Search PubMed⌕ Search

Biomedical subjects

R Beeuwkes

Publications and source records attributed to R Beeuwkes.

At least 19 recordsLinked to original sources
PubMed1991

Antisecretory effect of splanchnic nerve stimulation on choleratoxin-induced secretion in the cat, an effect mediated at the crypts.

The experiments were performed on cats anaesthetized with alpha-chloralose. Segments of the small intestine were perfused with sodium-free hypotonic choline-mannitol solution and intestinal net fluid transport was recorded with a volumetric technique. The content of sodium and chloride in the lamina propria of the small intestinal villus was measured with an electron microprobe in freeze-dried paraffin embedded tissue. In absorbing control intestine, there was an even distribution of electrolytes along the villi. Sympathetic nerve stimulation (5 Hz, 5 ms, 5 V) did not significantly affect electrolyte distribution and net fluid transport. Intestinal secretion was elicited by pretreatment of the intestine with cholera toxin. The concentration of sodium and chloride was elevated in the apical third of the villi in intestines during the secretion since secreted sodium from the crypts was reabsorbed into the villi. Sympathetic nerve stimulation decreased the cholera secretion significantly in intestines pretreated with cholera-toxin. Furthermore, the apical gradients of sodium and chloride in the villi, caused by the reabsorbed sodium and chloride, disappeared during sympathetic nerve stimulation. It is concluded that, in the used experimental model, the antisecretory effect of sympathetic nerve stimulation was caused by inhibition of crypt secretion and not by augmented villus absorption.

Animals↗
PubMed1990

Rupture of coronary vasa vasorum as a trigger of acute myocardial infarction.

Some controversy has always existed regarding the presence and extent of the vasa vasorum--the nutrient vessels in the wall of the human aorta--in the coronary arteries. Now, cinemicrographic studies using silicone polymer injections in cleared human hearts have identified the vasa vasorum of coronary arteries, revealing evidence of neovascularization in the region of atherosclerotic plaques. These studies suggest an important role for the vasa vasorum in the pathogenesis of coronary atherosclerosis and its sequelae, especially intramural hemorrhage and vascular spasm. The wall of the human coronary artery in regions of atherosclerotic injury may be particularly rich in capillary vessels of the vasa vasorum. From this, the evidence suggests that with the morning increase in blood pressure, fragile neovascular structures of the vasa vasorum may be more prone to rupture and may be responsible, in part, for the circadian variation in myocardial infarction.

Adult↗
PubMed1990

Villus and crypt electrolyte and fluid transport during intestinal secretion.

The apical parts of jejunal villi of net-absorbing intestine have been shown to contain sodium chloride concentration gradients which are associated with water absorption (Sjöqvist & Beeuwkes 1989). To determine whether these gradients are different in states of intestinal net secretion, jejunal segments of chloralose-anaesthetized cats were perfused with modified Krebs-Henseleit solutions while secretion was elicited by cholera toxin or vasoactive intestinal polypeptide (VIP). The segments were then rapidly frozen and freeze-dried, and sodium and chloride contents of the lamina propria of single villi were measured by X-ray microanalysis. The apical third of the villus was found to contain a concentration gradient of sodium and chloride when the lumen contained sodium, with no difference between secreting intestine and absorbing control intestine. When the intestine was perfused with hypotonic choline-mannitol solution, no sodium or chloride gradient was found. In this state, treatment of the intestines with secretagogues allowed development of an apical concentration gradient. This demonstrated that the absorptive function of the villus tip was unimpaired during secretion and that secretion from the crypt could supply sufficient electrolyte to allow formation of an apical gradient.

Animals↗
PubMed1989

Villous sodium gradient associated with volume absorption in the feline intestine: an electron-microprobe study on freeze-dried tissue.

