Regulation of the prefrontal cortical dopamine system by the neuroactive steroid 3a,21-dihydroxy-5a-pregnane-20-one

The dopamine innervation of the prefrontal cortex can be differentiated from other telencephalic dopamine projection fields by its sensitivity to stress. The stress-induced activation of the mesoprefrontal cortical dopamine system can be blocked by pretreatment with benzodiazepines. A group of neuroactive steroids that modulate GABA-induced chloride flux through means distinct from that of the benzodiazepines has recently been identified. Intraventricular administration of the neuroactive steroid 3 alpha,21-dihydroxy-5 alpha-pregnane-20-one resulted in a dose-dependent decrease in dopamine metabolites in the prefrontal cortex, but not in mesolimbic or striatal sites; sedative effects were not observed. Moreover, the neuroactive steroid selectively attenuated the stress-induced activation of the mesoprefrontal cortical dopamine system. These data suggest that neuroactive steroids may function as endogenous anxiolytic agents.

Effects of deoxycorticosterone treatment on beta-subunit mRNA for (Na + K)ATPase in brain regions determined by in situ hybridization

1. We have used in situ hybridization techniques to determine the mRNA for (Na + K)ATPase in 20 brain regions from control rats and rats treated with high doses of deoxycorticosterone (DOC). 2. DOC-treated rats developed a salt appetite following the second hormone administration on alternate days and were used after the fourth DOC administration. 3. DOC treatment did not change the number of silver grains/cell deposited in cells from Ca1, CA2, CA3, and CA4 hippocampal subfields, dentate gyrus, cerebral cortex, medial preoptic area (POA), substantia nigra, and periventricular gray matter. 4. Nonsignificant reductions were detected in lateral POA, medial and lateral septum, caudate-putamen, and three amygdaloid nuclei (cortical, basolateral, and central) from DOC-treated rats. 5. Significant reductions were obtained, after DOC administration, in arcuate and ventromedial hypothalamic nuclei and medial and lateral amygdala. 6. The results suggested that regulation of the beta-subunit mRNA of (Na + K)-ATPase may be related to the central actions of mineralocorticoids in the control of salt intake.

[Effect of hormone-induced stress and high altitude on the higher nervous activity of rats]

The hormonally induced stresses have been studied for their effect on higher nervous activity (HNA) of rats under conditions of low-(1760 m above the sea level) and highland (3200 m above the sea level). Hydrocortisone-induced stress (HIS) in mountains decreases to an optimal degree the latent period (LP) of conditioned reflex of active avoidance (CRAA) and strengthens differentiating inhibition (DI). In mountains and on plain it impedes appearance of extinctive inhibition (EI). DOCA-induced stress (DIS) has the same effect though in the emergency period of adaptation it sharply (unlike GIS) increases the number of cases of CRAA amnesia manifestation and prolongs their LP. ACTH-induced stress (AIS) makes the appearance of amnesia cases more frequent and prolongs LP of realized CRAA, unlike DIS, over all the periods of Alpine adaptation. However, DI strengthens, while EI is hindered irrespective of the altitude level. Injection stress in mountains occurs with deviations of HNA; the number of cases of the CRAA amnesia increases as well as differentiation disinhibition. DI fails rapidly being tested for strength. Adaptation of intact rats to highland occurs faithfully without essential changes of LP but with impeded development of EI.

Peripheral angiotensin II is not the cause of sodium appetite in the rat

Activation of the renin-angiotensin system has been shown to arouse both water and sodium intake in the rat. The following experiments examine the contributions of the peripheral and central renin-angiotensin systems to the expression of sodium appetite in the adrenal-intact rat. Firstly, we find that, unlike intracerebroventricular angiotensin II, intravenous administration of the hormone at dipsogenic doses does not arouse sodium intake in the sodium replete rat when given alone or in combination with systemic mineralocorticoid pretreatment. Secondly, in the sodium depleted rat, we find that interference with central, but not peripheral, angiotensin II action suppresses sodium appetite. Together, these data confirm recent evidence which demonstrates that it is angiotensin II of cerebral origin, not angiotensin II of renal origin, that is necessary for the expression of sodium appetite.

[Effects of desoxycorticosterone on 5-nucleotidase and adenosine deaminase activity in the hypothalamus and hippocampus of the rat brain]

Influence of single (enzyme activities was determined 5h after the preparation) and multiple (for 7 days) DOCA administration on 5'-nucleotidase (EC 3.1.3.5) and adenosine deaminase (ES 3.5.4.4) activities in homogenate and subcellular fractions of the hypothalamus and hippocampus of the rat brain has been studied. It has been shown that DOCA enhances adenosine metabolism in the hypothalamus activating both the enzymes while in the hippocampus 5'-nucleotidase activity increases whereas adenosine deaminase activity decreases. Possible ways of mineralocorticoid effects on adenosine system and the role of this nucleoside in these hormones mechanism of action on CNS functional activity are being discussed.

