Endocrine Abstracts

Growth hormone (GH) acts chronically to decrease adiposity, at least in part by the inhibition of lipogenesis. One or more of the twelve isoforms of Protein kinase C (PKC) may be involved in this chronic effect of GH on lipogenesis in adipocytes.

Two approaches were adopted to examine the role of PKC isoforms in GH signalling. The first method involved maintaining explants of Finn/Dorset sheep adipose tissue with insulin, GH or a combination of both, for 24h periods, up to 72h. Samples were prepared after 24h, 48h and 72h, and tested for the expression of PKC isoforms by Western blotting, using specific polyclonal antibodies (BD Transduction). A second method utilized inhibitors of PKC isoforms; GF109203X (inhibits alpha, beta, gamma, delta and epsilon), Go6976 (inhibits alpha and beta), Go6983 (inhibits alpha, beta, gamma, delta and zeta) and Rottlerin (inhibits delta); all were purchased from Calbiochem. For this experiment, explants were maintained for 48h with insulin, GH or a combination of both, plus or minus inhibitors for the final 24h period. Lipogenesis was then measured by the incorporation of acetate into lipid.

The results were analyzed using ANOVA (general liner model) followed by Tukey tests. Western blotting showed that GH had no effect on the amount of PKC alpha, beta or delta, but did reduce the amount of PKC epsilon (P<0.05). This effect was apparent regardless of the presence of insulin. Also, insulin caused an increase in the amount of PKC alpha (P<0.05). Chronic exposure to GH reduced the rate of lipogenesis (P<0.01); this effect was partially reversed by GF109203X (P<0.05), whereas the other inhibitors had no significant effect. By comaprison of the specificities of the inhibitors of the PKC isoforms, the finding also suggests a role for PKC epsilon in mediating the effect of GH on lipogenesis.