Water transport in biological tissue is driven by local osmotic gradients created by accumulation of actively transported ions in tissue compartments. To localize and measure such gradients, jejunal segments from the small intestine of anaesthetized cats were perfused with modified isotonic Krebs-Henseleit electrolyte solution, and net fluid transport was measured with a volumetric technique. The segments were then rapidly frozen, freeze-dried, and prepared for X-ray micro-analysis of elemental content. Whenever the lumen perfusate contained sodium, the apical third of the villus was found to have a sodium gradient rising to a tip concentration more than twice that at the base of the villus. This sodium gradient was associated with a chloride gradient and fluid absorption. No similar potassium gradient was found. When choline replaced sodium in the intestinal lumen, no gradient of sodium chloride was found and no net fluid absorption occurred. Absorption of fluid was thus apparently coupled to absorption of sodium through creation of a local osmotic gradient in the tip of the intestinal villus.

Animals↗
PubMed1986

The effect of atrial natriuretic factor on blood pressure, heart rate, and renal functions in conscious, spontaneously hypertensive rats.

Atrial natriuretic factors, polypeptides released by atrial myocytes, may play a role in the control of blood pressure and the regulation of renal salt and water excretion. Our studies were designed to assess the role of a synthetic peptide, atriopeptin II, on blood pressure and heart rate, renal hemodynamics, and salt and water excretion in conscious, spontaneously hypertensive rats and in normotensive Wistar-Kyoto rats. Changes in mean arterial pressure and heart rate were recorded following intravenous bolus injections (0.1, 1.0, 10, 100 micrograms/kg) of atriopeptin II in 5 spontaneously hypertensive and 5 Wistar-Kyoto rats. In a second group of rats the peptide was infused for 90 minutes in two different doses: low dose, 1 microgram/kg + 2 micrograms/kg/hr; and high dose, 10 micrograms/kg + 20 micrograms/kg/hr. Bolus injections of atriopeptin II resulted in dose-dependent decreases in mean arterial pressure in the hypertensive, but not in the normotensive, rats; heart rates remained unchanged. Blood pressure decreased gradually during the sustained infusion of both doses of atriopeptin II, with the spontaneously hypertensive strain showing increased sensitivity compared to the Wistar-Kyoto strain. Heart rate decreased in both strains during infusion of the high dose; the decrease was significant only in the hypertensive rats. The low dose of atriopeptin II increased the clearance of free water in both strains of rats; sodium excretion was increased only in the hypertensive rats. The high-dose atriopeptin II was associated with transient natriuresis, unaltered glomerular filtration rate, and decreased effective renal blood flow in both strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Contrasting views on the action of atrial peptides: lessons from studies of conscious animals.

In a rather short time, a consensus seems to have emerged among researchers regarding the mechanisms of the natriuretic and hypotensive actions of atrial natriuretic factor (ANF). According to the by now classic view, the natriuresis induced by ANF is mediated by changes in renal hemodynamics; vasorelaxation is proposed as the primary mechanism of its hypotensive action. Recent evidence, mostly from experiments with conscious animals, does not support this view. Results from experiments performed with chronically instrumented spontaneously hypertensive rats and normotensive (Wistar-Kyoto and Wistar) rats show that the natriuresis induced by a synthetic ANF is not accompanied by increases in glomerular filtration rate or renal blood flow. Measurement of cardiac output (CO) and blood pressure indicate that a decrease in CO, not a fall in total peripheral resistance, is the cause of the decrease in blood pressure. Based on this and other available evidence, a hypothetical scheme for the biological role of ANF is proposed.

Animals↗
PubMed1986

Essential hereditary hypertension in dogs: a new animal model.

The objective of this project is to characterize a genetically determined model of essential hypertension in dogs. A pair of unrelated dogs with essential hypertension were identified. Breeding of these dogs and back-cross matings have resulted in 24 offspring, approximately half of which have essential hypertension (systolic blood pressure 170 mmHg, diastolic 105 mmHg). Other offspring are either borderline hypertensive or normal. Blood pressure is measured in the trained, unanaesthetized state by direct arterial puncture. Offspring have normal plasma chemistries, electrolytes, glomerular filtration rate, plasma renin activity, aldosterone and catecholamines. These dogs appear to salt-sensitive compared with normal dogs. Further breeding studies will characterize this new model of hereditary essential hypertension.

