoxaemia include a redistribution of the cardiac output away from the periphery towards the adrenal, myocardial and cerebral circulations. A component of the peripheral vasoconstriction is mediated by increased release of catecholamines into the fetal circulation during acute hypoxaemia. Previously, we have shown that the chick embryo also shows an increase in peripheral vascular resistance during acute hypoxaemia and that this response becomes progressively larger towards the end of the incubation period. However, the ontogeny of the catecholaminergic response to acute hypoxaemia has not been investigated in this species. Fertilised chicken eggs were studied on days 10, 13, 16 and 19 of incubation (hatching is at 21 days). At each stage of incubation, blood samples were obtained from the chorioallantoic artery of the chick embryos during normoxia and after 5 min of hypoxaemia for measurement of plasma concentrations of adrenaline and noradrenaline by HPLC. Basal plasma adrenaline and noradrenaline concentrations by the end of the incubation period were much higher in the chick embryo than values reported for mammalian fetuses during late gestation. During normoxia, basal plasma noradrenaline concentration remained unchanged during development but plasma adrenaline concentration showed a developmental increase from < 25.1 pmol l-1 at day 10 to 3 nmol l-1 at day 19 of incubation. Acute hypoxaemia caused an increase in plasma noradrenaline and adrenaline from day 13 and day 16 of incubation, respectively. In addition, the increase in plasma adrenaline and noradrenaline and in the ratio of plasma adrenaline to noradrenaline during acute hypoxaemia became progressively larger by the end of the incubation period. These data show an ontogenic increase in basal plasma catecholamines and in the catecholaminergic response to acute hypoxaemia in the chick embryo during the last third of the incubation period.

Acute Disease↗
PubMed2000

Localization and age-related changes of nitric oxide- and ANP-mediated cyclic-GMP synthesis in rat cervical spinal cord: an immunocytochemical study.

An immunocytochemical technique was used to study the localization and developmental aspects of cyclic GMP (cGMP)-synthesizing structures in the cervical spinal cord of 2-week and 3-month-old Lewis rats in response to the nitric oxide (NO) donor sodium nitroprusside (SNP) and/or atrial natriuretic peptide (ANP). By using cell-specific markers, the cell structures involved were investigated. To visualize cGMP, a combined technique of low- and high-power magnification, using a confocal laser scanning microscope was used. NOS-mediated cGMP synthesis was observed in the cervical spinal cord in laminae I, II and III in 14-day-old rats, which activity was mainly absent at the age of 3 months. The involvement of NO in the NMDA-mediated increase in cGMP immunostaining (cGMP-IS) was demonstrated by the absence of cGMP-IS in slices incubated in the presence of NMDA together with the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). This NO-mediated effect of NMDA on cGMP-IS was completely absent in the 3-month-old rats. ANP-mediated cGMP synthesis resulted in an increase in cGMP in laminae I and II, which was generally similar at both ages. Astrocytes in both white and gray matter were found to be cGMP-IS in the basal, NO- and ANP-stimulated conditions. Using confocal laser microscopy, NO-mediated cGMP synthesis was observed in large cholinergic terminals nearby motor neurons in the ventral horn. An extensive colocalization between NO-stimulated cGMP synthesis and parvalbumin-positive (GABAergic) neurons and fibers was observed in all laminae. In the ANP-stimulated condition, a colocalization with parvalbumin structures was found in laminae II and III. No NO- or ANP-mediated cGMP synthesis was found in fibers immunopositive for the presynaptic glutamate transporter, serotonin, or tyrosine hydroxylase.

Age Factors↗
PubMed2000

Effect of perfluorochemical liquid ventilation on cardiac output and blood pressure variability in neonatal piglets with respiratory insufficiency.

Respiration and mechanical ventilation induce cyclic variation in cardiac output and blood pressure. We examined these phasic hemodynamic influences of mechanical ventilation during gas ventilation and partial and tidal liquid ventilation in 7 anesthetized and paralyzed young piglets (body weight, 3.0-4.9 kg) made respiratory-insufficient by repeated saline lung lavage. Nonlinear regression analysis of cardiovascular parameters vs. time was done to quantify respiratory-induced fluctuations in hemodynamic variables. The amplitude of oscillations was expressed as a percentage of the mean hemodynamic variable during the study period, and was called the relative oscillation amplitude. The relative oscillation amplitude of left ventricular stroke volume, left ventricular output, systemic arterial pressure, and systemic perfusion pressure was significantly larger (at least twofold) during tidal liquid ventilation compared to partial liquid ventilation. No such differences were observed between gas and partial liquid ventilation at comparable gas ventilator settings. We conclude that in this animal model, within-breath modulation of left ventricular output, systemic blood pressure, and perfusion pressure was significantly increased during tidal liquid ventilation as compared to partial liquid ventilation.

