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Biomedical subjects

M Harri

Publications and source records attributed to M Harri.

46 records · Page 3Linked to original sources
PubMed1982

Temperature responses of rats to treadmill exercise, and the effect of thermoregulatory capacity.

The relationship between work intensity and body temperature was investigated in the rat in an attempt to clarify whether alterations in thermoregulatory capacity can modify the rte and extent of body warming during exercise. Repeated noradrenaline injections led to increased hyperthermic response to that amine. However, during exercise these animals did not attain higher colonic temperatures as did the animals avoiding noradrenaline treatment. If noradrenaline was injected 60 min prior to test-exercise the body temperature of the rats rose to a higher level without the drug. The extent of this rise was, however, independent of the previous noradrenaline-treatment history. Beta blockade abolished the noradrenaline-induced hyperthermia but not the exercise-induced hyperthermia. Despite increased capacity for heat production, cold-acclimated rats did not attain higher colonic temperatures during exercise than did the running-trained, cold-stressed or sedentary control rats. However, the higher tail skin temperature of the cold-acclimated rats indicate that their heat production was enhanced but they maintained lower colonic temperature by dissipating the excess heat through the elevated blood flow to the tail and probably to other extremities. These results indicate that the rise in deep body temperature of the rats during work is proportional to work intensity and that the enhanced heat production capacity can be compensated for by increasing the heat loss activities.

Adaptation, Physiological↗
PubMed1982

Effects of the adrenergic nervous system on training-induced cardiac enlargement, and on the intrinsic rate and phenylephrine sensitivity of isolated rat atria.

Atria isolated from rats after 6 to 7 weeks running training or swim training in water at 30 degrees C beat at a slower rate than did the atria from sedentary control animals. If the rats received noradrenaline injections with each running session their atrial rate was even lower, while propranolol injections did not lead to lower intrinsic atrial rate. Repeated noradrenaline or propranolol injections alone or swim training in warm water (38 degrees C) did not result in altered atrial rate. A plot of the intrinsic atrial rate against heart weight yielded a significant (r = -0.803) negative relationship (y = 311 - 0.91 x). Swim training in cold water, or chronic noradrenaline injections led to a lessened sensitivity of isolated atria to phenylephrine while chronic beta blockade tended to increase the sensitivity. The results suggest that an intense, although transient, cardiac stimulation, typical of the combined action of running training and noradrenaline injections, results in a lower intrinsic atrial rate and greater cardiac enlargement, while a more sustained type of cardiac stimulation, as produced typically by repeated injections of noradrenaline, leads to less sensitivity to phenylephrine.

Adaptation, Physiological↗
PubMed1982

Modification of training-induced responses by repeated norepinephrine injections in rats.

Rats were subjected to daily (5 times/wk) running exercises, norepinephrine injections (0.5 mg/kg sc), or both for 9 wk; one rat group served as the control. Norepinephrine injections were used to potentiate the effect of the endogenous amine, the release of which is known to be stimulated by exercise. Changes observable in all treated rat groups included reduced weight gain, reduced food intake, decreased amount of epididymal fat, hypertrophy of the heart and adrenals, and increased tail skin temperature response to isoproterenol (0.2 mg/kg sc). The training-specific changes (increased activity of oxidative muscle enzymes) were not potentiated by training under the influence of exogenous norepinephrine administration. The changes produced by repeated norepinephrine injections alone (hypertrophy of the brown adipose tissue and increased colonic temperature response to isoproterenol) failed to develop if the rats underwent physical training in addition to drug treatment. Lower tail skin temperature in a cool environment (15 degrees C) was associated with norepinephrine treatment, whether or not there was simultaneous training. These results suggest that the chronic norepinephrine treatment-physical training combination led to complex adaptive changes that could not be systematically associated with either norepinephrine treatment or physical training alone.

Adipose Tissue, Brown↗
PubMed1982

Beta blockade and physical training in rats.

Beta adrenergic blocking agents are widely used in the treatment of hypertension. Recent findings indicate that long-term physical training also could reduce elevated blood pressure and many physicians therefore recommend their patients to include physical training in their everyday program. However, it is not known whether a combination of beta blockade and physical training influences the responses of an organism to physical training. This problem was investigated using laboratory rats as an experimental animal model. Both swimming and running training were used, and a group of animals was trained without any medication while the other group performed their daily training session under the influence of 10 mg/kg of propranolol. Some of the effects produced by swimming training, such as hypertrophy of brown adipose tissue and heart muscle, resting bradycardia, increased tachycardic and tail skin temperature responses to isoprenaline, increased calorigenic response to noradrenaline and delayed cooling rate in cold water were similar to those produced by cold acclimation or repeated noradrenaline injections. It is thus tempting to conclude that the training-induced release of noradrenaline was responsible for the changes mentioned. Propranolol, when associated with the training, effectively hampered these changes. Running training increased the activity of oxidative enzymes in the skeletal muscle much more than did swimming training or repeated noradrenaline injections. Furthermore, running training neither induced hypertrophy of the brown fat nor enhanced calorigenic response to noradrenaline; it even led to enhanced rate of body cooling in cold water. Therefore the adaptive changes caused by running training most probably are not due to cold acclimation effects in spite of that propranolol, when associated with the running sessions, antagonized the development of running-induced changes, too. Some of these changes, such as cardiomegaly, training bradycardia and elevated aerobic capacity, are often used as measures of physical fitness. Assuming that the purpose of physical training is to increase physical fitness, then a combination of beta blockade with training does not serve the purpose.

Animals↗
PubMed1981

Effects of ACTH and alprenolol treatments on muscle and brown fat enzyme activities and weights in the rat.

Chronic ACTH treatment (3 IU/kg daily for 8 days) caused an increase in wet weight of the interscapular brown adipose tissue (ISBAT) in the rat without affecting the enzyme activities of the cardiac or skeletal muscles or of ISBAT. On the other hand, chronic beta-blockade (alprenolol 10 mg/kg daily for 8 days) induced elevated activities in the oxidative enzymes of the ISBAT but not of the muscle tissues measured. Combined ACTH and alprenolol treatment also increased significantly the citrate synthase and malate dehydrogenase activities and protein concentration, but decreased the weight of ISBAT to normal. The results suggest that, although a direct antagonism between the beta-blockers and ACTH has not been demonstrated, beta-blockers can abolish the ACTH-induced weight gain of the ISBAT.

Adipose Tissue, Brown↗
PubMedDate not supplied

Relationship between hyponeophagia and adrenal cortex function in farmed foxes.

The adrenal cortex function of farmed blue (Alopex lagopus) and silver foxes (Vulpes vulpes) differing in their reaction in the feeding test were assessed. The urine cortisol:creatinine ratio was lower for those animals eating in the feeding test in comparison to those not eating in both species. In addition, eater silver foxes had lower baseline serum cortisol concentration and also lower serum cortisol concentration 2 h after ACTH administration than noneaters. There were no differences in any serum cortisol levels between the eater and noneater blue foxes. The weights of body and adrenals did not differ between confident and fearful animals in either species. The present study demonstrates that animals not eating in the feeding test may have higher fearfulness and be more stressed than animals eating.

Adrenal Cortex↗