Zinc and water intake in rats: investigation of adrenergic and opiatergic central mechanisms.
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We have demonstrated that central administration of zinc in minute amounts induces a significant antidipsogenic action in dehydrated rats as well as in rats under central cholinergic and angiotensinergic stimulation. Here we show that acute third ventricle injections of zinc also block water intake induced by central ss-adrenergic stimulation in Wistar rats (190-250 g). Central inhibition of opioid pathways by naloxone reverses the zinc-induced antidipsogenic effect in dehydrated rats. After 120 min, rats receiving third ventricle injections of isoproterenol (160 nmol/rat) exhibited a significant increase in water intake (5.78 +/- 0.54 ml/100 g body weight) compared to saline-treated controls (0.15 +/- 0.07 ml/100 g body weight). Pretreatment with zinc (3.0, 30.0 and 300.0 pmol/rat, 45 min before isoproterenol injection) blocked water intake in a dose-dependent way. At the highest dose employed a complete blockade was demonstrable (0.54 +/- 0.2 ml/100 g body weight). After 120 min, control (NaAc-treated) dehydrated rats, as expected, exhibited a high water intake (7.36 +/- 0.39 ml/100 g body weight). Central administration of zinc blocked this response (2.5 +/- 0.77 ml/100 g body weight). Naloxone pretreatment (82.5 nmol/rat, 30 min before zinc administration) reverted the water intake to the high levels observed in zinc-free dehydrated animals (7.04 +/- 0.56 ml/100 g body weight). These data indicate that zinc is able to block water intake induced by central ss-adrenergic stimulation and that zinc-induced blockade of water intake in dehydrated rats may be, at least in part, due to stimulation of central opioid peptides. (+info)
Effect of an exercise-heat acclimation program on body fluid regulatory responses to dehydration in older men.
(10/197)
We examined if an exercise-heat acclimation program improves body fluid regulatory function in older subjects, as has been reported in younger subjects. Nine older (Old; 70 +/- 3 yr) and six younger (Young; 25 +/- 3 yr) male subjects participated in the study. Body fluid regulatory responses to an acute thermal dehydration challenge were examined before and after the 6-day acclimation session. Acute dehydration was produced by intermittent light exercise [4 bouts of 20-min exercise at 40% peak rate of oxygen consumption (VO(2 peak)) separated by 10 min rest] in the heat (36 degrees C; 40% relative humidity) followed by 30 min of recovery without fluid intake at 25 degrees C. During the 2-h rehydration period the subjects drank a carbohydrate-electrolyte solution ad libitum. In the preacclimation test, the Old lost approximately 0.8 kg during dehydration and recovered 31 +/- 4% of that loss during rehydration, whereas the Young lost approximately 1.2 kg and recovered 56 +/- 8% (P < 0.05, Young vs. Old). During the 6-day heat acclimation period all subjects performed the same exercise-heat exposure as in the dehydration period. Exercise-heat acclimation increased plasma volume by approximately 5% (P < 0.05) in Young subjects but not in Old. The body fluid loss during dehydration in the postacclimation test was similar to that in the preacclimation in Young and Old. The fractional recovery of lost fluid volume during rehydration increased in Young (by 80 +/- 9%; P < 0.05) but not in Old (by only 34 +/- 5%; NS). The improved recovery from dehydration in Young was mainly due to increased fluid intake with a small increase in the fluid retention fraction. The greater involuntary dehydration (greater fluid deficit) in Old was accompanied by reduced plasma vasopressin and aldosterone concentrations, renin activity, and subjective thirst rating (P < 0.05, Young vs. Old). Thus older people have reduced ability to facilitate body fluid regulatory function by exercise-heat acclimation, which might be involved in attenuation of the acclimation-induced increase in body fluid volume. (+info)
An elderly patient with transient diabetes insipidus associated with lymphocytic infundibulo-neurohypophysitis.
