Pituitary pars intermedia

Dybdal N O, Levy M 1997 Pituitary pars intermedia dysfunction in the horse Part II. Diagnosis and treatment. In Proceedings of the 15th American... 

Schott H C 2002 Pituitary pars intermedia dysfunction equine Cushing s disease. Veterinary Clinics of North America Equine Practice 18 237-270 Schott H C, Coursen C L, Eberhart S W et al 2001... 

Scheme. Pituitary pars intermedia Cell types...

Fig. 260. Slender, twisted mitochondria with longitudinal cristae, and dense, round to oval secretory granules with delicate investing membranes in a pituitary pars intermedia cell (block 1240) of an intermittent hypoxic and reoxygenated rat (No. 8) medicated for 7 consecutive days with intraperitoneal injection of 15 mg carbocromene per kg body weightxday. 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. Eilm 633-41...

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. 

Figure 6. Effect of increasing concentrations of CRF on adenylate cyclase activity in bovine pars intermedia pituitary homogenate.

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... 

A diagnosis of ECD is usually confirmed by testing the pituitary-adrenal axis. Single or multiple measurements of plasma cortisol are not diagnostic for ECD. In fact, cortisol concentrations vary widely in normal horses and the values from horses with pars intermedia dysfunction are often within the reference range (Dybdal et al 1994). Additionally, cortisol concentrations may be... 

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... 

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... 

Corticotropin-lilte peptide, CLIP a peptide from the pars intermedia of rat and pig pituitaries. Its primary structure is idential to amino acid sequence 18-39 of ACTH. No definite function of CLIP is known. It may be a cleavage product of ACTH unavoidably formed during production of a-MSH. See Peptides, Fig.3. 

Melanotropin, melanocyte stimulating hormone, MSH a peptide hormone or neuropeptide produced by opiomelanotropinergic cells of the pars intermedia of the pituitary and by neurons in the central nervous system. In species lacking the pars intermedia (e.g. chickens, porpoise, whale), a-MSH is produced by the neurohypophysis Production of a-MSH by the pituitary is under control of MRH and MIH (see Re-... 

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... 

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