title: Homologous and heterologous desensitization of one of the pathways of the alpha 1-adrenergic action. Effects of epinephrine, vasopressin, angiotensin II and phorbol 12-myristate 13-acetate.
abstract: Activation of protein kinase C blocks the alpha 1-adrenergic action in hepatocytes. Preincubation of hepatocytes (in buffer with or without calcium) with vasopressin, angiotensin II, phorbol myristate acetate (PMA) or epinephrine + propranolol markedly diminished the alpha 1-adrenergic responsiveness of the cells (stimulation of ureagenesis) assayed in buffer without calcium. On the contrary, when the alpha 1-adrenergic responsiveness was assayed in buffer containing calcium no effect of the preincubation with vasopressin, angiotensin II or PMA was observed. Preincubation with epinephrine diminished the alpha 1-adrenergic responsiveness of the cells. In hepatocytes from hypothyroid rats the preincubation with the activators of protein kinase C (vasopressin, angiotensin II, phorbol 12-myristate 13-acetate and epinephrine) reduced markedly the alpha 1-adrenergic responsiveness of the cells, whereas in identical experiments using cells from adrenalectomized rats only the preincubation with epinephrine diminished the responsiveness. It is concluded that activation of protein kinase C induces desensitization of the alpha 1-adrenergic action in hepatocytes and that the calcium-independent pathway of the alpha 1-adrenergic action (predominant in cells from hypothyroid animals) resensitizes more slowly than the calcium-dependent pathway (predominant in cells from adrenalectomized rats). Epinephrine in addition to inducing this type of desensitization (through protein kinase C) leads to a further refractoriness of the cells towards alpha 1-adrenergic agonists.
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology*; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D010704:Phorbols / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014667:Vasopressins / Q000494:pharmacology*
chemical_list: D010704:Phorbols; D011942:Receptors, Adrenergic, alpha; D014667:Vasopressins; D000804:Angiotensin II; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D004837:Epinephrine