(11/197)
We present the eldest case ever reported of central diabetes insipidus (DI) associated with infundibulo-neurohypophysitis. A 77-year old woman, who complained of recent development of excessive thirst, polyuria and polydipsia, was referred to our hospital. The daily urine volume was markedly increased to 6 L. DDAVP administration effectively reduced urine volume and increased urine osmolality. The loading test using high-osmolar sodium chloride showed impaired excretion of vasopressin discordant with plasma osmolar changes. The anterior pituitary function was normal. Pituitary magnetic resonance imaging (MRI) showed thickening of the pituitary stalk and a lack of high-intensity signal of the neurohypophysis on T1-weighted images, suggestive of lymphocytic infundibulo-neurohypophysitis. The thickness of pituitary stalk on MRI improved 6 months later. DI was controlled with DDAVP for 40 days. This was followed by stabilization of the daily urine volume to less than 2.5 L without DDAVP. Our case is the eldest case of central DI associated with infundibulo-neurohypophysitis. The rapid remission of pituitary changes on MRI provides an insight that spontaneously partial remission of central DI may occur, resulting in transient polyuria and polydipsia. (+info)
Neuroimaging evidence implicating cerebellum in support of sensory/cognitive processes associated with thirst.
(12/197)
Recent studies implicate the cerebellum, long considered strictly a motor control structure, in cognitive, sensory, and affective phenomenon. The cerebellum, a phylogenetically ancient structure, has reciprocal ancient connections to the hypothalamus, a structure important in vegetative functions. The present study investigated whether the cerebellum was involved in vegetative functions and the primal emotions engendered by them. Using positron emission tomography, we examined the effects on the cerebellum of the rise of plasma sodium concentration and the emergence of thirst in 10 healthy adults. The correlation of regional cerebral blood flow with subjects' ratings of thirst showed major activation in the vermal central lobule. During the development of thirst, the anterior and posterior quadrangular lobule, lingula, and the vermis were activated. At maximum thirst and then during irrigation of the mouth with water to alleviate dryness, the cerebellum was less activated. However, 3 min after drinking to satiation, the anterior quadrangular lobule and posterior cerebellum were highly activated. The increased cerebellar activity was not related to motor behavior as this did not occur. Instead, responses in ancient cerebellar regions (vermis, fastigal nucleus, archicerebellum) may be more directly related to vegetative and affective aspects of thirst experiences, whereas activity in neocerebellar (posterior) regions may be related to sensory and cognitive aspects. Moreover, the cerebellum is apparently not involved in the computation of thirst per se but rather is activated during changes in thirst/satiation state when the brain is "vigilant" and is monitoring its sensory systems. Some neocerebellar activity may also reflect an intentionality for gratification by drinking inherent in the consciousness of thirst. (+info)
Long-term regulation of urea transporter expression by vasopressin in Brattleboro rats.
(13/197)
Regulation of urea concentration in the renal medullary interstitium is important for maintenance of hypertonicity and therefore the osmotic driving force for water reabsorption. Studies in Sprague-Dawley rats showed that restriction of water intake for 3 days results in upregulation of urea transporter (UT) mRNA in the inner stripe of outer medulla of the kidney (2.9-kb UT2) but not in the inner medulla (4.0-kb UT1). The present study was performed to investigate the role of vasopressin in long-term regulation of UT1 and UT2 in neurogenic diabetes insipidus (Brattleboro) rats treated with a 7-day continuous infusion of [Arg(8)]-vasopressin (AVP), [deamino-Cys(1), D-Arg(8)]-vasopressin (dDAVP) or vehicle. Northern analysis showed that water restriction alone had no effect on the level of UT2 mRNA in vehicle-treated Brattleboro rats but UT2 mRNA markedly increased and UT1 mRNA modestly decreased after treatment with dDAVP. In situ hybridization further demonstrated that the UT2 signal is upregulated and spread along the descending thin limbs of loops of Henle and that UT1 signal is downregulated in the inner medullary collecting ducts in vasopressin-treated rats, with a greater response for dDAVP compared with the AVP-treated group. Immunocytochemistry studies revealed that the UT1 and UT2 proteins are also modified in the same pattern as the transcript changes. Our studies reveal the role of vasopressin in long-term regulation of UT1 and UT2 expression during water restriction. (+info)
Vasopressin V(2)-receptor-dependent regulation of AQP2 expression in Brattleboro rats.
