Seven male mongrel dogs of 8.3--13.1 kg. were bilaterally adrenalectomized and maintained for one week on replacement therapy, discontinued early enough to eliminate feedback effects of glucocorticoids by experiment time. Each dog, under light Nembutal anesthesia, received two stepwise primed constant infusions of cortisol (i.v.), each lasting 90 minutes. 23 venous blood samples were withdrawn for determination of plasma ACTH concentrations by adrenal cell suspension bioassay and 25 samples for plasma cortisol determination, at various times before, during and after the cortisol infusions. ACTH secretion rates were calculated using previously determined ACTH clearance and distribution volume characteristics. As a mean of 6 animals, the cortisol concentration plateaux, which averaged 4.59 +/- 0.57 and 6.49 +/- 0.92 mug/100 ml., caused suppression of ACTH secretion (expressed as percentage of pre-period secretion rates) from 0% before cortisol to 65.05% suppression during plateau # 1 and to 95.3% suppression during plateau # 2. 70 minutes after the cessation of cortisol infusion the plasma cortisol had fallen to 1.95 +/- 0.43 mug/100 ml. with an associated 69.6% suppression of ACTH secretion rate. The suppression, associated with the two infusion periods and the delay associated with the recovery in the post-infusion period, suggests a delayed feedback of the order of 1 hour. The infused cortisol resulted in low physiological plasma levels of cortisol which had the following characteristics in these adrenalectomized dogs: metabolic clearance rates of 12.8 and 17.4 ml/kg. min associated, respectively, with mean plasma cortisol concentrations of 4.27 and 6.23 mug/100 ml. (MCR increasing with increasing cortisol concentration) and an apparent distribution volume of about 40% V (distribution volume not correlated with plasma cortisol levels). Also, results on an as yet incomplete series of stress (histamine, anoxia) experiments showing suppression of stress induced ACTH secretion by low physiological plasma concentrations of cortisol, are included in an appendix.

Isolated rat hearts were perfused by a modified Langendorff method to compare the effects of CO2 and H+ on their function. Carbon dioxide had a rapid negative inotropic effect which was not dependent on the perfusate pH, or on the concurrent negative chronotropic effect and change in coronary resistance. Carbon dioxide caused a negative chronotropic effect which was due, in part, to the decreased perfusate pH. This negative chronotropic effect was not due to the concurrent negative inotropic effect or to the changes in coronary resistance. Intermediate concentrations of CO2, between 6% and 20%, were found to have intermediate negative inotropic and chronotropic effects. Carbon dioxide at concentrations of 18% and 20% caused coronary resistance to increase. This increase was independent of perfusate pH, rate or tension changes. Carbon dioxide concentrations between 6% and 16% caused coronary resistance to decrease. Decreasing oxygen from 95% to 80% caused a positive inotropic effect. Perfusates saturated with 20% CO2 caused the release of some basic substances from the heart. This release was not dependent on decreased perfusate pH.

Experiments were designed to find whether ascorbic acid administration had any effect on the following parameters of metabolic alteration in cold-exposed animals: oxygen consumption, thyroxine secretory rate (TSR) and biosynthesis of ascorbic acid. The results obtained may be summarized as follows: (1) No effect of ascorbic acid on the metabolic rate could be detected. (2) In untreated animals the TSR is increased during the first week of cold exposure, returns to normal in the following weeks and rises again after ten weeks. In the treated animals the TSR is also increased during the first week of cold exposure, but significantly less so than in the untreated animals. No effect of ascorbic acid is observable at room temperature. (3) The rate of biosynthesis of ascorbic acid is not altered significantly during the first three weeks of cold exposure, neither in the treated nor in the untreated animals. After six weeks of continuous exposure to cold, the rate of biosynthesis is significantly increased in untreated animals; this increase is prevented by the administration of ascorbic acid. These results are discussed along with the current literature and it is concluded that the effect of ascorbic acid in cold exposed animals could be partly explained by a lowering of the requirements for thyroid hormones. Cellular mechanisms of this action are briefly discussed and avenues of future research pointed out.

