Effects of implantation of cortisol into the brain stem or pituitary gland on the adrenal response to stress in the rabbit

Small amounts of crystalline cortisol were implanted into the brain stem or the pituitary gland of rabbits; subsequently the adrenal response to immobilization stress was measured (as indicated by the rise in plasma corticoids) at weekly intervals for several weeks after implantation. The stress-induced adrenal activation was inhibited by implants into the anterior portion of the median eminence, the post-optic region and, to a lesser extent, the antero-medial part of the hypothalamus, between the supra-optic and paraventricular nuclei and the median eminence. No observable effect was induced by similar implants into the posterior hypothalamus, mesencephalon and adenohypophysis. Little correlation could be noted between inhibition of adrenal function and decline of adrenal weight.

Quantitative estimation of adrenocortical hormones and their alpha-ketolic metabolites in urine. III. Adrenocortical hypofunction

Urinary corticosteroid patterns were estimated in patients with adrenocortical insufficiency.

In patients with secondary adrenocortical hypofunction (Panhypopituitarism) the patterns reflect an abnormally low secretion of cortisol, corticosterone and Reichstein's S. The ratios between these corticosteroids are not altered. Aldosterone secretion can be temporarily normal or even increased. The THF/THE-ratio is elevated and this is presumably due to a diminished production of thyroid hormone.

In patients with primary adrenocortical hypofunction (Addison's disease) the patterns reflect an abnormally low secretion of corticosterone and aldosterone. Initially the secretion of cortisol can be within the normal range. The secretion of Reichstein's S is often normal or even increased. The ratios between the corticosteroids are altered in that the F/B-ratio is high and the F/S-ratio low. These characteristics, presumably due to excessive adrenocortical stimulation by endogenous ACTH, can be helpful in differentiating the two kinds of adrenocortical insufficiency and in diagnosing Addison's disease when the excretion of cortisol and its metabolites is still within the normal range.

THE RESPONSE OF EXPERIMENTALLY INDUCED MAMMARY TUMOURS IN RATS TO OVARIECTOMY

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EFFECT OF HYPOXIA ON SECRETION OF ACTH IN THE RAT

Body weights, organ weights, and blood and pituitary ACTH concentrations were determined in rats exposed continuously to 20.9, 15.0, or 10.0% O2 atmospheres at normal barometric pressure for periods ranging from 3 to 120 hr. Hypoxia resulted in some loss of body weight, and loss of weight of the thymus and the ovary. The weight of the adrenals increased. Blood ACTH rose rapidly after exposure to hypoxic conditions, remaining elevated for the duration of the experiment. Control animals (20.9% O2) placed in the same chamber had detectable blood ACTH only at the 3-hr sampling time. Pituitary ACTH also rose rapidly during hypoxia, the elevation being greatest with the most severe hypoxic state. The rate of ACTH synthesis and secretion in the resting state and during the stress of hypoxia is discussed.

OFF-PEAK ABSORPTION MEASUREMENTS IN FEULGEN CYTOPHOTOMETRY

The use of off-peak measurements in Feulgen cytophotometry is reported, using intact diploid (x) and tetraploid (y) nuclei of the human anterior pituitary gland as the experimental model studied. Results indicate that the ratio y/x is similar at the 14 wavelengths examined over the range 450 mµ to 650 mµ. The value of this ratio was 1.95, falling slightly under the theoretical ratio of 2.0. It was concluded that off-peak absorption measurements are of value in Feulgen cytophotometry. A discussion of the possible justification of off-peak absorption measurements was presented for the case in which the Beer-Lambert relationship was experimentally determined to be followed at a peak wavelength, for all concentrations under discussion, and the curves preceding and/or following the peaks were straight lines coming from a common point. If the curve best fitting the data is a straight line, it follows that the rate of change of absorbance with respect to a linear wavelength scale is constant. This means that for a given increase, or decrease, in wavelength, the same change in absorbance is obtained. From this it follows that absorbance readings at any wavelength in such a region will be equally valid to those taken at the peak. While the finding of such a linear relationship at several concentrations does not guarantee that it will occur at all other concentrations, it is suggestive. The closer the spectra approximate straight lines, the more valid does the use of off-peak measurements become.

