A cluster randomized controlled non-inferiority trial of 5-day Dose Adjustment for Normal Eating (DAFNE) training delivered over 1 week versus 5-day DAFNE training delivered over 5 weeks: the DAFNE 5 × 1-day trial

AIMS

To compare, in a randomized controlled non-inferiority trial, the outcomes of the traditional format for Dose Adjustment for Normal Eating structured education courses; that is, one delivered over 5 consecutive days (1-week course) with a variant of this format delivered 1 day a week for 5 consecutive weeks (5-week course).

METHODS

Adults with Type 1 diabetes, from seven UK Dose Adjustment For Normal Eating training centres, were individually randomized, stratified by centre, to receive either a 1-week or 5-week course. A qualitative study was embedded within the trial to explore patients' experiences.

RESULTS

In total, 213 patients were randomized and 160 completed the study procedures. In the per-protocol analysis, the difference in HbA1c levels (95% CI) between the arms at 6 months was 0.4 mmol/mol (-2.4, 3.1) or 0.03% (-0.22, 0.28) and -0.9 mmol/mol (-3.9, 2.2) or -0.08% (-0.36, 0.20) at 12 months. All confidence limits were within the non-inferiority margin of ± 5.5 mmol/mol (0.5%) for HbA1c %. For those patients with a baseline HbA1c of ≥ 58 mmol/mol (≥ 7.5%) the mean change (95% CI) in HbA1c was -2.2 mmol/mol (-4.0, -0.4) or -0.20% (-0.37, -0.04) at 6 months (P = 0.016), and -2.0 mmol/mol (-4.1, 0.04) or -0.18% (-0.37 to 0.004) at 12 months (P = 0.055). Episodes of severe hypoglycaemia were decreased by 82% [relative risk 0.18 (95% CI 0.03-0.936); P = 0.042], psychosocial outcomes improved significantly, and the difference between arms was not significant. Qualitative interviews showed that patients overwhelmingly favoured the format of course that they attended.

CONCLUSIONS

In summary, 5-week and 1-week Dose Adjustment for Normal Eating courses are equivalent in terms of biomedical and psychosocial outcomes, and we were persuaded that both course formats should be made available in routine care.

Do high fasting glucose levels suggest nocturnal hypoglycaemia? The Somogyi effect-more fiction than fact?

AIMS

The Somogyi effect postulates that nocturnal hypoglycaemia causes fasting hyperglycaemia attributable to counter-regulatory hormone release. Although most published evidence has failed to support this hypothesis, this concept remains firmly embedded in clinical practice and often prevents patients and professionals from optimizing overnight insulin. Previous observational data found lower fasting glucose was associated with nocturnal hypoglycaemia, but did not assess the probability of infrequent individual episodes of rebound hypoglycaemia. We analysed continuous glucose monitoring data to explore its prevalence.

METHODS

We analysed data from 89 patients with Type 1 diabetes who participated in the UK Hypoglycaemia study. We compared fasting capillary glucose following nights with and without nocturnal hypoglycaemia (sensor glucose < 3.5 mmol/l).

RESULTS

Fasting capillary blood glucose was lower after nights with hypoglycaemia than without [5.5 (3.0) vs. 14.5 (4.5) mmol/l, P < 0.0001], and was lower on nights with more severe nocturnal hypoglycaemia [5.5 (3.0) vs. 8.2 (2.3) mmol/l; P = 0.018 on nights with nadir sensor glucose of < 2.2 mmol/l vs. 3.5 mmol/l]. There were only two instances of fasting capillary blood glucose > 10 mmol/l after nocturnal hypoglycaemia, both after likely treatment of the episode. When fasting capillary blood glucose is < 5 mmol/l, there was evidence of nocturnal hypoglycaemia on 94% of nights.

CONCLUSION

Our data indicate that, in clinical practice, the Somogyi effect is rare. Fasting capillary blood glucose ≤ 5 mmol/l appears an important indicator of preceding silent nocturnal hypoglycaemia.

Frequency of biochemical hypoglycaemia in adults with Type 1 diabetes with and without impaired awareness of hypoglycaemia: no identifiable differences using continuous glucose monitoring

OBJECTIVE

Impaired awareness of hypoglycaemia (IAH) is a major risk factor for severe hypoglycaemia in Type 1 diabetes. Although biochemical hypoglycaemia is asserted to be more frequent in IAH, this has not been estimated accurately. The aim of this study was to use Continuous Glucose Monitoring (CGM) to quantify hypoglycaemia in IAH and evaluate its use in identifying impaired awareness of hypoglycaemia.

METHODS

Ninety-five patients with Type 1 diabetes were classified as having normal (n = 74) or impaired awareness (n = 21) using an established method of assessing hypoglycaemia awareness. Hypoglycaemia exposure was assessed prospectively over 9-12 months using weekly 4-point capillary home blood glucose monitoring (HBGM), 5 days of CGM and prospective reporting of severe hypoglycaemia. The frequencies of biochemical and severe hypoglycaemia were compared in patients with normal and impaired awareness of hypoglycaemia.

RESULTS

Patients with impaired awareness had a 3-fold higher incidence of severe hypoglycaemia than those with normal awareness [incidence rate ratio (IRR) 3.37 (95% CI 1.30-8.7); P = 0.01] and 1.6-fold higher incidence of hypoglycaemia on weekly HBGM [IRR 1.63 (95% CI 1.09-2.44); P = 0.02]. No significant differences were observed with CGM [IRR for sensor glucose < or = 3.0 mmol/l 1.47 (95% CI 0.91-2.39); P = 0.12; IRR for sensor glucose < or = 2.2 mmol/l 1.23 (95% CI 0.76-1.98); P = 0.40].

CONCLUSIONS

Patients with Type 1 diabetes with impaired awareness had a 3-fold higher risk of severe hypoglycaemia and 1.6-fold higher incidence of biochemical hypoglycaemia measured with weekly glucose monitoring compared with normal awareness, but 5 days of CGM did not differentiate those with impaired from those with normal awareness.

