Pars intermedia and pars distalis of the rat hypophysis were examined, following experimentally induced alterations in ACTH secretion. The concentration of ACTH in the pars inter-media is considerably greater than that in the pars distalis. At 1 month after adrenalectomy, the ACTH concentration in the pars distalis increased 3-fold, while that in the pars intermedia remained unchanged. Following chronic administration of cortisol, the ACTH concentration in the pars distalis fell to 27% of the control, while the fall in ACTH concentration in the pars intermedia was not significant. The immunoglobulin-peroxidase bridge technique, employing 17–39 ACTH antiserum, demonstrated the presence of ACTH-containing cells, both in the pars intermedia and in the pars distalis. Following adrenalectomy or chronic administration of cortisol, there was no change in the immunostaining or in the electron microscopic appearance of the cells of the pars intermedia. These findings suggest that although a relation between the pars intermedia and ACTH is established, this relation is different from that between the pars distalis and ACTH.

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A stereotaxic method is described for the in vivo study of neurohypophysial function in the rat. The infusion of nanogram quantities of acetylcholine or carbachol close to or directly into the neurohypophysis of water-loaded, ethanol-anesthetized rats resulted in a decreased urine volume and increased urine conductivity. These changes were matched by microunit quantities of Pitressin. It is concluded that acetylcholine may act directly on the neurohypophysis to modulate antidiuretic hormone release. The failure of earlier in vitro experiments to reveal this action may have been due to the high basal rate of hormone release in such experiments.