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  • Title: Comparison of in vivo and in vitro corticotropin-releasing hormone-stimulated release of proopiomelanocortin-derived peptides in cats.
    Author: Willemse T, Mol JA.
    Journal: Am J Vet Res; 1994 Dec; 55(12):1677-81. PubMed ID: 7887510.
    Abstract:
    In 6 cats, the effect of IV administration of various concentrations of ovine corticotropin-releasing hormone (oCRH) on plasma concentrations of cortisol, alpha-melanocyte-stimulating hormone (alpha-MSH), and adrenocorticotropic hormone (ACTH) was measured. After administration of 1.0 microgram of oCRH/kg of body weight, significant (P < 0.05) increases in plasma cortisol, alpha-MSH, and ACTH concentrations were observed. After administration of 0.1 microgram of oCRH/kg, significant increases were found only for cortisol and ACTH concentrations. In vitro release of ACTH from dispersed feline pars distalis cells in primary culture stimulated by oCRH and arginine vasopressin (AVP) was dose-dependent. Maximal stimulation was achieved by 1 nM oCRH or 100 nM AVP. The oCRH-stimulated ACTH release was partially inhibited by dexamethasone, and AVP-induced release was completely inhibited. Pars intermedia cells released 20 times as much alpha-MSH as ACTH. A dose-dependent inhibition of alpha-MSH release was induced by the dopamine agonist, bromocriptine. This inhibition could be partially abolished by coincubation with haloperidol. Bromocriptine had no effect on release of ACTH. In conclusion, oCRH stimulates the pars distalis and pars intermedia of the pituitary gland of cats. Release of ACTH is stimulated by a direct effect on the pars distalis. In addition, in cats, oCRH is a more potent secretagogue than is AVP. The MSH release from the pars intermedia is sensitive to dopaminergic inhibition, indicating that dopamine may have a central role in regulation of MSH secretion in cats.
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