A 'hypertensinogenic' class of steroid hormone activity in man?

1. Studies in sheep have led to the concept of a 'hypertensinogenic' (HT) steroid hormone activity, whereby the blood pressure (BP) raising effects of adrenocortical steroids can be separated from their in vivo glucocorticoid (GC) or mineralocorticoid (MC) activities. 2. The three main lines of evidence are as follows: (i) BP raising effects of ACTH cannot be reproduced by appropriate rates of infusion of steroids with GC and MC activities; (ii) certain steroids e.g. 9 alpha-fluorocortisol can increase BP at rates of infusion below threshold for in vivo GC or MC actions and for many steroids there is no correlation between GC, MC and HT effects; (iii) demonstration of differential antagonism of HT, MC and GC effects. 3. Studies in man show that the BP effects of ACTH are due to cortisol (F) at levels which have both MC and GC activity. However, BP effects of ACTH cannot be blocked by MC and GC antagonists. 4. Although complete separation of in vivo GC, MC and HT activities has not been possible in man, our own studies show a degree of dissociation. Taken together, these data suggest that steroids may raise BP by a HT mechanism distinct from classical in vivo MC or GC activities in man as well as sheep.

Infusion of atrial natriuretic hormone in DOCA/salt and spontaneously hypertensive rats

The effects of a 6-day infusion of atrial natriuretic hormone (ANH) on blood pressure and urinary sodium excretion were determined in conscious DOCA/salt and spontaneously hypertensive rats. The DOCA/salt rats were randomly divided into two groups after 4 weeks and either infused by osmotic minipump with 32.5 pmol/h of ANH in 0.1% gelatin vehicle or sham operated with emplacement of a blind cannula. Thirteen-week-old spontaneously hypertensive rats were studied in a similar fashion. The baseline systolic blood pressure prior to the infusion was 176 +/- 7 mmHg (x +/- SEM) in the ANH group and 169 +/- 5 mmHg in the sham group of DOCA/salt animals. The ANH infusion in the DOCA/salt animals dropped their blood pressure to 160 +/- 10 mmHg (p less than 0.01) compared to that in the sham controls which continued to rise to 200 +/- 7 mmHg. The blood pressure response to ANH infusion in the spontaneously hypertensive rats was slightly greater, with a blood pressure of 192 +/- 5 mmHg in the sham group and 132 +/- 3 mmHg in the ANH-infused animals. ANH infusion produces a qualitatively similar blood pressure response in the DOCA/salt rat as well as the other hypertensive models. This response is relatively less on a quantitative basis than that observed in the spontaneously hypertensive rats and is not related to changes in sodium balance or volume contraction.

[Effect of altered hormonal balance in the mother-fetus system on body weight, the adrenal glands, thymus gland and peripheral blood leukocyte composition in the offspring]

Pregnant rats have been injected intramuscularly with hydrocortisone-acetate or desoxycorticosterone-acetate (DOCA) for the III or the II-III trimesters of pregnancy. In the last case the animals are given not only greater doses of the hormones, but during a longer period. By the end of the pregnancy the drug dose decreases. In mother-rats after hydrocortisone injections the adrenals mass increases; after DOCA the body mass increases, and that of the adrenals drops. In the offspring hydrocortisone produces decline of the thymus and adrenals mass, as well as neutrophilic leucocytosis, lympho-, eosino-++- and monocytopenia. Just the opposite, DOCA results in lympho- and monocytosis, in increasing morphofunctional activity of monocytes. Common effects in hormonal action is demonstrated as underdevelopment of the adrenals, in decreasing thymus mass, in development of neutrophilic leucocytosis and eosinopenia. With increasing doses and duration of prenatal injections of corticosteroids in rats the mass of the adrenals and thymus drops even greater, stimulating effect of the hormones on the neutrophilic granulocytopoiesis decreases.