The effect of diacetyl-2,6-diiodohydroquinone (DDIH) on the calorigenic action of exogenous L-thyroxine and L-triiodothyronine was studied in normal and thyroidectomized male mice acclimated to 30° or 10°C. Two methods for determining the oxygen consumption rates (OCRs) were used: one was a modified Maclagan system in which the OCRs were determined on groups of eight mice; the other a system using single animals. The animals were pretreated with thyroxine or triiodothyronine in conjunction with DDIH, and their OCRs were determined using both methods. A comparison of the results showed that grouping had an effect, on the measured response in both treated and untreated animals. A series of experiments in which 131I-labled hormones were administered did not reveal any correlation between the amount of 131I excreted and the magnitude of increase in OCR in warm- and cold-acclimated mice. The calorigenic response of untreated and pretreated mice to noradrenaline was measured under two sets of environmental conditions. In one, untreated and pretreated mice were tested with noradrenaline, their OCRs being determined at the temperature of acclimation. In the other, the noradrenaline test was conducted after the animals had been exposed to 10° or 30°C for one hour. When noradrenaline was tested the temperature of acclimation, the results showed that pretreatment had an effect on the sensitivity to noradrenaline; DDIH generally inhibited the sensitivity of thyroxine pretreated mice and enhanced the sensitivity of triiodothyronine pretreated ones. Thyroidoctomy reduced the sensitivity to noradrenaline. When cold-acclimated, mice sensitive to the higher dosage of noradrenaline were placed at 30°C for one hour, they lost this sensitivity. This lack of sensitivity of cold-acclimated mice was contrary to the sensitivity seen in cold acclimated rats tested With a lower dosage of noradrenaline at 30°C and indicated a definate species difference. The difference in the response of mice to noradrenaline under the two environmental conditions indicated the importance of the temperature at which the test was conducted. The rapidity with which cold-acclimated mice lost their sensitivity to noradrenaline indicates a larger role for the nervous system in thermogenesis than is seen in the rat, and perhaps different means of nonshivering thermogenesis are to be found in these two species.

Abstract not available.

An attempt has been made to analyse the physical properties of the systemic arterial circulation by a standard engineering approach (transient analysis). This involved giving a square wave infusion of blood and interpretation of the pressure response. Development of a technique to give a square wave infusion of blood was required. This resulted in an infusion-giving apparatus which was composed essentially of a syringe whose action was controlled by a large, servo-controlled motor. The square wave effect was achieved by an electro-magnetic clutch-brake combination. The latter was capable of full activation within a 30 millisecond time interval. The whole apparatus was able to give a perfect square wave within the tolerance of these limits. Approximately 5% of the animals blood volume was slowly withdrawn into the infusion giving apparatus through a cannula in the right carotid artery. On activation of the electro-magnetic clutch, this blood was returned to the rabbit in the form of a square wave over a 2 - 3 second period. During this period, the heart was transiently arrested by vagus nerve stimulation. The pressure response of the arterial system to this square wave infusion of known flow rate was monitored in the right femoral artery with a pressure transducer. By relating the input flow pattern to the output pressure response, information could be obtained about the physical properties of the system. Direct pressure-flow studies across the whole systemic arterial circulation were found to be linear in the range of 90 to 40 mm Hg pressure. A 'critical closing pressure' was invariably present, and found to vary in value from 10 to 50 mm Hg. This necessitated a modification in the normal method of calculating total peripheral resistance to account for the true slope of the pressure-flow plot (herein called 'slope' resistance). It was found that the mean chord resistance value in a 5 to 6 lb. rabbit was approximately twice the magnitude of the mean slope resistance value (0.33 to 0.17 mm Hg/ml/min). Furthermore, these did not always vary in the same direction when a variety of different stresses were imposed on the circulation. Compliance value calculations demonstrated a hysteresis effect. The mean compliance value of the systemic arterial circulation in a 5 - 6 lb. rabbit measured during inflation was 0.037 ml/mm Hg: measured during deflation, it was 0.054 ml/mm Hg. There was good correlation between the compliance values measured by the square wave infusion method and by a method using excised lengths of aorta. An inertial component was found to be present which had an approximate mean value of 30 gm cm-4 in 5 - 6 lb. rabbits. The general response of the systemic arterial circulation to square wave infusion showed that it could primarily be considered to act as a linear first order system. The transient pressure response to a step function in flow was a single exponential curve with a mean of 509 msecs in inflation and 743 msecs in deflation. More exact modelling required consideration of the systemic arterial circulation as a third order system to account for the small inertial component. An electrical model was built whose response to a simulated square wave infusion of fluid, gave good correspondence to that obtained in the living rabbit. The correlation coefficient between cardiac output values measured by the square wave infusion technique and by the Fick method was +0.80. The effects of various CO2 concentrations, asphyxia, haemorrhage, nor-adrenalin infusion, and long-term cholesterol feeding on the rabbit systemic arterial circulation were investigated by this method.