INFLUENCE OF PROPYLTHIOURACIL AND THYROXINE ON SYNTHESIS AND SECRETION OF THYROID-STIMULATING HORMONE IN THE HYPOTHYROID RAT

Propylthiouracil (PTU) administration to rats produced a progressive and parallel increase in the serum TSH concentration and the thyroid weight over a one year period, but the pituitary TSH content followed a biphasic curve declining markedly for 4 weeks, returning to the control level in 10 weeks and then continuing to rise until a level 5 times the control was achieved after 32 weeks. Either physiologic replacement doses or toxic doses of thyroxine (DL-T4) caused depression of serum TSH levels, significant as early as one hour after administration, followed by an increased pituitary TSH content to as much as 8 times the starting level after 10-60 hours. Thus, T4 did not appear to directly inhibit TSH synthesis during this interval. The reaction appeared to be independent of the duration of prior PTU administration or the initial size and TSH potency of the pituitary gland or the dose of T4 between 2.5 μg/100 g in one day and 40 μg/100 g daily for 4 days. PTU was not essential to this reaction because it also occurred in radiothyroidectomized rats which never received PTU. This rise in pituitary TSH during the period when TSH secretion was suppressed indicated a net pituitary TSH synthesis of as much as 61 mU/h. These values were compatible with those obtained by indirect calculations and consistent with the temporary persistence of the pre-existing TSH synthesis rate although the possibility of the stimulation of TSH synthesis by the T4 was not excluded.

EFFECTS OF TESTOSTERONE ON PITUITARY CORTICOTROPHIN AND ADRENAL STEROID SECRETION IN MALE AND FEMALE RATS

Administration of a depot testosterone preparation to male and female rats resulted in no change in body or pituitary weight in either sex. Pituitary corticotrophin content was unaltered in male animals but was reduced in females. Adrenal weights and adrenal RNA and DNA contents were decreased in both sexes. Plasma corticosterone concentrations were unaffected in males but were reduced in female rats after stress or corticotrophin injection. Hepatic reduction of ring A in vitro and biological half-life of corticosterone in vivo were unchanged in male animals but impaired in females. Testosterone administration to intact male rats significantly increased adrenal steroidogenesis measured in vitro. A significant decrease in steroid production was found in intact females but increased steroidogenesis was observed in adrenals from testosterone-treated oophorectomized animals. No effect was obtained following addition of testosterone directly in vitro.

The data suggest that testosterone leads both to diminution of corticotrophin secretion and enhancement of adrenal steroid secretory capacity. In intact female rats, these effects are complicated by suppression of oestrogen secretion, the effects of which have been reported previously.

LIGHT: EVIDENCE FOR ITS DIRECT EFFECT ON HYPOTHALAMIC NEURONS

Continuous light impinging on the suprachiasmatic region of enucleate rats resulted in a constant estrous-like vaginal cycle. The lowest precentage of cornified cells was obtained from exposure of the arcuate or mammillary neurons to light. Ovarian and pituitary weight increased significantly after exposure of the arcuate region to continuous light.

DISTRIBUTION OF COPPER IN THE RAT

The concentrations of copper in organs of white male rats were measured. Highest concentrations were in the kidney (5.1 µg/g wet wt.), liver (4.4), heart (4.5), and pituitary (about 5). Hair contained about 30 µg/g. From the weights of the organs and their copper concentrations, the total copper contents of the organs and of the whole rat were calculated. The whole rat (250 g) contained slightly less than 0.5 mg, of which about half was in the skin and muscle. Balance studies indicated that approximately 300 µg of copper was excreted daily, almost exclusively in the feces. Relatively small amounts of copper were excreted in urine. When expressed as proportion of body weight, the weights of testes, pancreas, skin, and eyes were larger in the rat than in man, and adrenals, brain, and thyroid were considerably smaller.

INFLUENCE OF ALLOXAN DIABETES ON GROWTH HORMONE CONTENT OF THE RAT HYPOPHYSIS

Homogenates of adenohypophysial tissue obtained from alloxan-injected adult male rats varying in duration and severity of diabetes, as well as from diabetic rats maintained on an insulin-replacement regimen, were assayed in immature hypophysectomized female rats. The ability of these crude hypophysial extracts to encourage tibial cartilage width expansion, gain in body weight, and to depress hematocrit and blood urea levels was determined. Significant decrements in ability to increase epiphysial cartilage width and ability to depress hematocrits were noted 14 to 28 days following injection of alloxan. Increasing the intensity of the diabetic state was associated with decreased growth-promoting potency of hypophysial preparations as well as with decreased ability to influence hematological indices. Hypophysial extracts taken from insulin-treated diabetic rats contained more growth hormone than equivalent amounts of tissue obtained from control rats. It is concluded that the adenohypophyses of diabetic rats contain diminished amounts of growth hormone and that insulin repairs or encourages greater than normal accumulation of somatotrophin in these animals.