Comparing hormonal and symptomatic responses to experimental hypoglycaemia in insulin- and sulphonylurea-treated Type 2 diabetes

AIMS

Patients with diabetes rely on symptoms to identify hypoglycaemia. Previous data suggest patients with Type 2 diabetes develop greater symptomatic and hormonal responses to hypoglycaemia at higher glucose concentrations than non-diabetic controls and these responses are lowered by insulin treatment. It is unclear if this is as a result of insulin therapy itself or improved glucose control. We compared physiological responses to hypoglycaemia in patients with Type 2 diabetes patients treated with sulphonylureas (SUs) or insulin (INS) with non-diabetic controls (CON).

METHODS

Stepped hyperinsulinaemic hypoglycaemic clamps were performed on 20 subjects with Type 2 diabetes, 10 SU-treated and 10 treated with twice-daily premixed insulin, and 10 age- and weight-matched non-diabetic controls. Diabetic subjects were matched for diabetes duration, glycated haemoglobin (HbA(1c)) and hypoglycaemia experience. We measured symptoms, counterregulatory hormones and cognitive function at glucose plateaux of 5, 4, 3.5, 3 and 2.5 mmol/l.

RESULTS

Symptomatic responses to hypoglycaemia occurred at higher blood glucose concentrations in SU-treated than INS-treated patients [3.5 (0.4) vs. 2.6 (0.5) mmol/l SU vs. INS; P = 0.001] or controls [SU vs. CON 3.5 (0.4) vs. 3.0 (0.6) mmol/l; P = 0.05]. They also had a greater increase in symptom scores at hypoglycaemia [13.6 (11.3) vs. 3.6 (6.1) vs. 5.1 (4.3) SU vs. INS vs. CON; P = 0.017]. There were no significant differences in counterregulatory hormone responses or impairment of cognitive function among groups.

CONCLUSIONS

Sulphonylurea-treated subjects are more symptomatic of hypoglycaemia at a higher glucose level than insulin-treated subjects. This may protect them from severe hypoglycaemia but hinder attainment of glycaemic goals.

Thalamic neuronal dysfunction and chronic sensorimotor distal symmetrical polyneuropathy in patients with type 1 diabetes mellitus

AIMS/HYPOTHESIS

Although clear peripheral nerve pathological abnormalities have been demonstrated in diabetic peripheral neuropathy (DPN), there is little information with regard to brain involvement. Our aim was to use in vivo proton magnetic resonance specroscopy (H-MRS) in patients with DPN in order to assess the neuro-chemical status of the thalamus, which acts as the gateway to the brain for somatosensory information.

METHODS

Participants included 18 type 1 diabetic men (eight without DPN, ten with DPN) and six non-diabetic healthy volunteers, who all underwent detailed clinical and neurophysiological assessments yielding a Neuropathy Composite Score (NCS) derived from Neuropathy Impairment Score of the Lower Limbs plus seven tests of nerve function prior to investigation via a single-voxel H-MRS technique, which was used to sample ventral posterior thalamic parenchyma. Spectroscopic resonances including those due to N-acetyl aspartate (NAA) were assessed at both short and long echo-time, providing putative indicators of neuronal function and integrity, respectively.

RESULTS

At long echo-time we observed significantly lower NAA:creatine (p = 0.04) and NAA:choline (p = 0.02) ratios in DPN patients than in the other groups. No group differences were detected at short echo-time. We found a significant positive association between both sural amplitude (rho = 0.61, p = 0.004) and nerve conduction velocity (r = 0.58, p = 0.006) and NAA:creatine signal among participants with diabetes. Vibration detection threshold (rho = -0.70, p = 0.004) was significantly related to NAA:choline ratio. Heart rate variability with deep breathing (rho = -0.46, p = 0.05) and NCS (rho = -0.53, p = 0.03) were significantly related to NAA:creatine ratio.

CONCLUSIONS/INTERPRETATION

The significantly lower NAA:creatine ratio in DPN is suggestive of thalamic neuronal dysfunction, while the lack of difference in short echo-time between the groups does not suggest neuronal loss. Taken together with the observed correlations between NAA and neurophysiological assessments, these findings provide evidence for thalamic neuronal involvement in DPN.

Effects of NOS inhibition on the cardiopulmonary system and brain microvascular markers after intermittent hypoxia in rats

We previously demonstrated that rats subjected to intermittent hypoxia (IH) by exposure to 10% O(2) for 4 h daily for 56 days in a normobaric chamber, developed pulmonary hypertension, right ventricular hypertrophy and wall-thickening in pulmonary arterioles, compared with normoxic (N) controls. These changes were greater in rats subjected to continuous hypoxia (CH breathing 10% O(2) for 56 days). Cerebral angiogenesis was demonstrated by immunostaining with glucose transporter 1 (GLUT1) antibody, in viable vessels, in CH and to a lesser degree in IH. In this study, adult Wistar rats were subjected to the same hypoxic regimes and given the nitric oxide synthase (NOS) inhibitor N(6)-nitro-L-arginine methyl ester (L-NAME) in drinking water (NLN, IHLN and CHLN regimes) to induce hypertension. There was significant systemic hypertension in NLN and IHLN rats, compared with N and IH, but surprisingly not in CHLN compared with CH. Hematocrit rose in all hypoxic groups (up to 79% in CHLN). There was no significant pulmonary hypertension in IHLN versus NLN rats, although there was asymmetric wall thickening in pulmonary arterioles. Cerebral GLUT1 immunoreactivity increased with L-NAME, with or without hypoxia, especially in CHLN rats, but conspicuously there was no evidence of angiogenesis in brains of IHLN compared with NLN rats. NOS blockade may attenuate the cerebral and pulmonary vascular changes of IH while augmenting cerebral angiogenesis in continuous hypoxia. However, whether cerebral effects are due to systemic hypertension or changes in cerebral nitric oxide production needs to be evaluated.

