ADRENERGIC RECEPTOR-MEDIATED RESPONSE OF THE RABBIT SMALL AND LARGE INTESTINE

Abstract

Methoxamine, isoprenaline, salbutamol and dobutamine were used to inhibit the spontaneous contraction of various rabbit small and large intestinal sections. From the concentration of the drugs that produced a similar magnitude of inhibition of the spontaneous contraction, the following deductions were made: The small intestine compared to the large intestine responded more to methoxamine, indicating a predominant presence of α receptors in the small intestine. The reverse is true for isoprenaline, indicating a predominant presence of β receptors in the large intestine. Salbutamol exerted a much greater effect on the large intestine than on the small intestine, indicating that the β receptors of the large intestine are mainly of the β₂ type. The reverse is true for dobutamine, suggesting that the β receptors of the small intestine may be mainly of the β₁ type. The second deduction agreed with the findings of Nakahata and co-workers who reported similar, though qualitative, findings in the rat and rabbit intestine. The third and fourth deductions are interesting in that the facts complement the century old acupuncture classification of paired meridian which grouped the lung and large intestine as a pair and the heart and small intestine as another pair. The lung has β₂ and the heart β₁ receptors.