Effect of zinc on insulin binding to rat adipocytes and hepatic membranes and to human placental membranes and IM-9 lymphocytes

The effect of ionic zinc on the binding of 125I-insulin to a variety of tissues with well-characterized insulin receptors has been assessed. In the isolated rat adipocyte, zinc (250 to 1000 microM) showed dose-dependent stimulation of insulin specific binding, with little change in non-specific binding. This effect was rapid and sustained during a 60 min incubation and was due to a Zn-mediated increase in the number of available binding sites. No changes in binding affinity were apparent. A similar but smaller stimulation of insulin binding was observed at lower Zn concentrations (25-50 microM) in rat liver membranes. In this tissue, higher doses of Zn caused a marked rise in non-specific binding and resulted in the loss of any apparent specific binding of insulin. Similar effects were seen in IM-9 lymphocytes and human placental membranes, although in this latter case the Zn effect on non-specific binding was less marked. These data indicate that ionic zinc exerts a tissue-specific stimulation of insulin binding to its receptors. An intriguing corollary, that requires further study, is that this effect may be related to the known association of insulin with Zn, and thus to an enhancement of insulin action in vivo, at least on the adipocyte.     

Academic Freedom and the Professional Responsibilities of Applied Ethicists: A comment on Minerva

Academic freedom is an important good, but it comes with several responsibilities. In this commentary we seek to do two things. First, we argue against Francesca Minerva's view of academic freedom as presented in her article ‘New threats to academic freedom’ on a number of grounds. We reject the nature of the absolutist moral claim to free speech for academics implicit in the article; we reject the elitist role for academics as truth‐seekers explicit in her view; and we reject a possible more moderate re‐construction of her view based on the harm/offence distinction. Second, we identify some of the responsibilities of applied ethicists, and illustrate how they recommend against allowing for anonymous publication of research. Such a proposal points to the wider perils of a public discourse which eschews the calm and careful discussion of ideas.     

Demonstration of in vitro actions of growth hormone on isolated rat adipocytes

Previous studies have shown that adipocytes isolated from normal rats possess specific receptors for growth hormone (GH). Thus, we have now investigated the direct effects on such cells of GH added in vitro. The biological actions of GH determined were the stimulation of 14C-glucose oxidation to 14CO2 and conversion to 14C-lipid. As in adipose segments, hGH stimulation of these parameters required a 3-4 hr preincubation period in GH-free medium. The effect of hGH or bGH was dose-dependent with maximal effects at 1-2 micrograms/ml (CO2 55 +/- 13% stimulation above basal n = 9; lipid 33 +/- 4% n = 21, mean +/- SEM). The magnitude of the effect in isolated adipocytes was lower than that seen in adipose segments from similar groups of animals (lipid 67 +/- 26%, n = 4). The induction of responsiveness by preincubation was accompanied by a parallel increase in 125I-hGH binding. These studies have demonstrated that adipocytes from normal rats not only possess specific receptors for GH but also are metabolically responsive to GH added in vitro. These data suggest that the isolated rat adipocyte should be a useful model for further investigation of the relationship between GH receptor and post-receptor events.