Central epinergic inhibition of corticosterone release in rat

Drugs known to inhibit phenylethanolamine-N-methyltransferase (EC 2.1.1.28), the final enzyme in the epinephrine synthetic pathway were administered to rats and their effects on pituitary-arenal function studied. 2, 3-Dichloro-α-methylbenzylamine (DCMB) produced dose-related increases in plasma corticosterone in basal and stressed rats. Evidence for the central nature of this tonic inhibitory effect of epinephrine was its continued presence in adrenal demedullated rats. 2-chloro-3-trifluoromethyl-α-benzylamine (CTFMB) administration elevated plasma corticosterone and this effect was highly correlated to the decrease in hypothalamic epinephrine concentration in both sham operated and adrenal demedullated rats. These findings argue for tonic epinergic inhibition of pituitary-adrenal function.     

Effect of intravenous epinephrine infusion on plasma renin activity in adrenalectomized dogs

Previous experiments have shown that circulating epinephrine stimulates renin secretin and increases plasma renin activity (PRA) when it is infused intravenously, but not when it is infused directly into the renal artery at similar infusion rates. The present experiments were designed to test the hypothesis that the adrenal glands mediate the PRA response to intravenous epinephrine infusion. Accordingly, anesthetized dogs were prepared with either an acute bilateral adrenalectomy or a sham-adrenalectomy procedure. Epinephrine was then infused intravenously into each animal for 45 minutes at a rate of 25 ng X kg-1 X min-1. Time control experiments in which epinephrine was not infused were also conducted. In sham-adrenalectomized dogs, PRA (in nanograms per ml h-1) rose from 4.1 +/- 1.4 in the control period to 13.0 +/- 3.0 during intravenous epinephrine infusion (means +/- SE; p less than 0.01). In adrenalectomized dogs, PRA rose from 2.1 +/- 0.4 during the control period to 5.5 +/- 0.9 during intravenous epinephrine infusion (p less than 0.01). Neither the absolute increments in PRA nor the percent increases in PRA were significantly different between the two groups receiving epinephrine. PRA remained unchanged in time control experiments. These data demonstrate that the adrenal glands need not be present in order for intravenous epinephrine infusion to elicit an increase in PRA. The data do not support the hypothesis, therefore, that epinephrine-induced increases in PRA are initiated by receptors located within the adrenal glands.     

Effects of clentiazem (TA-3090) and nifedipine on basal circulating catecholamine levels and on stimulation-evoked adrenal catecholamine secretion in anesthetized dogs.

The effects of TA-3090 (clentiazem) and nifedipine on basal sympathoadrenal activity and on the adrenal medullary response during splanchnic nerve stimulation were studied in dogs anesthetized with sodium pentobarbital. Plasma concentrations of epinephrine and norepinephrine were measured in aortic and adrenal venous blood before and after acute administration of the drugs, as well as during left splanchnic nerve stimulation before and after administration of drugs. Following intravenous injections, TA-3090 (30, 100, and 300 micrograms/kg) did not affect basal circulating catecholamine levels, whereas nifedipine (10, 30, and 100 micrograms/kg) markedly increased aortic epinephrine and norepinephrine concentrations in a dose-dependent manner in correlation with progressive decreases in mean arterial pressure. The changes in aortic epinephrine and norepinephrine concentrations were inversely related to those in mean arterial pressure (r = 0.603, p < 0.01; r = 0.536, p < 0.01; respectively). In response to direct splanchnic nerve stimulation (2 Hz, 2 ms, 1 min, 12 V), adrenal venous epinephrine and norepinephrine concentrations significantly increased, with a high degree of reproducibility. The catecholamine responses to splanchnic nerve stimulation were not affected by either TA-3090 or nifedipine at any dose tested. The present results suggest that the increases in circulating catecholamine levels following nifedipine administration are due to baroreflex activation secondary to the drug-induced hypotension. The study indicates that both TA-3090 and nifedipine did not significantly affect L-type Ca2+ channels related to catecholamine release in the adrenal medulla under the present experimental conditions.     

Effect of thyroid status and cold stress on tyrosine hydroxylase activity in adrenal gland and brown adipose tissue.

