Histamine receptors in primate gallbladder

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Abstract
The effect of intravenous histamine on intragallbaladder pressure (GBp) and subsequent modification of the histamine response by H1-and H2-antagonists was investigated in an awake baboon model. Responses to specific H1-and H2-agonists were also examined in order to further elucidate gallbladder histamine responses. Gallbladder volume (GBv) was arbitrarily set at 60–70% of observed resting GBv, and drugs were then infused intravenously with continuous monitoring of GBp. Histamine administration resulted in a logarithmic dose-response curve with a maximal increase in GBp equal to 31.7 mm Hg at a dose of 0.0625 mg of histamine. Infusion of the H1-antagonist diphenhydramine hydrochloride (Benadryl) resulted in a decreased GBp response to histamine when compared to preblocker response at all doses studied. On the other hand, histamine response following administration of the H2-antagonist metiamide was significantly greater than the preblocker histamine response. Infusion of the H1-agonist 2-pyridylethylamine resulted in a dose-dependent increase in GBp similar to the histamine curve, while infusion of the H2-agonist dimaprit resulted in consistent decreases in GBp. These results extend previous observations in subprimate preparations and demonstrate the presence of both stimulatory H1-receptors and inhibitory H2-receptors in anin situ primate model.