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Biomedical subjects

R Jacob

Publications and source records attributed to R Jacob.

At least 235 records · Page 13Linked to original sources
PubMed1975

Cardiac hypertrophy due to physical exercise--an example of hypertrophy without decrease of contractility: unreliability of conventional estimation of contractility by simple parameters.

In 100 young, male Sprague-Dawley rats, a long term swimming training (2 hr/day for 8-12 weeks) produced an increase in heart weight of 10 percent, and an increase of about 15 percent in the relation of heart weight to body weight compared with control rats of the same age and initial weight. In examinations of the mechanical properties of the whole ventricle as well as of trabecular preparations, there was no evidence of impaired myocardial contractile ability because of the swimming training. Some parameters for the estimation of "contractility" increased, whereas others decreased. At a muscle length near lmax, the developed force and the maximal rate of force development were slightly augmented. The results reveal the limited value of some indices of contractility. Alterations in the shape of the contraction curve must to be considered adequately in order to avoid misinterpretations.

Animals↗
PubMed1975

[Influence of long-term swimming training on the structure and enzyme activity of myosin in the rat myocardium (author's transl)].

Intermittent hemodynamic loading of the rat myocardium due to swimming training for several weeks leads to a significant increase in the specific ATPase activity of myosin. This enzymatic alteration of the myosin molecule is accompanied by changes in the stoichiometry of its light chains which are of great significance for the ATPase activity. The maximum shortening velocity of the unloaded myocardium (Vmax), estimated on the basis of afterloaded contractions, shows a slight increase as a result of the physical training. Since, on the other hand, the increase is not significant using the quick release technique, a close relationship between the specific ATPase activity and the augmented cross-sectional contractile capability cannot be proved in our experiments.

Actomyosin↗
PubMed1975

Catecholamine antagonism of acetylcholine and dibutyrl guanosine 3',-5'-monophosphate in the mammalian ventricular myocardium.

After chemical sympathectomy we could demonstrate a negative inotropic effect of acetylcholine (ACh) on the cat ventricular myocardium as a direct catecholamine antagonism. Dose-response relationships for isoproterenol (IP) reveal a noncompetitive inhibition of the inotropic action of the catecholamine by ACh. A concentration of 10(-6) M ACh reduced the maximal IP-induced increase in tension by 58 +/- 13 percent (6-hydroxydopamine pretreatment) and by 65 +/- 10 percent (reserpine pretreatment); inhibition by endogenous ACh (released by field stimulation) was 36 +/- 10 percent and 38 +/- 8 percent, respectively. A concentration of 10(-3) M bibutyryl guanosine 3',5'-monophosphate (cAMP) produced a 17 +/- 7 percent reduction of the catecholamine-induced increase in tension (reserpine pretreatment). A cholinergic influence on the myocardial mechanics and metabolism of the heart may be relevant under stress situations. Vagal inhibition of the ventricular function is accentuated by an elevated sympathetic tone (Levy, 1971). If catecholamine-induced myocardial necrosis in addition to secondary effects of altered vessels are produced also by direct damage of the myocardial cell, then an influence of acetylcholine as a "natural" antagonist may be important.

Acetylcholine↗