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D P Richardson

Publications and source records attributed to D P Richardson.

At least 19 recordsLinked to original sources
PubMed2001

Spatial learning in the guinea pig: cued versus non-cued learning, sex differences, and comparison with rats.

This paper provides the first report of spatial learning in guinea pigs using the Morris water maze (MWM). Male and female guinea pigs were trained for 5 consecutive days (8 trials/day; acquisition phase) in either the visible (cued) or the hidden (non-cued) platform version of the MWM. In both tests, guinea pigs learned to navigate to the escape platform, as indicated by a decrease in escape latency over the 5 training days. There were no sex differences in either test version. A comparison of guinea pigs and male Wistar rats showed that performance during acquisition training was not different for the two species in the visible platform test, but rats performed better during the early training days in the hidden platform test. A retention test (probe trial) was given 5 days after the last acquisition training day. Again, there was no sex difference, and no difference between guinea pigs and rats. Finally, acquisition of a new escape response to a shifted platform location was equivalent for rats and guinea pigs of both sexes. These results demonstrate that guinea pigs show robust cued and non-cued learning in the MWM. Both acquisition and retention performance in guinea pigs is similar to that in rats, even though rats appear to have a slight advantage in the acquisition of non-cued, spatial information in this test. We conclude that the MWM provides a valuable paradigm to assess behavior and learning/memory in the guinea pig.

Animals↗
PubMed1995

Detection of aldehydes and their conjugated hydroperoxydiene precursors in thermally-stressed culinary oils and fats: investigations using high resolution proton NMR spectroscopy.

High field (400 and 600 MHz) proton NMR spectroscopy has been employed to investigate the thermally-induced autoxidation of glycerol-bound polyunsaturated fatty acids present in intact culinary frying oils and fats. Heating of these materials at 180 degrees C for periods of 30, 60 and 90 min. generated a variety of peroxidation products, notably aldehydes (alkanals, trans-2-alkenals and alka-2,4-dienals) and their conjugated hydroperoxydiene precursors. Since such aldehydes appear to be absorbed into the systemic circulation from the gut in vivo, the toxicological significance of their production during standard frying practices is discussed.

Aldehydes↗
PubMed1994

Generation of lipid peroxidation products in culinary oils and fats during episodes of thermal stressing: a high field 1H NMR study.

The oxidative deterioration of glycerol-bound polyunsaturated fatty acids (PUFAs) in culinary oils and fats during episodes of heating associated with normal usage (30-90 min at 180 degrees C) has been monitored by high field 1H NMR spectroscopy. Thermal stressing of PUFA-rich culinary oils generated high levels of n-alkanals, trans-2-alkenals, alka-2,4-dienals and 4-hydroxy-trans-2-alkenals via decomposition of their conjugated hydroperoxydiene precursors, whereas only low concentrations of selected aldehydes were produced in oils with a low PUFA content, lard and dripping when subjected to the above heating episodes. Samples of repeatedly used, PUFA-rich culinary oils obtained from restaurants also contained high levels of each class of aldehyde. The dietary, physiological and toxicological ramifications of the results obtained are discussed.

Aldehydes↗
PubMed1994

Cardiovascular actions of dopexamine in anaesthetized and conscious dogs.