(14/197)
The role of AVP-V(2) receptor (AVP-V(2)R)-dependent regulation of aquaporin-2 (AQP2) expression was evaluated in vasopressin-deficient Brattleboro (BB) rats. AQP2 levels were relatively high in BB rats (52 +/- 8% of levels in Wistar rats), and treatment with the AVP-V(2)R antagonist SR-121463A (0.8 mg/day) for 48 h was associated with 1) increased urine output (170 +/- 9%), 2), reduced AQP2 protein levels (42 +/- 10% in whole kidney and 53 +/- 8% in inner medulla), and 3) reduced AQP2 mRNA levels (36 +/- 7%). In addition, the levels of AQP2 phosphorylated in the protein kinase A (PKA) consensus site (Ser(256) of AQP2) was reduced to 3 +/- 1% of control levels. Lithium (Li) treatment of BB rats for 1 mo, known to reduce adenylyl cyclase (AC) activity, downregulated AQP2 protein levels (15 +/- 6%) and increased urine output (220%). Downregulation of AQP2 expression in response to SR-121463A or Li treatment indicates that AQP2 expression in BB rats depends in part on activation of AVP-V(2)Rs and that the signaling cascade(s) involves AC and hence cAMP. Complete water restriction of BB rats produced only a small increase in AQP2 mRNA (235 +/- 33%) and AQP2 protein (156 +/- 22%) levels. Immunoelectron microscopy confirmed the increase in AQP2 abundance but revealed no change in AQP2 apical plasma membrane labeling in response to thirsting. In conclusion, the expression and phosphorylation of AQP2 in BB rats are in part dependent on AVP-V(2)R signaling, and AVP-V(2)-mediated regulation of AQP2 trafficking and expression is effectively decoupled in BB rats, indicating differences in AVP-V(2)R-mediated regulation of AQP2 trafficking and expression. (+info)
Fluid and electrolyte supplementation for exercise heat stress.
(15/197)
During exercise in the heat, sweat output often exceeds water intake, resulting in a body water deficit (hypohydration) and electrolyte losses. Because daily water losses can be substantial, persons need to emphasize drinking during exercise as well as at meals. For persons consuming a normal diet, electrolyte supplementation is not warranted except perhaps during the first few days of heat exposure. Aerobic exercise is likely to be adversely affected by heat stress and hypohydration; the warmer the climate the greater the potential for performance decrements. Hypohydration increases heat storage and reduces a person's ability to tolerate heat strain. The increased heat storage is mediated by a lower sweating rate (evaporative heat loss) and reduced skin blood flow (dry heat loss) for a given core temperature. Heat-acclimated persons need to pay particular attention to fluid replacement because heat acclimation increases sweat losses, and hypohydration negates the thermoregulatory advantages conferred by acclimation. It has been suggested that hyperhydration (increased total body water) may reduce physiologic strain during exercise heat stress, but data supporting that notion are not robust. Research is recommended for 3 populations with fluid and electrolyte balance problems: older adults, cystic fibrosis patients, and persons with spinal cord injuries. (+info)
A case of renin-producing adrenocortical cancer.
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Here we report a case of a renin-producing adrenocortical carcinoma. A 57-year-old woman was referred to our hospital complaining of thirst and generalized muscle weakness. She was diagnosed as being hypertensive and diabetic with associated hypokalemia and she had a hard elastic mass with a diameter of 10 cm on the left side of her neck. An abdominal computed tomography scan revealed a suprarenal mass on the left side (8.5 x 8 x 6.5 cm). Endocrinological examination demonstrated a marked elevation in the patient's serum glucocorticoid and sex steroid hormones as well as plasma renin activity. Histological examination of a sample taken from the neck mass revealed a metastasis from an adrenal carcinoma, which was stained positively with antibodies against cytochrome P450 and renin, establishing the diagnosis of a renin-producing adrenocortical carcinoma. Trilostane was effective in reducing serum cortisol levels, but mitotane was ineffective. (+info)