HYPOCALCEMIC EFFECT OF PITUITARY POLYPEPTIDES IN RABBITS

A Study to Show the Effect of Pituitary Stalk-Section upon Urinary, Hypothalamic and Pituitary Hypocalcaemic Activities

The effect of pituitary stalk-section on the hypocalcaemic activity in urine, hypothalamus and pituitary gland was investigated in rats.

Intact rats and rats with pituitary stalk-section were made hypercalcaemic and their urines were injected to bio-assay rats. A hypocalcaemic factor was present in the urine of intact hypercalcaemic rats and on the contrary, this factor was absent from the urine of hypercalcaemic rats with pituitary stalk-section.

Hypothalamic and pituitary gland extracts obtained twenty-four hours after stalk-section, from guinea pigs, were injected to bio-assay rats. Pituitary extract had no hypocalcaemic activity, whereas hypothalamic extracts produced hypocalcaemia. Neither the injection of pituitary or hypothalamic extracts to TPTX rats produced hypocalcaemic effect.

Dissociation of the Hypocalcaemic Effect of Sheep Pituitary Extract from its Lipolytic Action

The relation between the calcium-lowering and lipid mobilizing effects of crude sheep pituitary extract given intravenously was investigated in rabbits. Pituitary extract produced hypocalcaemia and free fatty acid elevation in rabbits. The hypocalcaemic effect was not related to the lipolytic effect of the extract, since infusion of dextrose in water prevented the lipolytic effect without altering the hypocalcaemic effect of the pituitary extract.

Lipolytic potency of proopiomelanocorticotropin peptides in vitro

Four lipolytic active centers were localized in proopiomelanocorticotropin (POMC): in the N-terminal part of POMC ("tryptophane rich peptide"), in the N-terminal part of adrenocorticotropic hormone, in the middle portion of beta-lipotropin and in the C-terminal part of beta-lipotropin. The weak lipolytic activity of the "tryptophane rich peptide" is not mediated by its two partial sequences gamma-MSH and delta-MSH. The minimal amino acid sequence for obtaining lipolysis from the N-terminal part of ACTH was ACTH 4-10. Lengthening of this amino acid sequence on the N- or C- terminus resulted in a strong increase of lipolytic potency. The minimal effective sequence from the middle portion of beta-lipotropin was located in the amino acid residues 47-53 which are identical to ACTH 4-10. Additional amino acids on the N- and C-terminus (beta-lipotropin p 41-58 and beta-lipotropin h 35-56) lead also to increased lipolytic activity. The forth center of POMC resides in the C-terminal part of beta-lipotropin (residues 78-91) because sequences from the N-terminal part of beta-lipotropin 61-91 were ineffective. The order of potency of POMC peptides especially in respect to the minimal effective concentration was ACTH 1-13 (alpha-MSH) greater than beta-lipotropin p greater than ACTH greater than ACTH 1-10 greater than beta-lipotropin p 61-91.

Influence of alpha-MSH and ACTH on cortical bone remodelling in hypophysectomized rats

Hypophysectomy increases both periosteal resorption and endosteal apposition along the femur diaphysis in rat. Administration of alpha-MSH decreased the periosteal resorption but had no effect on the endosteal apposition. ACTH had only minor effects on the endosteum. Thus, alpha-MSH and ACTH, in the doses used, have different effects on cortical bone in rat. The effect of alpha-MSH on cortical bone could be an effect of the hormone alone or by its stimulation of other factors.

Calcium redistribution into subcutaneous fat at parturition in the dairy cow

Blood samples and subcutaneous fat biopsies from six dairy cows at -14, 0, 14, and 28 days of parturition were analyzed to test the hypothesis that movement of calcium into subcutaneous fat contributes to hypocalcemia of parturient paresis. Plasma and subcutaneous fat calcium decreased while plasma free fatty acids increased at parturition. No trends were significant in magnesium or total lipid content of subcutaneous fat. Calcium content of subcutaneous fat was related positively to calcium concentration in plasma.