Delta-sleep-inducing peptide sequels in the mechanisms of resistance to emotional stress.

The aim of this study is to investigate time-related changes in substance P (SP), beta-endorphin (BE), and corticosterone (CORT) levels due to DSIP aftereffects in the control and stress rats. Experiments were carried out on male Wistar and August rats. The SP and BE immunoreactivity in the hypothalamus and plasma samples was determined radioimmunologically. Blood CORT level was determined radioimmunologically. The rats were stressed at nighttime in special cages and tied by tails to the back side of the cage. The stress experiments were repeated for 12 hours for 5 days. There were 6 groups: 1. control animals, 2. stress animals, 3. rats that received DSIP in a dose of 60 nmol/kg one hour before decapitation, 4. rats in which DSIP was injected 24 hour before decapitation, 5. stressed rats in which DSIP was injected one hour before decapitation during the 5th exposure to stress, 6. stressed rats to which DSIP was injected 12 hours before the 5th exposure to stress, i.e., 24 hours before decapitation. Our experiments showed that DSIP administration induced marked changes in SP, BE, and CORT levels in hypothalamus and blood plasma. This suggests that the long-term stress-coping effect of DSIP depends on considerable changes in the level of other oligopeptides and hormones induced by DSIP. Evidently, DSIP triggers these processes inducing a cascade of interrelated molecular reactions radically different in animals with different resistance to emotional stress. This cascade of sequential reactions is different in Wistar and August rats differing by their resistance to emotional stress. DSIP administration stimulates the mechanism of resistance in August rats to a lesser extent than in Wistar animals.

[Changes in the content of substance P, beta-endorphin and corticosterone in the hypothalamus and blood of rats with emotional stress after the administration of the delta sleep-inducing peptide]. / Izmenenie soderzhaniia veshchestva P, beta-éndorfina i kortikosterona v gipotalamuse i krovi krys pri émotsional'nom stresse posle vvedeniia peptida, vyzvaiushchego del'ta-son.

The aim of this study was to investigate time-related changes in substance P (SP) beta-endorphin (BE), and corticosteron (CORT) levels induced by DSIP administration in rats subjected to emotional stress. Experiments were carried out in male Wistar and August rats with different resistance to emotional stress. At night rats were tied by their tails to the backside of the special cages. These stress-inducing procedure was repeated for 12 hours daily in the course of 5 days. SP and BE immunoreactivity in the hypothalamus and plasma and blood CORT level were determined radioimmunologically. Six groups of animals were formed: 1. control animals; 2. stressed animals; 3. rats which received DSIP in a dose of 60 nmol/kg one hour before decapitation; 3. rats to which DSIP was injected 24 hours before decapitation; 5. stressed rats to which DSIP was injected one hour before decapitation during the 5th exposure to stress; 6. stressed rats to which DSIP was injected 12 hours before the 5th exposure to stress, i.e. 24 hours before decapitation. Our experiments showed that DSIP administration induced marked changes in SP, BE, and CORT levels in the hypothalamus and blood plasma. This suggests that long-term stress-coping effects of DSIP in underlied by considerable changes in the content of other oligopeptides and hormones. Evidently, DSIP triggers these processes inducing a cascade of interrelated molecular reactions which are different in Wistar and August rats. It seems likely that DSIP administration stimulates the mechanisms of resistance in August rats to a lesser extent than in Wistar rats.

Amiloride blocks the onset of ACTH-induced hypertension in the sheep.

This study investigated the ability of two diuretics, amiloride and frusemide, to prevent the development of ACTH induced hypertension in conscious sheep. Infusion of amiloride (20 mg/day) or frusemide (50 mg/day) for three days into normotensive sheep did not have any significant effects on blood pressure. Amiloride blocked ACTH-induced hypertension and the sodium retention and hypokalemia which is usually associated with ACTH administration. Frusemide failed to completely block the hypertension and potassium loss, however it blocked the transient initial urinary sodium retention associated with ACTH-induced hypertension. As frusemide failed to completely block the hypertension it is unlikely that the amiloride effect is due primarily to effects on urinary Na excretion. It is possible that amiloride is exerting its antihypertensive effects by blocking sodium channels.

Adrenocortical steroid requirements for initiation of ACTH-dependent hypertension in sheep.

