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Biomedical subjects

K Steven

Publications and source records attributed to K Steven.

88 records · Page 5Linked to original sources
PubMed1981

A mathematical model of fluid transport in the kidney.

A mathematical model of the rat kidney is developed from glomerular and tubular submodels. It is assumed that all nephrons are identical, that the hydraulic pressure in the tubules obeys Hagen-Poiseuille's law, that the rate of fluid reabsorption depends on the flow rate of tubular fluid, and that the tubules are distensible. The independent variables of the model are selected to comply with experimental measurements in the hydropenic rat. The model is used to evaluate the mechanism of glomerulotubular balance: changing the mean ultrafiltration pressure to the glomerular capillaries has a substantial influence on glomerular filtration rate (GFR). A change in the rate of fluid reabsorption in the proximal tubules has a strong influence on GFR notwithstanding that the change in GFR is smaller than that in the rate of fluid reabsorption. The calculated values for the hydraulic pressure profile in the tubular system and the interstitial pressure during ureteral obstruction are in close agreement with experimental measurements. Increasing the arterial haematocrit above normal causes a substantial decrease in GFR, whilst reducing it below normal has only a small effect on GRF.

Animals↗
PubMed1981

Prostaglandin E2-mediated secretory diarrhea in villous adenoma of rectum: effect of treatment with indomethacin.

Biochemical and clinical evidence is presented to indicate that prostaglandin (PG)E2 is the mediator of fluid and electrolyte secretion by villous adenomas of the rectum. A 64-yr-old man with a 2-mo history of mucous diarrhea had, on admission, prerenal uremia, severe hyponatremia, and hypokalemia. At sigmoidoscopy an 11 X 11-cm villous adenoma of the rectum was revealed. The rectal fluid discharge was 1800-1825 ml/day, with sodium and potassium concentrations of 150 and 12 mEq/L, respectively. Immunoreactive PGE2 levels in the rectal effluents were high (viz. 1160-1250 pg/ml vs. 200-395 pg/ml) compared with those in stool water from patients with infectious diarrhea. The concentration of vasoactive intestinal polypeptide (VIP) in the tumor was lower (viz. 10.5 pmol/g vs. 100-700 pmol/g) than in normal colonic mucosa. Indomethacin treatment (24 mg X 4 daily) reduced the rectal PGE2 excretion from 2.2 to 0.3 microgram/day and caused a decrease in the rectal fluid loss of 850 ml/day associated with a similar reduction in rectal sodium excretion. Discontinuing medication, a rise in the rectal excretions of PGE2, fluid, and sodium was observed. In conclusion, PGE2 formation in the villous adenoma appears to be the cause of fluid secretion by the abnormal tumor epithelium. The use of PG synthetase inhibitors may facilitate the preoperative correction of severe fluid-electrolyte deficits in patients with large villous adenomas of the rectum.

Adenoma↗
PubMed1981

Renal function in streptozotocin-diabetic rats.

Renal function was examined with micropuncture methods in the insulin-treated streptozotocin-diabetic rat. Kidney glomerular filtration rate was significantly higher in the diabetic rats (1.21 ml/min) than in the control group (0.84 ml/min) Nephron glomerular filtration rate increased in proportion to the rise in kidney glomerular filtration rate (diabetic rats: 37.0 nl/min; control rats: 27.9 nl/min). Likewise renal plasma flow was significantly higher in the diabetic rats (4.1 ml/min) than in the control group (3.0 ml/min). Glomerular capillary pressure was identical in both groups (56.0 and 56.0 mmHg, respectively). The proximal intratubular pressure was significantly reduced in the diabetic rats (10.4 mmHg; control value: 12.5 mmHg). The effective glomerular ultrafiltration coefficient was slightly but not significantly higher in the diabetic rats (0.027 nl s-1mmHg-1) than in the control group (0.023 nl s-1mmHg-1). Kidney weight was significantly higher in the diabetic rats (1.15 g; control rats: 0.96 g) while body weight was similar in both groups (diabetic rats: 232 g; control rats: 238 g). Calculations indicate that the increases in transglomerular hydraulic pressure, renal plasma flow and ultrafiltration coefficient of the glomerular membrane contribute about equally to the rise in glomerular filtration rate. The increases in the values of the determinants of glomerular filtration rate may be the result of renal hypertrophy. These studies suggest that this model provides a useful method for investigating kidney function in diabetes, which may have relevance for our understanding of the kidney abnormalities in human diabetes.