1. Arterial blood pressure, heart rate and cardiac contractility were measured in pentobarbitone-anaesthetized mongrel dogs and in conscious, instrumented dogs. 2. In anaesthetized dogs (n = 5), dose-response curves were obtained by intravenous infusion of increasing doses of dopexamine (5-20 micrograms kg-1 min-1). Infusions were administered three times to each animal to determine whether the responses were reproducible. Dopexamine increased heart rate and myocardial contractility and decreased blood pressure. The dose-response curves for dopexamine did not differ significantly over time. 3. In a second group of dogs (n = 6), dose-response curves (5-20 mg kg-1 min-1) were obtained as above and repeated after the administration of amitriptyline (2 mg kg-1, i.v.). Amitriptyline caused a non-significant reduction in the inotropic and chronotropic responses to dopexamine. 4. Control dose-response curves for dopexamine (5-50 micrograms kg-1 min-1) were similarly obtained in a third group of dogs (n = 6), and repeated after bilateral vagotomy and sympathetic denervation of the heart. In these animals, a third dose-response curve for dopexamine was obtained after the administration of ICI 118551 (0.2 mg kg-1, followed by 0.2 mg kg-1 h-1). The chronotropic response to dopexamine was significantly reduced after cardiac denervation. There was a small, non-significant reduction in the inotropic and depressor responses after denervation. Administration of ICI 115881 significantly reduced both the inotropic and chronotropic response to dopexamine and caused a non-significant reduction in the depressor response. 5. The effect of raclopride (0.2 mumol kg-1, p.o.) was investigated by comparison of the dose-response curves for dopexamine in a control group of dogs (n = 6) to those obtained in dogs which had been pretreated with raclopride (n = 5). Raclopride had no significant effect on the cardiovascular responses to dopexamine. 6. In conscious, instrumented dogs (n = 5), pretreated with raclopride, dose-related positive inotropic and chronotropic and depressor responses to dopexamine infusions were recorded. The chronotropic responses in conscious animals were significantly greater than those in the anaesthetized animals.7. The results of this study indicate that both the positive inotropic and chronotropic actions of dopamine are due to a combination of direct, Beta2-adrenoceptor-mediated effects and the baroreceptor reflex response to the depressor action of the drug.

Adrenergic beta-Antagonists↗
PubMed1991

Purification and characterization of ornithine transcarbamylase from pea (Pisum sativum L.).

Pea (Pisum sativum) ornithine transcarbamylase (OTC) was purified to homogeneity from leaf homogenates in a single-step procedure, using delta-N-(phosphonacetyl)-L-ornithine-Sepharose 6B affinity chromatography. The 1581-fold purified OTC enzyme exhibited a specific activity of 139 micromoles citrulline per minute per milligram of protein at 37 degrees C, pH 8.5. Pea OTC represents approximately 0.05% of the total soluble protein in the leaf. The molecular weight of the native enzyme was approximately 108,200, as estimated by Sephacryl S-200 gel filtration chromatography. The purified protein ran as a single molecular weight band of 36,500 in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These results suggest that the pea OTC is a trimer of identical subunits. The overall amino acid composition of pea OTC is similar to that found in other eukaryotic and prokaryotic OTCs, but the number of arginine residues is approximately twofold higher. The increased number of arginine residues probably accounts for the observed isoelectric point of 7.6 for the pea enzyme, which is considerably more basic than isoelectric point values that have been reported for other OTCs.

Amino Acids↗
PubMed1991

The effects of neuropeptide Y on myocardial contractility and coronary blood flow.

1. This study was designed to assess the effects of exogenous neuropeptide Y (NPY) on cardiac contractility and coronary blood flow (CBF) in anaesthetized dogs and to evaluate the effect of NPY on the responses to sympathetic and parasympathetic stimulation and to inotropic agents. 2. Bolus doses of NPY (500 micrograms), administered via the femoral vein, increased mean arterial pressure. The pressor effect was associated with reductions in heart rate, CBF and cardiac contractility. 3. The effects of NPY (500 micrograms) on contractility and CBF were compared with that of vasopressin (VP) (1 unit). For similar reductions in CBF, NPY and VP had similar negative inotropic effects. Thus, it is likely that the negative inotropic response to NPY is not due to a direct effect of NPY on the heart muscle but is largely due to coronary vasoconstriction. 4. In the presence of NPY (500 micrograms, i.v.), there was an inhibition of the positive inotropic response to stimulation of the left cardiac sympathetic nerve (2 or 5 Hz, 0.05 ms). NPY also inhibited the negative inotropic response and chronotropic response to vagal stimulation (2, 3 or 5 Hz, 0.05 ms). 5. Dose-response curves were obtained for the inotropic, chronotropic and pressor responses to cumulative infusions of noradrenaline (n = 6) and dobutamine (n = 6). NPY had no effect on these dose-response curves. 6. The effect of NPY on the responses to salbutamol and impromidine was assessed. NPY did not alter the positive inotropic, chronotropic or depressor responses to these agonists. 7. Our results indicate that NPY has direct, postsynaptic vasoconstrictor activity and the reduction in myocardial contractility and heart rate are due to a combination of coronary vasoconstriction, baroreceptor reflex activation and presynaptic inhibition of transmitter release from sympathetic nerves. The welldocumented inhibitory effect of NPY on the chronotropic response to parasympathetic stimulation was confirmed and similar inhibition of the inotropic response to both sympathetic and parasympathetic stimulation was demonstrated. Since there was no modulation of the inotropic effects of exogenous alpha- and beta-adrenoceptor or H2-receptor agonists, it is concluded that the effects of NPY on myocardial contractility are exerted presynaptically.

