The importance of the prolonged postnatal period in determination of heart atrial muscarinic receptor and β-adrenoceptor densities

Abstract

Our previous work indicated that hyperstimulation of muscarinic receptors brought about profound changes not only in the density of the muscarinic receptors, but also of the β-adrenoceptors both in vivo and in vitro. Now we try to identify the changes in receptor densities when the neuronal input from the autonomic nerves is disrupted, i.e. when neonatal rats were injected with 6-hydroxydopamine (6-OHDA; able to destroy sympathetic nerves). Although the interruption of neuronal input was successful as indicated by norepinephrine uptake, there was no change in receptor densities in the rat heart atria when 6-OHDA was applied in the first postnatal week only. When we repeated the 6-OHDA treatment consequently (on 14 th, 21 st and 28 th postnatal day) there were clear increases of both receptor types (muscarinic receptors rise to 139% of control, β-adrenoceptors to 134% of control). The atrial muscarinic receptor number was increased (to 146% of control) also when we combined the first week 6-OHDA application with another factor (when the pups abide with mother till the 56th day). The simple non-weaning of animals has no effect on the receptor densities. We can therefore conclude that the first week application of 6-OHDA was insufficient in changing the receptor number and that only repeated 6-OHDA administration was able to change them. Similarly, combination with other factor: non-weaning led to the muscarinic receptors increase. Our results can indicate the importance of the prolonged postnatal period for the heart muscarinic and β-adrenergic receptor number determination.