Effect of chronic dietary treatment with 1-tryptophan on spontaneous salt appetite of rats

Chronic dietary treatment with 1-tryptophan (2.5 and 5.0% in food) reduced the exaggerated spontaneous NaCl intake induced by deoxycorticosterone acetate (DOCA) in rats. In the absence of DOCA, chronic (4-week) dietary treatment with 1-tryptophan (5.0% in food) failed to affect significantly spontaneous NaCl intake. In addition, treatment with tryptophan in the absence of DOCA failed to affect significantly systolic blood pressure, plasma renin activity, plasma aldosterone concentration, and the weights of the heart, kidneys, adrenals, and thyroid gland. It also failed to affect the specific binding of [125I]-Ang II to neuronal membranes isolated from the diencephalon of the rats. However, the contents of both serotonin and 5-hydroxyindoleacetic acid in the lower brain stem were increased significantly by chronic treatment with tryptophan. These results suggest that the effect of chronic treatment with tryptophan to reduce the salt appetite of DOCA-treated rats is a specific effect of this amino acid under these conditions and may be related to the ability of tryptophan to prevent the upregulation of specific Ang II receptors induced by DOCA.

Modulation of Na-K-ATPase activity in the mouse medullary thick ascending limb of Henle. Effects of mineralocorticoids and sodium

This study investigates the effect of variations in mineralocorticoid as well as cell sodium delivery and uptake on Na-K-ATPase activity in the mouse medullary thick ascending limb of Henle (mTALH). Pharmacologic doses of the mineralocorticoid deoxycorticosterone acetate (DOCA) resulted in a 28% increase of Na-K-ATPase activity. Furosemide-induced inhibition of sodium uptake by the mTALH cell also resulted in Na-K-ATPase activity reduction (45%). Sodium deprivation did not cause a clear change in enzyme activity, either at 3 d or 2 wk, likely reflecting the result of the opposing influences of decreased sodium delivery and increased endogenous aldosterone. Finally, the behavior of Na-K-ATPase activity at 3 d of sodium deprivation in the mTALH contrasted with a 60% increase in activity observed in the cortical collecting tubule, a nephron segment known to be responsive to mineralocorticoid, and this heterogeneity of response may suggest an important role for the mTALH in maintaining salt homeostasis.

Induction, prevention and mechanisms of contrast media-induced acute renal failure

This study describes the development of an experimental model of reversible acute renal failure following infusion of contrast media radiographic dye. Experiments were also performed to investigate possible methods of prevention as well as examine single nephron mechanisms involved in the pathogenesis of the renal failure. Acute renal failure was consistently produced by indomethacin treatment (18 mg/kg) and an intravenous infusion of contrast media (7 ml/kg) into New Zealand rabbits that had been on a low sodium diet for one week. Glomerular filtration rate (GFR), measured by daily creatinine clearance in unanesthetized animals, was significantly decreased (P less than 0.001) 24, 48, and 72 hours following infusion of the contrast dye. Two weeks after induction of acute renal failure, GFR had returned to control. GFR was unchanged during the same time period when the sodium deprived rabbits were given either indomethacin or contrast media alone. Chronic administration of DOCA (1 mg/kg s.c.) and saline drinking water which increased sodium and solute excretions and decreased plasma renin activity also prevented the decrease in GFR. However, acute infusion of either saline or mannitol, which transiently increased sodium and solute excretions and decreased plasma renin activity, did not protect against the development of acute renal failure. Light microscopy revealed no glomerular or tubular changes and no visible obstruction. Micropuncture experiments were performed on three additional groups of anesthetized rabbits: control, acute renal failure, and recovery. Recovery rabbits were allowed a two week period after renal failure before they were micropunctured.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory influences of the adrenal steroid, 3 alpha, 5 alpha-tetrahydrodeoxycorticosterone [correction of tetrahydroxycorticosterone] on aggression and defeat-induced analgesia in mice

The effects of intraperitoneal administrations of the deoxycorticosterone metabolite, 5 alpha-pregnane-, 21 diol-20-one (3 alpha, 5 alpha-tetrahydrodeoxycorticosterone; alpha-THDOC) on the responses to aggression and defeat-induced analgesia were examined in subordinate intruder male mice in "resident-intruder" pairings. alpha-THDOC reduced in a dose-dependent mannter (1-20 mg/kg) the number of bites and time to obtain defeat in subordinate mice during the agonistic encounters, as well as attenuating defeat-induced analgesia. These inhibitory effects of alpha-THDOC were separate from its sedative actions at 20-30 mg/kg. In addition, the stereo-isomer, 3 beta-pregnane-3 alpha, 21 diol-20-one (20 mg/kg) had no significant effects on the agonistic encounters and defeat, indicating that the inhibitory effects of alpha-THDOC on agonistic interactions are stereospecific. Pretreatment with the benzodiazepine antagonist Ro 15-1788 (5 and 10 mg/kg) attenuated the inhibitory effects of alpha-THDOC on defeat-induced analgesia. Ro 15-1788 (5, 10 mg/kg) by itself, however, had minimal effects on these agonistic interactions and subsequent defeat-induced analgesia. These results indicate that the naturally occurring steroid, alpha-THDOC, has significant effects on responses to aggression and defeat-induced analgesia.

