Changes in Protein Secretion by Rat Submandibular Glands in Response to Isoproterenol, a-Methylnoradrenaline, and Clonidine during Post-natal Development

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Abstract
We studied developmental changes in salivary volumes and proteins secreted by the submandibular glands of male rats at weekly intervals from two to ten weeks of age in response to the β1-, α1-, and α2- adrenoceptor agonists, isoproterenol (IPR), a-methylnoradrenaline (a-mNA), and clonidine (Clonid). The types of proteins in saliva samples were determined and compared by isoelectric-focusing electrophoresis with the Phast system in both the gradient pH -3.5-to-5 and pH-3.5-to-9 gels by means of silver staining. Salivary volume and protein concentration in saliva samples elicited by IPR and a-mNA were positively related to the weight of the submandibular glands up to six or seven weeks of age, whereas in saliva elicited by Clonid, no relation was found. The isoelectric-focusing electrophoretic patterns of proteins secreted by the glands in response to three stimuli were different from each other during post-natal development. Within one stimulation, differences were also observed at two and three weeks of age for Clonid, and from seven weeks of age for the three stimuli, respectively. The a-type proteins, but not the β-type proteins, were very similar to those in extracts from glands of rats at seven weeks of age. Almost all of the a-type proteins, but not the β-type proteins, reacted with antibodies to two proteases. We conclude that functional maturation precedes morphological maturation in the submandibular glands of rats.