Hypoxia-induced changes in parasympathetic neurochemical markers in guinea pig heart.

Exposure of animals to hypoxia produces cardiovascular changes including right ventricular hypertrophy and alterations in heart rate. The activity of choline acetyltransferase, a neurochemical marker of parasympathetic innervation, and the density of muscarinic cholinergic receptors, measured by the binding of [3H]quinuclidinyl benzilate, were analyzed in the hearts of guinea pigs exposed to hypobaric hypoxia. We found a significant increase in the activity of choline acetyltransferase in the sinoatrial node in response to hypoxia after 7 or 14 days. In addition, we found significant decreases in the muscarinic receptor density in several contractile and conducting regions. The decrease in receptor density may reflect regulation by the level of occupancy; an increased occupancy may produce a decrease in muscarinic receptor number.