Response of isolated white fat cells to anti-malarial drugs

Effects of bilirubin on fat cell metabolism and lipolysis

Bilirubin (0.45 mM) inhibited lipolysis and stimulated [1-14C]glucose oxidation by rat fat cells in the presence of an equimolar concentration of bovine serum albumin. Bilirubin was an insulinlike agent with respect to inhibition of lipolysis and stimulation of glucose oxidation. There was a marked inhibition of adenylate cyclase activity of fat cell ghosts by 0.001--0.1 mM bilirubin in the absence of albumin, which was largely reversed by the addition of albumin. Although both bilirubin and free fatty acids bind to albumin, the primary binding sites appear to be separate. The effects of bilirubin at a molar ratio to albumin of 2 or less were not influenced by free fatty acid-to-albumin ratios up to 3. Triglyceride lipase activity of partially purified rat fat cell homogenates was inhibited by bilirubin in the presence of an equimolar concentration of bovine albumin. These data indicate that the antilipolytic action of bilirubin is probably due to direct inhibition of triglyceride lipase through a mechanism that does not involve competition with free fatty acids for binding to albumin.

Cyclic AMP, cyclic GMP, and glucocorticoids as potential metabolic regulators of epidermal proliferation and differentiation

The two cyclic nucleotides, cyclic AMP and cyclic GMP, appear to be central to the metabolic regulation of cell proliferation and differentiation in various cells. Moreover, in many systems glucocorticoids appear to act in concert with or parallel to cyclic AMP. The available evidence suggests that these three molecular species--cyclic AMP, cyclic GMP, and glucocorticoids--may be essential to the normal regulation of epidermal proliferation and differentiation. In 1970, we suggested that perturbed epidermal homeostasis, exemplified by psoriasis, might be associated with low cellular levels of cyclic AMP and, in 1972, with high levels of cyclic GMP as well. Subsequent measurements of these two cyclic nucleotides in our laboratory showed a probable reduction in the cyclic AMP/cyclic GMP ratio in lesional psoriatic tissue. This led to the hypothesis that the cardinal features of psoriatic epidermis--glycogen accumulation, excessive proliferation, and reduced cell specialization--are the results of this reduced ratio. A corollary of this hypothesis was that a psoriatic lesion could not begin or exist without this altered cyclic nucleotide ratio. Recently, four different agents--lithium, a beta adrenergic blocking agent, antimalarials, and iodide--have been found to exacerbate psoriasis and to reduce the formation of cyclic AMP in various tissues. Consequently we believe that cyclic nucleotides are of central importance in the pathogenesis of the epidermal component of psoriasis.