Metabolic Functions of the Endocrine Glands

Abstract

As in the past several years, it has been impossible to mention here all the papers appearing in the period of review which might have been included under the title of this chapter. Emphasis has been placed on the metabolic functions of the hormones with evidence bearing on the physiology of the endocrine glands as such included only in certain instances. With few exceptions, no discussion has been attempted of papers which have been available to the author only in abstract form. THE HYPOPHYSISActivation of the adenohypophysis.-It has become apparent that most of the anterior lobe hormones, like those of the neurohypophysis, are secreted not at constant rates, but that the functioning of the gland must be controlled in such a way that the trophic hormones are released at rates varying with the physiological state and needs of the animal. The nature of the mecha nisms which may excite secretion by the adenohypophysis is now under active investigation (1, 2). Green & Harris suggested earlier that local neuro humoral stimulation of the gland might occur via pathways from hypo thalamic areas and the hypophyseal-portal blood vessels. These authors have now confirmed by direct observation in the living rat the direction of flow of blood in these vessels as from the median eminence toward and into the pars distalis (3). Harris has'further pointed out that after stalk section, re generation of the portal vessels may occur readily (4, 5). Unless measures are taken to prevent this, as by insertion of a plate of some sort, severing the direct neura1 pathways from the hypothalamus to the pituitary would not necessarily interrupt permanently the vascular connections. In stalk-sec tioned rats, Cheng et at. (6) observed maximal reduction in the adrenal ascorbic acid after injection of histamine. Later, they reported submaximal stimulation of the adrenal by histamine in hypophysectomized rats bearing intra-ocular grafts of anterior lobe tissue (7). Fortier & Selye (8), using cold as a stimulus, reported identical changes in adrenal ascorbic acid in normal or stalk-section�d rats and in hypophysectomized animals with intra-ocular grafts. I t would appear that in the rat, at least, neither neural nor vascular connections with the hypothalamus are required for increased secretion of adrenocorticotrophic hormone (ACTH) folIowing stress.

The effect of cortisol on the activity of glutamate-pyruvate transaminase and the formation of glycogen and urea in starved rats

“…This probably reflects a higher than normal concentration of these substances in the plasma (Ingle, 1949). An increased synthesis of urea is well established as a response to cortisol treatment and is thought to be related to a primary action of the steroid in changing the steady-state balance of protein metabolism in peripheral tissues so as to favour protein breakdown (Russell, 1951).…”

Metabolic Effects of Thyroid Hormones and Cortisone in the Hypophysectomized Rat

“…In the absence of urinary nitrogen data, we can only speculate concerning the possible specific dynamic action of amino acids liberated following the extensive mobilization of body protein which would be expected from a dose of cortisone as high as 5 mg./kg./day (cf. Russell, 1951). However, all stabilized animals maintained their body weights well during and following the injection periods.…”

The effect of insulin on the anaerobic metabolism of rat diaphragm

“…This facilitation has sometimes been visualized as the removal of a 'permeability barrier' to glucose which is presumed to exist in the membrane. A third hypothesis, which has been suggested in various forms by Polis, Polis, Kerrigan & Jedeikin (1949), Russell (1951), Haugaard, Marsh & Stadie (1951, and others, is that insulin increases glucose utilization by making more adenosine triphosphate (ATP) available to hexokinase, possibly by increasing the efficiency of oxidative phosphorylation.…”