Animals↗
PubMed2000

Effects of hypothermia and gender on survival and behavior after perinatal asphyxia in rats.

Previous studies in rats have demonstrated that perinatal asphyxia (PA) produces long-term morphological alterations, particularly affecting hippocampus. neostriatum, and cerebral cortex. These changes were prevented by applying hypothermia during the asphyctic insult. Because these cerebral areas are involved in cognitive and motor functions, the aim of the present study was to determine whether periods of PA during normothermia or hypothermia produces long-term behavioral impairments in rats of both sexes. The cognitive and motor functions were studied using the spatial Morris water maze (MWM) task at 1.5 months, and the open field at 5 months, respectively. The present study revealed that female rats had a higher survival rate than males after PA in normothermic conditions (p < 0.014). and that hypothermia drastically prolonged the time of survival in both sexes (p < 0.001). There were no differences in learning and memory functions between groups or male and female rats when tested with MWM. Rats subjected to hypothermia treatment did not show differences in the MWM compared to controls. A lower locomotor activity in the open field test was only observed in male rats that suffered 15 and 20 min of PA in normothermia (p < 0.05). Hypothermia treatment prevented this hypoactivity. PA in females, even if severe, did not affect the motor activity. The data of both behavioral tests showed differences between sexes, i.e., the female rats learned the MWM task slower, and were more active in the open field. This work lends further support for the hypothesis that hypothermia can prevent mortality as well as long-term sequelae induced by PA.

Animals↗
PubMed2000

Perinatal asphyxia results in changes in presynaptic bouton number in striatum and cerebral cortex-a stereological and behavioral analysis.

Deficits in cognitive function have been related to quantitative changes in synaptic population, particularly in the cerebral cortex. Here, we used an established model of perinatal asphyxia that induces morphological changes, i.e. neuron loss in the cerebral cortex and striatum, as well as behavioural deficits. We hypothesized that perinatal asphyxia may lead to a neurodegenerative process resulting in cognitive impairment and altered presynaptic bouton numbers in adult rats. We studied cognitive performance at 18 months and presynaptic bouton numbers at 22 months following perinatal asphyxia. Data of the spatial Morris water escape task did not reveal clear memory or learning deficits in aged asphyctic rats compared to aged control rats. However, a memory impairment in aged rats versus young rats was observed, which was more pronounced in asphyctic rats. We found an increase in presynaptic bouton density in the parietal cortex, whereas no changes were found in striatum and frontal cortex in asphyctic rats. An increase of striatal volume was observed in asphyctic rats, leading to an increase in presynaptic bouton numbers in this area. These findings stress the issue that volume measurements have to be taken into account when determining presynaptic bouton density. Furthermore, perinatal asphyxia led to region-specific changes in presynaptic bouton numbers and it worsened the age-related cognitive impairment. These results suggest that perinatal asphyxia induced neuronal loss, which is compensated for by an increase in presynaptic bouton numbers.

Adult↗
PubMed2000

Contractile and relaxing reactivity in carotid and femoral arteries of chicken embryos.

In the embryo, hypoxemia causes redistribution of cardiac output from the periphery toward the heart and the brain. In view of this, we investigated developmental changes in the contractile and relaxing properties of the peripheral femoral artery (Fem) and the more central carotid artery (Car) at 0.7, 0.8, and 0.9 of the chicken embryo incubation time. Isolated arteries were studied in myographs and were exposed to norepinephrine or phenylephrine. High K(+) (125 mM) and electrical field stimulation (0.25-16 Hz) were used to induce receptor-independent and neurogenic contractions. Relaxing responses to ACh were evaluated in the absence and presence of the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) and before and after endothelium removal. alpha(1)-Adrenergic contractile responses increased in a time-dependent manner and were significantly larger in Fem than in Car. Neurogenic contractions and adrenergic nerves could only be demonstrated in Fem at 0.9 incubation. ACh caused relaxation in both Fem and Car at 0.7, 0.8, and 0.9 incubation. The NO-independent part of the relaxation was more pronounced in Car than in Fem at all developmental stages. We conclude that the chicken embryo is a useful model to investigate the development of vasomotor control and vascular heterogeneity. The observed regional vascular differences may contribute to cardiac output redistribution during hypoxia in the embryo and might result from endothelial and neurogenic influences on vascular smooth muscle differentiation.

Acetylcholine↗
PubMed2000

A feedback controller for the maintenance of FRC during tidal liquid ventilation: theory, implementation, and testing.

