Aggregation of platelets with ADP
Aggregation processes are studied using an aggregometer that reflects the progress of aggregation graphically as a curve;ADP serves as an aggregation stimulant [Menshikov VV, 1987].
Before the addition of a proagregant( ADP), random oscillations of the optical density curve are possible. After the addition of the aggregate, oscillations appear on the curve due to a change in the form of the platelets. Oscillations decrease in amplitude, optical density decreases. Platelets combine into aggregates and the curve deviates upward( primary wave).When the ascent passes into the "plateau", a release reaction occurs, and the curve rises even more( secondary wave).
When a small dose of ADP is applied to the aggregate, a double aggregation wave is recorded. The first phase( primary wave) depends on the added exogenous ADP, and the second phase( the secondary aggregation wave) is due to the release reaction of the intrinsic agonists contained in the granules of the platelets. Excessively introduced large doses of ADP( usually 1x10-5 mol) lead to the fusion of the first and second aggregation waves. To achieve a two-wave aggregation, ADP is usually used at a concentration of 1x10-7 moles.
When analyzing aggregation patterns, attention is drawn to the general nature of aggregation( one-wave, two-wave, complete, incomplete, reversible, irreversible), the difference between the optical density of the plasma before the beginning of aggregation and after achieving maximum aggregation( characterizes the intensity of aggregation), as well as a decrease in the optical density of plasma inthe first minute of aggregation or the slope of the curve at the stage of rapid aggregation( characterizes the rate of aggregation).It is important to note that the appearance of two-wave aggregation with stimulation of ADP and adrenaline in concentrations that cause a normally reversible aggregation( usually 1-5 μmol) indicates an increase in the sensitivity of platelets to these inducers, and the development of single-wave incomplete( and often reversible)at concentrations of 10 μmol and more - on the violation of the release of platelets. In clinical studies, the use of ADP in concentrations of 1x10-5 moles( to achieve single-wave aggregation) and 1x10-7 moles( for achieving two-wave aggregation) is generally accepted.
Depending on the functional-morphological characteristics of platelets, the following groups of thrombocytopathies are distinguished.
Reduction of aggregation in response to the introduction of ADP is observed with pernicious anemia, acute and chronic leukemia, myeloma. In patients with uremia, with the stimulation of collagen, adrenaline, ADP, aggregation is reduced. Hypothyroidism is characterized by a decrease in aggregation with stimulation of ADP.Acetylsalicylic acid, penicillin, indomethacin, chloroquine, diuretics( in particular, furosemide when used in high doses) contribute to the reduction of platelet aggregation , which should be taken into account when treating these drugs.
In surgical operations complicated by bleeding, violations in the system of vascular-platelet hemostasis in most cases are caused not by a violation of aggregation and other functional properties of platelets, but by the presence of thrombocytopenia of one degree or another.