HISTOLOGICAL EFFECTS OF INTRA-TESTICULAR INJECTIONS OF CADMIUM CHLORIDE IN DOMESTIC FOWL

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FINE STRUCTURE OF THE NEUROHYPOPHYSIS OF THE OPOSSUM (DIDELPHIS VIRGINIANA)

The neurohypophysis of the opossum (Didelphis virginiana) was studied by electron microscopy in order to amplify Bodian's classic light microscopic observations in which he demonstrated a definite lobular pattern. The lobule of the opossum neurohypophysis is divided into three regions: a hilar, a palisade, and a septal zone. The hilar portion contains bundles of nerve fibers, the extensions of the hypothalamo-hypophyseal tract containing neurofilaments but few neurosecretory granules. In the opossum, pituicytes have a densely fibrillar cytoplasm. Herring bodies are prominent in the hilar region. They are large bodies packed with neurosecretory granules that have been described as end bulb formations of axons. From the hilar region, axons fan out into a palisade zone where the nerve terminals packed with neurosecretory granules, mitochondria, and microvesicles abut upon basement membranes. The neurosecretory granules are similar to those present in the neurohypophysis of other mammals, except for an occasional huge granule of distinctive type. Material morphologically and histochemically resembling glycogen occurs as scattered particles and as aggregates within nerve fibers. The septal zone, containing collagen, fibroblasts, and numerous small capillaries, is separated from the adjacent glandular tissue by a basement membrane.

RELEASE OF THYROTROPHIN IN VIVO AND IN VITRO BY SYNTHETIC NEUROHYPOPHYSIAL HORMONES

The influence of synthetic oxytocin and synthetic lysine-8-vasopressin on the release of thyrotrophin (TSH) from slices of the "basophilic" zone of bovine anterior pituitary glands was determined. Up to 10-fold stimulation of TSH release occurred in the presence of the peptide hormones at low concentrations (approximately 10−11 to 10−9 M). Concentrations greater than 10−9 M were less stimulatory, ineffective, or inhibitory. In general, vasopressin stimulated at lower concentrations than did oxytocin. The dose–response curve of oxytocin began to descend at lower concentrations than did that of vasopressin.Stimulation of I131 discharge from the thyroids of propylthiouracil (PTU)-treated, day-old chicks was produced by the intraperitoneal injection of as little as 4 ng vasopressin or 25 ng oxytocin. As the injected dose of either peptide was increased beyond an optimal level, there was less enhancement of I131 discharge, and, with further increases, inhibition. The decreasing response began with lower doses of oxytocin than of vasopressin. The similarities of the dose–response curves of thyroid I131 discharge and of in vitro release of TSH indicate that the in vivo effects of injected neurohypophysial peptides are mediated through the release of endogenous TSH.

ELECTRICAL PROPERTIES OF HYPOTHALAMIC NEUROENDOCRINE CELLS

Goldfish hypothalamic neuroendocrine cells have been investigated with intracellular recordings. The cells showed resting potentials of 50 mv and action potentials up to 117 mv followed by a long lasting and prominent diphasic hyperpolarizing afterpotential. The action potential occurred in two steps indicating sequential invasion. "Total" neuron (input) resistance was measured to be 3.3 x 10⁷ Ω and total neuron time constant was 42 msec. Orthodromic volleys, produced by olfactory tract stimulation, generated graded excitatory postsynaptic potentials. These neuroendocrine cells seem, therefore, to have electrical membrane properties that are similar to those of other central neurons. Antidromic volleys (pituitary stimulation) produced inhibitory post-synaptic potentials whose latency was only slightly longer than that of the antidromic spike indicating the presence of recurrent collaterals. This finding suggests that the concept of the neuroendocrine cell as a neuron whose axon forms contacts only on blood vessels and not on other neurons or effector cells is too restrictive. Perfusion of the gills with dilute (0.3 per cent) sea water produced an inhibition of spontaneous activity. This inhibition is discussed in relation to recent work which demonstrates that goldfish hypothalamic hormones facilitate Na⁺ influx across the gill membrane.