Wg Zijlstra

SPECTROPHOTOMETRY OF HEMOGLOBIN AND HEMOGLOBIN DERIVATIVES

Publisher Summary This chapter presents a discussion of spectrophotometry of hemoglobin and hemoglobin derivatives. Many special photometers (hemoglobinometers, oximeters, etc.) presently available for the determination of hemoglobin and hemoglobin derivatives are mentioned only incidentally. Numerous (spectro) photometric methods are developed for the determination of oxyhemoglobin, either as oxyhemoglobin fraction or as oxygen saturation. Many conventional two-wavelength spectrophotometric methods are available, most of them involving the use of an isobestic point in the absorption spectra of Hb and HbO 2 —for example, a wavelength at which the absorptivity of the two components has the same value. This yields a single, linear relationship between the oxygen saturation and the ratio of the light absorbances of the sample at the two wavelengths used. All methods for the spectrophotometric determination of hemoglobin derivatives depend on the validity of the Lambert-Beer law. Many two-wavelength methods are also used in the determination of common dyshemoglobins in human blood (HbCO, Hi, SHb). In all of these methods, the samples undergo some kind of pretreatment so that, besides the dyshemoglobin species to be determined, only one other hemoglobin derivative is present.

Composition of postnatal weight loss and subsequent weight gain in small for dates newborn infants

ABSTRACT. Using a sucrose and deuterium oxide dilution technique body water compartments and solids were serially determined in small for dates newborn infants at birth, at the moment of maximum postnatal weight loss and on recovery of birth weight. Compositions of weight loss and subsequent weight gain were calculated from the differences in body water compartments and solids between the first and the second and the second and the third study, respectively. Birth weight of the infants was 1.55 ± 0.46 kg (mean ± SD) (n=7). gestational age was 35.7 ± 3.1 weeks. Results show that despite changes in extra‐ and intracellular water volumes during weight loss, total body water volume and solids per unit of body weight remained remarkably constant throughout the study. Compositions of weight loss and subsequent weight gain were simlar to body composition. This suggests that in small for dates newborn infants postnatal weight loss is the result of catabolism rather than dehydration and subsequent weight gain is the result of growth rather than rehydration.

Metabolic and hormonal responses to adrenoceptor antagonists in exercising rats.

alpha- and beta-adrenoceptors play a key role in the regulation of nutrient supply to working muscles during exercise. To assess their influence in the regulation of substrate utilization, rats were studied during alpha- or beta-adrenoceptor blockade. Energy metabolism was studied by means of indirect calorimetry before, during, and after moderate swimming exercise. Blood samples were taken for the determination of nutrient and hormone concentrations. In addition, central venous blood samples were withdrawn for determination of blood gases, pH, and total hemoglobin concentration (c/Hb). alpha- and beta-adrenoceptor blockade decreased the rates of energy expenditure (EE) and fat oxidation (fat-ox) during and after swimming in comparison to swimming without adrenoceptor blockade. The oxidation of carbohydrates (CHO-ox) was increased in both cases. alpha-Blockade prevented the exercise-induced increase in blood glucose, plasma free fatty acids (FFA) were not affected, and plasma insulin, norepinephrine (NOR), epinephrine (EPI), and lactate were markedly increased. beta-adrenoceptor blockade prevented the exercise-induced increases in blood glucose and FFA. EPI increased slightly more than and NOR less than in the control experiment. The exercise-induced decrease in insulin was more pronounced after beta-blockade. alpha-Blockade caused a less pronounced decrease in venous oxygen saturation (SO2) and tension (PO2) than in the control experiment. The exercise-induced increase in carbon dioxide tension (PCO2) was almost absent. After beta-blockade, venous SO2 and PO2 decreased more and PCO2 increased more than in the control experiment. It is concluded that both alpha and beta-blockade restrict the rate of EE during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Incomplete Cardiac Vagal Blockade with Atropine in the Anesthetized Dog

SummaryIn dogs in neurolept-anesthesia the successive administration of α- and β-adrenergic blocking agents and atropine, which should cause the functional equivalent of surgical denervation of the heart, always results in a marked tachycardia. The same is observed in conscious dogs, but not during methoxyflurane anesthesia. Bilateral vagotomy and administration of hexamethonium abolish the tachycardia. These observations demonstrate the presence of a vagally mediated chronotropic effect which becomes manifest when the inhibitory vagal effect is eliminated through blockade of the muscarinic receptors with atropine.

Standardized Induction of Myocardial Ischaemia in the Dog

Ischaemia in the entire left ventricular wall was induced in dogs by installment of ameroid constrictors on the left anterior descending (LAD) and left circumflex (LC) branches of the left coronary artery (series A). Ischaemia in the anterior left ventricular wall was induced by installment of an ameroid constrictor on LAD and ligation of all (series B) or part of (series C) the subepicardial intercoronary anastomoses between LC and LAD. The effect of the operation was studied by electrocardiography and coronary angiography and, post mortem by radiography of the coronary arteries and histopathology of myocardium and coronary arteries. The high early mortality rate in series A and B precludes the further use of these procedures. In series C the mortality rate was low and in half of the cases lasting myocardial ischaemia of the anterior wall of the left ventricle was produced. The development of a small myocardial infarction was inevitable, but it was healed by the time the sought after state of stable myocardial ischaemia was reached.

