Saul Lande

Anterior Pituitary Peptides and Avoidance Acquisition of Hypophysectomized Rats

Publisher Summary The pituitary-adrenal system plays an essential role in the defense mechanism of the organism in response to noxious stimuli. These stimuli, which may be of neurogenic or emotional and of somatic or systemic character, invariably cause the discharge of adrenocorticotropic hormone (ACTH) from the adenohypophysis and the subsequent secretion of adrenocortical hormones. Removal of the whole pituitary gland or the adenohypophysis alone causes a severe deficit in the ability to acquire a conditioned avoidance response. The administration of adrenal maintenance doses of ACTH improves the rate of avoidance acquisition of hypophysectomized or adenohypophysectomized rats. Further studies with the heptapeptide ACTH in hypophysectomized rats revealed that it had no effect on adrenal weight, plasma corticosterone, or thymus weight, indicating the absence of corticotropic activities. Nor does the peptide affect the gonads because atrophy of the testes in the hypophysectomized rat is not influenced by chronic treatment with ACTH. Behavioral deficiency of the hypophysectomized rat certainly is linked in some extent to metabolic derangements and physical weakness that occur as a result of hypophysectomy.

High-performance displacement chromatography of melanotropins and their derivatives

Mixtures containing derivatives of the biological active peptide alpha-melanocyte stimulating hormone (alpha-MSH) or beta-melanocyte stimulating hormone (beta-MSH) were purified by using reversed-phase chromatography in the displacement mode. On a 250 x 4.6 mm octadecyl silica column and with instrumentation used in analytical high-performance liquid chromatography about 30 mg of the peptide mixture were separated by using an aqueous solution of benzyldimethyldodecylamonium bromide as the displacer in a single chromatographic run. The results demonstrate the advantages of displacement over elution in preparative chromatography of peptides on the scale of tens of milligrams that is typical for physiological tissue extracts and in solid-phase peptide synthesis.

Unique Pituitary Peptides with Behavioral-affecting Activity

Publisher Summary This chapter highlights the unique pituitary peptides with behavioral-affecting activity. Initial screening studies for behavioral-affecting activity were performed on hypophysectomized rats. Four unique porcine pituitary peptides are isolated and partially characterized, which upon subcutaneous administration potently facilitate acquisition of conditioned avoidance responses in hypophysectomized rats and inhibit extinction of avoidance responses in intact rats. The profound deficit in acquisition and retention of conditioned avoidance responses (CARS) imposed on rats by hypophysectomy can be substantially reversed by subcutaneous administration of corticotrophin (ACTH) and certain subunits thereof, as well as by the melanotrophins and pitressin. The potent behavioral effects of synthetic corticotrophin subunits in conjunction with an apparent lack of peripheral action suggested the possible existence of naturally occurring pituitary peptides with similar biological activity. The availability of a porcine pituitary extract in a large quantity afforded the opportunity to undertake a search for such compounds.

Racemization of α-melanotropin

Abstract Racemization of the amino acid residues of α-melanotropin was measured after exposure of the peptide to alkali for various lengths of time. Rates of racemization were then compared to the rate of transformation by alkali of α-melanotropin into a hormone with prolonged melanotropic activity. When in vitro prolongation became maximal, serine, methionine, histidine, phenylalanine and arginine were racemized 50–70%, glutamic acid, tyrosine and tryptophan 30–40% and lysine, proline and valine 10% or less. Racemization of a particular amino acid residue in α-melanotropin could not be associated with induction of prolongation of activity. Rather, partial racemization at multiple sites in the molecule seems almost as effective as extensive or total racemization of a single residue in producing a hormone with prolonged biological effects.

Purification of Porcine and Human ACTH

Homogeneous ACTH from porcine and human sources can now be prepared in moderate quantities because suitable starting material is available, and fractionation on large Sephadex and carboxymethyl cellulose columns is readily reproducible. The purified peptides are necessary for immunologic, metabolic and chemical studies. To prepare porcine adrenocorticotropic hormone, the starting material is the fraction made for clinical use by carrying the extraction of whole pituitaries through an oxycellulose adsorption step. For human adrenocorticotropic hormone, by-products from preparations of human growth hormone are used. Detailed procedures for purifying adrenocorticotropic hormone isolated from human and porcine sources are described below.

Pituitary peptides. Naturally occurring analogues of porcine corticotropin.

Three new peptides with high steroidogenic activity in vivo have been isolated from porcine pituitary extracts. Similar in molecular weight to porcine ACTH, they differ from the usual amino acid composition in molar ratios of aspartic acid, threonine, serine, glycine, valine, methionine and phenylalanine.