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      Characteristics of Receptors for Dopamine in the Pars intermedia of the Amphibian Xenopus laevis

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          Abstract

          While mammalian dopamine receptors have been extensively characterized, very little attention has been given to these receptors in lower vertebrates. Dopamine is thought to be a physiologically important melanotropin release-inhibiting factor in amphibians. By administering selective dopamine receptor agonists and antagonists to superfused neurointermediate lobes of Xenopus laevis and monitoring their effect on the release of melanophore-stimulating hormone (MSH), we have examined the characteristics of the receptors involved in the dopamine-induced inhibition of MSH secretion. The results show that the receptor system involved has characteristics of both classical D-2 receptors and α-adrenergic receptors. This is concluded from: (1) the agonistic effect of both the D-2 receptor agonists LY-171555 and apomorphine; (2) the antagonism of this effect, not only by the D-2 receptor antagonists sulpiride, domperidon and haloperidol, but also by the α-adrenergic receptor antagonist phentolamine, and (3) the observation that the effect of adrenaline, which is extremely potent in inhibiting MSH release, could be fully blocked by D-2 receptor antagonists. Both the fact that the dopamine-induced inhibition of MSH secretion could not be blocked by haloperidol, domperidon and phentolamine, and that adrenaline-induced inhibition was hardly blocked by phentolamine, led us to suggest the possible presence of multiple receptors or receptor sites. We find no evidence for the involvement of dopamine D-1 receptors in the regulation of MSH release. The effects of dopamine agonists and antagonists were also studied in vivo by monitoring changes in pigment dispersion of dermal melanophores. The results are consistent with our in vitro findings and indicate, moreover, that in the living animals there must also be a non-catecholaminergic system involved in the inhibition of MSH release from the pars intermedia.

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          Author and article information

          Journal
          NEN
          Neuroendocrinology
          10.1159/issn.0028-3835
          Neuroendocrinology
          S. Karger AG
          0028-3835
          1423-0194
          1986
          1986
          01 April 2008
          : 44
          : 4
          : 446-456
          Affiliations
          aDepartment of Zoology, Faculty of Science, Catholic University, Nijmegen, The Netherlands; bLaboratoire d’Endocrinologie, Faculté des Sciences et des Techniques, Université de Rouen, Mont-Saint-Aignan, France
          Article
          124685 Neuroendocrinology 1986;44:446–456
          10.1159/000124685
          3822075
          © 1986 S. Karger AG, Basel

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          Page count
          Pages: 11
          Categories
          Original Paper

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