Malathion is one of the organophosphorus insecticides least toxic to mammals. The toxicity of this compound in chick embryos is known; however, its teratogenic nature has not been recorded. Concentrations from 1.17 to 116.6 milligrams per egg were injected into the yolk sacs of 1 to 12 day incubated chicken eggs, and various types of abnormalities were produced. Injections of 3.99 and 6.42 milligrams malathion into the yolk sacs of 4 and 5 day incubated eggs produced deformed chicks with a combination of sparse plumage, micromelia, overall growth retardation and beak defects.All known breakdown and related products of malathion were investigated as to their teratogenicity; however, only the parent compound and malaoxon were capable of producing the aforementioned terata. Malathion causes a reduction in growth to, embryos from eggs injected on days 4 and 5 of incubation. Various metabolites were injected along with malathion into fertile eggs in an attempt to determine the possible effect of the latter compound on metabolism. Of the compounds injected, tryptophan prevented both the malformations and the growth retardation while nicotinamide, nicotinic acid, and quinolinic acid prevented the malformations only. A tryptophan assay revealed a reduction of total tryptophan content in malathion treated embryos indicating a reduction in uptake of this amino acid from the yolk. Other compounds related to tryptophan by electronic reactivity enhanced the effect of malathion. Several NAB or NADp linked dehydrogenasas were investigated by histochemical and biochemical methods on both malathion treated and untreated embryos. A cholinesterase assay on embryo homogenates revealed no apparent relationship between cholinesterase levels and teratisms.

The effect of an intravenous infusion of ethanol upon the rates of glucose production (Ra) and overall glucose utilization (Rd) was examined in conscious dogs. The animal were studied in the postabsorptive state under basal conditions; during insulin-induced hypoglycaemia; in diabetes induced by pancreatectomy or after a four day fast. The rates of glucose production and utilization were calculated using 3H-labelled glucose as tracer. Changes in blood lactate, plasma glucose and radioimmunoreactive insulin concentrations were followed during the administration of ethanol. The estimated rate of ethanol utilization was determined in the four different states studied. The primed infusion of 0.24--0.29 mM/kg·min ethanol did not change the plasma glucose concentrations nor the rates of glucose production and utilization in normal or diabetic dogs in the postabsorptive state. A significant decrease in Ra prevailed for fifty-five minutes after the beginning of an ethanol infusion at the rate of 0.04 mM/kg·min to dogs fasted for four days. When the same dogs were again fasted for the same duration and administered ethanol at the rate of 0.25 mM/kg min, there was no significant changes in Ra. When insulin was infused at the rate of 4-7 mU/kg min in the presence of ethanol, ethanol had no effect upon the increase in Ra. during insulin-induced hypoglycaemia. During ethanol infusions to fasted of diabetic dogs, blood lactate concentrations increased and insulin levels did not change. In five of the six paired experiments in which hypoglycaemia was induced with insulin with or without ethanol, the plasma insulin concentrations were consistently higher in the presence of ethanol although the metabolic clearance rates of glucose remained unchanged. The estimated rates of ethanol utilization were reduced by fasting but not in diabetes or during insulin-induced hypoglycaemia. In conclusion, ethanol did not interfere with the elevated rate of gluconeogenesis in diabetes nor did it interfere with the hepatic response to hypoglycaemia.

