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R I Aizman

Publications and source records attributed to R I Aizman.

8 recordsLinked to original sources
PubMed1997

Circadian variation in the natriuresis produced by potassium intake in the rat.

To determine if there was an endogenous circadian regulation of the renal natriuretic response to acute potassium loading, unanesthetized rats, either fed or fasted, were given an intragastric infusion of KCl over 100 min at the times of maximum and minimum circadian sodium excretion, i.e. in the early dark and early light phase of a 12 hour dark/light cycle. During KCl infusion plasma potassium concentration as well as sodium and potassium excretion progressively increased. Cumulative sodium excretion was greater in dark than light phase, and was greater in fed than fasted rats. Sodium excretion was greater at any given elevated level of plasma potassium in the dark than light phase. The results suggest that reported variations in the effects of high potassium diets on sodium excretion, blood pressure, or circulatory pathology in hypertension, may in part be explained by variations in the time of oral potassium intake.

Animals↗
PubMed1996

Ontogeny of K+ transport in rat distal colon.

Infants need to retain more K+ than adults to avoid growth retardation. Since the K+ requirements are different in infants (I) and in adults (A), the mechanisms regulating K+ homeostasis should also be different. The colon plays an important role for the regulation of K+ homeostasis. Colonic K+ transport is bidirectional. In this study we have examined the development of colonic K+ transport with special reference to the contribution of different K(+)-transporting pathways. The net colonic K+ uptake, as determined by in vivo perfusion studies and by 86Rb uptake, was significantly higher in I than in A rats. In both I and A colon, approximately 80% of total 86Rb uptake was dependent on vanadate-sensitive P-type adenosinetriphosphatases (ATPases), but the contribution of these different ATPases changes during development. The activity of colonic Na(+)-K(+)-ATPase, measured as ouabain-sensitive Na(+)-dependent ATP hydrolysis and as 86Rb uptake, was lower in I than in A rats. In contrast, the activity of K(+)-ATPases located in apical membrane and measured as ouabain insensitive and SCH-28080 sensitive, as ouabain-sensitive Na(+)-independent ATP hydrolysis, and as 86Rb uptake was significantly higher in I than in A rats. The ratio between apically located K(+)-ATPases and basolateral Na(+)-K(+)-ATPase activities was almost 3.2-fold higher in I than in A colon. We identified with Northern blot the expression of the colonic H(+)-K(+)-ATPase and the Na(+)-K(+)-ATPase alpha-subunits. The alpha-mRNA expression of both ATPases was significantly higher in I than in A rats. The pH and K+ sensitivity of the ouabain-insensitive, SCH-28080-sensitive K(+)-ATPase was the same in I and A colons. In conclusion, the relative activity of apical K+ absorbing ATPases is higher in the I than in the A colon, which should aid infants in retaining K+.

Adenosine Triphosphatases↗
PubMed1996

Early effects of uninephrectomy on K homeostasis in unanesthetized rats.

Mechanisms underlying the change in K excretion (UKV) during the first 6 days after uninephrectomy (UNX) were examined in unanesthetized rats. Arterial plasma K concentrations (PK) were 0.55 meq/l above control values at 12 and 24 h after UNX but were not significantly different 36-72 h after UNX. To determine if there was an increased sensitivity of the distal K secretory mechanism to increases in PK, an intragastric KCl infusion was given. The delta UKV/delta PK per kidney values were in the following order: 6-day UNX > 2-day UNX > control. In the normal rats, an acute increase of 0.5 meq/l in PK increased UKV by an amount approximating 25% of the increase in UKV observed 12-24 h after UNX. Amiloride, administered 48 h after UNX, increased Na excretion per kidney and decreased UKV per kidney approximately twice as much in UNX as in control groups. Thus an adaptive increase of amiloride-inhibitable K secretion occurred within 2 days of UNX and continued to increase thereafter. This K adaptation may have been induced by transient increases in PK.

Adaptation, Physiological↗
PubMed1994

Circadian rhythms and time course of adaptive sodium and potassium excretion in rats after uninephrectomy.

The relationship between renal circadian cyclic excretion and renal compensatory adaptation after uninephrectomy for K, Na, and water was studied. Rats in a 12:12-h light-dark environment were given a liquid diet, and urine was collected for 16 days with consecutive 90-min periods. Days 1-4 were control, 5-10 followed a sham operation, and 11-16 followed uninephrectomy. The major findings were 1) the circadian cycles in excretion were virtually unchanged after sham and uninephrectomy; 2) an adaptive increase in excretion of Na, K, and water by the remaining kidney occurred within 90 min after uninephrectomy; 3) after uninephrectomy the distribution of the 24-h increment in excretion for the remaining kidney closely followed the preexisting pattern of circadian excretion for Na but was evenly distributed between light and dark phases for K; and 4) after uninephrectomy the ratio of excretion to intake was unchanged. This is the first study to document the time course of adaptation to uninephrectomy using consecutive brief collections over several days in unanesthetized and undisturbed rats. Adaptation after uninephrectomy occurred essentially immediately; was maintained unchanged; and preserved Na, K, and water homeostasis. Uninephrectomy did not alter the circadian control of excretion.

Animals↗
PubMed1993

The central nervous system in potassium homeostasis.

There is considerable evidence that the central nervous system (CNS) is significantly involved in potassium homeostasis: (a) Potassium-specific receptors located in the liver or hepatic portal circulation initiate a reflex increase in potassium excretion via vagal afferents. This reflex is lost or diminished with hypophysectomy. (b) Oscillators, presumably located in the hypothalamus, determine a circadian rhythm in the renal excretion of potassium. The efferent control factors are unknown. (c) Exogenous hypophysial peptides (vasopressin, oxytocin, and alpha-, beta-, and gamma-MSH) stimulate increased potassium (and sodium) excretion. (d) Hypophysial gamma-MSH or a related hypophysial peptide stimulates an increase in the excretion of potassium (and sodium) following uninephrectomy in the rat. This adaptive response involves cerebral, naloxone-inhibitable opioid receptors. (e) Intra-third-ventricular infusion of hypertonic NaCl initiates an increased potassium (and sodium) excretion through undetermined humoral mechanisms and is blocked by prior hypophysectomy. (f) In rats depleted of potassium by low potassium intake or by production of DOCA hypertension, an inhibition of skeletal muscle Na+, K(+)-ATPase ion pump activity is directed by hypothalamic centers and involves inhibition by alpha-adrenergic activity of slow twitch fibers and inhibition by undetermined humoral factors of fast twitch fibers. (g) Potassium receptors, either demonstrated or inferred, initiate reflex increases in respiration, heart rate, blood pressure, and peripheral tissue potassium uptake as well as a reflex inhibition of skeletal muscle ion pumps. (h) Evidence for CNS regulation of potassium intake is equivocal. Major gaps exist in this emerging picture of neuroendocrine involvement in potassium homeostasis.

Animals↗
PubMed1991

Water-salt metabolism of feti and pregnant rats with venous congestion.

Water and salt metabolism was studied in feti and pregnant rats with experimental venous congestion by measuring water and electrolyte content in the kidney, liver, cerebrum, skin hypodermic tissue, muscle, heart. In the kidney, venous occlusion resulted in increased potassium content. The role of the placenta is discussed.

Animals↗
PubMedDate not supplied

Water-electrolyte balance in overmature fetuses.

The water and electrolyte contents of various fetal and maternal tissues were studied at the final stage of embryogeny and during prolonged pregnancy. The data indicate that the placenta in prolonged pregnancy can act as a depot organ for water and sodium.

Animals↗