Zinc absorption by intestines of rats fed either zinc-deficient or zinc-adequate diets was measured by simultaneous luminal and vascular perfusion. The rate of absorption increased steadily for the first 30-40 min of perfusion over the entire lumen zinc concentration range examined (8-234 microM). During the last 10 min of perfusion the absorption rate did not change appreciably with time (steady state), and absorption by intestines from the zinc-depleted rats showed evidence of both carrier-mediated (saturable) and nonmediated (nonsaturable) components. The former had a Km of 55 microM and a Jmax of 3.3 nmol X min-1. In contrast, the absorption rate during the last 10 min of the perfusion period was a sigmoidal function of the luminal zinc concentration with intestines from zinc-adequate rats. The cytosol 65Zn concentration increased proportionately with increased luminal 65Zn concentration but was significantly greater in intestines from zinc-depleted rats. Both high-molecular-weight species and metallothionein accounted for this increase in cytosolic 65Zn. An increase in the vascular bed zinc concentration increased the amount of zinc transferred to the mucosal cytosol but did not increase the amount transferred to the lumen. These results suggest a second mechanism of absorption may be induced during a dietary zinc depletion that is carrier mediated. Moreover, while zinc is transferred in the vascular-to-mucosal direction from the vascular supply, little actually enters the lumen.

The effect of glucocorticoids on respiratory glycoconjugate (RGC) secretion was studied in a cat tracheal organ culture system. Dexamethasone (10(-5) to 10(-9) M) added to culture medium for 24 h caused a dose-related reversible inhibition of RCG of as much as 40% with a peak effect at 24 to 60 h after initiation of dexamethasone treatment. A monoclonal antilipocortin antibody added to the cultures blocked the inhibitory effect of dexamethasone on RGC secretion and accelerated the reversal of the dexamethasone effect after discontinuation of dexamethasone treatment. A control antibody without antilipocortin activity had no effect on RGC secretion or dexamethasone-induced inhibition of RGC secretion. Measurement of the concentration of lipocortin in airways revealed a 220% increase after treatment with dexamethasone for 24 h. We conclude that dexamethasone inhibits RGC secretion through the induction of lipocortin synthesis.

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The present study describes the separation and purification of a reverse transcriptase and cellular DNA polymerases from the human spleen of a patient with myelofibrotic syndrome. The specific requirements with respect to bivalent cations and template-primers for DNA polymerase-alpha, DNA polymerase-beta and DNA polymerase-gamma, as well as for the reverse transcriptase, are reported. Sedimentation-velocity measurements of the purified enzymes gave values of 150000, 40000, 100000 and 70000 daltons for DNA polymerase-alpha DNA polymerase-beta, DNA polymerase-gamma and the reverse transcriptase respectively. Serological studies have shown that the reverse transcriptase from human spleen is not antigenically related to cellular DNA polymerase-alpha, -beta or -gamma, but is antigenically related to reverse transcriptase from simian sarcoma virus and gibbon-ape leukaemia virus.