Effects of Perinatal Exposure to Hypoxia upon the Pulmonary Circulation of the Adult Rat

The hypothesis on Fetal and Infant Origins of Adult Disease proposes that an altered in utero environment may impair fetal development and physiological function, increasing susceptibility to disease in adulthood. Previous studies demonstrated that reduced fetal growth predisposes to adult cardiovascular diseases. Maternal smoking and high altitude are also linked to reduced fetal growth and adult disease, and both cause fetal hypoxia. We therefore wanted to determine whether fetal hypoxia produces alterations in the adult pulmonary vasculature. Body and ventricular weight, pulmonary arterial compliance and vasoreactivity to potassium chloride (KCl), prostaglandin F2alpha (PGF2alpha), acetylcholine (ACh) and sodium nitroprusside (SNP) were studied in adult rats exposed to 10 % hypoxia throughout the perinatal period, compared to age-matched controls. Rats exposed to perinatal hypoxia had reduced body weight (199+/-15 vs. 294+/-10 g, P<0.001), elevated right ventricular weight (70.3+/-8.8 vs. 51.4+/-1.2 mg/100 g, P<0.05), elevated left ventricular weight (281+/-27 vs. 232+/-5 mg/100 g, P<0.05), reduced pulmonary arterial compliance (35.2+/-2.0 vs. 46.4+/-2.4 microm/mN, P<0.05) and reduced maximal pulmonary vasoconstriction to KCl (1.74+/-0.14 vs. 2.63+/-0.31 mN/mm, P<0.01), and PGF2(2alpha) (1.40+/-0.14 vs. 2.47+/-0.44 mN/mm, P<0.05). Perinatal exposure to hypoxia had a profound effect upon the adult pulmonary circulation, which could predispose to cardiopulmonary diseases in adulthood.

Effects of perinatal exposure to hypoxia upon the pulmonary circulation of the adult rat

The hypothesis on Fetal and Infant Origins of Adult Disease proposes that an altered in utero environment may impair fetal development and physiological function, increasing susceptibility to disease in adulthood. Previous studies demonstrated that reduced fetal growth predisposes to adult cardiovascular diseases. Maternal smoking and high altitude are also linked to reduced fetal growth and adult disease, and both cause fetal hypoxia. We therefore wanted to determine whether fetal hypoxia produces alterations in the adult pulmonary vasculature. Body and ventricular weight, pulmonary arterial compliance and vasoreactivity to potassium chloride (KCl), prostaglandin F2alpha (PGF2alpha), acetylcholine (ACh) and sodium nitroprusside (SNP) were studied in adult rats exposed to 10 % hypoxia throughout the perinatal period, compared to age-matched controls. Rats exposed to perinatal hypoxia had reduced body weight (199+/-15 vs. 294+/-10 g, P<0.001), elevated right ventricular weight (70.3+/-8.8 vs. 51.4+/-1.2 mg/100 g, P<0.05), elevated left ventricular weight (281+/-27 vs. 232+/-5 mg/100 g, P<0.05), reduced pulmonary arterial compliance (35.2+/-2.0 vs. 46.4+/-2.4 microm/mN, P<0.05) and reduced maximal pulmonary vasoconstriction to KCl (1.74+/-0.14 vs. 2.63+/-0.31 mN/mm, P<0.01), and PGF2(2alpha) (1.40+/-0.14 vs. 2.47+/-0.44 mN/mm, P<0.05). Perinatal exposure to hypoxia had a profound effect upon the adult pulmonary circulation, which could predispose to cardiopulmonary diseases in adulthood.

Vasoreactions to acute hypoxia, whole lungs and isolated vessels compared: modulation by NO

We aimed to explain diverse pulmonary vascular responses to hypoxia in different preparations and their modulation by NO. In rats we compared isolated perfused lungs (IPL), small vessels in vitro (PRVs) and in vivo preparations. In IPL and in vivo, acute and chronic nitric oxide synthase (NOS) blockade with L-NAME left normoxic pulmonary artery pressure unchanged but enhanced hypoxic vasoconstriction, hypoxia-induced pulmonary vasoconstriction (HPV). PRVs in vitro, precontracted with PGF(2alpha), showed four tension changes in acute hypoxia: dilatation, contraction, dilatation, contraction. Acute and chronic NOS blockade reduced the first two phases. In non-precontracted PRVs (from other laboratories), NOS inhibition enhanced HPV as in vivo and IPL; attenuation of HPV seems associated with precontraction. Thus reduced NOS activity does not cause pulmonary hypertension but exaggerates HPV. In IPL, prolonged severe hypoxia caused biphasic vasoconstriction separated by dilatation; the time course resembled that seen in PRVs. We suggest that the sequence of events during hypoxia in PRVs can be detected in whole lung preparations.

Adverse pulmonary vascular effects of high dose tricyclic antidepressants: acute and chronic animal studies

Overdose of tricyclic antidepressants, which inhibit cellular serotonin (5-HT) uptake, sometimes causes acute respiratory syndrome-like symptoms. Their acute and chronic cardiopulmonary actions, which might be implicated, utilising both in vivo and ex vivo animal studies, were investigated in this study. Acute amitriptyline (AMI), iprindole and imipramine caused dose-dependent prolonged rises in pulmonary artery pressure and oedema in anaesthetised cats in vivo. Acute AMI, in isolated ex vivo blood-perfused rat lungs, also caused dose-dependent sustained vasoconstriction, which could be attenuated with either calcium channel inhibition or a nitric oxide donor. It was demonstrated that the pressor effects of AMI were not due to release of histamine, serotonin, noradrenaline, or the activities of cycloxygenase or lipoxygenase. After AMI, hypoxic pulmonary vasoconstriction and the pressor actions of 5-HT and noradrenaline were diminished, possibly due to uptake inhibition. Activities of the endothelial-based enzymes, nitric oxide synthase and endothelin-converting enzyme, were undiminished. Large acute doses of AMI caused oedema with rupture of capillaries and alveolar epithelium. Chronic iprindole raised pulmonary artery pressure and right ventricle (RV)/left ventricle (LV) + septal (S) weight. Chronic AMI led to attenuation of the pressor action of 5-HT, especially when associated with chronic hypoxic-induced pulmonary hypertension. RV/LV+S weight increased, attributable to LV decline. The acute and chronic effects observed might have relevance to clinical overdose, while the attenuation of acute effects offers possible therapeutic options.