A tyrosine hydroxylase activity (THa) of 1.4 nanomoles DOPA formed per hour per mg of protein has been found in brown adipose tissue homogenate; a value of 30.3 nanomoles was found in the corresponding adrenal homogenate. The THa of brown adipose tissue of normal rat increases markedly upon intermittent exposure to cold temperature and is greatly increased in the thyroidectomized rat. In adrenal gland there is, upon intermittent cold stress, an increase in the THa of normal and of thyroidectomized rats, but no increase in the THa of animal receiving triiodothyronine.     

Effect of chronic cadmium treatment on rat adrenal catecholamines.

Daily intraperitoneal injection of cadmium chloride (1 mg/kg) for 45 days significantly increased adrenal weights and augmented the levels of adrenal norepinephrine and epinephrine as well as the activity of adrenal tyrosine hydroxylase. Discontinuation of the heavy metal treatment for 28 days, in rats previously injected with cadmium for 45 days, restored the activity of tyrosine hydroxylase as well as the amount of norepinephrine and epinephrine. In contrast, adrenal weights were restored only partially following the withdrawal of cadmium treatment. Evidence indicates that the changes in adrenal catecholamine metabolism may be the result of stress induced by chronic exposure to this heavy metal. In addition, some of the untoward effects such as hyperglycemia and arterial hypertension seen during cadmium toxicity might be related to increased synthesis of epinephrine in adrenal glands.     

Plasma catecholamines in the aorta and the phrenicoabdominal vein in exercising dogs

Plasma epinephrine and norepinephrine concentrations were measured in the aorta and phrenicoabdominal vein in five dogs at rest and during short-duration mild- and moderate-intensity exercise and during prolonged mild-intensity exercise. Plasma epinephrine and norepinephrine concentrations increased with exercise in both the aorta and the phrenicoabdominal vein. Plasma epinephrine concentration was much higher in the phrenicoabdominal vein than in the aorta (24-43 times). Plasma epinephrine concentrations in the aorta and phrenicoabdominal vein were significantly correlated (r = 0.88). This confirms that peripheral epinephrine concentration is a reliable index of the activity of the adrenal medulla during exercise. The epinephrine-to-norepinephrine ratio in the phrenicoabdominal vein was stable (4:1) throughout the experimental protocol, suggesting that the proportion of the two amines released by the adrenal medulla did not vary through this range of adrenal activity in dogs.     

Hormonal regulation of thermogenesis in goslings. Possible role of the thyroid gland.

The experiments performed on 90 male goslings showed that 6 h cold exposure (5 +/- 1 degree C) of the specimens 3, 10 and 21-day-old increases considerably 131I uptake by their thyroid gland. After single subcutaneous injection of thyroxine (100 mug/kg) no significant alterations of the metabolic rate, during 4 h measurements, in comparison with the pre-injection value were observed. Since, in control birds about 17% decrease of the metabolic rate within the same time occurred, as the effect of fasting, it was concluded that thyroxine does have the calorigenic effect. The metabolic rate of the goslings 5 to 7-day-old treated with thyroxine for four consecutive days (100 mug/kg daily) and the control ones was very similar. In the older goslings (22--24 days) thyroxine treatment significantly elevated the metabolic rate. Direct (extrathyroid) effect of TSH on heat production, did not occur in goslings.     

A role for thyroid hormones in the development of premigratory disposition in redheaded bunting,Emberiza bruniceps

