Frequency-dependent autoinhibition of histamine release from rat cortical slices: a possible role for H3 receptor reserve.

The inhibition of histamine release after depolarization of rat cerebral cortex slices by electrical stimulation and mediated by the postulated presynaptic autoreceptor (H3) depends strongly on the conditions of stimulation. Using electrically stimulated slices of the cortex a rightwards shift of the concentration-response curve of histamine (an H3 agonist) was observed on increasing the frequency of stimulation. The pA2 value of the H3 antagonist impromidine was, however, not altered at different stimulation frequencies; for a partial agonist only the maximal effect was influenced. These results indicate the existence of a receptor reserve at the H3 autoreceptor.