Effects of zinc deficiency on developmental changes in alkaline phosphatase and carbonic anhydrase activities in the submandibular gland of the rat

Abstract

The alkaline phosphatase (AP) and carbonic anhydrase (CA) activities were studied in male rats placed at weanling age on a diet containing 0.4 parts/10 6 of zinc for periods of 9, 18 and 27 days. Weight-matched pair-fed rats were kept on the same diet supplemented with 40 parts/10 6 of zinc. The body weight of controls showed a continuous increase; body weight of zinc-deficient animals remained unchanged. Zinc concentration in submandibular gland was the same in all groups of control and zinc-deficient animals. AP activity, chiefly localized in the myoepithelial cells, progressively increased in controls from day 9 to 27. AP activity in the zinc-deficient animals did not increase. It was lower than in controls even at 9 days and further decreased with prolonged zinc deficiency. CA activity, chiefly localized in cells of the duct system, rose with age in the controls at twice the rate of AP activity, a rise attributed to the steep rise in proportion of duct cells reported for this age span. By contrast, CA activity in the glands of zinc-deficient rats remained constant at all periods of deficiency, accounting for the increasing difference from controls with prolonged zinc deficiency. Failure of CA activity to rise with age in zinc-deficient rats is attributed to failing proliferation of duct cells, reflecting the inhibition of cell proliferation reported for many tissues of the zinc-deficient animals, a view supported by the maintenance of unchanged body weight over a 4-week-period. Inhibition studies using acetazolamide showed identical degress of inhibition in homogenates from control and deficient animals over a wide range of inhibitor concentrations. Rats fed for 9 days on the zinc-supplemented diet after 27 days on the deficient diet doubled their weight and showed AP and CA activities of the same level as controls that were pair-fed for 27 days and given unrestricted food for the last 9 days.