Animals↗
PubMed1980

Influence of orchidopexy for cryptorchidism on subsequent fertility.

The concentration of spermatozoa in ejaculate from testes that had been subjected to orchidopexy during childhood was studied in semen samples taken after unilateral vasectomy of the contralateral normal testis in 4 patients. The counts were extremely low, which suggests that this operation does not improve fertility later in life. Sperm concentration is not influenced by unilateral vasectomy or by inguinal herniotomy during childhood.

Adult↗
PubMed1979

Influence of intratubular pressure on proximal tubular compliance and capillary diameter in the rat kidney.

Tubular compliance is the response of tubular diameter to changes in intratubular pressure [7]. Proximal tubular compliance was determined directly by measurements of tubular diameter and pressure and indirectly using a mathematical model of tubular fluid flow based on measurements of the hydraulic pressure gradients along the tubule under free flow conditions and during an induced pressure reduction at the end of the proximal tubule. The two independent methods yielded similar values for compliance. Proximal tubular compliance was found to depend upon the intratubular pressure: tubular compliance was significantly higher (P less than 0.001) when the intratubular pressure was reduced below normal (1.0 micron cm H2O-1) than when the pressure was increased above the control value (0.4 micron cm H2O-1). Almost identical compliance values were measured in sodium pentobarbital and inactin anaesthetized rats (P greater than 0.8). Intratubularpressure changes resulted in inverse changes in the diameters of the adjacent capillaries, suggesting that the peritubular capillaries are distensible structures.

Animals↗
PubMed1978

Polyglycolic acid versus chromic catgut in bladder surgery.

The clinical importance of calcified deposits on sutures in bladder surgery was evaluated in a blind paired randomised trial of 3/0 chromic catgut versus polyglycolic acid 3/0. Cystoscopy with photographic recording was performed 8 weeks after operation in 40 patients without and 8 patients with previous or present bladder stones. None had visible calcified deposits at that time and sutures were only visible in 1 patient from each of the 2 groups without bladder stones. It was concluded that neither chromic catgut nor polyglycolic acid sutures carry any significant risk of bladder stone formation, whether infection is present or not; the conclusion includes both patients with and without previous bladder stones, but is less firm in the former because of the small number of patients studied.

Bacteriuria↗
PubMed1977

Angiotensin II induced reduction of peritubular capillary diameter in the rat kidney.

Large peritubular capillaries were infused consecutively (20 nl-min-1) in random sequence with isotonic saline and angiotensin II (20-80 ng-ml-1). The diameters of the infused capillaries were measured, without knowledge of the infusate used, from colour photographs of the infused area. Angiotensin II induced a significant (p less than 0.001) decrease in capillary diameter (delta = 1.2 +/- 0.2 (SE) micron and delta = 2.1 +/- 0.2 (SE) micron with 20 ng-ml-1 and 80 ng-ml-1 angiotensin II infusates, respectively). This decrease was shown to be independent of external tubular compression: separate experiments in which the surrounding tubules were collapsed by injection of oil blocks yielded similar results. The possibility that the observed reduction in diameter was caused by an angiotensin II induced change in capillary permeability to the staining solution was excluded, since the angiotensin II effect was unchanged when fluorescent dextran (mol. wt. 150 000) was substituted for lissamin green. These experiments indicate that peritubular capillaries contract actively when infused with angiotensin II.

Angiotensin II↗