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Biomedical subjects

R Tirri

Publications and source records attributed to R Tirri.

At least 37 records · Page 2Linked to original sources
PubMed1982

Inhibitory adrenergic control of heart rate of perch (Perca fluviatilis) in vitro.

1. Adrenaline and noradrenaline, but not isoprenaline or phenylephrine, showed a negative chronotropic effect on the isolated perch heart. 2. This adrenergic effect was blocked by an alpha-adrenergic antagonist, phentolamine, but not by a beta-blocker, propranolol, suggesting the role of alpha receptors in this action. 3. When a ligature between the atrium and the ventricle was used, adrenaline inhibited the beating of the atrium but not of the ventricle. This suggests that the negative chronotropic effect occurred in the whole heart through an atrial pacemaker (sinus node). 4. The sensitivity of the heart to the adrenergic effect was temperature-dependent and greater at low test temperature. At 15 degrees C pD2 for noradrenaline was 6.45 +/- 0.20 and for adrenaline 6.33 +/- 0.20. At 24 degrees C the values were 5.44 +/- 0.12 and 5.67 +/- 0.15, respectively.

Animals↗
PubMed1982

Characterization of contractions in mechanically and enzymatically isolated myocardial cells from the rat heart ventricles.

Single spontaneously beating myocardial cells were prepared by mechanical or enzymatical isolation. Using a TV camera and videotape recorder, beating parameters were characterized in different buffer solutions in regard to temperature and integrity of sarcolemma, which was tested by ability of cells to exclude a vital stain, Evans blue. The mechanically disaggregated cells were totally permeable to this stain, but about 60% of the enzymatically isolated myocytes were able to exclude the stain. The myocytes prepared in the presence of calcium were most tolerant to physiological concentration of calcium. Contractions were mainly of phasic type where the velocity of contraction wave was very slow (50-330 microns/s). The velocity was not correlated to the beat rate. Temperature dependence of the velocity was positively correlated with the integrity of sarcolemma. Beat rate was inversely related to the integrity of sarcolemma being slowest in calcium tolerant enzymatically isolated cells. Beat rate of calcium sensitive myocytes was higher but unstable and the temperature dependence of the rate was steeply reduced and even reversed during the incubation. Some calcium tolerant myocytes generated occasionally an electric type of contraction which came in bursts and was characterized by synchronous sarcomere shortening without any contraction wave.

Animals↗
PubMed1981

Cholinergic responses in different sections of rat airways.

Effect of cholinergic agonists on rat airway smooth muscle were studied, 4 different preparations were used: the trachea and the bronchus representing the extrapulmonary airways, the bronchiole and the parenchymal strip representing the intrapulmonary airways. The dose-dependent isometric contractile responses of these 4 preparations to acetylcholine (ACh) and carbacholine (CCh) were determined. A significant difference in sensitivity to both ACh and CCh was observed between the extrapulmonary and intrapulmonary airways. When pD2-values of these preparations were compared, the trachea and the bronchus showed to be 10--100 times more sensitive to these drugs than the bronchiole and the parenchymal strip. A significant difference between the trachea and the bronchus was also found in the pD2-values to ACh, the bronchus being more sensitive than the trachea. This difference in sensitivity was probably due to a greater activity of cholinesterase (ChE) in the tracheal tissue, for the difference was not seen in response to ACh with physostigmine or to CCh. It is suggested that there are more cholinergic receptors in the tracheal and bronchial smooth muscles than in the muscles of the bronchioles and the parenchymal tissue.

Acetylcholine↗
PubMed1980

Characterization of contractions in mechanically disaggregated myocardial cells from the rat.

Myocardial cell groups, mechanically disaggregated from the rat heart, beat spontaneously in a medium which resembles intracellular fluid. The cells, initially functioning in an uncoordinated way, i.e. each cell in its own rhythm, gradually become coordinated as a function of time. After 90 min of incubation at 15 degrees C all the cell groups were functioning in a coordinated way. The initiation of coordination was temperature-dependent. Lowering the temperature from 15 degrees C to 10 degrees C significantly delays the coordination, only 75% of the cell groups being coordinated after 90 min. The contraction wave in coordinated cell groups was very slow; 90 +/- 7 micrometers/s at 20 degrees C, 100 +/- 6 micrometers/s at 30 degrees C and 100 +/- 7 micrometers/s at 35 degrees C. The velocity of contraction waves was not significantly temperature-dependent, suggesting a neonenzymatical type of propagation. It also seems too slow to be an electrical event. Apparently the contraction waves are propagated by diffusion of Ca2+. The addition of caffeine to the medium hastened the coordination of contractions, but Na-azide strongly inhibited it. The results indicate that the sarcoplasmic reticulum functions in the coordination of contractions, probably by releasing Ca2+ for the activation of the myofilaments.