Effects of radiographic contrast media on pulmonary vascular resistance of normoxic and chronically hypoxic pulmonary hypertensive rats

Intravascular radiographic contrast media (RCM) can be associated with significant morbidity in patients with pulmonary hypertension (PH). This study investigated the direct effect of the four main classes of RCM (high osmolar ionic monomer "diatrizoate"; low osmolar ionic dimer "ioxaglate"; low osmolar non-ionic monomer "iopromide"; and iso-osmolar non-ionic dimer "iotrolan") in ex vivo isolated rat lungs perfused with blood at 20 ml min(-1) under basal conditions (air + 5% CO2 ventilation, pulmonary artery pressure (Ppa) 16-20 mmHg) and when Ppa was raised by hypoxic vasoconstriction in normal rats (2-3% O2+5% CO2 ventilation, Ppa increased by 4-14 mmHg). The effects of low osmolar RCM (ioxaglate, iopromide and iotrolan) were also studied in rats with PH induced by chronic hypoxia (3 weeks 10% O2, Ppa 26-36 mmHg). Increasing volumes (0.05 ml, 0.1 ml, 0.3 ml, and 0.5 ml) of RCM, mannitol (osmolar and pH control) or normal saline (volume control) were added to the 10 ml blood reservoir (n=4-9 per group). In normal rats, RCM caused a dose-dependent slow rise in Ppa. The maximum rise in mean+/-SEM Ppa at the cumulative dose of 0.95 ml was ioxaglate 13.8+/-1.6 mmHg>iotrolan 7.3+/-1.7 mmHg=diatrizoate 9.8+/-2.2 mmHg>iopromide 3.0+/-0.8 mmHg (p<0.05). The rise in Ppa induced by ioxaglate and iotrolan was significantly greater than in the mannitol and saline controls (p<0.05). Pre-treatment with endothelin receptor A/B blockade (SB209670) did not abolish the rise in Ppa induced by diatrizoate (0.95 ml) in the normal rat (3.8+/-1.3 mmHg diatrizoate alone and 3.4+/-1.1 mmHg in the presence of 40 microM SB209670, n=5 per group). When Ppa was raised by acute hypoxia, ioxaglate and diatrizoate (0.5 ml) caused a fall in Ppa (percentage fall -53+/-23 and -118+/-10, respectively, p<0.001) while iotrolan and iopromide caused a small further rise in Ppa, which was significant with iotrolan at a dose of 0.3 ml (percentage rise in pressure 14.2+/-2.3, p<0.05). In chronic pulmonary hypertensive rats, RCM (0.95 ml) caused an overall slow progressive rise in Ppa (iopromide 6.8+/-1.7 mmHg< ioxaglate 11.6+/-2.5 mmHg=iotrolan 12.7+/-1.1 mmHg). However, ioxaglate initially induced an acute fall of Ppa (maximum fall 4.22+/-0.9 mmHg, p<0.05) for almost 20 min. In summary, iopromide induced the least change in Ppa of normal and pulmonary hypertensive rats. The pathophysiology of the effects of RCM on the pulmonary circulation remains uncertain.

The effect of antihistamine, endothelin antagonist and corticosteroid prophylaxis on contrast media induced bronchospasm

Bronchospasm is a well recognized adverse reaction to radiographic contrast media (RCM) and may occur more frequently in asthmatics and atopics. This study was designed to identify RCM which are most likely to cause bronchospasm and to investigate underlying mechanisms mediating this response. Guinea pigs (mean body weight 550 g, n = 46) were anaesthetized with Hypnorm (5 ml kg-1) and Hypnovel (2 ml kg-1) and tracheal, jugular and pleural cannulae introduced. Total airways resistance (Raw) was calculated from the slope of the pressure/flow relationship. The effects of RCM (diatrizoate 370 mgI ml-1, ioxaglate 320 mgI ml-1, iotrolan 300 mgI ml-1 and iopromide 300 mgI ml-1) at a dose of 4 ml kg-1 body weight or control solutions matched for volume, pH and osmolarity administered via the jugular vein on Raw were studied. The effects of pre-treatment (30 min before the administration of RCM) with antihistamine (Mepyramine (30 mg kg-1 i.p.)) or non-selective endothelin receptor antagonist (SB209670 (1 mg kg-1 i.v.)) were investigated. The effectiveness of corticosteroids prophylaxis (prednisolone (20 mg kg-1 i.p.)) administered 18-24 h and 1 h pre-RCM was also assessed. Control animals received normal saline pre-treatment before RCM administration. Lungs were taken for histological examination 30-40 min post-administration of RCM. Only ioxaglate caused a significant (p < 0.05) increase in Raw (5.19 +/- 0.58 to 13.95 +/- 3.53 mmHg ml-1 min-1). Neither mannitol nor saline control solutions had any effect on Raw. Pre-treatment with Mepyramine, SB209670 or prednisolone caused no significant change in the ioxaglate induced increase in Raw. Histological examination of lung tissue from ioxaglate treated animals showed no important abnormalities. In summary, only the ionic dimer ioxaglate caused an increase in Raw. This effect was independent of osmolarity and could be the result of the chemical composition of the contrast agent. It was not an inflammatory response and could not be prevented by prophylactic treatment with antihistamine, endothelin antagonist or corticosteroids. The mechanisms responsible for the increase in Raw remain uncertain.