Excessive fat deposition and zugunruhe (nocturnal restlessness), two characteristics of premigratory disposition, are displayed in caged redheaded buntings. In earlier experiments thyroid ablation was found to inhibit premigratory fattening in this bird. Also, seasonal investigations on thyroid hormonal profiles indicated a distinct rise in circulating tri-iodothyronine just before spring migration, most likely as a result of increased peripheral monodeiodination of thyroxine. The physiological relevance of these findings has been assessed in the present paper. Results indicated that removal of thyroid gland completely prevented development of zugunruhe and fat deposition; replacement therapy with T4 or T3 restored both. Thyroxine-induced fattening in thyroidectomized birds was found to be dose responsive. In two experiments in thyroidectomized and intact birds each suppression of extrathyroidal conversion of thyroxine into triiodothyronine by iopanoic acid completely suppressed zugunruhe and fattening in thyroidectomized as well as intact birds, arguing for a role of triiodothyronine in migratory physiology. Blockage of thyroxine to triiodothyronine conversion, however, did not suppress feather regeneration, indicating that unlike effects on migratory parameters in the same individuals thyroxine-induced feather regeneration does not involve prior monodeiodination to triiodothyronine. Thus, contrary to the prevailing view that triiodothyronine alone is the finally active thyroid hormone (thyroxine being a precursor), both thyroxine and triiodothyronine may have specific roles to play in the physiology of seasonal events, and peripheral conversion of thyroxine to triiodothyronine may be one of the physiological devices to ensure that energetically incompatible events like migration and moulting do not occur simultaneously. Results also indicate that increasing spring daylengths which are known to trigger avian migration may influence peripheral conversion of thyroxine to triiodothyronine possibly imparting to this physiological process an adaptive value in the timing of seasonal events.Abbreviations IOP iopanoic acid - NS normal saline - RIA radioimmunoassay - T4 thyroxine - T3 triiodothyronine - Tx thyroidectomized     

Kappa-opioid agonist induced diuresis. Is it mediated by a blood-borne factor of adrenomedullary origin?

Intravenous administration of the kappa-opioid agonists U50488H, tifluadom, and ethylketocyclazocine induced a characteristic diuresis in conscious, intact, saline-loaded rats. Naloxone pretreatment antagonized U50488H-induced diuresis. The diuretic response to the kappa-opioid agonists was significantly attenuated in adrenal demedullated rats. However, basal urine output, the diuretic response to furosemide, and the antidiuretic response to the mu-opioid agonist buprenorphine were unaffected. Transfusion studies established that 1 mL of blood, from intact donor rats treated with U50488H, induced a diuretic response when administered to intact or demedullated recipient rats, whether or not the recipients had been pretreated with naloxone. However, blood from demedullated rats treated with U50488H was unable to induce diuresis in intact or demedullated recipients. The results indicate that kappa-opioid agonist induced diuresis appears to be mediated by a nonopioid blood-borne "diuretic factor" of adrenomedullary origin and that this factor might be responsible for the dependence of the diuretic response upon an intact and functional adrenal medulla in conscious rats.     

Plasma catecholamine responses to tyrosine hydroxylase inhibition and cold exposure

The acute effect of α-methyl-p-tyrosine (αMPT), a tyrosine hydroxylase inhibitor, on plasma levels of norepinephrine (NE), epinephrine (E), dopamine (DA), and adrenal cholesterol content in male rats at room temperature (24°C) and during acute cold exposure (4°C) was evaluated. Compared to saline-treated controls, αMPT: 1) significantly reduced plasma NE and DA in both normal and cold stress conditions, 2) significantly increased plasma E in both environments, and 3) stimulated the adrenal cortex. These findings suggest that tyrosine hydroxylase inhibition and consequent catecholamine synthesis blockade disrupts the homeokinesis of adrenergic processes and may present a significant stress to the intact animal.     

Direct innervation of white fat and adrenal medullary catecholamines mediate photoperiodic changes in body fat

Seasonal adjustments in Siberian hamster adiposity are triggered by day length changes [i.e., short "winter-like" days (SDs) elicit body fat decreases vs. long "summer-like" days (LDs)]. These and other white adipose tissue (WAT) mass decreases traditionally have been ascribed to lipolysis triggered by sympathetically mediated, adrenal medullary released epinephrine; however, recent evidence suggests that direct sympathetic innervation of WAT also is important. Therefore, the contributions of WAT sympathetic innervation and adrenal medullary catecholamines to SD-induced decreases in adiposity were tested. Siberian hamsters were surgically bilaterally adrenal demedullated (ADMEDx) or sham ADMEDx, and all had one inguinal WAT (IWAT) pad sympathectomized via locally injected guanethidine, with the contralateral pad serving as a within-animal innervated control. One-half of the hamsters remained in LDs; the remainder was transferred to SDs. Guanethidine and ADMEDx abolished IWAT norepinephrine and adrenal epinephrine contents, respectively. Although sympathetic denervation or ADMEDx alone did not block SD-induced decreases in IWAT mass, their combination did. These results suggest that both adrenal catecholamines and the sympathetic innervation of WAT interact to decrease SD-induced decreased adiposity.     

