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Biomedical subjects

A Trzebski

Publications and source records attributed to A Trzebski.

83 records · Page 5Linked to original sources
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The local effect of pH changes in the cerebrospinal fluid on the ventrolateral areas of medulla oblongata and on the spinal cord surface on the activity of cardiac and vertebral sympathetic nerves.

Application of acid cerebrospinal fluid at pH 6.8 to the ventral surface of the medulla oblongata in cats increased the arterial blood pressure and the activity of the vertebral nerve and enhanced respiratory modulation of the vertebral and cardiac nerves. Alkaline cerebrospinal fluid at pH 7.7 applied to the ventral surface of the medulla oblongata increased the arterial blood pressure without changes in the sympathetic nerve activity. When the spinal cord was superfussed with artificial acid cerebrospinal fluid at the Th1 level the activity of the vertebral nerve and cardiac nerve increased and the arterial blood pressure rose. The authors discuss the possibility of regulation of the activity of sympathetic neurons in the medulla and spinal cord by means of direct action of pH and pCO2 on the neurons, or through an indirect effect mediated by superficial chemoreceptors of the medulla oblongata. The role of local changes of the brain blood flow in the mechanism of these results is discussed as well.

Animals↗
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Influence of alpha and beta adrenergic receptors blockade on the adrenolytic effect of muscular work.

The changes in the response of adrenergic receptors alpha and beta in the blood vessels in the working muscles in a hindlimb in cats were studied after intra-arterial administration of noradrenaline, isoprenaline and during electric stimulation of the sympathetic trunk. The experiments were carried out during alpha-adrenergic receptors blockade with dihydroergotamine (0.3 mg/kg) beta-adrenergic receptors blockade with propranolol (1 mg/kg) and blockade of acetylcholine M receptors with atropine (0.5 mg/kg). The investigations were performed at rest, during exercise (electric stimulation of the sciatic nerve) and after the exercise. The following results deserve attention: 1) beta-adrenergic receptors blockade reduced significantly the alpha-adrenolytic effect of exercise restoring the ability of blood vessel to constriction in response to noradrenaline; 2) the vasodilator effect of isoprenaline evident in resting state and maintained to some extent during exercise was abolished completely by preceding alpha-adrenergic blockade. The changes in the reactivity of resistance vessels in working skeletal muscles to noradrenaline, with abolition of its vasoconstrictor effect, have been shown by Rein [7] and others authors [2, 5]. Similarly, it is well known that the resistance vessels contain two types of adrenergic receptors alpha and beta, and that the response of the vessels to stimulation of these receptors are different [1]. In view of the recently published observations of Jarhult and Lundvall suggesting that the beta-adrenergic receptors play an important physiological role [6] in the arterial part of the microcirculation [6] and in view of the hypothesis put forward by Kunos and Szentivanyj that alpha and beta receptors can be transformed depending on the intensity of tissue metabolism [8] it seemed worth while to study more systematically the changes of the reactivity of alpha and beta adrenergic receptors in the vascular bed of the skeletal muscles during and after muscle exercise.

Animals↗
PubMedDate not supplied

Role of the adrenergic receptors in the central mechanism of the cardiovagal component of the arterial baroreceptor reflex.

The effects of clonidine (1.5 mcg/kg of body weight), L-DOPA (4 mg/kg) and propranolol (0.1 mg/kg) on the reflex bradycardia caused by stimulation of the arterial baroreceptors were studied in 46 waking cats in encephale isole preparations. The drugs were administered into the vertebral artery. They increased the gain of the cardiovagal reflex from the arterial baroreceptors by 162%, 162.5%, 150% respectively with regard to the control values. A similar effect of clonidine and propranolol was manifested also in cats with spinal cord destroyed between the segments C1 to Th12. The effects of clonidine and L-DOPA on the cardiovagal component of the reflex were abolished by aceperon (4 mg/kg) injected into the vertebral artery.

Animals↗
PubMedDate not supplied

Chronotropic response of isolated guinea pig atria to alterations in pCO2, bicarbonate, and pH.

