| Abstract: | The effects of HgCl2 and ouabain on vasopressin release and Ca2+ uptake and distribution was examined in the neurointermediate lobe of the rat pituitary. HgCl2 (0.5 mM) inhibited vasopressin release by approx. 90% in both basal and potassium depolarized states. With 0.1 mM HgCl2 vasopressin release was inhibited by 50% in the depolarized state, but release was not effected in basal state. On the other hand, ouabain (0.5 mM) caused a 3-fold stimulation of vasopressin release in the depolarized state. Both HgCl2 (0.5 mM) and ouabain (0.5 mM) increased net 45Ca+2 uptake by about 80% in groups of neurointermediate lobes. Following 45Ca+2 uptake, HgCl2 (0.5 mM), which is absorbed by the neurointermediate lobe, produced an increase in cytosolic 45Ca+2 content and a decrease in mitochondrial 45Ca+2 content compared to control. In comparison, ouabain (0.5 mM), which does not penetrate the neurointermediate lobe, gave no change in cytosolic 45Ca+2, but an increase in mitochondrial 45Ca+2. These results suggest that HgCl2 inhibits vasopressin release from the neurointermediate lobe of the rat pituitary at a point distal to Ca+2 uptake by the gland. |