Plasma epinephrine in chronically adrenodemedullated rats: lack of response to acute or chronic exercise.

Even if it is well established that epinephrine is a hormone originating from the adrenal medullae, the reappearance of circulating epinephrine has been reported in rats a few days after adrenodemedullation. To verify if the extra-adrenal tissue responsible for this epinephrine production can be stimulated, sham-operated or adrenodemedullated rats, either trained or kept sedentary, were submitted to an acute exercise stimulation test. Blood sampling was done before and after the test in precannulated rats for the determination of plasma epinephrine, norepinephrine, and corticosterone levels. Basal epinephrine levels were significantly reduced in trained and sedentary adrenodemedullated rats compared with their sham-operated counterparts. In response to exercise, there was no significant rise in epinephrine levels in both groups of adrenodemedullated rats. The norepinephrine levels in the basal state and in response to exercise were not altered by adrenodemedullation nor by physical conditioning. Basal corticosterone levels were similar between adrenodemedullated and sham-operated animals, either trained or kept sedentary. In response to exercise, corticosterone levels increased significantly in each group of rats but to a lesser extent in both groups of adrenodemedullated animals. These data indicate that the extra-adrenal epinephrine secretion that develops in the absence of adrenal medullae is not influenced by acute exercise nor by physical training.     

Role of the sympathoadrenal system in the regulation of glycogen metabolism in resting and exercising skeletal muscles.

The purpose of the present study was to characterize the role of catecholamines in the regulation of skeletal muscle glycogen metabolism during exercise. Using the rat hindlimb perfusion technique we have measured skeletal muscle glycogen content, glycogen phosphorylase and synthase activities in sympathectomized and/or demedullated rats under epinephrine treatment (10(-7) M) at rest and during muscle contraction. When epinephrine and/or norepinephrine deficiency was induced, muscle contraction resulted in a decrease in glycogen content (-63%) despite a decrease in glycogen phosphorylase activity ratio (0.25 to 0.11; p less than 0.001) and an increase in glycogen synthase activity ratio (0.13 to 0.27; p less than 0.001). Under these conditions, epinephrine treatment further reduced glycogen content while blunting the changes in the activity ratio of the rate-limiting enzymes. These data indicate that catecholamines do not play a primary role in skeletal muscle glycogen breakdown during acute exercise and suggest that allosteric regulators may be of prime importance.     

In vitro formation of thyroid hormones from 3,5-diiodothyronine by supernatant of submaxillary gland

Cell-free extracts of submaxillary glands from rat and goat iodinate exogenously added 3,5-diiodothyronine to form 3,5,3’-triidothyronine and thyroxine. This capacity was elevated after either thyroidectomy or exposure of rats to cold (3 ±1 ‡C) for 5 h. However, there was no further increase of iodination of 3,5-diiodothyronine when the thyroidectomized rats were exposed to cold stress. The submaxillary extracts have the ability to incorporate radioactive iodide into 3,5-diiodothyronine, 3,5,3’-triiodothyronine and thyroxine. The presence of 3,5-diiodothyronine was also detected in the soluble supernatant of submaxillary extract.     

Effects of exercise on plasma catecholamine levels in the toad, Bufo paracnemis: role of the adrenals and neural control

Resting plasma epinephrine (E) and norepinephrine (N) concentrations for intact toads (Bufo paracnemis) were 5.57+/-1.0 and 0.88+/-0.38 ng/ml, respectively. Exercise induced a significant increase in heart rate, blood pressure and plasma epinephrine (about 4.3 times), whereas norepinephrine remained unchanged. The resting [E]/[N] ratio was 6.3 and increased to 32.9 during exercise. Adrenal denervation did not alter the basal plasma catecholamine or norepinephrine levels after exercise, but prevented the increase in epinephrine during exercise, suggesting that in the intact toad this increase is due to adrenal secretion whereas resting norepinephrine may be liberated by extra-adrenal chromaffin tissues. This also suggests that the adrenal glands can release selectively the two catecholamines. The increases in heart rate and blood pressure in denervated toads were not significantly different from those of intact animals, suggesting that during exercise the sympathetic nerves play the main role in inducing cardiovascular responses. Spinal transection induced a significant increase in basal norepinephrine levels, which remained elevated after exercise. Since spinal toads are unable to perform spontaneous movements it is possible that this increase may be caused by this stressful condition. The increases in heart rate and blood pressure observed in spinal toads during exercise may be due to direct mechanical effects of venous return on the heart.     

