Descripción: The relationship between antidopaminergic drugs and glucose has not been extensively studied, even though chronic neuroleptic treatment causes hyperinsulinemia in normal subjects or is associated with diabetes in psychiatric patients. We sought to evaluate dopamine D2 receptor (D2R) participation in pancreatic function. Glucose homeostasis was studied in D2R knockout mice (Drd2-/-) mice and in isolated islets from wild-type and Drd2-/- mice, using different pharmacological tools. Pancreas immunohistochemistry was performed. Drd2-/- male mice exhibited an impairment of insulin response to glucose and high fasting glucose levels and were glucose intolerant. Glucose intolerance resulted from a blunted insulin secretory response, rather than insulin resistance, as shown by glucose-stimulated insulin secretion tests (GSIS) in vivo and in vitro and by a conserved insulin tolerance test in vivo. On the other hand, short-term treatment with cabergoline, a dopamine agonist, resulted in glucose intolerance and decreased insulin response to glucose in wild-type but not in Drd2 -/- mice; this effect was partially prevented by haloperidol, a D2R antagonist. In vitro results indicated that GSIS was impaired in islets from Drd2-/- mice and that only in wild-type islets did dopamine inhibit GSIS, an effect that was blocked by a D2R but not a D1R antagonist. Finally, immunohistochemistry showed a diminished pancreatic β-cell mass in Drd2-/-mice and decreasedβ-cell replication in 2-month-old Drd2-/- mice. Pancreatic D2Rs inhibit glucose-stimulated insulin release. Lack of dopaminergic inhibition throughout development may exert a gradual deteriorating effect on insulin homeostasis, so that eventually glucose intolerance develops. Copyright © 2010 by The Endocrine Society.

Descripción: The present study focused on interactions between signaling pathways activated by progestins and by type I and II receptor tyrosine kinases (RTKs) in mammary tumors. An experimental model in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in Balb/c mice was used. MPA-stimulated proliferation, both in vivo and in vitro, of progestin-dependent tumors induced up-regulation of ErbB-2 protein levels and tyrosine phosphorylation of this receptor. Combinations of antisense oligodeoxynueleotides (ASODNs) directed to ErbB-2 mRNA with ASODNs directed to the insulin-like growth factor-I receptor (IGF-IR) were used to study the effect of the simultaneous block of these receptors on the MPA-induced proliferation of epithelial cells from the progestin-dependent C4HD line. Neither synergistic nor additive effects on the inhibition of MPA-induced proliferation of C4HD cells were observed as a result of the combination of these ASODNs. Suppression of IGF-IR expression by ASODNs resulted in complete abrogation of MPA-induced phosphorylation of ErbB-2 in C4HD cells, whereas blockage of ErbB-2 did not affect IGF-IR phosphorylation. These results show the existence of a hierarchical interaction between IGF-IR and ErbB-2, by means of which IGF-IR directs ErbB-2 phosphorylation. We demonstrated, for the first time, that this hierarchical interaction involves physical association of both receptors, resulting in the formation of a heteromeric complex. Furthermore, confocal laser microscopy experiments demonstrated that MPA was able to induce co-localization of ErbB-2 and IGF-IR. This hetero-oligomer was also found in MCF-7 human breast cancer cells in which association of IGF-IR and ErbB-2 was induced by heregulin and IGF-I.