Pituitary gland pars intermedia

Beech J 1987 Tumors of the pituitary gland (pars intermedia). In Robinson N E (ed) Current therapy in equine medicine, 2nd edn. Saunders, Philadelphia, PA, pp. 182-185... 

Distribution of Cadmium in the Central Nervous System After Parenteral or Oral Administration, walsh and Burch studied the distribution of ""Cd in normal dogs after intravenous injection and found no uptake in the brain, phrenic nerve, or brachial plexus up to 48 h after the injection. Autoradiographic studies with intravenously administered ° Cd revealed only traces of cadmium in the brain parench3mia, whereas pronounced accumulation was seen in the pia mater, choroid plexus, and hypophysis. " Within the pituitary, the pars intermedia contained less cadmium than the rest of the gland. " Arvidson and Tjalve found accumulation of ""Cd also in the pineal gland of rats 1 week after intravenous injection (Figs. 6, 7). 

The pituitary gland is situated in sella turcica or hypophyseal fossa of the sphenoid bone attached to the brain by a stalk which is continuous with the part of brain i.e. hypothalamus and there is a communication between the hypothalamus and the pituitary gland by means of nerve fibres and a complex of blood vessels. Pituitary gland consists of three parts - anterior lobe or adenohypophysis, posterior lobe or neurohypophysis and middle lobe or pars intermedia. 

Connected to the brain by a stalk (Fig. 30-1), the pituitary gland releases at least ten peptide or protein hormones that regulate the activity of other endocrine (hormone-producing) glands in distant parts of the body. The pituitary is composed of several distinct parts the anterior lobe (adenohypophysis), a thin intermediate portion (pars intermedia), and a posterior lobe (neurohypophysis). Each has its own characteristic endocrine functions. 

Pituitary Hormones. The hormones of the hypophysis (pituitary gland) are quite numerous, being secreted variously in three parts of the gland — the ncurohypophysis (posterior lobel. the adenohypophysis (anterior lithe), and the pars intermedia, which connects the other two. 

Triphenyltin hydroxide caused dose-related cystoid changes in the pars intermedia of the pituitary gland for male and female mice administered this compound for 52 or 104 weeks at doses of 0.3-6.2 mg/kg/day (Tennekes et al. 1989a). Up to 40% of the males and 80% of the females were affected at 52 weeks by the highest dose. At the end of 104 weeks, 72.3% of the high dose males and 55.6% of the females exhibited the cystoid changes. The lower incidence in females at 104 weeks related to a high early mortality from fatal pituitary adenomas (see Section 2.2.2.8). 

The above-described data show that CRF added to cells of the rat Intermediate lobe In culture causes a rapid stimulation of oe-MSH release and cyclic AMP accumulation, thus demonstrating a direct action of the peptide on pars intermedia cells (15). It is however difficult, using intact cells, to dissociate between increases in cyclic AMP levels due to stimulation of adenylate cyclase activity or to Inhibition of cyclic nucleotide phosphodiesterase or to a combination of both effects. Definitive proof of the role of adenylate cyclase In the action of CRF In the intermediate lobe of the pituitary gland is provided by the following findings of a CRF-lnduced stimulation of adenylate cyclase activity in homogenate of rat and bovine pars Intermedia cells. 

ECD is nearly always associated with hypertrophy, adenomatous h3q>erplasia or, in the most advanced cases, a functional adenoma of the pars intermedia of the pituitary gland. This condition was first described in 1932 however the exact pathogenesis, diagnostic plan and appropriate treatment regimen are still under dispute. Although, all breeds of horses and both sexes... 

Cystic hyperplasia of the pars intermedia of the anterior pituitary gland was found in one of five female beagle dogs after 8.3 years of treatment with an average dose of 10 mg/kg/day of MBOCA (Stula et al. 1977). This change was not present in other treated dogs or in controls and was not... 

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. 257. Pars intermedia of the pituitary gland (block 1029) of a rat (No. 1) treated for 7 days with intraperitoneal injection of 1.5 ml Tyrode s solution per kg body weight x day. On August 4, 1976 under pentobarljital 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 632-11...

During its organogenesis, the hypophysis leaves tracks in an area between the pharynx and the hypophysis. Again, small epithelial nodules of hypophyseal cells are inserted within the mucosa. These residues of embryological structures may develop into hypophyseal tumors that are found in the roof of the nasopharynx, in the body of the sphenoid bone, in the capsule of the pituitary gland, within the pars intermedia, and around the infundibulum. Such tumors are most frequently found in the pituitary capsule and the infundibulum. 

The pituitary body, or hypophysis, is double in origin and multiple in functions. From the stomodceal pouch of Rathke is developed the anterior lobe and the -pars intermedia from the floor of the third ventricle are formed the pars nervosa of the posterior lobe, the infundibulum and the tuber cinereum. The pituitary autacoids are of two types secretions acting directly on other tissues, and hormo-kinetic secretions acting indirectly by stimulating other endocrine glands. 

The hypophysis (pituitary gland) is an accessory gland of the brain. It consists of two anatomically distinct organs, the anterior lobe and the posterior lobe, and each lobe elaborates several different hormones. A middle lobe (pars intermedia developed to different extents in different animals), produces another hormone. The second part of Table XVIII (Section 1) lists all the different hypophyseal hormones. Many hormones of the anterior lobe are master hormones (Section 1). 

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