Effect of functional adrenalectomy on glucagon secretion and circulating catecholamines during insulin hypoglycemia in the dog

The present study was carried out to determine whether an increase in the pancreatic immunoreactive glucagon (IRG) secretion during the acute phase of insulin-induced hypoglycemia depends on circulating catecholamines of adrenal origin. Hypoglycemia was induced by a bolus insulin injection (0.15 IU/kg, i.v.) in dogs anesthetized with sodium pentobarbital (35 mg/kg, i.v.). Plasma aortic epinephrine (E) and norepinephrine (NE) concentrations increased significantly 30 min after the injection of insulin. At this time point, a functional adrenalectomy (diversion of bilateral adrenal venous blood from the systemic circulation) was performed for 5 min. The increased aortic E and NE concentrations significantly decreased reaching, within 5 min, a level below the corresponding preinjection control value. The basal output of pancreatic IRG (6.58 +/- 1.12 ng/min, n = 6) significantly increased (24.93 +/- 2.77 ng/min, p less than 0.05, n = 6) 30 min after insulin injection. During the functional adrenalectomy, the increased pancreatic IRG output diminished rapidly, within 5 min, to approximately 50% (11.73 +/- 3.19 ng/min, p less than 0.05, n = 6) of the value observed 30 min after insulin administration. In the other group of dogs receiving sham adrenalectomy, the increased aortic E and NE concentrations and pancreatic IRG output following insulin injection remained elevated above the levels observed immediately before the sham adrenalectomy. The net decrease in IRG output during the adrenalectomy was significant (p less than 0.05) compared with the corresponding net IRG output observed in the sham group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Preimplantation genetic diagnosis (PGD) influences adrenal development and response to cold stress in resulting mice

Preimplantation genetic diagnosis (PGD) has gained widespread application in clinical medicine and hence the health of PGD offspring needs to be systematically assessed. Given the critical role of the stress response in growth and health, assessments of the development and function of the stress system might help to clarify the health outcomes of PGD. In this study, we constructed a PGD-conceived mouse model and used naturally conceived mice as controls; we used this model to evaluate the potential effect of PGD procedures on the stress system of the offspring. Serum and tissues of stress organs, namely the hypothalamus, locus coeruleus and adrenal gland, were collected from 5-week-old mice in the basal state or after cold stress. The serum levels of stress-related hormones and the structural and functional indices of the stress organs were then examined. In the basal state, ultrastructural abnormalities and low expression of genes involved in steroid hormone synthesis were found in the adrenals of the PGD mice, which had low corticosterone and high epinephrine levels compared with those of control mice. After acute cold stress, the PGD mice continued to show structural and glucocorticoid secretion abnormalities resulting in a late response to the environmental change. Thus, our study indicates that PGD manipulations affect adrenal development, result in structural and functional abnormalities of the adrenals in the offspring and influence their reactivity and adaptability to cold stress.     

Plasma free and sulfate conjugated catecholamine levels during acute physiological stimulation in man

The responses of plasma free and sulfate-conjugated catecholamines to acute physiological stimulation was examined in normal male subjects. Catecholamines were measured with a sensitive radioenzymatic assay incorporating simultaneous hydrolysis of sulfate conjugates and O-methylation of free norepinephrine and epinephrine. Following 20 minutes recumbency after venepuncture 30 +/- 3% of norepinephrine and 16 +/- 5% of epinephrine was in thr free form. Free catecholamines generally increased during standing, cold immersion and isometric handgrip, but sulfates did not change. Bicycle ergometry markedly increased free catecholamines which rapidly returned to basal levels at the end of exercise. In contrast, sulfated norepinephrine decreased substantially with exercise in all subjects but returned to basal levels 3 minutes after stopping exercise. Epinephrine sulfate varied considerably between subjects but showed a similar, although smaller, fall with exercise. Thus, during physiological stimulation, which caused increases in free norepinephrine and epinephrine levels in plasma, the only consistent change in sulfated catecholamines was a marked fall in norepinephrine sulfate after bicycle exercise. This may indicate saturation of sulfotransferase activity, substrate inhibition or impaired tissue conjugation.     