[Neuromodulator mechanism of the inhibitory effect of deoxycorticosterone on the aggressive-defensive behavior of the rat]

DOCA (0.3 mg/kg i.p.) inhibited the shock-induced aggression in male rats. This behavioural reaction was also inhibited by activation of brain beta-adrenergic and nicotinic receptors. The inhibitory hormone effect was potentiated to a considerable extent (p less than 0.05-0.001) by central beta-adrenergic stimulation but was blocked by beta-antagonist administration. However, it was independent of facilitatory and inhibitory actions on the brain nicotinic receptors. It is concluded that the DOCA inhibitory effect on the shock-induced defensive fighting involved the facilitation of the brain beta-adrenergic receptor activation.

Sex difference in the development of deoxycorticosterone-salt hypertension in the rat

To investigate a possible sex difference in the development of deoxycorticosterone (DOC)-salt hypertension in rats, systolic blood pressure was measured over 6 weeks in unilaterally nephrectomized male and female rats with or without DOC-salt treatment. Throughout the treatment, systolic blood pressure was significantly lower in female than in male DOC-salt rats (at the end of the sixth week: 190 +/- 8 vs 163 +/- 7 mm Hg, p less than 0.05). The difference in blood pressure was also confirmed by the direct measurement of mean arterial pressure at the end of the experiment. The 24-hour urinary excretion of vasopressin was significantly higher in male control rats than in female control rats; however, no difference was observed between male and female DOC-salt rats, in which the urinary excretion of vasopressin was four to five times higher than in control rats. The plasma vasopressin concentration was higher in DOC-salt rats, but there were no differences between sexes. There were no differences in the metabolic clearance rate of vasopressin among the four groups of rats. This indicates that the elevated plasma vasopressin concentration in DOC-salt hypertensive rats is due to increased release of the hormone, rather than to impaired metabolism. Thus, although vasopressin plays a pivotal role in the pathogenesis of DOC-salt hypertension, the sexual dimorphism in this form of hypertension cannot be attributed to differences in the secretion, metabolism, or plasma concentration of vasopressin.

Sleep induction by an adrenal steroid in the rat

The ring A reduced metabolites of deoxycorticosterone and progesterone, 3 alpha, 5 alpha-tetrahydrodeoxycorticosterone (THDOC) and 3 alpha-hydroxy-5 alpha-dihydroprogesterone (3 alpha-OH-DHP) have been shown to be potent barbiturate-like ligands of the benzodiazepine receptor complex. The former has also been reported to have anxiolytic effects in mice and rats. In the present study, sleep recordings were obtained on rats given 5 and 10 mg/kg of these steroids alone and in combination with flurazepam. THDOC, but not 3 alpha-OH-DHP, had potent dose-dependent sleep-inducing properties and increased nonREM sleep. Flurazepam had similar hypnotic effects and also reduced REM sleep. There were no significant interactions between THDOC and flurazepam, except in the case of REM latency, which tended to increase when the two compounds were given together. In summary, THDOC, a mineralocorticoid metabolite found in brain, has sedative properties and could conceivably play a role in stress responses.

Effects of altered dietary calcium intake in experimental hypertension: role of intracellular free magnesium

Blood pressure, ionic and hormonal effects of high (1.8%) versus low (0.2%) dietary calcium intakes were explored in uninephrectomized DOC-NaCl rats, in two-kidney, one clip (2K, 1C) Goldblatt hypertensive rats and their respective controls. High-calcium diets lowered blood pressure (P less than 0.05) in DOC-NaCl and in control uninephrectomized rats drinking 1% NaCl. However, calcium loading in renin-dependent 2K, 1C rats elevated blood pressure (P less than 0.05) but had no effect in sham-operated controls. Plasma renin activity rose in all animals, while serum ionized calcium rose significantly only in dietary salt-loaded animals. Intracellular free magnesium levels were consistently, inversely linked to blood pressure (r = -0.92, P less than 0.001). This linkage was independent of plasma renin activity, serum ionized calcium values and dietary calcium content. These results demonstrate that the same alteration in dietary mineral content can produce opposite blood pressure effects in different pathophysiological subtypes of hypertensive disease. We conclude that intracellular free magnesium levels directly participate in the final common pathway of events regulating blood pressure and vasoconstrictor tone.

