A Growth-Suppressive Influence of l-Isoproterenol on Postnatally Developing Parotid Gland of Rat 1

Summary

Administration of l-isoproterenol for 8 days during the early phase of postnatal development when mitosis is normally high and cells are in the process of differentiation leads to suppression of mitotic rate and decrease in gland levels of DNA. Acceleration of differentiation, with increases in total RNA, cell and gland size were also observed. The accelerated differentiation may be the consequence of the inhibition of mitosis. If administration of isoproterenol is delayed until after weaning when cell division is markedly decreased and cells more nearly resemble those of adults, the usually expected hyperplasia as well as hypertrophy are observed. The spatial orientation of the β-adrenergic receptors appears to be a critical factor in these growth responses, since the d-isomer, injected in the same doses as the l-isomer, failed to cause significant effects. Finally, chronic administration of propranolol does not modify the course of postnatal growth in rat parotid, suggesting that β adrenergic receptors normally have little role in postnatal development of parotid.

I wish to thank Ayerst Laboratories, New York for kindly supplying propranolol (Inderal).