1. Previous studies demonstrated that the combined infusion of cortisol (F), aldosterone (ALDO), deoxycorticosterone (DOC), corticosterone (B), 11-deoxycortisol (S), 17 alpha-hydroxyprogesterone (17 alpha OHP) and 17 alpha, 20 alpha- dihydroxy-4-pregnane-3-one (17 alpha 20 alpha OHP), at rates equivalent to their production during adrenocorticotrophic hormone (ACTH) treatment, reproduced the pressor and metabolic responses to ACTH administration in sheep. 2. This study examined which of these adrenocortical steroids were necessary for the initiation of the hypertension produced by these steroids in sheep. 3. Infusion of F, ALDO, 17 alpha OHP and 17 alpha 20 alpha OHP together, increased MAP by 19 mmHg, similar to both complete steroid cocktail (+25 mmHg) or ACTH administration (+21 mmHg). Infusion of F, 17 alpha OHP and 17 alpha 20 alpha OHP increased MAP by +7 mmHg. Infusion of ALDO, 17 alpha OHP and 17 alpha 20 alpha OHP had no effect on MAP. Thus F and ALDO were essential for the pressor effects of the steroid infusion. 4. To determine the role of glucocorticoid activity in the MAP rise, prednisolone, a non-pressor glucocorticoid, was substituted for cortisol. Combined prednisolone, ALDO, 17 alpha OHP and 17 alpha 20 alpha OHP infusion did not raise blood pressure. This suggested that the mineralocorticoid component rather than glucocorticoid component of cortisol's activity was involved in the pressor response. 5. Aldosterone (7 micrograms/h) was substituted for cortisol, giving a total of 10 micrograms/h aldosterone. High dose ALDO (10 micrograms/h), 17 alpha OHP and 17 alpha 20 alpha OHP infusion raised blood pressure by 18 mmHg. Thus, the essential role of cortisol appeared to be due to its occupancy of mineralocorticoid receptors, rather than glucocorticoid receptors. 6. Given that ACTH produces a transient initial increase in aldosterone secretion of up to 10 micrograms/h, it appears that aldosterone and not cortisol is essential for the pressor effects of ACTH. 7. Hypertension resulting from the combined steroid infusion in the sheep appears to be produced by a mechanism which involves a complex interaction between ALDO, F, 17 alpha OHP and 17 alpha 20 alpha OHP. Therefore, the putative 'hypertensinogenic' receptor may be multivalent with binding sites for F, ALDO and 17 alpha 20 alpha OHP, or is a site of single interactive receptors for these steroids and that F exerts its permissive action by occupying the same site as ALDO on the hypertensinogenic receptors.

Nucleotide sequence of the gene coding for ovine corticotropin-releasing factor and regulation of its mRNA levels by glucocorticoids.

The ovine gene CRF, coding for corticotropin-releasing factor, has been isolated and the nucleotide sequence determined. The degree of nucleotide sequence homology between the ovine and human CRF genes is unusual, in that the 5' flanking regions are more highly conserved than the protein-coding regions. This striking degree of homology would indicate that a strong selective pressure is being exerted over an extensive area of the 5' flanking region, which could include transcriptional control elements. The 5' flanking region of the ovine CRF gene contains five elements which share homology with the glucocorticoid receptor DNA binding sequence. Also Northern blot analysis indicates that hypothalamic CRF mRNA levels are negatively regulated by glucocorticoids. Dexamethasone treatment halves the CRF mRNA content of the hypothalamus, whereas adrenalectomy causes a three- to four-fold increase in CRF mRNA levels.

The effects of calcium and vitamin D on blood pressure in conscious sheep.

The metabolic and haemodynamic effects of elevating plasma calcium levels were examined in both normal and ACTH-hypertensive sheep. Six weeks of dietary Ca++ supplementation did not alter plasma calcium levels, blood pressure or heart rate. Five days of CaCl2 infusion (2 mmol/h) or intravenous vitamin D injections elevated plasma ionised and total Ca++ levels and heart rate but mean arterial pressure was unchanged. As in other species, elevation of plasma Ca++ levels over 4 hours by infusion of CaCl2 at 2, 5, and 10 mmol/h increased mean arterial pressure and decreased heart rate. The course of ACTH-induced hypertension was not altered in animals supplemented with CaCl2 in their drinking water for 6 weeks nor by intravenous injection of vitamin D for 5 days. This study does not support a major role for altered plasma ionised or total Ca++ levels in the genesis of ACTH-dependent hypertension in the sheep.

A comparison of the haemodynamic effects of dietary sodium restriction and acute sodium depletion in the conscious sheep.

The use of a low Na, low K sorghum grain diet supplemented with intraruminal electrolyte infusions has enabled dietary manipulation of sodium status to be studied in the sheep. Dietary sodium restriction reduced urinary sodium excretion within 24 h with maximal retention after 3 days. There were no other substantial metabolic or haemodynamic changes. A more severe form of sodium deficiency produced by parotid salivary drainage resulted after only 2 days in a sodium deficit 3-4 times that seen with 14 days of sodium restriction. Extracellular fluid volume and cardiac output decreased. Blood pressure was unchanged but there was an increase in peripheral resistance and plasma renin concentration.

Blood pressure and metabolic effects of 9-alpha-fluoro-hydrocortisone in sheep.

9 alphafluorohydrocortisone (9 alphaFF) is an analogue of hydrocortisone with both 'mineralocorticoid' and 'glucocorticoid' activity. 9 alphaFF was infused at 0.2, 0.63 and 2.0 mg/day for 5 days to intact conscious trained sheep. At high dose (0.63 and 2 mg/day) 9 alphaFF raises blood pressure in sheep, (mean arterial pressure rise 32 and 29 mm Hg respectively on the fifth day), lowers plasma [K], raises plasma [Na] and produces initial urinary sodium retention. At low dose (0.2 mg/day) blood pressure is raised (+16 mm Hg on day 5) but plasma and urinary electrolytes are unaltered. 9 alphaFF had no effect on water intake or urine output at any dose. In all animals withdrawal of 9 alphaFF was associated with a natriuresis. On the basis of its affinity for 'mineralocorticoid' and 'glucocorticoid' ovine renal receptors, 9 alphaFF at low dose may raise blood pressure by mechanisms not simply related to its 'glucocorticoid' and/or 'mineralocorticoid' action.