Biomedical subjects
Publications and source records attributed to S Srinivasan.
The traits, earlobe attachment, hand clasping and arm folding, are found to show a high degree of homogeneity in the Tamil Brahmans. The latter appear to be closest to the Bengali Brahmans, with respect to all three traits, and differ significantly from other Brahman populations, with respect to earlobe.
Primary cultures of mouse adrenocortical tumors provide a sensitive system for investigating the effects of the enterotoxin of the V. cholerae (choleragen) on cyclic-AMP metabolism in the intact cell. Like ACTH, the toxin stimulates the synthesis and release of steroids from these cells but its mode of action differs from that of ACTH. The steroidogenic response to ACTH is immediate and of limited duration. The initial rate of steroidogenesis is the highest. In contrast, the steroidogenic response to choleragen is preceded by a 30-240 minute lag period which is inversely related to the concentration of the toxin. Whereas prolongation of the response to a single dose of ACTH requires hormone concentrations above those producing maximal initial steroidogenic activity, persistent steroidogenesis is induced at all levels of the toxin. Steroidogenic responses are detectable with 10 pg/ml of choleragen or less. The respective effects of ACTH and choleragen on cyclic-AMP synthesis and release into the medium parallel those on steroidogenesis. Intracellular cyclic-AMP levels in ACTH-treated cells reach a peak within 20-30 minutes and decline to normal levels within 2-4 hours. In choleragen-treated cells, after the lage period, the levels of intracellular cyclic-AMP remain above control levels indefinitely. The effects of ACTH and choleragen on cyclic-AMP biosynthesis are additive at all levels of the two compounds. The effects of choleragen are blocked by prior treatment of the toxin with a five-fold molar excess of ganglioside GM1, a presumed constituent of the toxin-binding site.
Extensive serum lipid analyses, with specific emphasis on the concentration of serum beta and pre-beta-lipoproteins, were made on 93 patients who had a clinical diagnosis of angina pectoris and were undergoing coronary angiographic studies. Those individuals with abnormal angiographic evidence of obstructive coronary artery disease, including a group with a prior myocardial infarction, have almost uniformly elevated serum beta-lipoprotein levels when related to an arbitrary division based on the mean values for a "normal" adult population at a similar age level. Compared to serum cholesterol and serum triglycerides, the serum lipoprotein concentrations, specifically beta-lipoproteins, appear to be a more useful parameter for predicting the existence of coronary artery disease. Further studies relating clinical risk factors to coronary artery disease might be better approached by using angiography of coronary vessels rather than myocardial infarction or sudden death from coronary artery disease as an endpoint of morbid data.
An increase in the incidence of thromboembolic disorders has been associated with oral contraceptive use, though the causative mechanisms remain unclear. Our studies indicate that the contraceptive steroids, irrespective of the intermediary metabolic processes involved, cause changes in the surface charge characteristics of the blood vessel wall and blood cells in the following cases: (i) in experiments using dogs, the hormonal steroids result in a greater reduction in the pore surface charge of veins than in arteries; (ii) in rats, the current induced mesenteric occlusion times are significantly lowered following administration of combined contraceptives steroids; (iii) in humans, the electrophoretic mobilities of erythrocytes and platelets from women taking Ovral and Demulen are lower than in controls, and (iv) there is no significant alteration of plasma coagulation times of women who are on injectable progestin therapy. Demulen and Ovral appear to result in a slight decrease in activated partial thromboplastin times compared to controls.
In previous studies from our laboratories, it was shown that metals and alloys which register negative potentials in blood vs the normal hydrogen electrode tend to be antithrombogenic while those with positive potentials are invariably thrombogenic. The present paper deals with a novel approach of maintaining an implanted metallic prosthesis at a negative potential. A copper vascular prosthesis in a dog was maintained at cathodic potentials by a small amplitude (+/- 10 mV) high-frequency ac (100 kHz) on the prosthesis. The prostheses were removed after 2 hours, 6 hours, 1 day, and 42 days, with subsequent visual and scanning electron microscopic examination of the prostheses completed. All tubes were free of thrombus deposits. Minimal junctional thrombi were found, probably due to differences in physicochemical characteristics of the vascular prostheses and recipient vessels. The results are compared with those in the control group (copper tubes with no current) and dc polarized copper tubes. While the control tubes occluded in 2 to 6 hours, the dc and ac polarized tubes remained patent. Of the ac and dc polarized tubes, the former tubes lasted up to 6 weeks with less thrombus deposit. The mechanism of operation of the ac polarized copper prosthesis is not fully understood.
The effects of electric currents on the uptake of fluoride ions by human teeth, in vitro were determined by measuring the change in fluoride ion concentration of the electrolyte in which teeth were subjected to the electrochemical treatment. There was an enhanced uptake when the gold electrode embedded in the tooth was polarized anodically. Evidence that the fluoride ions were taken upon by the teeth was shown by subsequent cathodic polarization of the gold electrode in a fluoride free electrolyte and by measurement of fluoride release into the solution.
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