The haemodynamic effects of iodinated water soluble radiographic contrast media: a review

All classes of iodinated water-soluble radiographic contrast media (RCM) are vasoactive with the iso-osmolar dimers inducing the least changes in the vascular tone. The mechanisms responsible for RCM-induced changes in the vascular tone are not fully understood and could be multifactorial. A direct effect on the vascular smooth muscle cells causing alterations in the ion exchanges across the cell membrane is thought to be an important factor in RCM-induced vasodilatation. The release of the endogenous vasoactive mediators adenosine and endothelin may also play a crucial role in the haemodynamic effects of RCM particularly in the kidney. In addition, the effects of RCM on blood rheology can cause a reduction in the blood flow in the microcirculation. The purpose of this review is to discuss the pathophysiology of the haemodynamic effects of RCM and to offer some insight into the biology of the endothelium and vascular smooth muscle cells as well as the pharmacology of the important vasoactive mediators endothelin and adenosine.

Ventilatory effects of radiographic contrast media

Respiratory adverse reactions have been reported with the use of contrast media. This study investigates the effects of different radiographic contrast media (RCM) on ventilation and blood gases. Tidal volume and respiratory rate of male Wistar rats anaesthetised with Inactin (100 mg kg-1 intraperitoneally), were measured continuously by integration of tracheal airflow. Contrast media (diatrizoate 370, ioxaglate 320 and iopromide 300) or mannitol controls matched for volume, pH and osmolarity (4 ml kg-1) were administered via a jugular cannula (n > or = 6 per group). Carotid artery blood was sampled at 2, 7, 12, 17, 25 and 30 min post-injection for PaO2, PaCO2 and pH. Systemic blood pressure was monitored from the same cannula. No significant reduction was observed in minute ventilation (tidal volume x respiratory rate per minute) with any of the contrast media. All contrast media and control solutions produced a fall in PaO2 within 4 min; returning to basal levels at 10 min (diatrizoate 35.6% (p < 0.05), ioxaglate 15.2% (p < 0.02), iopromide 16.2% (p < 0.01); controls: 17.3% (p < 0.01), 13.5% (p < 0.02) and 12.0% (NS), respectively). The fall in PaO2 induced by diatrizoate was significantly (p < 0.05) larger in comparison to the other groups. Ioxaglate, iopromide and their mannitol controls induced a comparable fall in PaO2. There was a concurrent rise in PaCO2 and fall in pH that reached significance for diatrizoate (p < 0.01). The changes in blood gases with RCM administration cannot be explained by changes in ventilation and may be due to an effect on pulmonary perfusion.

The pulmonary hypertensive fawn-hooded rat has a normal serotonin transporter coding sequence

The coding sequence of the serotonin transporter gene was compared in two strains of rat-the Wistar and the fawn-hooded rat (FHR). The FHR has an inherited platelet storage-pool deficiency and a widespread impairment of serotonin storage. It is also susceptible to systemic and pulmonary hypertension. The FHR provides a model to study the genetics in human systemic and pulmonary hypertension. We measured platelet function in these two strains by measuring incorporation of radiolabeled serotonin into a platelet suspension and found significant differences in serotonin uptake and release. The coding sequence for the serotonin transporter in the FHR has yet to be reported. No differences were found in the predicted amino acid sequence between these two strains of rat, either in the platelet or the lung samples or when compared with the published sequence of the brown rat. We conclude that differences in the primary structure of the serotonin transporter gene do not account for the altered serotonin storage in the FHR strain.

Effects of radiographic contrast media on the tension of isolated small pulmonary arteries

The aim of the study was to establish the direct effects of radiographic contrast media (RCM) on the tension of isolated small pulmonary arteries and to investigate any mediation by nitric oxide (NO) and endothelin (ET). Small pulmonary arteries (0.3-0.6 mm in diameter) from male Wistar rats were mounted in a Cambustion vessel myograph and vessel wall tension recorded. The effects of 10, 20, 40, 80, 150, 200 and 250 mgl mI-1 of diatrizoate, ioxaglate, iopromide and iotrolan and their mannitol osmolar control from basal condition, and when the vessels were preconstricted with prostaglandin F2 alpha (PGF2 alpha) either submaximally (10 microM) or maximally (100 microM), were studied. The constrictor response to diatrizoate (40 mgI ml-1) was tested in the presence of non-selective endothelin receptor antagonist (10 microM SB209670). The dilator response to ioxaglate (80 mgI ml-1) was tested in the presence of L-nitroarginine methyl ester (L-NAME, 100 microM). All RCM caused biphasic changes in tension, a small transient fall (dilatation) followed by a sustained rise (constriction). Mannitol caused constriction only. The potency order of constrictions at 10-40 mgI ml-1 was diatrizoate > iopromide > ioxaglate > iotrolan. When the vessels were preconstricted with PGF2 alpha, RCM caused predominantly dilatation; ioxaglate produced the largest effect (-42.1 +/- 3.1%, n = 12). Mannitol caused constriction only. SB209607 had no effect on the constrictor effect of diatrizoate [41.9 +/- 2.3 alone, 42.1 +/- 2.7 with SB209670, n = 10]. L-NAME had no effect on the dilator response to ioxaglate [-38.2 +/- 1.6 alone, -43.6 +/- 2.2 with L-NAME, n = 8]. It is tempting to postulate that dimeric RCM may cause the least changes in the pulmonary circulation during angiography.

