Thirst Perception And Drinking In Euhydrate And Dehydrate Human Subjects

Summary: Studies on how the body senses the need to correct extracellular and intracellular volumes and ionic concentration changes is relatively scanty. The present studies were designed to determine the effect of oral distilled water (DW) and saline loads, gargling with DW and DW preload on thirst perception (TP) and drinking in euhydrate and dehydrated subjects. The subjects were healthy male volunteers between the ages of 17 and 35 years. Group A subjects were given DW or various concentrations of sodium chloride (NaCl) orally. Subjects in groups B, C and D were dehydrated for 18 hours before the experiment. Group B gargled 500ml of DW in divided volume of 50ml at five minutes interval over a period of 50 minutes. Group C gargled with DW and different concentrations of NaCl. Group D were preloaded with four volumes of DW before ad libitum DW intake. TP was rated using the Visual Analogue Scale. Results showed that in Group A, drinking DW reduced TP, suggesting that baseline TP in normal euhydrate subjects is slightly elevated. Drinking DW reduced TP more than drinking NaCl solutions. Gargling resulted in a gradual fall in TP. The decrease in TP was statistically significant after 30 minutes of gargling. Gargling with different concentrations of NaCl solutions resulted in significant reductions in TP in all the groups. There was a significant decrease in TP in the group preloaded with 1000ml of distilled water at 5 minutes of rehydration. At 20 minutes TP was abolished suggesting that approximately 1000ml of water was needed for the rehydration. These results show that baseline TP in euhydrates is elevated and that TP increases in dehydrated subjects. Gargling reduces TP, but did not abolish thirst. It is suggested that a fall in plasma osmolality due to drinking may be responsible for abolishing thirst

Estimation of Plasma Arginine Vasopressin Concentration Using Thirst Perception and Plasma Osmolality Values

Summary: In human, thirst and antidiuretic hormone (ADH) are controlled by similar sensitive osmoregulatory mechanisms such that above a certain osmotic threshold (280-288 mOsm/kg H20) there is a linear relationship between the increase in plasma osmolality and increase in ADH and thirst. The purpose of this study was to estimate plasma arginine vasopressin (PAVP) using thirst perception (TP) and plasma osmolality (POSM) values before and at 60 minutes in control or euhydrate (group A, 0.0 ml/kg body weight of distilled water), hydrated (group B, 7.1ml/kg body weight of distilled water) and dehydrated (group C, 0.0 ml/kg body weight of distilled water) subjects. A total of twenty five (25) subjects between the ages of 18 and 30 years were used for the study. Calculated POSM and TP values were used to estimate the PAVP concentration. Data were presented as Mean ± SEM. Analyses of results were done using ANOVA and Student t-test. The estimated values of PAVP using TP and POSM respectively at baseline levels were similar in euhydrate (2.22+2.00 vs 2.40+2.10 pg/ml), hydrate (2.22+1.34 vs 2.40+1.72 pg/ml) and in dehydrate (7.05+1.70 vs 6.92+1.94 pg/ml). Sixty minutes later, the values remained similar in euhydrate (3.29+2.40 vs 4.16+2.10 pg/ml), hydrate (1.92+1.60 vs 1.79+1.25 pg/ml) and in dehydrate (8.40+1.40 vs 9.20+1.50 pg/ml). The results show that there was a positive relationship between PAVP calculated from TP and POSM values. We therefore concluded that plasma arginine vasopressin concentration may be estimated using thirst perception and/or plasma osmolality values. Estimation of PAVP using plasma osmolar changes affected by glucose and urea may be inappropriate.Keywords: Arginine vasopressin, Thirst perception, Plasma Osmolality

Relationship between thirst perception and plasma arginine vasopressin concentration in man