METABOLIC AND HORMONAL RESPONSES TO ADRENOCEPTOR ANTAGONISTS IN 48-HOUR-STARVED EXERCISING RATS

The influence of 48 hours of starvation on sympathoadrenal regulation of nutrient utilization was investigated in rats. To assess the role of alpha- and beta-adrenoceptors, rats were studied during alpha- and beta-blockade. Energy metabolism was measured using indirect calorimetry before, during, and after moderate swimming exercise (approximately 60% maximal O2 consumption [VO2max]). Additionally, blood samples were taken for determination of nutrient and hormone concentrations. In 48-hour-starved rats, under baseline conditions, there was a reduction in energy expenditure (EE) accompanied by a shift toward fat oxidation (fat-ox) in comparison to fed rats. Exercise-induced responses in EE, fat-ox, and carbohydrate oxidation (CHO-ox) did not differ from those in fed rats. In starved rats, a stronger response to exercise of the sympathoadrenal system was observed. In comparison to control 48-hour-starved rats, blockade of alpha- and beta-adrenoceptors led to a reduction in the exercise-induced increase in EE and fat-ox. The rate of CHO-ox was slightly reduced after blockade of either adrenoceptor type. Alpha-blockade prevented the exercise-induced increase in blood glucose. Plasma free fatty acid (FFA) was not affected. Blood lactate, plasma insulin, norepinephrine (NOR), and epinephrine (EPI) were increased after alpha-blockade. Due to beta-blockade, exercise-induced increases in glucose and FFA were prevented. Blood glucose even declined below the baseline value. EPI showed an exaggerated increase, and NOR showed a smaller increase. Results obtained in starved rats support the idea that alpha-adrenoceptor blockade-induced changes in energy metabolism are the result of a diminished oxygen supply due to diminished circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

CARDIOACCELERATORY EFFECT OF MUSCARINIC BLOCKING-AGENTS IN THE DOG

To test whether the tachycardia in response to atropine after adrenergic blockade is partly due to a central excitatory action, the effects of atropine, methylatropine and methylscopolamine were compared in dogs in neurolept-anesthesia. The latter two agents proved to have effect, similar to atropine. A central action is therefore improbable. It was possible to partly abolish the tachycardia by hexamethonium. The cardioacceleration by atropine, methylatropine and methylscopolamine, so far as it is not caused by muscarinic receptor blockade, can be explained by the unmasking of an underlying acceleratory tone.

ACUTE CIRCULATORY EFFECTS OF DOXORUBICIN IN THE CONSCIOUS DOG

Experimental work on the mechanisms of acute doxorubicin-induced cardiotoxicity may contribute to a better understanding of the clinical problem of cardiac failure after treatment with anthracycline derivatives. We studied aortic pressure and heart rate continuously for 1 h following a bolus injection of doxorubicin (1 mg/kg) in 7 dogs. In contrast with previous studies in intact animals, no anesthesia was used in order to eliminate possible interactions of doxorubicin with other drugs. One minute after doxorubicin injection a severe hypotension was observed, the average nadir in systolic and diastolic pressure being 62% and 42% of initial values. Surprisingly, the decrease in arterial blood pressure was not accompanied by cardiac acceleration. Doxorubicin, apparently interferes with the normal regulation of heart rate through the baroreceptor control system. Although several theories have been put forward regarding the mechanisms governing acute anthracycline cardiotoxicity, our knowledge of the phenomenon is still incomplete.

Influence of high-dose methotrexate on the distribution of body fluid volumes in the dog

SummaryWe studied the influence of high-dose methotrexate (HDMTX) on body fluid volumes in the dog, using indicator dilution techniques. In six healthy mongrel dogs total body water volume (TBW), extracellular water volume (ECW), body mass, and plasma osmolality were measured before and after infusion of both saline and HDMTX. TBW and ECW were determined simultaneously, using a double-indicator (D2O/ferrocyanide), single injection technique. In vitro experiments confirmed the reliability of ferrocyanide as an indicator for ECW, also in the presence of methotrexate. Results showed an increase in ECW after HDMTX (P=0.029, paired Students t-test), while TBW remained constant. Infusion of the same volume of isotonic saline in the control experiments did not result in any demonstrable change in either TBW or ECW. Therefore, infusion of HDMTX appears to cause a water shift from the intracellular to the extracellular compartment. Such a change in body water volumes may have implications for estimates of body composition and for pharmacokinetic studies in cancer patients receiving HDMTX.

CYTOSTATIC AGENTS AND BODY-FLUID VOLUMES IN THE HEALTHY DOG

We hypothesized that cytostatic agents per se, apart from the malignancy, may have an effect on body water distribution. The influence of high dose methotrexate (HDMTX) and doxorubicin on body fluid volumes in the dog was investigated. Firstly, total body water (TBW), extracellular water (ECW), body weight and plasma osmolality were measured in six healthy mongrel dogs with permanent catheters in aorta and pulmonary artery, before and after infusion of isotonic saline and HDMTX (dose=250 mg/kg in isotonic solution), respectively. TBW and ECW were determined simultaneously, using a double indicator (D2O/ferrocyanide), single injection technique. D2O was determined in red cells by an infrared spectrophotometric method; ferrocyanide (hexacyanoferrate II, Fe(CN)64∼) levels were spectrophotometrically assessed in plasma. One hour after HDMTX infusion we observed a increase in mean ECW from 225 to 244 ml/kg body weight (p=0.011, paired Students t-test); this is an increase of 8.4 %. Mean TBW remained the same. The increase in ECW could not be explained by a simple volume effect as an equal volume of saline did not yield a significant change in extracellular fluid volume. Plasma osmolality decreased only 1% and therefore a simple osmotic mechanism was unlikely to have caused the observed fluid shift. No other drugs, known to influence water distribution, e.g. barbiturates, were administered. Results suggest a water shift across the cell membrane due to an effect of HDMTX. Similar experiments using doxorubicin (1 mg/kg) did not show any significant change in either TBW or ECW.