Effect of fenspiride on pulmonary function in the rat and guinea pig

1. Fenspiride is an anti-inflammatory agent that may have a role in reversible obstructive airways disease. Small, but significant, improvements have been seen in airways function and arterial oxygen tension in patients with mild chronic obstructive pulmonary disease. These changes have been attributed to the anti-inflammatory properties of the drug. However, airways function can be improved by other means, e.g. improved ventilation/perfusion ratio or reduced airways resistance. The possibility that fenspiride may have actions other than anti-inflammatory was investigated in two animal species. 2. In the rat, actions on the pulmonary circulation were investigated in the isolated perfused lung, but fenspiride proved to be a poor pulmonary vasodilator, showing only a small reversal of the raised pulmonary artery pressure induced by hypoxia. 3. Ventilation was measured in the anaesthetized rat using whole-body plethysmography. Fenspiride caused no increase in ventilation or changes in arterial blood gases. However, a profound hypotensive action was observed with high doses. 4. The possibility that a decrease in airways resistance (R(aw)) might occur with fenspiride was investigated in anaesthetized guinea pigs. Capsaicin (30 mumol/l) was used to increase baseline R(aw) through bronchoconstriction. Fenspiride gave a dose-dependent partial reversal of the raised R(aw), and its administration by aerosol proved as efficacious as the intravenous route. In addition, the hypotensive side-effect found with intravenous injection was alleviated by aerosolized fenspiride.(ABSTRACT TRUNCATED AT 250 WORDS)

An analysis of the action of an analogue of almitrine bismesylate in the rat model of hypoxic lung disease

Chronically hypoxic (CH) and normoxic control rats were used to assess the action of S9581, a water-soluble analogue of almitrine bismesylate. S9581 increased ventilation (Ve) by 34% in control and 20% in CH rats. During acute hypoxia Ve was raised and S9581 caused a further increase of 20% in both groups. Low doses of S9581 and almitrine enhanced the hypoxic ventilatory response in CH rats while high doses depressed it in both groups. Effects of S9581 on the pulmonary circulation were assessed in the isolated perfused lung of rats. As with almitrine a complex relationship of dose-dependent vasoconstriction and dilatation was revealed. In low doses, S9581 enhanced the hypoxic pulmonary vasoconstrictor response to 2% O2 whilst this was attenuated by high doses in both control and CH rats. S9581 seemed to act like almitrine bismesylate on both the ventilation (peripheral chemoreceptor) and the pulmonary circulation. For studying almitrine-like activity the water solubility of S9581 provides considerable advantages for the researcher.

Interactions between hypoxic and almitrine-induced vasoconstriction in the rat lung

1. To test whether almitrine might improve the arterial partial pressure of O2 in patients with chronic obstructive airways disease by improvement of ventilation-perfusion matching, we looked at the interaction between hypoxic and almitrine-induced vasoconstriction in isolated rat lungs perfused with blood at constant flow. Increases in pressure represented increases in resistance. 2. Almitrine, given in increasing doses between challenges with 2% O2, enhanced hypoxic vasoconstriction at low doses but attenuated it at high doses. 3. Stimulus-response curves to hypoxia of increasing severity gave a sigmoid curve. 4. Almitrine solvent caused small changes in pulmonary artery pressure and shifted the stimulus-response curve slightly in a parallel fashion. 5. Small doses of almitrine enhanced the action of mild to moderate hypoxia, medium doses attenuated moderately severe hypoxia, whereas high doses depressed vasoconstriction due to all degrees of hypoxia. 6. These effects of almitrine on hypoxic vasoconstriction were compared with the effect of solvent by analysis of variance; the results substantiated significant enhancement of hypoxia by small doses and attenuation by large doses. 7. In patients, if similar effects apply, small doses of almitrine would assist ventilation-perfusion matching, but large doses might worsen it. 8. Almitrine-induced vasoconstriction was attenuated by a fall in perfusate temperature in a similar manner to hypoxic vasoconstriction. It was also attenuated by three drugs, chlorpheniramine, propanolol and diethylcarbamazine, all of which also decrease hypoxic vasoconstriction. The similarity between hypoxic and almitrine-induced pulmonary vasoconstriction is further confirmed.

Enhanced reactivity to bradykinin, angiotensin I and the effect of captopril in the pulmonary vasculature of chronically hypoxic rats

We compared the reactivity of pulmonary vessels to bradykinin (BK) and angiotensin I (AI) in normal and chronically hypoxic rats; the latter have pulmonary hypertension and muscularized pulmonary arterioles. These peptides are respectively inactivated and activated by the angiotensin converting-enzyme (ACE) on pulmonary endothelium. Isolated lungs were perfused at a constant flow rate when changes in pulmonary artery pressure (Ppa) reflect changes in vascular resistance. Dose-response curves to BK (1 ng-10 micrograms) were derived during normoxia and pre-constriction by hypoxia; BK both decreased and increased vascular resistance, i.e. vasodilation and vasoconstriction. In normal rats only constriction was seen in normoxia, which reflected low basal vascular tone, whereas in chronically hypoxic rats there was only dilatation which reflected high basal vascular tone. In hypoxia in normal rats, low doses caused dilatation, high doses constriction; in chronically hypoxic rats there was again only dilatation which was larger than in controls. After the ACE-inhibitor captopril, constriction was exaggerated in control rats in both normoxia and hypoxia and took place in chronically hypoxic rats after high doses in both normoxia and hypoxia; oedema often followed. Dose-response curves to AI (1 ng-micrograms) in normoxia showed greatly enhanced pressor responses in chronically hypoxic compared with normal rats, probably attributable to increased sensitivity to angiotensin II (AII) rather than enhanced conversion of AI to AII. Captopril caused a proportionate reduction in responses in both groups of rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced reactivity to bradykinin, angiotensin I and the effect of captopril in the pulmonary vasculature of chronically hypoxic rats