The effect of respiratory and metabolic alterations of extracellular pH on the rate of spontaneous contractions of isolated atria of guinea pig hearts was examined using a CO2HCO3 buffer system. The rate of contractions increased with the increase in pH in the range of 6.8 to 8.25. Respiratory and metabolic alterations of pH produced quantitatively similar chronotropic responses. However, time-course of rhythm change was significantly faster during respiratory alterations of pH. When perfusate pCO2 and bicarbonate were simultaneously raised at constant pH, the rate of contractions initially fell and then returned to the control value. On the return to control solution a rapid rise in the rate of contractions was followed by a slow return to the control value. We conclude that the chronotropic responses to acid-base alterations are mediated by changes in the intracellular pH.

Acid-Base Equilibrium↗
PubMedDate not supplied

Circulatory responses to acute hypoxia in spontaneously hypertensive and normotensive rats.

Experiments were carried out on 6-7 months old spontaneously hypertensive rats (SHR) (NIbm) of the Okamoto-Aoki strain and age matched normotensive control rats (NCR) of the same age group. Acute hypoxia produced bradycardia and a fall of blood pressure in artificially ventilated NCR and a biphasic heart rate response (acceleration-deceleration) in SHR. After bilateral vagotomy or atropine administration a pressor response to hypoxia occurred in NCR and SHR. We conclude that adult SHR exhibit reduced sensitivity of the cardio-vagal component of the arterial chemoreflex.

Acute Disease↗
PubMedDate not supplied

Influence of clonidine upon sympathetic component of the carotid chemoreceptor reflex.

The central influence of clonidine on the sympathetic component of carotid chemoreflex was verified in chloraloseurethane anaesthetised cats. The electrical stimulation of sinus nerve evoked only the excitatory responses in the sympathetic cardiac and renal nerve in the full range of stimulus strength. The excitatory response in the sympathetic renal nerve was completely depressed during the central cardiodepressor action of clonidine. Taking into account that the evoked excitatory responses in the sympathetic nerves were mainly the result of chemoreceptor carotid afferent fibre stimulation, it was concluded that clonidine depresses centrally carotid chemoreceptor reflex.

Animals↗
PubMedDate not supplied

Effect of osmotic stimuli on the carotid baroreceptor and chemoreceptor discharges in cats.

In 15 cats under chloralose-urethan anaesthesia carotid sinus area was arterially isolated and perfused with artificially pulsatile pressures. Solutions of NaCl, of various osmolality, mannitol, glucose and bicarbonate were locally perfused through the isolated carotid area and the single baroreceptor and chemoreceptor fibre activity was recorded with standard technique. An increase in the osmolality of the perfused fluid evoked an increase of the single baroreceptor discharge. Each pulse pressure produced more spikes of higher frequency in big A type baroreceptor fibres. Clear effects were observed during perfusion of 300 mM NCl solutions. Solutions of higher osmolility transformed rhythmical pulse pressure discharge into continuous baroreceptor firing. The excitatory effects of hyperosmolar solutions were reversible after switching to the perfusion fluids of normal osmolality. An increased activity was also observed in the single carotid chemoreceptor fibres. It is concluded that both baro- and chemoreceptors are sensitive to osmotic stimulation.

Animals↗
PubMedDate not supplied

Effect of bilateral lesions of the solitary tract nucleus on arterial blood pressure in spontaneously hypertensive rats of Okamoto strain.

Bilateral electrolytic lesions of the solitary tract nucleus in control Wistar albino rats as well as in Okamoto rats with spontaneous arterial hypertension caused a considerable rise in the arterial blood pressure. Quantitative comparison of blood pressure rise in normotensive and hypertensive rats demonstrated that the rise in the systolic and mean blood pressure was not significantly different in both groups of animals. However, the rats with spontaneous hypertension reacted, with a greater rise in the diastolic pressure. A characteristic feature observed in the normotensive rats was a high rise in pulse pressure following lesion of the solitary tract nucleus while in the rats with spontaneous hypertension this change was not found. The authors conclude that increased peripheral vascular resistance in the rats with spontaneous hypertension is not due to inhibition or resetting of the baroreceptor reflex.

Animals↗