CHARACTERIZATION OF ANDROGEN RECEPTORS FOR TESTOSTERONE AND 5-ALPHA-DIHYDROTESTOSTERONE IN THE MOUSE SUBMANDIBULAR-GLAND

In the mouse submandibular gland, sex difference becomes evident on day 30, when the granular convoluted tubules (GCT) of the gland rapidly grow in response to drastically increased levels of circulating testosterone and 5 alpha-dihydrotestosterone (DHT) in the male. Testosterone and DHT may act separately on the gland, because the mouse gland can not convert testosterone to DHT. Therefore, we studied properties of the androgen receptor of the mouse submandibular gland using both these circulating androgens as ligands. Analyses of sucrose density gradient centrifugation and Scatchard plots demonstrated that the mouse submandibular gland contained two types of cytosolic receptors: one is the low-affinity, high-capacity receptor of smaller molecular size at about 3S to be bound with both testosterone and DHT, and the other is the high-affinity, low-capacity DHT specific receptor of larger molecular size at about 8S. The apparent dissociation constant (K-D) of the low-affinity receptor for testosterone and DHT was 0.53-0.62 nM, and that of the high-affinity DHT specific receptor was 0.07-0.11 nM. K-D for each ligand was similar between the sexes and was constant on day 20 through day 90 of age. Maximum bindings of both cytosolic receptors were significantly higher in the male than in the female at 20 and 30 days of age. On the other hand, the cross-competition experiment was allowed to elucidate which androgen was predominant for cytosolic receptors of the mouse gland. When testosterone and DHT were applied at the serum concentrations to the cytosol of the male gland, the cytosolic receptors were bound 28% with testosterone and 72% with DHT on day 20, and they were occupied 60% by testosterone and 40% with DHT on days 30 and 90. Therefore, these results suggest that the mouse glands may respond to serum DHT to induce cell proliferation of GCT around day 20 and then the gland may respond to both serum testosterone and DHT to induce the early masculine development and maintenance of GCT in fully-stimulated states, and that occurrence of sex difference of the gland may be controlled by androgen binding activities of the receptor around day 20 to 30.