activity

activity (ak-tiv´i-te)

1. In electroencephalography, the presence of neurogenic electrical energy. 2. In physical chemistry, an ideal concentration for which the law of mass action will apply perfectly; the ratio of the a. to the true concentration is the a. coefficient (gamma), which becomes 1.00 at infinite dilution. 3. For enzymes, the amount of substrate consumed (or product formed) in a given time under given conditions; turnover number.
blocking a. repression or elimination of electrical activity in the brain by the arrival of a sensory stimulus.
insulin-like a. (ILA) a measure of substances, usually in plasma, that exert biologic effects similar to those of insulin in various bioassays; sometimes used as a measure of plasma insulin concentrations; always gives higher values than immunochemical techniques for the measurement of insulin.
intrinsic sympathomimetic a. (ISA) the property of a drug that causes activation of adrenergic receptors so as to produce effects similar to stimulation of the sympathetic nervous system.
nonsuppressible insulin-like a. (NSILA) plasma insulin-like a. not suppressed by antibodies to insulin and mostly present after pancreatectomy. Nonsuppressible insulin-like a. is mostly the action of polypeptide insulin-like growth factors IGF-I and IGF-II.
optical a. the ability of a compound in solution (one possessing no plane of symmetry, usually because of the presence of one or more asymmetric carbon atoms) to rotate the plane of polarized light either clockwise or counterclockwise.
plasma renin a. (PRA) estimation of renin in plasma by measuring the rate of formation of angiotensin I or II.
specific a. 1. radioactivity per unit mass of the stated element or compound; 2. for an enzyme, the amount of substrate consumed (or product formed) in a given time under given conditions per milligram of protein; 3. a. per unit mass of the stated radionuclide.
triggered a. one or a series of spontaneously generated heart beats originating from an action potential that produces an after-depolarization which reaches activation threshold.

 

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