Animals↗
PubMed1985

Transmembrane potential of renal papillary epithelial cells: effect of urea and DDAVP.

To define how renal papillary epithelial cells respond to wide changes in the ionic and osmotic composition of their environment, measurements were made of the transmembrane potential differences (PD) of rat renal papillary epithelial cells in vitro in media containing 100 mM NaCl, 100 mM KCl, 1.5 mM CaCl2, and 1 mM MgSO4 plus varying amounts of urea and/or sucrose up to 1,400 mM. Glass microelectrodes (resistance 25-75 M Omega) were used. With added sucrose, no change in PD from the initial value of -9.3 +/- 1.3 (SD) mV (n = 29) (cell interior negative) was found. With added urea, alone or while osmolality was maintained nearly constant with sucrose, the PD changed in a triphasic manner, depolarizing to -5.3 mV at 50 mM urea, hyperpolarizing to -20.0 mV at 150 mM urea, and then depolarizing again to -5.5 mV at 1,400 mM urea. When bath potassium was decreased to 10 meQ/liter (choline replacement) the PD hyperpolarized to -46.9 +/- 5.0 (SD) mV (n = 32). DDAVP, a nonpressor vasopressin analogue, and 8-bromo-cAMP depolarized the membrane to -5 mV in the presence of urea but did not change PD when urea was absent. These observations suggest an interaction between urea and ionic movement or conductance in rat renal papillary epithelial cells.

Animals↗
PubMed1982

Urolithiasis in rats with diabetes insipidus (Brattleboro strain rats).

Brattleboro strain rats homozygous for hypothalamic diabetes insipidus (DI rat) excrete nearly their body weight per day in dilute urine and yet can form bladders stones composed of struvite and apatite. Studies were undertaken to investigate this apparent paradox. The results show that DI rat urine is indeed undersaturated with respect to struvite and apatite. However, chronic infection of DI rat urine with a urease-containing organism (Proteus mirabilis) results in the rapid formation of large struvite/apatite bladder stones. It is concluded that the Brattleboro strain DI rat, like man and unlike other rats, forms struvite/apatite calculi only in the presence at chronic urinary tract infection.

Animals↗
PubMed1982

Oral antidiuretic therapy: studies in the diabetes insipidus rat.

In hypothalamic diabetes insipidus, water balance is achieved primarily through the thirst mechanism. The administration of an antidiuretic agent in the drinking water should restore the antidiuretic response to volume and osmoregulatory drive. To test this hypothesis, homozygous Brattleboro strain rats were given arginine vasopressin (AVP) or 1-desamino-8-D-arginine vasopressin (dDAVP) in the drinking water in concentrations of 10-10,000 micrograms/l (AVP) and 5-10,000 micrograms/l (dDAVP). Oral AVP was found to be ineffective. Oral dDAVP resulted in 1) a progressive increase in dDAVP dose, from 2.3 to 2,559 micrograms.day-1.kg-1; 2) a dose-dependent increase in urine osmolality from 306 to 1,796 mosmol/kg; and 3) a dose-dependent decrease in urinary solute excretion. At each dDAVP dose level, stable physiological states were achieved within 24 h. Similar antidiuretic states were achieved when dDAVP was administered in increasing doses or when therapy was initiated at a high dose. These findings demonstrate that inclusion of an appropriate antidiuretic agent in the drinking water can restore the renal response to volume-osmoregulatory drive.

Administration, Oral↗
PubMed1982

The renin angiotensin system in conscious Brattleboro strain rats.

Plasma renin activity (PRA) was measured in conscious Brattleboro strain, vasopressin (AVP)-deficient diabetes insipidus (DI) and heterozygous rats with the aid of chronically implanted catheters. Baseline, dehydration-stimulated, and hemorrhage-stimulated levels of PRA were elevated in DI rats, as compared to levels in heterozygous controls. Replacement therapy with either AVP or the nonpressor AVP analog dDAVP reduced PRA to control levels. The high level of PRA in DI rats was associated with the lack of endogenous antidiuretic activity per se and not the pressor activity associated with the vasopressin molecule. Thus, elevated PRA in the chronic absence of AVP (in DI rats) most probably results indirectly from the chronically reduced plasma volume reported associated with hypothalamic diabetes insipidus.