The aim of this study was to explore the feasibility of the use of tissue cultures for studying some of the mechanisms of synaptic transmission in the mammalian CNS. The cerebellar cultures are particularly suitable because their morphological features have been studied in detail, offering a possibility of correlating electrophysiological and morphological data. Another advantage of the cerebellum is that its structure and function are relatively well known in vivo so the validity of the tissue culture model can be well tested in this case. It is well known from previous studies that functional synapses develop in the cerebellar cultures. However, the patterns of synaptic connections in cultures, in particular the interactions between cortex (Cx), deep cerebellar nuclei (DN) and brain stem (BS) have not been investigated. Electrophysiological experiments were performed on fully developed cultures 3-4 weeks old. The cultures were placed in a perfusion chamber mounted on the stage of an inverted microscope so the electrodes could be placed near the neurones under visual control. The temperature of the perfusing solution (Earle's balanced salt solution) was maintained at 35-37°C and the pH at 7.3-7.4. One region of the cultures was usually activated by brief electrical pulses and synaptically evoked responses were sought in a different region. Stimulation of the DN area resulted in a synaptic activation of about 50% of the Cx neurones whereas a stimulation of the Cx area evoked 30% of the DN neurones antidromically. On the basis of known conduction velocities and latencies of the synaptically evoked responses it has been concluded that in culture DN neurones form a synaptic projection to the Cx area, which resembles a mossy fiber pathway found in the intact cerebellum (Tolbert et al. , 1976). Electron microscopic observations in culture give supporting evidence for the mossy type projection from the DN to the Cx (Hendelman et al., 1978). Another synaptic pathway which has been well documented in culture is the monosynaptic inhibitory projection from the Cx region to the DN. Satisfactory electrophysiological and morphological evidence has been obtained to suggest that the projection is monosynaptic and that it can be routinely reproduced in culture. Electrophysiological characteristics of the pathway resemble those described in vivo by Ito et al. (1970a). Using pharmacological blockers, such as Bicuculline, Picrotoxin and Strychnine, it has been shown that GABA is probably the neurotransmitter responsible for the inhibition. This observation is similar to that of Obata et al. (1970a) who studied an analogous synaptic connection in the lateral vestibular nucleus of cats. In addition to the two major pathways demonstrated in cultures, evidence for recurrent axon collaterals of DN neurones and possibly Purkinje neurones has been obtained which again is in agreement with previous morphological observations in culture as well as in vivo. The presence of inhibitory interneurones in the Cx area was also evident. Neurones from the BS area, which can be included with the cerebellar cultures, have also been studied in spite of their uncertain identity. No firm evidence could be obtained as to the terminations of these neurones in other areas of the cultures but the results suggest that these neurones are excitatory and that they are interconnected by excitatory synapses which are possibly formed by the terminals of their own recurrent axon collaterals. A sparse inhibitory projection from the Cx to the BS area has been shown. Such a detailed demonstration of the synaptic interconnections in tissue cultures which resemble those in vivo provides a background for further experimentation. The tissue culture model of the Cb can be used for investigation of the mechanisms of synaptic transmission and the action of various pharmacological agents on the neurones. The advantage of such a model system lies primarily in its accessibility to pharmacological manipulations which are often difficult in the intact brain.

A new staining technique has been developed for the thyroid gland of the rat which in addition to being an excellent histological stain is a histochemical method for the rapid identification of the colloid containing iodinated thyroglobulin from that which contains biologically inactive protein material. Various indices such as incorporation of radioiodine 131, gland weight, epithelial height, and total number of follicles have been used totest the validity of the color reaction in the colloid. The comparison of these diverse indices of thyroid activity show that the blue colloid is directly related to the physical activity of the gland. As a result of our studies further insight has been gained into several aspects of thyroid physiology: (a) in the normal rat only about fifty percent of the gland contains active colloidal material; (b) complete incorporation of iodine 131 into the colloid requires longer than twenty-four hours in the normal rat; (c) information on the role of thiouracil raises the question of its action in iodine deficient rats; (d) evidence is offered for intracellular protein binding of iodine rather than the view that it is restricted to the follicular colloid; (e) additional evidence is presented that short exposure to cold brings about an immediate physiological and morphological response by the thyroid; (f) ascorbic acid has no apparent effect on the thyroid itself; (g) evidence favors the view that the pituitary gland is the rate-controlling principle in thyriod hormonogenesis; (h) the histochemical method may be of value in pathological diagnosis of thyriod slices and biopsies.