We compared the reactivity of pulmonary vessels to bradykinin (BK) and angiotensin I (AI) in normal and chronically hypoxic rats; the latter have pulmonary hypertension and muscularized pulmonary arterioles. These peptides are respectively inactivated and activated by the angiotensin converting-enzyme (ACE) on pulmonary endothelium. Isolated lungs were perfused at a constant flow rate when changes in pulmonary artery pressure (Ppa) reflect changes in vascular resistance. Dose-response curves to BK (1 ng-10 micrograms) were derived during normoxia and pre-constriction by hypoxia; BK both decreased and increased vascular resistance, i.e. vasodilation and vasoconstriction. In normal rats only constriction was seen in normoxia, which reflected low basal vascular tone, whereas in chronically hypoxic rats there was only dilatation which reflected high basal vascular tone. In hypoxia in normal rats, low doses caused dilatation, high doses constriction; in chronically hypoxic rats there was again only dilatation which was larger than in controls. After the ACE-inhibitor captopril, constriction was exaggerated in control rats in both normoxia and hypoxia and took place in chronically hypoxic rats after high doses in both normoxia and hypoxia; oedema often followed. Dose-response curves to AI (1 ng-micrograms) in normoxia showed greatly enhanced pressor responses in chronically hypoxic compared with normal rats, probably attributable to increased sensitivity to angiotensin II (AII) rather than enhanced conversion of AI to AII. Captopril caused a proportionate reduction in responses in both groups of rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Reactivity and site of vasomotion in pulmonary vessels of chronically hypoxic rats: relation to structural changes

The high pressure muscular pulmonary circulation of chronically hypoxic (CH) rats was compared with the low pressure circuit in control (C) rats; differences were found in the effects of lung inflation, in pressure/flow relations during lung inflation, in reactivity to autocoids, and in responses to pulmonary dilator drugs. Isolated blood-perfused lungs of CH rats (2 to 3 wk in 10% O2) were compared with those of C rats kept in air. High inflation (alveolar) pressure (Palv) caused a rise in pulmonary artery pressure (Ppa) close to delta Palv in both groups; in CH rats, Ppa continued to rise, whereas it adapted to a lower level in C rats. Pressure-flow (P/Q) lines were measured at high and low Palv, all in Zone 2 state. In normoxia, high Palv caused a parallel shift in the P/Q line close to delta Palv in both C and CH rats. However, during hypoxic pulmonary vasoconstriction (HPV), high Palv caused a shift in the P/Q line less than delta Palv in C rats and greater than delta Palv in CH rats. Similar differences between C and CH rats were seen during constriction caused by almitrine, a drug that simulates HPV. Thus, these stimuli affect vessels that are functionally "extra-alveolar" in C rats but functionally "alveolar" in CH rats. We consider whether vasoconstriction by hypoxia and almitrine moves peripherally to the newly muscularized alveolar arterioles that are found in CH rats. Reactivity of lung vessels to bradykinin, angiotensin-1, and platelet-activating factor was greater in CH than in C rats, possibly also associated with muscularization of arterioles in the former.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of almitrine bismesylate on breathing pattern during hypoxia/hypercapnia in rats and ferrets

1. Ventilatory measurements and functional residual capacity (FRC) were recorded from anaesthetized rats and ferrets using a whole body plethysmograph. Simulation of aspects of human chronic obstructive airways disease (COAD) was attempted by making animals acutely hypoxic or hypoxic and hypercapnic by causing them to breath appropriate gas mixtures or by increasing the tracheal resistance or dead-space. Some chronically hypoxic rats, which have muscularized pulmonary arterioles similar to COAD patients, were also studied. 2. In 18 chronically hypoxic (CH) rats and 17 littermate control rats (C), breathing air, doses of almitrine bismesylate caused greater increases in ventilation (VE) in C than in CH rats. FRC, which was initially greater in CH rats, increased significantly in both groups after almitrine. 3. In C rats, breathing hypoxic or hypoxic/hypercapnic gas mixtures caused large increases in VE. Slow infusions of almitrine caused a further increase in VE usually via an increase in tidal volume (VT) but not frequency (f). 4. In two series of rats (n = 9; n = 6) severe and moderate degrees of tracheal obstruction caused a fall in PaO2 and a rise in PaCO2, a fall in VE due to both VT and f and large changes in oesophageal pressure (Poes), which often became positive on expiration. Almitrine infusions usually caused a rise in PaO2, a rise in VT and no change in f; with moderate obstruction, Poes also rose. The results were thought to depend on the balance between improved ventilation and increased O2 demand of the respiratory muscles. 5. Eleven ferrets were made hypoxic and hypercapnic by adding a large dead-space to the trachea. A slow infusion of almitrine caused a significant rise in PaO2 before any significant change in VE was detected; PaCO2 fell at some time during the infusion, but not significantly. The initial significant rise in PaO2, at 2.5 min, was not associated with significant changes in T1 (time of inspiration) and VT/TI. At 5 min VT/TI and PaO2 were all significantly altered. 6. Infusions of almitrine into hypoxic and hypercapnic animals caused improvements in the arterial oxygen tension which were associated with subtle changes in the breathing pattern; inspiratory time and inspiratory flow rate changed in the absence of an increase in total VE. Possible conclusions with respect to the action of almitrine in patients with COAD are discussed.

Effect of alveolar pressure on pulmonary artery pressure in chronically hypoxic rats

The effect on pulmonary artery pressure of a rise in alveolar pressure differed in chronically hypoxic rats (10% O2 for 3-5 weeks) compared with control rats. Chronically hypoxic rats have newly muscularised walls in arterioles in the alveolar region. Isolated lungs of chronically hypoxic and control rats were perfused with blood under conditions in which alveolar pressure was greater than left atrial pressure during both normoxia and hypoxia. Alveolar pressure was the effective downstream pressure. Pressure-flow lines were measured at low and high alveolar pressure (5 and 15 mmHg). During normoxia pressure-flow lines of chronically hypoxic rats had a steeper slope (higher resistance) and greater extrapolated intercept on the pressure axis (effective downstream pressure) than control rats. In both groups of rats the change from low to high alveolar pressure during normoxia caused an approximately parallel shift in the pressure-flow line similar to the change in alveolar pressure. During hypoxia, which led to an increase in slope and intercept in both groups of rats, the effect of a rise in alveolar pressure differed in chronically hypoxic from control rats. In control rats there was a small parallel shift in the pressure-flow line that was much less than the increase in alveolar pressure; in chronically hypoxic rats there was a large parallel shift in the pressure-flow line that was greater than the increase in alveolar pressure. Thus in chronically hypoxic rats hypoxic vasoconstriction probably occurred mainly in muscular alveolar vessels, whereas in control rats it probably occurred upstream in extra-alveolar vessels. At constant blood flow the relation between pulmonary artery pressure and alveolar pressure was measured while alveolar pressure was reduced from approximately 15 mmHg to zero during both normoxia and hypoxia. In control and chronically hypoxic rats the slope of this line was less than 1. At an alveolar pressure of 2-3 mmHg there was an inflection point below which the line was nearly horizontal in control but negative in chronically hypoxic rats. During hypoxia the inflection point increased in control but not in chronically hypoxic rats, whereas the preinflection slope became negative. Apart from a rise in pulmonary artery pressure at all values of alveolar pressure, which occurred in both groups of rats, there was no change in the form of the curve in chronically hypoxic rats during hypoxia. These results also suggest constriction of extra-alveolar vessels in control rats and alveolar vessels in chronically hypoxic rats during hypoxia.