Effects of streptozotocin-diabetes and l-thyroxine treatment on plasma amino acid levels in thyroidectomized rats

1) Thirty days after surgical thyroidectomy, one group of rats were made diabetic by treatment with streptozotocin and were studied for the next 14 days. These diabetic thyroidectomized animals were similar in body weight to their thyroidectomized controls but had higher plasma concentrations of most amino acids. 2) Treatment with 0.5, 1.0 or 2.0 micrograms of L-thyroxine/100 g body wt for 7 days prior to sacrifice produced no changes in either parameter in the diabetic thyroidectomized animals. On the contrary, in thyroidectomized controls, the L-thyroxine treatment was followed by a dose-dependent increment in body weight. In these animals, the administration of 0.5 microgram of L-thyroxine per day was associated with a marked rise in the plasma level of most amino acids, while only basic amino acid levels increased with 1.0 microgram, and levels decreased with 2.0 micrograms. 3) In the diabetic thyroidectomized rats treated with insulin for the last 7 days before sacrifice, body weight gain and the biphasic change of plasma amino acid levels were restored. 4) It is proposed that treatment of thyroidectomized controls with small doses of L-thyroxine accelerate protein breakdown accompanied by minor changes in amino acid utilization, while this latter effect increases with higher doses of the hormone. 5) Present results demonstrate that a certain amount of circulating insulin is required to obtain the response to exogenous thyroxine in diabetic thyroidectomized animals. Results are discussed in terms of the role of interhormone synergism as it affects normal sensitivity of the different hormones.     

Direct evidence that an increase in aortic norepinephrine level in response to insulin-induced hypoglycemia is due to increased adrenal norepinephrine output

This study reports on the major source of circulating norepinephrine that is known to increase, progressively, during sustained hypoglycemia induced by intravenous insulin administration. Plasma concentrations of epinephrine, norepinephrine, and dopamine were simultaneously determined for adrenal venous and aortic blood in dogs anesthetized with sodium pentobarbital. The model used allowed us to perform a functional adrenalectomy (ADRX), while continuously monitoring the adrenal medullary secretory function. Under basal conditions, the net output (micrograms/min) of adrenal epinephrine, norepinephrine, and dopamine were 0.169 +/- 0.074, 0.067 +/- 0.023, and 0.011 +/- 0.003, respectively. Plasma concentrations (ng/mL) of aortic epinephrine, norepinephrine, and dopamine were 0.132 +/- 0.047, 0.268 +/- 0.034, and 0.034 +/- 0.009. Following insulin injection (0.15 IU/kg, i.v.), the net output (micrograms/min) of adrenal epinephrine, norepinephrine, and dopamine increased gradually (p less than 0.05), reaching the values of 0.918 +/- 0.200, 0.365 +/- 0.058, and 0.034 +/- 0.007 30 min after insulin administration. Similarly, aortic epinephrine, norepinephrine, and dopamine concentrations (ng/mL) increased significantly (p less than 0.05) to 0.702 +/- 0.144, 0.526 +/- 0.093, and 0.066 +/- 0.024. The aortic glucose concentration (mg/dL) was diminished from 81.8 +/- 4.1 to 36.9 +/- 3.4 (p less than 0.01). After taking the blood sample at 30 min following insulin administration, ADRX was immediately performed. Five minutes after the onset of ADRX, the net output (micrograms/min) of adrenal epinephrine, norepinephrine, and dopamine increased further to 1.707 +/- 0.374 (p less than 0.05), 0.668 +/- 0.139 (p less than 0.05), and 0.052 +/- 0.017.(ABSTRACT TRUNCATED AT 250 WORDS)