Effects of progestins in salivary gland morphology and in serum pituitary hormone levels. (a) Salivary glands from control, MPA, or Pg-treated BALB/c or C57BL/6 mice. Pellets were implanted subcutaneously and the animals killed after 2 months. MPA increased the development of convoluted granular ducts (arrow). No differences were observed between both strains of mice (400×, bar: 120 μm). (b) Serum PRL, Pg, GH, and IGF-I levels measured by radioimmunoassay in control BALB/c or C57BL/6 female mice and after 24 hours of MPA or Pg treatment. No differences were detected in C57BL/6 mice as compared with BALB/c mice. Furthermore, Pg and MPA treatment induced an increase in PRL levels in both strains (P < 0.001, two-way ANOVA). The increase in Pg levels after progesterone administration was also similar in both strains (P < 0.001, two-way ANOVA). Gray bars: BALB/c; black bars: C57BL/6. ANOVA, analysis of variance; GH, growth hormone; IGF, insulin-like growth factor; MPA, medroxyprogesterone acetate; Pg, progesterone; PR, progesterone receptor; PRL, prolactin.