Action of almitrine on the pulmonary vasculature in ferrets and rats

The action of almitrine on pulmonary vessels was studied under constant ventilation during normoxia and hypoxia. We used ferrets, in which one lobe of lung was perfused with venous blood at constant flow rate in vivo and isolated lungs perfused with blood at constant flow in both ferrets and normal and chronically hypoxic (three weeks in 10% O2) rats. Almitrine caused constriction of the relaxed vessels of normoxic lung. During hypoxic pulmonary vasoconstriction, when pulmonary artery pressure (Ppa) was raised, almitrine had a dual action; it caused further constriction followed by dilatation over a wide dose range (0.7-118 micrograms X kg-1 in ferrets). Similar effects were seen in normal and chronically hypoxic rats; the latter have narrowed muscularized arterioles like patients with chronic obstructive airways disease. Almitrine caused a larger rise in Ppa in normoxic than hypoxic rat lungs (7.9 instead of 1.7 mmHg; p less than 0.001) and dilatation followed constriction in the latter. Verapamil reduced both the constrictor action of almitrine and hypoxic vasoconstriction and there was a strong correlation between the effect of the two stimuli before and after verapamil (r = 0.9). Attempts to identify a substance which might cause the dilator action of almitrine were unsuccessful.

Mechanical properties and reactivity of vessels in isolated perfused lungs of chronically hypoxic rats

1. Chronically hypoxic rats kept in 10% (v/v) O2 for 3--6 weeks, were compared with littermate control rats. Pulmonary vascular resistance, measured from the slope of the pressure-flow relationship in isolated lungs perfused with blood of normal packed cell volume was higher in chronically hypoxic than control rats even during normoxia. 2. Chronically hypoxic rats weighed less than control rats but their pulmonary vascular volume, measured with labelled albumin was similar to control rats. This, together with evidence that the number of precapillary vessels is not reduced, does not suggest a large reduction in the vascular bed in chronic hypoxia. 3. A greater vasodilator action of isoprenaline and adenosine in chronically hypoxic than control lungs suggested a higher normoxic vascular tone. This higher tone was not the sole cause of increased resistance in chronically hypoxic lungs, since maximal vasodilatation did not reduce resistance to control levels. The chief cause was probably encroachment of new muscle on the vascular lumen of small vessels. 4. Pulmonary arterial compliance was reduced in chronically hypoxic lungs. 5. Reactivity of vessels to ventilation hypoxia, over a wide range of oxygen tension, to angiotensin II (ANG II) and to adenosine 5'-triphosphate (ATP) was significantly greater in chronically hypoxic than control lungs, but thresholds to these stimuli were not reduced.

H1 and H2 histamine actions on lung vessels; their relevance to hypoxic vasoconstriction

Pulmonary vasomotor actions of histamine and the possible relationship of histamine to hypoxic pulmonary vasconstriction were studied in anaesthetized cats with one lobe of lung perfused at constant flow and in isolated perfused rat and ferret lungs. In the cat histamine caused dilatation, biphasic responses and constriction with increasing doses. Histamine induced dilatation was better demonstrated during hypoxic vasoconstriction and was reduced by an H2 histamine antagonist; constriction with histamine was abolished by an H1 antagonist. Histamine also caused both vasodilatation and vasoconstriction in ferret lungs. A mast cell stabilizing agent had no effect on hypoxic pulmonary vasoconstriction in cats or rats. This response was unaffected in cats but greatly reduced in rats and ferrets by cyproheptadine, a combined histamine and 5-hydroxy-tryptamine inhibitor. It was unaffected in cats but abolished in ferrets an H1 histamine inhibitor. It was again unaffected in cats but greatly reduced in rats and ferrets by an H2 histamine inhibitor. These species differences may reflect differences in mechanism but more probably reflect non-specific effects of the inhibitors in certain circumstances. However, when drugs nearly abolished hypoxic vasoconstriction, ATP still caused vasoconstriction.

The action of hypercapnia during hypoxia on pulmonary vessels

Two opposing actions of CO2 on pulmonary vessels, vasoconstriction and vasodilatation, were studied in dogs, cats, ferrets and rats using isolated lungs or a lobe of lung in vivo. Both preparations were perfused at a constant flow rate so that changes in inflow pressure at constant outflow pressure represented changes in vascular resistance. Lungs were ventilated with 5-15 percent CO2 during hypoxic vasoconstriction in order to permit demonstration of dilatation and because the two stimuli frequently concur. During hypoxia CO2 caused further constriction, dilatation or a biphasic response. Only constriction occurred in dogs and only dilatation in rats. Constriction predominated in cats but dilatation sometimes occurred in later tests in isolated lungs and after a carbonic anhydrase inhibitor. All three responses were seen in ferrets. The type of response did not depend on CO2 concentration. In rats dilatation turned to constriction after beta-adrenoreceptor blocking drugs. The vessels affected by dilatation could not be determined. Thus CO2 can enhance or diminish the action of hypoxia but the circumstances determining one or other action are not resolved.