Localization of phosphorus metabolites and sodium ions in the rat kidney

Relative amounts of phosphorus-containing metabolites and sodium ions present in different regions of the in vivo rat kidney were obtained using a surface-coil probe and recently developed NMR rotating-frame methods. During altered physiologic states, changes in distribution of metabolites and sodium ions within the kidney were identified in one-dimensional metabolite maps. This technique may have important applications to disorders commonly found in clinical medicine.

An attempt to develop a model to study the effects of intrathecal steroids

An attempt has been made to develop a chronic inflammatory arachnoiditis model in the rat to study the influence of subarachnoid or epidural steroids. Through chronically implanted catheters in Wistar rats (250-350 g), either triamcinolone (3.5-350 micrograms) or methylprednisolone (3.5-350 micrograms) was injected intrathecally, daily for 7 days or weekly for 7 weeks. Some rats also received 100 mg kg-1 cefoxitin and 0.5 mg deoxycortone by intramuscular injection. Equivalent control groups were included. High doses of intrathecal steroids caused marked weight loss and infection and many rats died. These effects were mitigated at a lower dosage especially by the addition of cefoxitin and deoxycortone. The effects of triamcinolone were more marked than those of methylprednisolone. No systematic histological evidence of neurotoxicity was observed after either steroid. Injections of talc failed to cause arachnoiditis or meningitis probably because sufficient particulate talc could not be injected through the narrow catheter.

Increased vasopressinergic activity following DOCA administration in the rat

The dynamics of hypothalamic arginine vasopressin (AVP) release was examined during the development of hypertension in rats with deoxycorticosterone (DOCA)-NaCL induced hypertension. Experiments were performed in four groups of uninephrectomized Sprague-Dawley rats 3, 7, 14 and 21 days after treatment with: (I) DOCA and 1% saline (DOCA-NaCl); (II) DOCA, regular chow, and tap water (DOCA-R-H2O); (III) regular chow and 1% saline (NaCl); and (IV) regular chow and tap water (H2O). Systolic blood pressure (BP) was significantly elevated in DOCA-NaCl and DOCA-R-H2O (183 +/- 5 and 155 +/- 4 mm Hg, respectively) but not in an additional control group which received DOCA and a low NaCl diet (119 +/- 2 mm Hg). Plasma AVP and hypothalamic AVP release were increased in all DOCA treated groups at each time point studied, while plasma osmolality was similar in each group. These studies demonstrate increases in the hypothalamic release of AVP in DOCA-NaCl hypertensive animals, but suggest that they are due to the mineralocorticoid and are independent of blood pressure and NaCl intake.

Reduced activity of locus coeruleus neurons in hypertensive rats

The influence of blood pressure on locus coeruleus (LC) neuronal activity was investigated in chloral hydrate anesthetized rats. Mean spontaneous firing rate of LC neurons was reduced by 25% in deoxycorticosterone acetate (DOCA-salt) treated Sprague-Dawley rats and by 19% in spontaneously hypertensive rats (SHR) as compared to their corresponding control animals. In acute experiments performed on normotensive rats, peripherally induced blood pressure changes elicited reciprocal changes in cell firing of the majority of LC neurons. The findings suggest that LC may have a role in long-term regulation of blood pressure.

Impaired baroreflex sensitivity in the aetiology of salt hypertension in the rabbit

This study was designed to see whether normotensive rabbits with an impairment in baroreflex control of heart rate due to genetic factors are more susceptible to high salt or deoxycorticosterone acetate (DOCA)-salt hypertension. The baroreflex sensitivity of 27 conscious rabbits was assessed by both the 'steady-state' and 'ramp' methods in response to injections of phenylephrine (2.5-30 micrograms/kg). Animals with differing baroreflex sensitivities were then given 4 weeks treatment with 8% NaCl and 1.3% KCl in food (treatment A), or DOCA (25 mg pellet, subcutaneously) with 0.5% NaCl and 0.13% KCl in drinking water (treatment B). A third group were maintained on a regular diet of food and water (controls). A highly significant negative correlation (r = 0.91, P less than 0.01) was found between the increase in mean arterial pressure (MAP) produced either by treatment A or treatment B and the baroreflex sensitivity before treatment. There was no significant correlation between the increase in MAP and initial MAP; increase in body weight; serum K+ after treatment; baroreflex sensitivity before treatment, when assessed by the 'ramp' method. It is concluded that animals with low baroreflex sensitivity due to a reduced ability to suppress cardiac sympathetic activity in response to a pressor stimulus, are more likely to develop hypertension as a result of salt loading. It remains to be determined whether the susceptibility to salt of rabbits with lower baroreflex sensitivity is also associated with a difference in the renal excretion of Na+ ions.