Expression and postnatal changes of adrenergic receptor subtype mRNA in rat submandibular glands

Adrenergic receptors (ARs) are involved in regulating saliva secretion and composition in salivary glands. Nine AR subtypes, including three alpha (1) -ARs (alpha (1a)-, alpha (1b) - and alpha (1d)-ARs). three alpha (2)-ARs (a lpha (2A)-, alpha (2B)- and alpha (2C)-ARs) and three beta -ARs (beta (1) b eta (2)- and beta (3)-ARs). have been identified through molecular cloning. The five subtype genes, alpha (1a)-, alpha (1b)-, alpha (2B)-. beta (1)-, and beta (2)-ARs, were expressed in rat submandibular glands. In contrast, the other four subtype mRNAs, alpha (1d)-. alpha (2B)-, alpha (2C)- and bet a (3)-ARs, were not detected by reverse transcription-polymerase chain reac tion (RT-PCR). The steady-state mRNA expression for the five AR subtypes in rat submandibular glands was measured by quantitative competitive RT-PCR u sing synthetic DNA as internal standard at different stages of postnatal de velopment. The relative rank order of AR subtype mRNA expression was alpha (1a) > beta (2) > beta (1) > alpha (2A) > alpha (1b) at all stages except t hat beta (1)- and alpha (2A)-subtypes were reversed at 2 weeks of age. The gene expression of alpha (1a)-AR subtype relative to total AR was low at 2 weeks of age and increased and reached a maximum at 6 weeks of age, whereas those patterns of alpha (2A)-, beta (1)- and beta (2)-AR subtypes were sim ilar to each other and their gene expressions were high at 2 weeks of age a nd then decreased. On the other hand, the gene expression of alpha (1b)-AR subtype did not change over the different stages in relation to that of a h ousekeeping gene, glyceraldehyde 3-phosphate dehydrogenase, and to total AR . Although rat submandibular glands contain the five AR subtype mRNAs. dist inct subtype-specific expression is evident. (C) 2001 Elsevier Science Ltd. All rights reserved.