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Biomedical subjects

S Sinha

Publications and source records attributed to S Sinha.

At least 505 records · Page 28Linked to original sources
PubMed1977

Effects of insulin, ADH, and cyclic AMP on sodium transport in the toad bladder.

These studies further define the mechanisms by which insulin stimulates Na transport in the toad bladder. Serosal but not mucosal addition of insulin, 100-1,000 mU/ml, stimulated short-circuit current (SCC) by 25-50%. The initial rise in SCC occurred at 5 min and the peak response at 15-25 min. Doses of insulin greater than 250 mU/ml increased SCC values for up to 3 h. Actinomycin D did not block the early rise in SCC produced by insulin, but it blocked the delayed effects. Insulin increased SCC in substrate-depleted bladders, although the increase in SCC was less (P less than 0.01) than in nonsubstrate-depleted bladders. Pyruvate addition to substrate-depleted bladders restored to normal the rise in SCC observed after insulin. Simultaneous addition of ADH and insulin led to an increase in SCC that was greater than the sum of the responses observed when each hormone was added independently. Synergistic effects on SCC were also obtained with cyclic AMP and insulin. Insulin did not increase cyclic AMP levels in toad bladder epithelial cells. It is suggested that insulin stimulates active Na transport by two mechanisms: 1) a rapid phase, which may involve unmasking of pump sites within the membrane, and 2) a delayed effect which seems to require protein synthesis. The synergism of which seems to require protein synthesis. The synergism of insulin with ADH or cyclic AMP may reflect a facilitative effect of insulin on ADH or cyclic AMP-sensitive pump sites or, alternatively, the uncovering of latent pump sites that then may be available to stimulation by ADH or cyclic AMP.

Animals↗
PubMed1977

Effects of ionophore A23187 on base-line and vasopressin-stimulated sodium transport in the toad bladder.

The cation specific ionophore A23187 (Io) is a useful tool for studying the role of intracellular Ca++ (Ca++)i in physiologic processes. The present studies explore the role of (Ca++)i on Na transport in the toad bladder. Scraped bladder cells exposed to 1 muM Io for 60 min took up 100% more 45Ca than control cells. Io, 1 muM, added to the serosal side of bladders incubated in standard Ringers containing 2.5 mM Ca++ inhibited short circuit current (SCC) values by a mean of 30% at 60 min and 50% at 90 min. Io did not inhibit SCC significantly in bladders incubated in Ringers containing 0.2 mM Ca++. These data indicate that the effects of Io on SCC depend on the levels of external Ca++ and suggest that entry of Ca++ into cells mediates the inhibition of base-line SCC. PReincubation of the bladders with either lanthanum chloride or pentobarbital prevented the increased 45Ca uptake produced by ionophore as well as theinhibition of SCC caused by the antibiotic. Vasopressin, antidiuretic hormone (ADH). 10 MU/ml, increased peak SCC by 247% in bladders preincubated for 1 h in Ringers with 2.5 mM Ca++ and 1 muM Io and by 318% in control bladders (P less than 0.01). Bladders exposed to 1 muM Io in Ringers with 0.2 mM Ca++ had an increase in SCC after ADH comparable to that observed in controls. Since the effects of ADH on SCC are mediated by cyclic AMP, we tested the effects of Io on cAMP production by scraped toad bladder cells. ADH increased cAMP from 8 to 30 pmol/mg protein in controls but it did not increase cAMP over base-line values in the presence of Io when the Ringers contained 2.5 mM Ca++. Io did not inhibit cAMP production in response to ADH when the Ca++ in the Ringers was 0.2 mM. The results indicate that Io inhibits baseline and ADH stimulated SCC by increasing (Ca++)i or Ca++ bound to the cell membrane. It is suggested that: ()( (Ca++)i or membrane-bound Ca++ plays a key role in base-line and ADH stimulated Na transport in the toad bladder; (2) inhibition of ADH stimulated SCC may be due inpart to decreased cAMP generation in response to ADH when (Ca++)i or membrane-bound Ca++ levels are increased.

Animals↗
PubMed1975

Development of longitudinal retraction of carotid arteries in neonatal dogs.

Longitudinal retraction of carotid arteries, was examined in 105 neonatal puppies as a measure of longitudinal traction. Percent vessel retraction increased linearly with age. This was attributed to stretching of the vessels by growth and to changes in connective tissue composition. The mechanical significance of artery retraction was discussed.

Age Factors↗
PubMed1975

Localized myocardial responses to stimulation of small cardiac branches of the vagus.

Direct electrical excitation of small cardiac branches from the thoracic vagus elicited highly localized and differential responses from individualized segments of the myocardium. For example, small nerves from the vagus at the level of the superior pulmonary veins frequently induced moderate inhibition in contractile force of the ipsilateral atrium with little or no influences elsewhere. Branches from more rostral levels of the thoracic vagus induced changes in atrial contractility, with or without changes in sinoauricular (SA) nodal discharge rates, and often with partial or complete artioventricular (AV) nodal blockade.Excitation of individual, small vagal branches sometimes initiated acceleration in artrial rate and augmentation in atrial contractile force concurrently with complete AV nodal blockade. The negative dromotropic response was eliminated by atropine, leaving only the positive chronotropic and inotropic changes, thus revealing the intermingling of both sympathetic and parasympathetic components even in these small branches. There are frequently in excess of 20 small branches from the vagal trunk between the level of the caudal cervical ganglion and the superior pulmonary vein on each side which will induce highly selective changes in cardiac function upon stimulation. Inhibitory branches are particularly concentrated in the region of the recurrent laryngeal nerve on either side.

Animals↗
PubMedDate not supplied

MR imaging signal response to sustained stimulation in human visual cortex.

The response of signal intensity to transient (on-off) motor and sensory stimulation has been well studied; however, the dependence of signal response on the duration of stimulus requires further characterization. The objective of this study was to determine the time course of signal response in the human visual cortex to prolonged, sustained stimulation and to examine possible contributory physiologic mechanisms. Nine healthy volunteers underwent magnetic resonance (MR) imaging during sustained visual stimulation with light-proof binocular goggles. With photic stimulation, activation was observed in all subjects as an increase in signal intensity of the visual cortex. With sustained stimulation, a gradual decrease in signal intensity was subsequently observed, with progression toward an apparent steady state. Correlation with positron emission tomographic, MR spectroscopic, and visual evoked-potential data suggests that the initial uncoupling of cerebral blood flow and oxidative metabolism with a neuronal activation burst may represent a transient phenomenon. This quick-response phase may proceed to an equilibrium coupling of flow and oxidative metabolism, with a gradual normalization of venous deoxyhemoglobin levels and signal intensity.

Adult↗
PubMedDate not supplied

Black blood dual phase turbo FLASH MR imaging of the heart.

An MR imaging scheme for dark blood cardiac images acquired simultaneously in end diastolic and end systolic phases, in breath-hold times, is presented. The sequence consists of a magnetization preparation period followed by two segmented k-space acquisitions. Image quality was investigated with respect to different sequence parameters (optimal values are indicated in brackets): (a) echo time (TE)/repetition time (TR)/ flip angle (FA) (3/6.2 msec/20 degrees); (b) number of lines/ segments in the acquisition window (11 lines/segment); (c) location of acquisition windows and inversion time; and (d) thickness of slice "reinverted" during preparation (1.53 times the acquisition slice thickness). The image quality of the basal slices at end systole was critically dependent on the last parameter. High quality short axis views of the heart, with good blood signal suppression, were acquired with the optimized sequence on four volunteers from apex to base at two phases in 10 breath-holds.

Blood↗