Animals↗
PubMed1981

Application of scanning electron microscopy to x-ray analysis of frozen-hydrated sections. I. Specimen handling techniques.

X-ray microanalysis of frozen-hydrated tissue sections permits direct quantitative analysis of diffusible elements in defined cellular compartments. Because the sections are hydrated, elemental concentrations can be defined as wet-weight mass fractions. Use of these techniques should also permit determination of water fraction in cellular compartments. Reliable preparative techniques provide flat, smooth, 0.5 micrometers-thick sections with little elemental and morphological disruption. The specimen support and transfer system described permits hydrated sections to be transferred to the scanning electron microscope cold stage for examination and analysis without contamination or water loss and without introduction of extraneous x-ray radiation.

Animals↗
PubMed1981

Application of scanning electron microscopy to x-ray analysis of frozen-hydrated sections. II. Analysis of standard solutions and artificial electrolyte gradients.

New specimen handling and analytic techniques for the application of x-ray microanalysis to studies of cell and organ biology have been recently described (Saubermann et al., 1981, J. Cell Biol. 88:257-267). Based on these techniques, absolute quantitative standardization has been established through x-ray analysis of frozen-hydrated and then dried sections of independently measured standard solutions of elements. These experiments demonstrate that the specific techniques employed have a probable error of less than 10%. Artificial electrolyte gradients established in gelatin were subjected to analysis to determine whether there was elemental displacement under non-membrane-limited conditions at the temperatures employed for sectioning (-30 degrees to -40 degrees C). No significant difference was observed between such gradients in serial sections cut at -30 degrees and -80 degrees C. Similarly, no additional ice-crystal-damage artifact was found in sections cut at -30 degrees C when compared with sections cut at -80 degrees C. Thus, in terms of ice-crystal size, gradient maintenance, and compartmental differentiation, cryosectioning at -30 degrees to -40 degrees C was not associated with redistribution incompatible with 1- to 2-micrometers spatial resolution, and absolute measurements of elemental concentration were practical within regions of this size.

Chlorides↗
PubMed1981

Application of scanning electron microscopy to x-ray analysis of frozen-hydrated sections. III. Elemental content of cells in the rat renal papillary tip.

The electrolyte and water content of cellular and interstitial compartments in the renal papilla of the rat was determined by x-ray microanalysis of frozen-hydrated tissue sections. Papillae from rats on ad libitum water were rapidly frozen in a slush of Freon 12, and sectioned in a cryomicrotome at -30 to -40 degrees C. Frozen 0.5-micrometer sections were mounted on carbon-coated nylon film over a Be grid, transferred cold to the scanning microscope, and maintained at -175 degrees C during analysis. The scanning transmission mode was used for imaging. Structural preservation was of good quality and allowed identification of tissue compartments. Tissue mass (solutes + water) was determined by continuum radiation from regions of interest. After drying in the SEM, elemental composition of morphologically defined compartments (solutes) was determined by analysis of specific x-rays, and total dry mass by continuum. Na, K, Cl, and H2O contents in collecting-duct cells (CDC), papillary epithelial cells (PEC), and interstitial cells (IC) and space were measured. Cells had lower water content (mean 58.7%) than interstitium (77.5%). Intracellular K concentrations (millimoles per kilogram wet weight) were unremarkable (79-156 mm/kg wet weight); P was markedly higher in cells than in interstitium. S was the same in all compartments. Intracellular Na levels were extremely high (CDC, 344 +/- 127 SD mm/kg wet weight; PEC, 287 +/- 105; IC, 898 +/- 194). Mean interstitial Na was 590 +/- 119 mm/kg wet weight. CI values paralleled those for Na. If this Na is unbound, then these data suggest that renal papillary interstitial cells adapt to their hyperosmotic environment by a Na-uptake process.

Animals↗