Albuterol↗
PubMed1990

Increased sensitivity to isoprenaline following digoxin pretreatment in anaesthetised and conscious dogs.

STUDY OBJECTIVE: The aim of the study was to evaluate the effect of chronic digoxin therapy on cardiac sensitivity to isoprenaline. DESIGN: Responses to isoprenaline were examined in both conscious and anaesthetised dogs pretreated with digoxin, and compared with conscious or anaesthetised controls with no digoxin pretreatment. Isoprenaline infusion (0.001-0.1 micrograms.kg-1.min-1) in pretreated groups was performed 7 d after digoxin dosing was stopped, when plasma digoxin concentrations were zero. SUBJECTS: Mongrel dogs of either sex (15-25 kg) were used in the experiments, done under anaesthetic. They were divided into three groups (n = 6 per group): group A were controls; groups B and C were pretreated with digoxin 500-750 micrograms.d-1, for 14 d (B) and 7 d (C). For the experiments in conscious animals, six mongrel dogs (25-30 kg) and two greyhounds (25-30 kg) were used; group D (n = 6) were treated with digoxin for 20-40 d; group E (n = 2) were treated for 7 d. MEASUREMENTS AND RESULTS: Heart rate, blood pressure and myocardial contractility (dP/dt: integrated isometric tension) were measured during isoprenaline infusion. Digoxin pretreatment for 14 d did not significantly change the chronotropic or depressor responses to isoprenaline in anaesthetised dogs but there was a 10-fold increase in inotropic sensitivity to isoprenaline following withdrawal. When the pretreatment period was reduced to 7 d there was no change in any of the responses to isoprenaline. In conscious dogs there was also a significant increase in inotropic sensitivity to isoprenaline after digoxin withdrawal, but this was not so marked as in anaesthetised dogs. In conscious dogs chronotropic sensitivity to isoprenaline was also increased. CONCLUSIONS: It is possible that the inotropic effect maintained during the 2 weeks of digoxin treatment may cause substantial withdrawal of sympathetic tone to the heart, with a consequent increase in beta adrenoceptor number or sensitivity, which could be detected a week after digoxin withdrawal.

Anesthesia, General↗
PubMed1987

Positive inotropic effects of histamine in anaesthetized dogs.

1 The cardiovascular effects of histamine were examined in dogs anaesthetized with pentobarbitone 2 The effect of histamine on heart rate, blood pressure, left ventricular pressure, dP/dtmax and dP/dt: IIT (integrated isometric tension) was compared in the presence and absence of autonomic reflexes and blood pressure control. 3 In innervated animals with no attempt to control blood pressure, histamine produced dose-dependent decreases in blood pressure and heart rate and either positive or negative inotropic actions. 4 When autonomic reflexes were abolished, this variability in inotropic response was reduced and histamine produced a slight positive inotropic response. There was a decrease in blood pressure and a positive chronotropic response to histamine. 5 When blood pressure was controlled and the cardiac nerves were intact, histamine produced a decrease in heart rate. However, in the denervated animals, there was a slight increase in heart rate. 6 Inotropic responses to histamine in the blood pressure controlled groups were less variable than when blood pressure was uncontrolled. In all of these animals there was an increase in contractility, the increase being more marked in the denervated group. 7 The H2-receptor agonist impromidine produced a positive inotropic action in intact animals with uncontrolled blood pressure.

