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Biomedical subjects

A K Sen

Publications and source records attributed to A K Sen.

At least 91 records · Page 5Linked to original sources
PubMed1979

Possible role of cyclic GMP in stimulus-secretion coupling by salt gland of the duck.

Stimulation of salt galnd secretion in domestic ducks in vivo increased the cyclic GMP concentration of the tissue, but had no effect on cyclic AMP levels. Methacholine, which is known to stimulate sodium transport by the glands both in vivo and in vitro, stimulated ouabain-sensitive respiration in salt gland slices. Cyclic GMP stimulated ouabain-sensitive respiration to the same extent as methacholine. Guanylate cyclase stimulators, hydroxylamine and sodium azide, also stimulated ouabain-sensitive respiration. The stimulation of ouabain-sensitive respiration by methacholine was blocked either by atropine or by removal of calcium from the incubation medium. The stimulation of ouabain-sensitive respiration by cyclic GMP still occurred in the absence of calcium. The above observations seem to indicate that cyclic GMP acts as a tertiary link in the process of stimulus-secretion coupling in the tissue.

Animals↗
PubMed1978

Structural studies of a specific polysaccharide isolated from non-agglutinable Vibrio.

The purified, specific polysaccharide from Vibrio cholera type NAG, NV 384, O-antigen, 2A, 2B human, contains glucose (5.14%), galactose (4.21%), mannose (64.8%), xylose (3.16%), arabinose (1.98%), fucose (1.50%), mannuronic acid (14.3%), phosphate (0.32%), 2-amino-2-deoxy-D-glucose (2.9%), and 2-amino-2-deoxy-D-galactose (1.0%). Various reactions have shown that the material comprises a phosphoric diester-linked polysaccharide containing mainly ( 1 leads to 2)-linked mannopyranose residues that are highly branched with other sugar residues.

Chemical Phenomena↗
PubMed1978

Post-obstructive nephropathy in the rat: relationship between NA-K-ATPase activity and renal function.

Na-K-ATPase activity and renal function were compared in rats studied after relief of 24 h of unilateral or bilateral ureteral ligation (UUL or BUL), that is, in the absence or presence of post-obstructive diuresis. Na-K-ATPase activity in the outer medulla of the rat kidney after relief of UUL was not significantly altered immediately but was markedly reduced 1 and 3 days post-obstruction. The decrease in medullary Na-K-ATPase activity was not significantly different from that observed after relief of BUL. These results indicate that decreased Na-K-ATPase activity in the post-obstructive kidney is not responsible for post-obstructive diuresis and is not due to uremia, but is a local phenomenon which is probably secondary to altered renal structure or function. It may be due to decreased filtered sodium load or direct tubular damage, but other data suggests that the decreased medullary solute concentration gradient in the post-obstructive kidney (UUL or BUL) may influence Na-K-ATPase activity which, in turn, contributes to the decreased ability to conserve sodium and water.

Animals↗
PubMed1977

Coronary reactions to cardiac hyperactivity and to hypoxia in isolated perfused heart of rat.

1. Continuous recording of cardiac force of contraction, heart rate and coronary flow from isolated perfused hearts of rats was used to study coronary reactions: (a) to cardiostimulation with noradrenaline, CaCl2, or electrically induced tachycardia; (b) to short duration stoppage of coronary inflow (hypoxia). 2. The heart rate was controlled by electrical pacing. Coronary vasodilatation resulted from cardiostimulation or hypoxia. This coronary response was greater at higher heart rates. 3. In parallel experiments administration of noradrenaline to hearts paced at different frequencies resulted in a rate-dependent elevation of adenosine-3',5'-cyclic monophosphate (cyclic AMP). 4. Duration of hypoxia leading to different degrees of reactive hyperaemia did not change the cardiac cyclic AMP levels. 5. Coronary vasodilatation due to increased cardiac metabolism produced by noradrenaline, Ca2+ or tachycardia was enhanced by the phosphodiesterase inhibitors diazoxide and papaverine while it was inhibited during the administration of prostaglandin E2.6. Reactive hyperaemia was unaffected by diazoxide, papaverine or prostaglandin E2. 7. Catecholamine depletion by reserpine did not influence metabolic coronary dilatation nor the reactive hyperaemic responses. 8. We postulate that there are at least two types of coronary reactions: one in response to hypoxia, 'reactive hyperaemia', and another resulting from cardiac hyperactivity, 'metabolic coronary dilatation'. The latter, blocked by prostaglandin E2 and enhanced by diazoxide or papaverine, would be triggered by cyclic AMP while reactive hyperaemia would result from other mechanisms.

