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J. N. BALL AND BRIDGET I. BAKER
Fig. 14. AnguiUu unguillu. ACTH cells in pituitary of a sham-interrenalectomized
control. PbH-PAS, X1100.
with thyroidal activation, and other effects of the drug have been observed with long treatment in the eel (Olivereau, 1965). However, there
can be no doubt that the initial and most marked hypophysial effect of
SU 4885 is to provoke enhanced secretion of ACTH, and that this originates in the E cells. Surgical removal of the interrenal in Anguilla has
confirmed this earlier work (Figs. 14 and 15) , resulting in activation of
the E cells specifically ( Olivereau and Olivereau, 1968). However, interrenalectomy, unlike SU 4885 treatment, did not lead to stimulation of the
TSH cells, suggesting that the action of the drug on these cells may be
direct rather than mediated via the ACTH-interrenal axis. Unpublished
work on P. latipinna has shown that if cortisol treatment is combined
with SU 4885, the interrenal stimulation (i.e., elevated ACTH secretion)
is prevented, and correspondingly the e cells are not activated.