A STUDY DESIGNED TO EXPLORE THE HYPOTHESIS THAT BETA-1 ADRENOCEPTORS ARE INNERVATED RECEPTORS AND BETA-2 ADRENOCEPTORS ARE HORMONAL RECEPTORS

  • 1 January 1981
    • journal article
    • research article
    • Vol. 216  (2) , 395-400
Abstract
The chronotropic responses to sympathomimetic amines in rat atria were mediated by .beta.-1 adrenoceptors. This was like guinea pig (.beta.-1) but unlike cat (.beta.-1 and .beta.-2). Extraneuronal uptake of isoproterenol into rat atrial myocardial cells was detected by fluorescence histochemistry but uptake was less than was seen in cat atria. It did not modulate responses of rat atrial preparations to isoproterenol. The lack of specific extraneuronal uptake in guinea-pig atrial myocardial cells was confirmed. Collation of data on the atria of the 3 spp. with data already available on guinea-pig trachea allowed the following conclusions. All 4 tissues contained a population of .beta.-1 adrenoceptors and were adrenergically innervated. .beta.-2 Adrenoceptors were present in cat atria and guinea-pig trachea and the tissues possessed a functionally effective extraneuronal metabolizing system for catecholamines. .beta.-2 Adrenoceptors were not detected in guinea-pig or rat atria and in these tissues extraneuronal uptake was absent (guinea-pig) or not functionally effective (rat). .beta.-1 Adrenoceptors may be innervated receptors mediating responses to neuronally released norepinephrine, i.e., .beta.-2 adrenoceptors are hormonal receptors mediating responses to circulating epinephrine and extraneuronal metabolizing systems apparently are of particular importance in the dissipation of circulating catecholamines acting on .beta.-2 adrenoceptors.

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