Plasma vasopressin levels in healthy young men in response to stimulation of the peripheral arterial chemoreceptors by almitrine bismesylate.

The plasma arginine vasopressin (AVP) concentration, the plasma osmolality as well as the systemic arterial blood pressure, the heart rate, and the minute ventilation were determined in four healthy, normotensive, normoxic young men undergoing moderate osmotic diuresis. Each subject was measured in two experiments, both lasting from 7:30 a.m. to 6:00 p.m.. In one of them they obtained 50 mg almitrine bismesylate (Vectarion) at 12:00 o'clock, whereas the other test served as control experiment. There were only negligible changes of the parameters measured in the control experiments and also only weak responses of the cardiorespiratory values in the almitrine treated group. Compared with the data obtained 30 min before administration of the drug, measurements carried out 90 min after the ingestion showed a decrease of plasma AVP in all four subjects through plasma osmolality was increased in three of the four cases. A comparison of the mean values of all data obtained in the morning, i.e. before the oral administration of the drug, with those determined in the afternoon revealed that three out of four subjects had responded to almitrine with a fall of plasma AVP regardless of an increase of plasma osmolality in all these three cases. One person did not react to almitrine ingestion, neither with plasma AVP nor with plasma osmolality. In the control experiments the corresponding reaction pattern was uncharacteristic. The data do not support the assumption that arterial chemoreceptor stimulation increases plasma AVP. They rather indicate that excitation of these pO2-sensors in normoxic humans suppresses plasma AVP by mechanisms so far unknown.