Pituitary pars distalis

Pro-opiomelanocortin, pro-opiocortin a protein (M, 31,000) from the pars distalis and pars intermedia of the pituitary. P. contains the sequences of ACTH and p-LPH (see Peptides, Fig. 3). In the pars distalis, ACTH is released from P. to regulate adrenocortical function. In the pars intermedia, P. is cleaved to unprocessed a-MSH, which then undergoes amidation and acetylation to a-MSH (see Melanotropin). 

The pituitary gland Figure 4.1) is a bilobed structure located in the sella turcica, immediately below the median eminence area of the hypothalamus. The 2 lobes are derived embryologically from different sources. The anterior lobe or adeno-hypohysis, which is differentiated into 3 distinct zones, the pars distalis, pars intermedia and the pars tuberalis, is derived from ectodermal tissue of the oral... 

The pathway by which MSH-RIF and MSH-RF reach the pituitary gland is unclear. Unlike the pars distalis, the pars intermedia is well supplied with neurones from the hypothalamus but its blood supply is poor. Accordingly it has been suggested that the hypothalamic hormones are released from nerve endings within the pars intermedia, but further experimental evidence is needed to substantiate such a hypothesis. 

Fig. 263. An agranular cell in the pars distalis of the pituitary gland (block 1240) of a rat (No. 8) medicated for 7 consecutive days with intraperitoneal injection of 15 mg carbocro-mene per kg body weight x day. On the last 4 days of experimentation the animal was exposed to an atmosphere containing only 5 % oxygen for 30 min. On August 4, 1976, half an hour after the last exposure under pentobarbital anaesthesia (30 mg/kg), the animal was perfused from the abdominal aorta with 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer (pH 7.4). Postfixation with 1 % osmium tetroxide in sodium cacodylate buffer. Embedded in Epon 812 and sectioned at 50 nm. Lead citrate and uranyl acetate. Film 633-34...

The distribution of lysosomal enzyme including /3-glucuronidase has been studied in the pars distalis of the amphibian pituitary and the reaction is mainly found in tlie lobules of globular basophils (Waechtler and Pearce, 1966). 

---