[Interrelationships between pars intermedia and posterior pituitary with regard to corticotrophic and thyrotrophic...

Functional interrelationships between the pars intermedia and posterior pituitary were proved under different experimental conditions. After stimulation of the thyrotropical axis of rats by an acute intraperitoneal application of 50 microgram TRH/rat the nuclear sizes of the thyroid follicular and the anterior pituitary thyrotropical cells increased according to a monophasic time curve with maximal amplitude at the time of 30 minutes. Interestingly, the nuclear sizes of the posterior pituitary cells were also enhanced. Under the same experimental conditions the nuclear areas of the cells of the external layer of the adrenal zona fasciculata decreased as did the nuclei of the pars intermedia cells (without regard to the cell type or localization of the cells in the intermediate lobe). Stimulation of the adrenocorticotropical axis by an acute injection of 0.2 ml isotonic saline solution/rat was followed by a time-dependent increase of nuclear sizes of the fasciculata cells and pars intermedia, whereas the nuclear volumes of the thyroid follicular cells, the anterior pituitary thyrotropical cells and the posterior pituitary cells decreased. Thus the functional state of the pars intermedia was in accordance with that of the adrenal cortex. Also the posterior pituitary cells responded to stimuli applied to the thyrotropical axis at the same degree as the thyrotropic organs themselves. Between the nuclear sizes of the pars intermedia and posterior pituitary we established the same inverse functional relationships as between the adrenal cortex and the thyroid gland.