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Biomedical subjects

M C Churchill

Publications and source records attributed to M C Churchill.

45 records · Page 3Linked to original sources
PubMed1979

Renal function in Lophius americanus: effects of angiotensin II.

Arterial blood pressure, urine flow rate, and plasma and urine electrolytes were measured in the aglomerular goosefish (L. americanus) before, during, and after the intravenous infusion of angiotensin II (from 5 to 280 ng/min.kg body wt). Increases in arterial blood pressure were directly related to the logarithm of the angiotensin infusion rate (r = 0.62, P less than 0.005). Angiotensin also increased urine flow from 0.676 +/- 0.065 to 0.755 +/- 0.068 ml/h.kg body wt (P less than 0.005) and Na excretion from 41.0 +/- 5.5 to 54.4 +/- 7.0 mumol/h.kg body wt (P less than 0.001). In 17 of the 19 fish infused with angiotensin the diuretic and natriuretic effects were directly related to the logarithm of the infusion rate (r = 0.44, P less than 0.04 and r = 0.51, P less than 0.02, respectively). There was no relationship between the pressor and the diuretic or natriuretic effects of angiotensin II. These results are consistent with inhibitory effects of angiotensin on solute transport by aglomerular tubules.

Angiotensin II↗
PubMed1979

Phenytoin stimulates renin secretion from rat kidney slices.

Phenytoin stimulated renin secretion from rat renal cortical slices. A sigmoid relationship was found between stimulatory effect and log concentration, from 1 to 8 mg/100 ml. The ED5C was 2.8 mg/100 ml. Basal secretion and the stimulation of secretion elicited by phenytoin were blocked by incubating slices in a K-free medium and by adding 1 mM ouabain to the medium (both of which inhibit Na,K-adenosine triphosphatase activity and increase intracellular Na concentration), and by reductions in the Na concentration of the incubation medium. NaCl in the incubation medium was replaced by choline chloride so that osmolality and Cl concentration were held constant. It is suggested that renin secretion rate is directly related to the transmembrane Na gradient, that phenytoin stimulates secretion by increasing the gradient, and that ouabain, K-free medium and reductions in Na concentration of the medium inhibit secretion by reducing the gradient.

Animals↗
PubMed1977

Tubulo-glomerular feedback in the rat.

Using conventional micropuncture techniques in 53 adult Sprague-Dawley rats anesthetized with sodium pentobarbital, single nephron GFR at proximal sites (snGFRprox) averaged 30+/-1 nl/min (76 tubules) and at distal sites (snGFRdis), 33+/-2 nl/min (90 tubules). Thus, in spite of interruption of macula densa fluid flow during its measurement, snGFRprox was not significantly greater than snGFRdis (p less than 0.05). Whole kidney GFR averaged 0.9+/-0.07 ml/min before and 1.0+/-0.05 ml/min during an intravenous infusion of SQ20,881, a substance which inhibits production of angiotensin II. Similarly, snGFRdis was unaffected by SQ20,881; the mean difference between paired snGFRdis (collection during NaCl infusion minus recollection at same sites during SQ20,881 infusion) was 6+/-4 nl/min (p less than 0.5). These results suggest that under the conditions of the experiments, tubulo-glomerular feedback is not operative and that angiotensin II plays no role in controlling filtration.

Animals↗
PubMed1975

Renin and distal tubule Na during stop flow in dogs.

Using radioimmunoassay techniques, arteria (A) and renal venous (RV) plasma renin activities were measured in sodium pentobarbital-anesthetized dogs during clearance and stop-flow periods. Changes in RV-A renin were used to estimate changes in renin secretion. RV-A renin increased during stop flow from its average value during clearance periods, whether 10% mannitol in 0.15 M NaCl or 10% mannitol in 0.1 M Na2SO4 was being administered intravenously. However, RV-A renin during mannitol + NaCl stop-flow periods was significantly greater than during mannitol + Na2SO4 stop-flow periods. Distal tubular fluid Na concentrations as indicated by stop-flow analysis were higher during the latter. These observations suggest that a macula densa stimulus, Na concentration, and/or load, may control renin secretion during ureteral occlusion.

Aminohippuric Acids↗