Fig. 2.

Leptin suppresses proinsulin mRNA levels in human islets in high (11.1 mM), but not normal (5.6 mM), concentrations of glucose. Aliquots of human islets were cultured for 48 h in the absence (A; vehicle) or the presence (B) of 6.25 nM human leptin. RNA concentrations were determined by semiquantitative RT-PCR as previously described (51). Actin mRNA served as a control. The bar graphs represent the relative amounts of RT-PCR products determined by fluorescence densitometry (see Materials and Methods). Values are the mean ± SEM (n = 3). The densitometric value for 5.6 mM glucose at 6 h was arbitrarily set at 1.0.