Pars Tuberalis

Human pars tuberalis consists mainly of gonado-tophs interspersed with few corticotrophs and thy-reotrophs. Somatotrophs and lactotrophs were not identified by Asa etal. (1983). The subpopulation of gonadotophs possesses all organelles required for synthesis and storage of hormones but showed ultrastuctural features of functional inactivity. 

In the monkey, many cells of the pars tuberaUs produce P-luteinizing hormone and some P-folUcle-stimulating hormone (Bock et al. 1999) 

In the rat, the pars tuberahs consists of several layers of relatively small epithelial cells along the ventral surface of the median eminence (Oota and Kurosumi 1966). The epithelial cells maybe classified into two types specific secretory cells and follicular cells (Dellmann et al. 1974). The follicular 

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Gauer, F Masson-Pevet, M. Pevet, P. (1993). Melatonin receptor density is regulated in rat pars tuberalis and suprachiasmatic nuclei by melatonin itself. Brain Res. 602, 153-6. 

Prolonged exposure to melatonin leads to time-dependent sensitization of adenylate cyclase and down-regulates melatonin receptors in pars tuberalis cells from ovine pituitary. Endocrinology 132, 285-92. 

From the evidence accumulated so far, it seems likely that the cAMP signal transduction pathway will be a major effector of a stimulatory signal to the pars tuberalis, which can be regulated by melatonin [115]. The effect of aluminum as AlF41 has been studied on inositol phosphate accumulation, calcium mobilization, and cyclic AMP production in ovine pars tuberalis cells [116]. In the presence of 10 mmol L-1 LiCl, AlF41 stimulated the net accumulation of inositol phosphates over a 40-min incubation. Lithium is a known inhibitor of phosphatases in the inositol phosphate-recycling pathway. The results show the existence of a lithium-sensitive phosphoinositide signaling. 

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... 

Fig. 261. Slender, twisted mitochondria with longitudinal cristae, and dense, round or oval membrane-bound secretory granules in a pituitary pars tuberalis cell (block 1029) from a rat (No.l) treated for 7 consecutive days with intraperitoneal injection of 1.5 ml Tyrode s solution per kg body weight x day. On August 4, 1976 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 632-10...

During hibernation (mid February), the number of secretory vesicles in the pars tuberalis cells of the garden door mouse was considerably reduced (Dellmann et al. 1974). The profiles of the rough endoplasmic reticulum, after having lost their ribosomes, tended to become closely apposed. 

Functional receptors for melatonin have been localised and characterised on the pars tuberalis of a number of mammalian species (Morgan etal. 1991, Bockers et al. 1995, Bockmann et al. 1996). Using forskolin (1 [aM), as a non-specific stimulant of adenylate cyclase, melatonin (10 nM) was shown to inhibit the formation of cyclic AMP by 80-90 % in ovine pars tuberalis cells both before and after PercoU centrifugation (Morgan et al. 1991). 

The size of the pars tuberalis of the hypophysis varies considerably depending upon the species. It is large in the cat and dog and small in humans. The pars tuberalis is made of glandular chords that form vesicles containing colloid material. In contrast to the pars intermedia, the pars tuberalis contains many capillaries and neurofibers. 

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