Animals↗
PubMed1977

Effect of osmolality on renal medullary Na-K-ATPase activity in the postobstructive kidney.

The aim of this study was to determine the effect of changes in osmolality on the reduced renal medullary Na-K-ATPase (EC 3.6.1.3) activity of the postobstructive kidney. The effect of osmolality on renal medullary Na-K-ATPase activity was studied by incubating tissue slices from sham-operated and bilaterally obstructed rats in media with osmolality varied before enzyme isolation using sodium chloride, choline chloride, or sucrose. Both sham-operated and bilaterally obstructed rat renal medullary enzyme showed a similar increase in activity with increased osmolality due to sodium chloride. Medullary Na-K-ATPase from the postobstructive kidney also showed increased activity with osmotic changes induced by choline chloride or sucrose. It is proposed that the decrease of Na-K-ATPase activity observed after bilateral ureteral obstruction is due, at least in part, to the loss of the solute concentration gradient in the kidney.

Adenosine Triphosphatases↗
PubMed1976

Induction of the catalytic protein of (Na+ plus K+)-ATPase in the salt gland of the duck.

The (Na+ plus K+)-ATPase activities in salt gland homogenates increased 3- to 4-fold after saline treatment of ducks for 3 weeks. The ATPase was purified to a specific activity of 460 and 1015 mumol Pi/mg protein per h, respectively, in control and saline-treated ducks. The catalytic protein was identified on polyacrylamide electrophoresis gels by phosphorylating the enzyme with (32P)ATP. The molecular weight of the protein was estimated to be 98 000. The amount of catalytic unit increased commensurately with the enzyme activity after saline treatment. It is therefore concluded that the increased enzyme activity is due to a de novo enzyme synthesis and is not an activation effect. Phospholipid concentration in the salt gland tissue increased 1.7-fold after the saline treatment. Significant increases occurred in the percentage of the total phospholipids as phosphatidylserine and sphingomyelin. In the partially purified (Na+ plus K+)-ATPase preparation, the percentage composition of phosphatidylserine and phosphatidylethanolamine increased after saline treatment.

Adenosine Triphosphatases↗
PubMed1976

Urinary cyclic AMP in relation to lithium treatment in manic-depressive illness.

Urnary cyclic AMP was measured longitudinally in six patients with bipolar affective disorder. The values varied from 3.55 to 19.0 mugmol/24 hours with considerable variation between subjects. Three of these patients improved with administration of lithium carbonate. This improvement was not correlated with a change in cyclic AMP excretion. Five normal male volunteers were studied over a 5-day period. The urinary excretion for this group showed the same large intersubject variability but smaller intrasubject variation as was found for the patient group. It is suggested that erroneous results may be obtained for urinary cyclic AMP excretion if mean group values are used from patients not studied longitudinally.

Adult↗
PubMed1976

Prostaglandin E2 and cyclic AMP in the coronary vasodilatation due to cardiac hyperactivity.

In the isolated perfused rat heart, the dose-related cardiostimulation produced by norepinephrine (NE) or calcium chloride (Ca2+) was followed by a corresponding increase in coronary flow (CF) and in the cardiac level of adenosine 3',5'-cyclic phosphate (cAMP). Prolonged prostaglandin E2 (pge2) infusion did not change the basic force of contraction, CF, or cAMP level but when NE or Ca2+ were administered, only the responses of the CF and the cAMP were diminished. A phosphodiesterase inhibitor, diazoxide (Dx), caused insignificant increase in the basal cAMP, without affecting the force of contraction or CF. With NE or Ca2+, during Dx both the changes in CF and cAMP were augmented compared to the nontreated hearts. The inhibitory effects of NE or Ca2+ remained unchanged. Propranolol abolished the NE but not the Ca2+ effects. It is suggested that PGE2 modulates the cardiac cAMP level and that the latter plays an important role in the adaptive regulation of the CF. It is also postulated that changes in cAMP levels may be brought about by the hyperactivity per se produced by a variety of cardiostimulating agents.

Animals↗