Pars Intermedia and Pars Distalis:Two Sites of ACTH Production in the Rat Hypophysis

Abstract

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.

Experimental Alterations of Endorphin Levels in Rat Pituitary

“…A common biochemical origin of ACTH, <x-MSH, /3-LPH and /3-END is suggested by their unique tissue location within rat pars intermedia [Howe, 1973;Kraicer et al, 1973;LaBella et al, 1976;Pelletier et al, 1977;Bloom et al, 1977], as well as by the presence here of a 31,000 dalton precursor molecule [Mains et al, 1977] Howe andThody [1969, 1970] have re ported that lesions of the PVN of the hypo thalamus, or administration of hypertonic sa line in place of drinking water, induce a rise in neurointermediate lobe MSH. In contrast, Taleisnik et al [1967Taleisnik et al [ , 1972 found a reduction in pituitary MSH activity following these pro cedures.…”

Molecular weights of adrenocorticotropic hormone in extracts of anterior and intermediate-posterior lobes of mouse pituitary.

“…In this way it is possible to confirm the existence of peaks of biological ACTH activity that coincide with each peak of immunological ACTH activity. The ACTH activity in tumor cell extracts and tumor cell tissue culture medium can be grouped into three molecular weight classes: molecular weight 20,000-30,000 (20-30k ACTH), molecular weight 6500-9000 (6.5-9k ACTH), and molecular weight 4000-5500 (4-5.5k ACTH) (45 (3)(4)(5)(6)(7)(8)(9)(10)(11)(12), mice (10,13), cows (3,4,14), pigs (4,15), and rabbits (4) contain ACTH activity. In contrast to the distribution of ACTH between these two lobes, growth hormone, thyroid stimulating hormone, prolactin, and the gonadotropins are found only in the anterior lobe (1,2 (2,9,10), but a clean separation of these lobes is difficult (8), so the amount of ACTH (2,3,12).…”

Stress-Induced Secretion of Pro-Opiomelanocortin-Derived Peptides in Rats: Relative Importance of the Anterior and Intermediate Pituitary Lobes

“…The relative contribution of the AL and IL to the hor mone response was studied by selective blockade of either of the two lobes by DEX, which selectively inhibits secre tion from the corticotropes (AL) [19][20][21][22][23], or BR, which selectively inhibits the melanotropes (IL) via D2-receptor activation. DEX totally blocked the ACTH response to both types of stress whereas BR had no such effect.…”