The necessity of controlling functional residual capacity (FRC) during tidal liquid ventilation has been recognized since the first description of this respiratory support technique by Kylstra et al in 1962. We developed a microcomputer feedback system that adjusts the inspired tidal volume (VT,I) of a liquid ventilator based on the end-expiratory quasi-static alveolar pressure (PA,EE), in order to maintain a stable FRC. The system consists of three subunits: (1) a tracheal pressure catheter to estimate breath by breath FRC changes, derived from PA,EE changes, and (2) a roller pump interfaced with (3) a personal computer in which a closed-loop control is implemented. The regulator sets the actual PA,EE against the corresponding desired value. Any discrepancy is offset by changes in VT,I and the required change in pump velocity is communicated to the roller pump. The size of any change in pump velocity is determined to both the observed and target or desired PA,EE (i.e., the error) and the (calibration) pressure-volume curve. To evaluate the efficacy of the controller, a set of laboratory bench tests were conducted under steady state and transient conditions. Closed-loop control was effective in keeping FRC and PA,EE near the desired level, with an acceptable oscillatory behaviour. The feedback controller successfully compensated for transient disturbances of PFC liquid balance. The steady state stability was confirmed during a five hour period of liquid ventilation in five preterm lambs.

Algorithms↗
PubMed2000

Conventional gas ventilation, liquid-assisted high-frequency oscillatory ventilation, and tidal liquid ventilation in surfactant-treated preterm lambs.

This study was designed to compare the efficacy and potential protective or injurious effects of tidal liquid ventilation (TLV), liquid-assisted high-frequency oscillatory ventilation (LA-HFOV), and high PEEP conventional mechanical ventilation (CMV) in neonatal respiratory distress syndrome. Preterm lambs (124-126 days gestation), prophylactically treated with natural surfactant, were allocated to one of the treatment modalities or to an untreated fetal control group (F), euthanised after tracheal ligation. LA-HFOV animals received an intratracheal loading dose of 5 mL x kg(-1) followed by a continuous intrapulmonary instillation of 12 mL x kg(-1);h(-1) FC-75 perfluorocarbon liquid. The ventilation strategies aimed at keeping clinically appropriate arterial blood gases for a study period of 5 hours. A histological lung injury score was calculated and semiquantitative morphometry was performed on lung tissue fixed by vascular perfusion. The alveolar-arterial pressure difference for O2 was significantly lower throughout the study in TLV compared to CMV lambs; at 1, 2, and 5 hours, oxygenation was better in TLV when compared to LA-HFOV. Total lung injury scores in TLV lambs were significantly lower than in either CMV or LA-HFOV animals, but higher when compared to F. CMV and LA-HFOV induced an excess of collapsed and overdistended alveoli, whereas in TLV alveolar expansion was normally distributed around predominantly normal alveoli. CMV and LA-HFOV, but not TLV, were associated with an excess of dilated airways. Thus, in the ovine neonatal RDS model, TLV compared favourably to either gas ventilation strategy by its more uniform ventilation, reduced lung injury, and improved gas exchange.

Analysis of Variance↗
PubMed1999

Adrenergic and vasopressinergic contributions to the cardiovascular response to acute hypoxaemia in the llama fetus.

1. The effects of fetal intravenous treatment with phentolamine or a vasopressinergic V1-receptor antagonist on the fetal cardiovascular responses to acute hypoxaemia in the llama were investigated. 2. Six llama fetuses were surgically prepared between 60 and 70 % of gestation under general halothane anaesthesia with vascular catheters and transit-time ultrasonic flow probes around a carotid artery and a femoral artery. At least 4 days after surgery all fetuses were subjected to a 3 h experiment: 1 h of normoxia, 1 h of hypoxaemia and 1 h of recovery while on slow i.v. infusion with saline. On separate days this experiment was repeated with fetal i.v. treatment with either phentolamine or a V1-receptor antagonist dissolved in saline. 3. During saline infusion all llama fetuses responded to acute hypoxaemia with intense femoral vasoconstriction. Phentolamine during normoxia produced hypotension, tachycardia and vasodilatation in both the carotid and the femoral circulations. During hypoxaemia, fetuses treated with phentolamine did not elicit the pronounced femoral vasoconstriction and all died within 20 min of the onset of hypoxaemia. A V1-receptor antagonist produced a femoral vasodilatation during normoxia but did not affect the fetal cardiovascular responses to acute hypoxaemia. 4. In conclusion, alpha-adrenergic and V1-vasopressinergic mechanisms contribute to a basal vasoconstrictor tone in the femoral circulation in the llama fetus. The enhanced femoral vasoconstriction during acute hypoxaemia in the llama fetus is not mediated by stimulation of V1-vasopressin receptors, but is dependent on alpha-adrenergic receptor stimulation. Such alpha-adrenergic efferent mechanisms are indispensable to fetal survival during hypoxaemia in the llama since their abolition leads to cardiovascular collapse and death.

Adrenergic alpha-Antagonists↗