We examined the possibility that measurements of thirst perception in man using the visual Analogue Scale (VAS) can be used to estimate plasma arginine vasopressin concentration in man. In thirty normal subjects (male=15 and female=15), thirst perception (TP, cm) was rated and 5.0ml blood samples were collected for the measurement of plasma arginine vasopressin (PAVP) using Enzyme Immunoassay kit. Male subjects were statistically significantly older and taller than the females. However, the blood pressures, body weight and body mass index were similar. There was no significant difference, male vs. female in TP (5.26±0.51 vs. 5.39±0.53cm), calculated plasma osmolality from TP, Posm (298.5±1.7 vs. 299.0±1.8mOsm/kgH2O) and measured plasma arginine vasopressin, PAVP (4.85±0.30 vs. 4.71±0.31pg/ml). Furthermore, the calculated PAVP from TP, PAVP-TP was similar (5.40±0.69 vs.5.60 ±0.70pg/ml). When PAVP was calculated from plasma osmolality, PAVP-Posm the values were also similar (6.10±0.70 vs. 6.30±0.80pg/ml). There was no statistically significant difference between the measured PAVP as well as those calculated from TP and from plasma osmolality. It is thus reasonable to conclude that plasma arginine vasopressin concentration maybe estimated using thirst perception and/or plasma osmolality

The role of oropharnygeal receptors in thirst perception after dehydration and rehydration

This study examined the effect of drinking and gargling on thirst perception (TP) in 33 young dehydrated female subjects (18-25yrs), using the visual analogue scale (VAS). Group A subjects drank, while group B gargled the fluid provided - 0.0%, 0.9% and 1.8% NaCl (7.0 ml/kg body weight of fluid). The procedure was  alternated two weeks later. All subjects dehydrated for 18 hours prior to the study, and the last 12-hour urine was collected and volume recorded. Subject who provided a 12hr urine volume greater than 400ml was excluded from the study. After recording the baseline TP, and voiding the bladder, drinking/gargling was done within 5 minutes, and the subsequent TPs were recorded at 5 minutes interval for 25 minutes. Blood samples were collected before and at the end of the 30 minutes, when urine volumes were recorded. Drinking (0.0% and 1.8% NaCl) resulted in an initial decrease in thirst perception, which was statistically significant (p<0.05) only up to 10 minutes. Water intake ad libitum (mean ± SEM) at the end of the 30 minutes was statistically significantly lower (p<0.05) only in the group that drank 0.0% NaCl. Gargling on the other hand did not affect TP and water intake throughout the period of study. It can be concluded that drinking, but not  gargling reduces thirst perception irrespective of the tonicity of the fluid as earlier reported (Obika et. al., 2009; Salata et. al., 1987). This study suggests that the oropharyngeal receptors for TP are activated by recurrent stimulation by the act of drinking rather than gargling.Keywords: Dehydration, Rehydration, Oropharyngeal Receptors, Thirst perception, Drinking, Gargling

Effect of Hibiscus sabdariffa on Blood Pressure and Electrolyte Profile of Mild to Moderate Hypertensive Nigerians: A Comparative Study with Hydrochlorothiazide

Background: Hibiscus sabdariffa (HS) is widely consumed in Nigeria as a refreshing beverage and also as an antihypertensive agent. Since three decades ago when its antihypertensive activities were reported in several animal experiments, its consumption has greatly increased.Aim: The aim of this study is to investigate the effect of HS consumption on blood pressure (BP) and electrolytes of mild to moderate hypertensive Nigerians and compare it with that of hydrochlorothiazide (HCTZ), a diuretic widely used as first‑line antihypertensive drug.Subjects and Methods: Eighty newly diagnosed, but untreated mild to moderate hypertensive subjects attending Medical Out‑Patients clinic of Enugu State University Teaching Hospital, Enugu, were recruited for the study. They were randomly divided into three groups: A, B and C. Those in Groups A were given placebo; those in Group B took HCTZ while those in Group C were given HS. Treatment lasted for 4 weeks. BP, serum, and urine electrolytes were measured at baseline, weekly during treatment and 1 week after withdrawal of treatment.Results: At the end of treatment, both HCTZ and HS significantly (P < 0.001) reduced systolic BP, diastolic BP, mean arterial pressure and serum Na+ compared to placebo. When compared to each other, HCTZ significantly (P < 0.001) reduced serum Na+ and Cl− compared to HS and significantly (P < 0.001) increased K+ and Cl− output in urine. After withdrawal of treatment, the fall in BP and serum Na+ in HS group were significant compared to HCTZ where they returned to baseline values. No side effect was reported during the study.Conclusion: HS was a more effective antihypertensive agent than HCTZ in mild to moderate hypertensive Nigerians and did not cause electrolyte imbalance. HS showed longer duration of action compared to HCTZ and reduction in serum Na+ may be another antihypertensive mechanism of action of HS.Keywords: Clinical Trial, Essential Hypertension and Electrolytes, Hibiscus sabdariffa, Hydrochlorothiazid