Proceedings of The Physiological Society

University College London (2011) Proc Physiol Soc 24, C07 and PC07

Oral Communications

Relationship between thirst perception and plasma arginine vasopressin concentration in man

L. F. Obika1, E. Amabebe2, F. K. Idu3

1. Physiology,, University of Benin,, Benin City, Nigeria. 2. Physiology, University of Benin, Benin City, Nigeria. 3. Optometry, University of Benin, Benin City, Nigeria.

It is well established that plasma osmolality is a major determinant of the release of arginine vasopressin (Thompson et. al., 1991) and that oral fluid loads and dehydration show a consistent thirst perception variation in man (Obika et al., 2009). We examined the possibility that measurements of thirst perception using the Visual Analogue Scale (VAS) can be used to estimate plasma arginine vasopressin concentration in man. In thirty normal subjects (males = 15 and females = 15, after giving their informed consent) thirst perception (TP, cm) was rated (Thompson et al., 1991) and 5.0 ml blood samples were collected from the ante-cubital vein for measurement of plasma arginine vasopressin (Pavp, pg/ml) concentration using Enzyme Immunoassay Kit (Assay Designs, Ann Arbor, USA). The table below shows the anthropometric data of the subjects. Although male subjects were statistically significantly older and taller than the females, the body mass indexes (BMI) were similar (24.5 ± 0.5 vs 25.5 ± 0.8 Kg/m2; male vs female), as well as the blood pressures and body weights. There was no statistically significant difference, male vs. female in TP (5.26 ± 0.51 vs 5.39 ± 0.53 cm), calculated plasma osmolality from TP values, i.e., Posm = 10TP/3 + 281 (298.5 ± 1.7 vs. 299.0 ± 1.8 mOsm/kg H20), and measured plasma arginine vasopressin (4.85 ± 0.30 vs. 4.71 ± 0.31 pg/ml). Furthermore, the calculated Pavp from TP, i.e., Pavp = (TP - 1.2)/0.75 (Igbokwe and Obika, 2008) were also similar (5.40 ± 0.69 vs. 5.60 ± 0.70 pg/ml). When Pavp was calculated from plasma osmolality, Pavp = 0.43(Posm - 284.3) (Thompson et al., 1986), the values were also similar (6.10 ± 0.70 vs.6.30 ± 0.80 pg/ml). Although the measured plasma arginine vasopressin concentration was significantly lower than the estimated values from TP and osmolality, there was no statistically significant difference between the Pavp calculated from TP and that from plasma osmolality. It is reasonable to conclude that plasma arginine vasopressin concentration may be estimated using thirst perception rating or plasma osmolality values.

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