Anesthesia↗
PubMed1983

Iron absorption from a malted cocoa drink fortified with ferric orthophosphate using the stable isotope 58Fe as an extrinsic label.

The potential use of an extrinsic label to measure iron absorption from a ferric orthophosphate-fortified malted cocoa drink was examined by measuring the solubility of the FePO4 in 0.1 M-hydrochloric acid. The validity of using the stable isotope 58Fe as an extrinsic label was tested by comparing Fe absorption by rats from wheat flour extrinsically-labelled with 58Fe or 59Fe. Fe absorption from a malted cocoa drink (20 g powder made up with hot water) fortified with FePO4 (0.5 mg Fe/g powder) was measured in human subjects using 58Fe as an extrinsic label. Absorption was calculated by measuring unabsorbed 58Fe in faeces. Absorptions of Fe from the drink fortified with either FePO4 or ferrous sulphate were compared. The effect of the addition of ascorbic acid to the drink (1 mg/g powder) on Fe availability was also examined. The effect of fasting on Fe absorption from the drink was determined in rats by giving the drink to fasting animals or shortly after they had consumed a small meal. The FePO4 was totally soluble in 0.1 M-HCl and there were no differences in absorption between 58Fe- and 59Fe-labelled wheat flour. In the human experiment the proportion of Fe absorbed from the drink plus FePO4 and ascorbic acid was (mean with SE) 0.25 (0.02), from the drink plus FePO4 0.24 (0.02) and from the drink plus FeSO4 0.23 (0.03). Fasting had a significant effect on Fe availability; rats given the drink shortly after a small meal absorbed less than half as much Fe as those given the drink on a fasted stomach. It was concluded that the FePO4 used to fortify the malted cocoa drink was as well absorbed as FeSO4 but that the high levels of absorption were a reflection of the fasting condition of the subjects. The level of ascorbic acid was not great enough to enhance the availability of the FePO4 any further.

Adult↗
PubMed1983

The selectivity of beta-adrenoceptor antagonists on isoprenaline-induced changes in heart rate, blood pressure, soleus muscle contractility and airways function in anaesthetized cats.

The beta-adrenoceptor antagonist of propranolol, metoprolol, atenolol and butoxamine in anaesthetized cats has been measured and compared with the activity of four synthetic phenylethanolamine derivatives. The effects of isoprenaline on four parameters in the anaesthetized cat: heart rate, blood pressure, soleus muscle contractility and airway reactance, were measured and the modification of the isoprenaline dose-response relation by each of the antagonist drugs assessed. Parallel shifts in log dose-response curves for isoprenaline were caused by propranolol for all parameters, by metoprolol and atenolol for each parameter except blood pressure, and butoxamine for each except soleus muscle and heart rate. Selectivity of action of the antagonists between different organs was measured by comparing DR10 values, computed from isoprenaline dose-ratios. Propranolol was the most potent antagonist and showed slight selectivity of action on soleus muscle compared with heart. Atenolol and metoprolol were approximately equipotent and were cardioselective at low doses only. Butoxamine was the least potent antagonist and possessed non-beta-adrenoceptor effects on the parameters measured. Each of the new compounds, 4'-bromo-2'-methoxy-N-isopropyl phenylethanolamine, the 4'-chloro- and 4'-methyl analogues, and 4'-methoxy-N-t-butyl phenylethanolamine, was a potent antagonist but did not exhibit any selectivity of action. The results suggest no clear separation of beta-adrenoceptors into beta 1- and beta 2-subclasses in organs of the cat. There is no apparent separation of beta-adrenoceptor-mediated effects on skeletal muscle and airways.

Adrenergic beta-Antagonists↗