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In vivo and in vitro studies of urinary concentrating ability in potassium-depleted rabbits.

Raymond, K H; Davidson, K K; McKinney, T D
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1985 Português
Relevância na Pesquisa
18.457201%
The factors responsible for the urinary concentrating defect associated with the potassium-depleted (KD) state are uncertain. The present studies were designed to, first, determine whether a urinary concentrating defect exists in potassium-depleted rabbits and, second, to use the technique of in vitro perfusion to evaluate directly the antidiuretic hormone (ADH) responsiveness of cortical collecting tubules (CCT) in this setting. Feeding female New Zealand White rabbits a potassium-deficient diet for 2 wk caused a significant fall in plasma potassium levels in both the ad-libitum and controlled water intake groups (P less than 0.001). Muscle potassium content after 2 wk of potassium restriction fell from 45.6 +/- 0.9 to 29.0 +/- 1.2 meq/100 g fat-free dry solids (P less than 0.001). Renal papillary sodium content fell significantly from a control value of 234.6 +/- 8.0 to 182.46 +/- 10.0 meq/kg H2O after 2 wk of potassium restriction. Maximal urinary osmolality measured after 12 h of dehydration and 1.25 U pitressin IM was significantly decreased in rabbits after 2 wk of potassium restriction in both the ad-libitum and controlled water intake groups (P less than 0.001). The relationship between plasma potassium concentration and maximum urinary osmolality was significantly correlated in both the ad-libitum and controlled water intake groups...

Pathogenesis of nephrogenic diabetes insipidus due to chronic administration of lithium in rats.

Christensen, S; Kusano, E; Yusufi, A N; Murayama, N; Dousa, T P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1985 Português
Relevância na Pesquisa
17.042891%
A polyuric syndrome with nephrogenic diabetes insipidus (NDI) is a frequent consequence of prolonged administration of lithium (Li) salts. Studies in the past, mainly the acute and in vitro experiments, indicated that Li ions can inhibit hydroosmotic effect of [8-arginine]vasopressin (AVP) at the step of cAMP generation in vitro. However, the pathogenesis of the NDI due to chronic oral administration of low therapeutic doses of Li salts is not yet clarified. We conducted a comprehensive study to clarify the mechanism by which Li administered orally for several weeks induces polyuria and NDI in rats. Albino rats consuming a diet which contained Li (60 mmol/kg) for 4 wk developed marked polyuria and polydipsia; at the end of 4 wk the plasma Li was 0.7 +/- 0.09 mM (mean +/- SEM; n = 36). Li-treated rats had a significantly decreased (-33%) tissue osmolality in papilla and greatly reduced cortico-papillary gradient of urea (cortex--43%; medulla--64%; papilla--74%). Plasma urea was significantly (P less than 0.001) lower in Li-treated rats (5.4 +/- 0.2 mM) compared with controls (6.8 +/- 0.3 mM). Medullary collecting tubules (MCT) and papillary collecting ducts (PCD) microdissected from Li-treated animals had higher content of protein than MCT and PCD from the control rats. The cAMP accumulation in response to AVP added in vitro was significantly (delta = -60%) reduced. Also...

Concentrating defect in the adrenalectomized rat. Abnormal vasopressin-sensitive cyclic adenosine monophosphate metabolism in the papillary collecting duct.

Jackson, B A; Braun-Werness, J L; Kusano, E; Dousa, T P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1983 Português
Relevância na Pesquisa
18.210259%
Among other defects in water metabolism, adrenal insufficiency is associated with an inability to concentrate urine maximally in both man and experimental animals. Recent studies in the rabbit cortical collecting tubule have suggested indirectly that this defect may result from impaired cyclic AMP (cAMP) formation in response to antidiuretic hormone stimulation. In the present study, we examined key elements of arginine vasopressin (AVP)-dependent cAMP metabolism in the papillary collecting duct (PCD), microdissected from 8-d adrenalectomized (ADX) and sham-operated control rats. AVP-sensitive adenylate cyclase (ADC) activity in PCD did not differ between control and ADX rats. cAMP-phosphodiesterase activity (cAMP-PDIE), measured at 10(-6) M cAMP substrate concentration, was significantly higher (delta + 31.6%) in PCD of ADX rats compared with controls. Incubation of intact PCD from ADX rats with AVP resulted in an accumulation of cAMP (delta - 48.5%) significantly lower than observed in control PCD. Chronic administration of dexamethasone reduced cAMP-PDIE activity in PCD of ADX rats to levels close to or below those observed in control rat PCD, and also resulted in a restoration of AVP-stimulated cAMP accumulation to levels approaching control values. Results indicate that the impaired maximal urinary concentrating ability associated with adrenal insufficiency may be due...

Asset pricing using trading volumes in a hidden regime-switching environment

Elliott, R.J.; Siu, T.K.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em //2015 Português
Relevância na Pesquisa
17.042891%
By utilizing information about prices and trading volumes, we discuss the pricing of European contingent claims in a continuous-time hidden regime-switching environment. Hidden market sentiments described by the states of a continuous-time, finite-state, hidden Markov chain represent a common factor for an asset’s drift and volatility, as well as its trading volumes. Using observations about trading volumes, we present a filtered estimate of the hidden common factor. The asset pricing problem is then considered in a filtered market, where the hidden drift and volatility are replaced by their filtered estimates. We adopt the Esscher transform to select an equivalent martingale measure for pricing and derive a partial-differential integral equation for the option price.; Robert J. Elliot, Tak Kuen Siu

Cellular Action of Vasopressin in Medullary Tubules of Mice with Hereditary Nephrogenic Diabetes Insipidus

Jackson, Brian A.; Edwards, Richard M.; Valtin, Heinz; Dousa, Thomas P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1980 Português
Relevância na Pesquisa
17.042891%
Our previous studies (1974. J. Clin. Invest.54: 753-762.) suggested that impaired metabolism of cyclic AMP (cAMP) may be involved in the renal unresponsiveness to vasopressin (VP) in mice with hereditary nephrogenic diabetes insipidus (NDI). To localize such a defect to specific segments of the nephron, we studied the activities of VP-sensitive adenylate cyclase, cAMP phosphodiesterase (cAMP-PDIE), as well as accumulation of cAMP in medullary collecting tubules (MCT) and in medullary thick ascending limbs of Henle's loop (MAL) microdissected from control mice with normal concentrating ability and from mice with hereditary NDI.