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Biomedical subjects

R Beeuwkes

Publications and source records attributed to R Beeuwkes.

10 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↗
PubMed1979

Effects of AVP and DDAVP on plasma renin activity and electrolyte excretion in conscious dogs.

Uninephrectomized adult female dogs with chronic indwelling catheters were maintained on a low sodium diet and studied without anesthesia. Following hydration with 3% dextrose, an intravenous infusion of either arginine vasopressin (AVP) or of 1-desamino-8-D-arginine vasopressin (DDAVP) was begun. The dose was calculated to achieve a near maximal physiological plasma concentration of AVP, or an equimolar concentration of DDAVP. Both AVP and DDAVP increased urinary osmolality from less than 60 to over 800 mosmol/kg H2O within 1 h. AVP infusion increased mean arterial pressure and renal electrolyte excretion and decreased heart rate and plasma renin activity (PRA), while DDAVP was without effect on these parameters. AVP infused into the renal artery at doses which did not alter systemic pressure and heart rate caused kaliuresis and reduced PRA. We conclude that the AVP-induced inhibition of renin secretion and increase in renal electrolyte excretion are not secondary to increased tubular permeability to water, but must represent a more specific action of AVP which is not shared by DDAVP.

Animals↗
PubMed1979

Electron probe studies of Na+ - K+-ATPase.

Use of appropriate reaction conditions allows direct quantitative measurements of the activity of Na-K-ATPase to be made with the electron probe microanalyzer. In addition, the demonstration by microanalysis of the linearity of the complete cytochemical reaction sequence is the first detailed analysis of the elemental sequence in a histochemical method and provides the basis for a visual semi-quantitative analysis of enzyme activity in tissue sections. This technique indicates the potential of electron probe microanalysis as a basic tool in enzymology.

Animals↗
PubMed1979

Techniques for quantitative organic analysis in microdroplets.

Techniques are described for the chemical analysis of urea by means of X-ray microanalysis. A selective labelling reagent, thioxanthen-9-ol, is used to precipitate urea together with a sulfur label. Reagents are added to and removed from microdroplets of 50 picoliter volume by means of oil-water partition. The sensitivity of the method is less than 1 picomole. The possibility of extension of these techniques to other analyses is discussed.

Chemical Phenomena↗
PubMed1978

The renal circulations.

The plural is used advisedly. Each of several microcirculations with specialized structural and functional properties is necessary to the physiologic functioning of the kidney. Newly elucidated aspects of renal vascular anatomy are mapped out and clearly related to the exchange processes that occur at the capillary level in each part of the nephron to produce the final ureteral urine of the required volume and composition.

Absorption↗
PubMed1978

Renal excretion of prostaglandins E2 and F2alpha in diabetes insipidus rats.

On the assumption that the antagonism between prostaglandin E2 and vasopressin might represent a negative feedback system, we evaluated the hypothesis that vasopressin stimulates, in vivo, the renal production of prostaglandins. For these studies we used Brattleboro homozygous rats with diabetes insipidus and Long-Evans rats for controls, Brattleboro homozygotes show a substantial reduction in the renal excretion of prostaglandin E2 and prostaglandin F2alpha. Homozygotes excreted 39 +/- 5 ng/24 h prostaglandin E2 and 40 +/- 4 ng/24 h prostaglandin F2alpha, compared to 217 +/- 40 and 221 +/- 18 ng/24 h, respectively, in control rats (P less than 0.001). Therapy of homozygotes with vasopressin tannate in oil resulted in a prompt increase in the urinary excretion of prostaglandin E2 and prostaglandin F2alpha. 1-Desamino-D-arginine vasopressin, a nonpressor analogue of vasopressin, also enhanced the renal production of prostaglandin E2. We conclude that vasopressin (antidiuretic hormone) stimulates renal production and excretion of prostaglandin E2 and prostaglandin F2alpha in vivo. It is possible that this increment of prostaglandin synthesis serves a negative feedback function by modulating the action of vasopressin on the renal tubule.

Animals↗
PubMed1977

Cutting work in thick section cryomicrotomy.

The forces during cryosectioning were measured using miniature strain gauges attached to a load cell fitted to the drive arm of the Porter-Blum MT-2 cryomicrotome. Work was calculated and the data normalized to a standard (1 mm X 1 mm X 0.5 micrometer) section. Thermal energy generated was also calculated. Five parameters were studied: cutting angle, thickness, temperature, hardness, and block shape. Force patterns could be divided into three major groups thought to represent cutting (Type I), large fracture planes greater than 10 micrometer in length (Type II), and small fracture planes less than 10 micrometer in length (Type III). Type I and Type II produced satisfactory sections. Work in cutting ranged from an average of 78.4 muJ to 568.8 muJ. Cutting angle and temperature had the greatest effect on sectioning. Heat generated would be sufficient to cause through-section melting for 0.5 micrometer thick sections assuming the worst possible case, namely that all heat went into the section without loss. Presence of a Type II pattern (large fracture pattern) is thought to be presumptive evidence against thawing.

Frozen Sections↗
PubMed1975

Tubular organization and vascular-tubular relations in the dog kidney.

Tubular organization and vascular-tubular relations were studied by double injection in canine kidneys. Blood vessels were injected via the artery after perfusion fixation. Tubules were injected by micropipettes inserted into the urinary spaces of selected glomeruli in cleared slices. One hundred proximal convoluted tubules, 16 Henle loops, and 5 distal convoluted tubules were defined. Only subcapsular proximal convolutions were perfused by efferent vessels arising from the same glomerulus (43 of 55). In midcortex, proximal convolutions were generally perfused over less than half their length by the parent efferent (21 of 31). Here tubules entirely perfused by the parent efferent were rare (2 of 31). No inner cortical proximal convolutions were perfused by the efferent from the same glomerulus (0 of 14). Henle's loops were found to be perfused by the efferents of many glomeruli regardless of the cortical position of the parent glomerulus. Distal convolutions shared the perfusion of proximal convolutions of the same glomerulus. Thus, each nephron is apparently functionally dependent on efferent blood from glomeruli of many other nephrons. New synoptic diagrams of canine renal organization are presented.

Animals↗
PubMed1975

Renal sodium-potassium adenosine triphosphatase. Optical localization and x-ray microanalysis.

The distribution of sodium-potassium adenosine triposphatase (Na-K-ATPase) activity in kidney sections has been studied by a method based on the hydrolysis of p-nitrophenyl phosphate in alkaline medium containing dimethyl sulfoxide. The products at each stage in the reaction sequence have been subjected to electron probe microanalysis. The initial product was identified as a mixture of KMgPO4 and Mg(PO4)2, and sequential analysis demonstrated the linearity of conversion of this product to a visible form. In human, rabbit and rat kidneys the distribution of activity was found to be essentially identical, with highest levels located in thick ascending limbs and distal convoluted tubules. The initial reaction was completely potassium dependent and was inhibited by ouabain in concentrations reflecting the relative sensitivity of microsomal Na-K-ATPase in each species. Measurement of initial product phosphorus by means of the electron probe is presented as a practical technique for direct quantitation of Na-K-ATPase activity in identified tubule segments.

Adenosine Triphosphatases↗