instruction:
Given an abstract of a paper, generate a title for this paper such that conveys the key focus of the paper.
question:
Abstract: Cell cultures of human keratinocytes contain membrane-associated thioredoxin reductase that is extremely active in reducing radicals on the outer plasma membrane. This enzyme activity was confirmed by its purification from cultures of stratified human keratinocytes by affinity column chromatography. The enzyme was assayed both in vivo and in vitro using a spin-labeled quaternary ammonium compound as the substrate, under saturating conditions in free radical substrate. Specific activities were determined by monitoring the sequential decrease in the amplitude of the electron spin resonance signal per unit of cell protein. The following properties were found: Cultures of adult stratified cells have approximately twice the thioredoxin reductase activity of neonatal cells. The enzyme is inhibited by thioprotein inhibitors (i.e., parachloromecuribenzoate and dinitrochlorobenzene). The activity is regulated by calcium concentrations of the cell culture medium. Stratified keratinocytes are half as active in medium containing 2 mM Ca++ compared with 0.1 mM Ca++ concentration. Product inhibition of the enzyme occurs with oxidized coenzyme NADP+ (i.e., 87% inhibition of enzyme activity over 30 min). The enzyme is heat stable at temperatures of 70 degrees C for 10 min. It is inactivated at 75 degrees C. A comparative study of thioredoxin reductase activity on stratified differentiated and undifferentiated rapidly growing cells was performed. Also, enzyme activity was quantitated for cultured keratinocytes isolated from vitiliginous and normal skin of the same donor. The results of this study, and the connection between this enzyme activity and UV-generated free radicals are reconciled in terms of the mechanism of action and metabolic activity of thioredoxin reductase.
answer:
Free radical reduction by thioredoxin reductase at the surface of normal and vitiliginous human keratinocytes.

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Abstract: I have suggested that the X-linked gene Tabby (Ta) and its autosomal mimics in the mouse may be homologous with the genes for sex-linked anhidrotic (hypohidrotic) ectodermal dysplasia (Christ-Siemens-Touraine syndrome, CST) and its apparent autosomal mimics in the human. In the present study, I examined whether anhidrosis, a cardinal feature of CST, is present in the putative mouse sex-linked model, Tabby. The results demonstrate that whereas normal mice perspire on the volar and plantar surfaces of their paws, hemizygous Ta/Y male mice show anhidrosis and absence of sweat glands, as do human hemizygous male sufferers of CST. This result is strongly supportive of the hypothesis that Ta is homologous to the gene for CST.
answer:
Anhidrosis and absence of sweat glands in mice hemizygous for the Tabby gene: supportive evidence for the hypothesis of homology between Tabby and human anhidrotic (hypohidrotic) ectodermal dysplasia (Christ-Siemens-Touraine syndrome).

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Abstract: Calcium absorption in spontaneously hypertensive rats (SHR) has been reported to be increased, decreased or not different from their normotensive Wistar Kyoto (WKy) control. One postulated reason for these conflicting results is an abnormal sensitivity to the intestinal effects of 1,25(OH)2D3 (1,25D3). Previous studies in everted duodenal sacs and perfused duodenum examined the acute response to 1,25D3 only in 12-week-old SHR, which however already had higher basal rates of calcium absorption. Inability to stimulate Ca absorption further was an unexcluded possibility. To test this hypothesis more vigorously, balance and in situ duodenal 45Ca uptake studies were performed in SHR and WKy using four separate protocols yielding the following results. First, in response to pharmacological doses of 1,25D3 (25 ng/100 g body wt/day X 3), four-week-old normotensive female SHR had higher net calcium absorption (41.4 vs. 31.1 mg/day; 61.6 vs. 48.1%), similar to the increases seen in the untreated state. These results suggest intrinsic epithelial differences independent of 1,25D3. Ca absorption was similarly higher in 1,25D3 treated male SHR (42.9 vs. 36.7 mg/day; 60.1 vs. 53.7%). Second, at 12 to 14 weeks of age, low doses of 1,25D3 (8 ng/100 g body wt/day X 6) stimulated net Ca absorption in the female SHR (33.0 to 39.1 mg/day), but not in WKy (26.8 to 29.3 mg/day). In the male, positive effects were again seen only in the SHR (25 to 45 mg/day). Third, in response to three weeks of dietary Ca deprivation, in situ duodenal 45Ca uptake, measured in the conscious awake state, was higher in 35-week-old SHR (70.9 vs. 53.0%).(ABSTRACT TRUNCATED AT 250 WORDS)
answer:
Response of spontaneously hypertensive rats to 1,25(OH)2D3 in vivo.