Abstract— In in vitro experiments on rat hypothalamic homogenates the effects of biogenic amines such as histamine (HA), noradrenaline (NA), dopamine (DA), serotonin (5-HT) and drugs such as isoprenaline (ISP), 2-(2-pyridyl)ethylamine (H2 stimulant—Hls), 4-methyl-histamine (H2 stimulant H2s), mepyramine (H1 antagonistp Hla), cimetidine (H2 antagonist—H2a) were tested on adenylate cyclase activity. HA possessed a powerful stimulating effect on hypothalamic adenylate cyclase activity, higher than that shown by the other substances.
The stimulating effect of HA was greatest in hypothalamic tissue from male rats, while tissue from females showed only a modest stimulation. H2s, induced a greater stimulation of adenylate cyclase than Hls. On the other hand, the H2a inhibited HA stimulation to a greater extent than the Hla, Hla and H2a, when used together, completely inhibited the HA stimulation. HA may have a neurotrans-mitter role in the hypothalamus, and in this area there appears to be a mixed population of H1 and H2 receptors, with a majority of H2 receptors.