Animals↗
PubMed1977

Alpha-receptor subsensitivity of isolated atria from rats following physical training or repeated ACTH-injections.

Decreased chronotropic and inotropic sensitivity of isolated atria to phenylephrine but not to isoprenaline was found in rats following repeated physical training by swimming or repeated ACTH-injections. These changes were induced within a week of subjection of animals to these treatments. It is concluded, that these effects are mediated by increased adrenergic activity which results in this subsensitivity of alpha-receptors.

Adrenocorticotropic Hormone↗
PubMed1976

The effect of cyclophosphamide on the experimental inflammation induced by the toxic mushroom Cortinarius speciosissimus in the rat kidney.

A single intraperitoneal dose of cyclophosphamide (150 mg/kg) given at the same time as an oral dose of Cortinarius speciosissimus prevented the renal inflammation induced by this toxic mushroom in the male rat. Furthermore, a scar formation around dilated collecting ducts was clearly reduced by cyclophosphamide treatment. In general the only lesions observed in the cyclophosphamide treated animals were dilated collecting ducts in the outer medullary zone, the epithelia of which were either in regenerative mitosis or were atrophic. Apparently the primary sites of action of Cortinarius toxins in male rats are the collecting ducts of the outer medullary zone. When inflammation and the subsequent scar formation is prevented by cyclophosphamide, the damaged tubules can regenerate by mitotic activity and perhaps restore normal function.

Animals↗
PubMed1975

Nephrotoxicity of Cortinarius speciosissimus: a histological and enzyme histochemical study.

The nephrotoxicity of the mushroom species Cortinarius speciosissimus was studied in the rat. Dried, homogenized mushroom was given orally via gastric tubing. The development of the kidney damage was followed by both histological and enzyme histochemical methods. The first signs of kidney damage were interstitial infiltrates occurring mainly in the outer medullary zone, observed two days after the administration of the mushroom. Focuses of inflammation, which gradually scarred, appeared after four days. Chiefly necrotic changes occurred in the tubuli of the cortical zone. Valine residue cleaving aminopeptidase disappeared from the necrotic tubuli at a noticeably greater rate than arginine residue cleaving aminopeptidase. A high activity of arginine residue cleaving aminopeptidase was observed in the inflammatory focuses located in the outer medullary zone, showing the important role of this enzyme in kidney inflammation.

Aminopeptidases↗
PubMed1975

Temperature dependence of brain ATPases in immature and adult rats.

In immature rats the temperature dependence of Na+-K+ ATPase of a crude homogenate of brain shows a compex curve with two activity maxima. When EDTA was present in the homogenization medium the curve obtained was of simpler, curvilinear type showing an increased activity at temperatures above 20 degrees C. The Na+-K+ ATPase activity in similar preparation from adult brain were not complex but curvilinear whether EDTA was used or not; however, EDTA increased the activity at temperatures above 20 degrees C. When such chelating agents as EDTA or histidine were used in preparation of microsomes from immature rat brain, the temperature dependence curve of Na+-K+ ATPase in this membrane fraction was changed to a steeper and simpler curve with increased activity especially at temperatures above 20 degrees. These agents, however, did not eliminate totally the complex shape of curve found in microsomes prepared without the presence of any chelating agents. When microsomes were prepared by using NaI-technique the temperature dependence of this enzyme was linear between temperatures 15-14 degrees, the activity being 4-5-fold higher than in the ordinary microsomal preparation. A stimulation of the Mg2+ ATPase by Na+ ions (100mM) was found at temperatures below 30 degrees but an inhibition by the same concentration of Na+ at upper temperatures. This effect together with the lowered activity due to bivalent metal ions (e.g. Ca2+, Cu2+) in 'crude' preparations was thought to be reasons for the complex shape of temperature dependence curve of Na+-K+ ATPase activity.

Adenosine Triphosphatases↗