Macrocyclic phospholipids containing 32-44 ring atoms were synthesized by a route involving a high-temperature Glaser oxidation as the key step. These lipids are analogous to mammalian phospholipids except a single extra carboncarbon bond joins the chain termini. The new lipids offered, therefore, an opportunity to examine thermotropic properties of their membranes when the chains within a given molecule are unable to move independently of one another. It was concluded that chain "tethering" (a) raises the transition temperatures substantially for all but the shortest lipids, (b) lowers enthalpies of transition by, in part, reducing the number of gauche C-C linkages created during the melting process, and (c) lowers entropies of transition by impeding motional freedom within the liquid-crystalline phase. Molecular mechanics calculations on the macrocyclic lipids are described briefly.

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To evaluate the effect of glucocorticoids on corticosteroid binding globulin (CBG), we measured the binding capacity and binding affinity of cortisol for CBG in normal subjects, patients receiving glucocorticoids and patients with Cushing's syndrome. Normal subjects had a mean binding capacity of 3.8 (+/- SD 0.7) X 10(-7) mol/l and mean binding affinity of 1.96 +/- 0.48 X 10(-8) M. Patients with Cushing's syndrome had a 40% decrease in binding capacity (2.3 +/- 0.4 X 10(-7) mol/l) compared to control subjects and significantly lower mean binding capacity than patients receiving pharmacological (2.9 +/- 0.6 X 10(-7) mol/l) and physiological doses of glucocorticoids (3.4 +/- 0.6 X 10(-7) mol/l) (P = 0.05 one-way analysis of variance). Patients with endogenous cortisol excess also had significantly lower mean binding affinity (1.54 +/- 0.37 X 10(-8) M) than normal subjects and glucocorticoid treated subjects. These changes suggest that both endogenous and exogenous glucocorticoids can modulate circulating levels of CBG and may have important implications for patients receiving steroid therapy.

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