Effect of EXP 3174 on blood pressure of normoreninemic renal hypertensive rats.

This study examined the effect on mean blood pressure of a new orally active nonpeptide angiotensin II (Ang II) receptor antagonist, EXP 3174, in doses that completely block exogenous Ang II action. Anesthetized and conscious two-kidney, two clip chronic renovascular hypertensive rats and sham-operated animals were used. In anesthetized hypertensive rats, intracerebroventricular administration of the inhibitor had no effect on blood pressure, whereas blood pressure was normalized by intravenous injection of the antagonist (163 +/- 12 to 110 +/- 9 mm Hg, P < .05). In sham anesthetized rats, intravenous injection of EXP 3174 also lowered blood pressure (112 +/- 6 to 96 +/- 6mm Hg, P < .05). In conscious rats, intravenous EXP 3174 induced a fall in pressure that was larger in hypertensive (156 +/- 9 to 132 +/- 5 mm Hg, P < .05) than in sham (104 +/- 3 to 94 +/- 4 mm Hg, P < .05) rats. Plasma renin activity was very high in anesthetized animals (hypertensive versus sham, 87.8 +/- 8.3 versus 95.7 +/- 10.2 ng Ang I/mL per hour); differences were not significant either between anesthetized hypertensive and sham or in conscious animals (hypertensive versus sham, 9.42 +/- 1.58 versus 6.74 +/- 2.32 ng Ang I/mL per hour). Angiotensinogen concentration was higher in cerebrospinal fluid in anesthetized hypertensive rats (36.4 +/- 3.0 versus 26.0 +/- 2.4 ng Ang I/mL, P < .05) and in the artery wall of hypertensive conscious rats (103.1 +/- 10.3 versus 75.2 +/- 7.8 ng Ang I/g, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Vasopressinergic mechanisms in the nucleus reticularis lateralis in blood pressure control.

We sought to determine whether arginine vasopressin (AVP) modulates arterial pressure (AP) by a receptor-mediated action in the nucleus reticularis rostroventrolateralis (nRVL). Immunocytochemical labeling with an antiserum against a synthetic AVP conjugate revealed a discrete although modest presumptive neuropeptidergic innervation of the nRVL. Electron microscopic analysis of vasopressinergic processes in the nRVL revealed that AVP-like immunoreactivity (AVP-LI) was primarily in axons and axon terminals. Immunoreactive terminals contained numerous small clear vesicles and large dense core vesicles and formed synapses with unlabeled dendrites. In the nRVL, retrograde transport-immunofluorescence data demonstrated close appositions between vasopressinergic beaded processes and a compact subambigual column of reticulospinal neurons labeled by deposits of cholera toxin beta-subunit into the thoracic spinal cord. Similar methods were used to define the origins of the AVP-afferent projection to nRVL. These retrograde transport-immunofluorescence studies demonstrated numerous retrogradely labeled neurons in the hypothalamus, including the paraventricular nucleus (PVN), after injections of a retrograde tracer, Fluoro-Gold into the ventrolateral medulla. However, double-labeled neurons were rare and confirmed a diffuse AVP afferent innervation of the sympathoexcitatory area. Microinjection of AVP into the nRVL in anesthetized rats produced a large dose-related increase in AP different from control at a dose of 1 pmol or higher. AVP injected intravenously elevated AP only at significantly higher doses. Microinjections of AVP into the nucleus tractus solitarii (NTS) had a smaller effect whereas into the caudal ventrolateral medulla exerted no effect on AP. Bilateral microinjections of an AVP antagonist, d(CH2)5[Tyr(Me)2]AVP into the nRVL produced no change in AP but blocked the increase produced by subsequent injections of AVP. An acute hemorrhage produced by withdrawal of 2 ml of blood from the femoral vein did not alter AP. However, bilateral microinjections of the AVP antagonist into the nRVL 5 min after hemorrhage decreased AP. In contrast, the AVP-antagonist injected intravenously after hemorrhage had no effect on AP. Our data suggest that under conditions demanding increased sympathetic drive to maintain AP, such as hemorrhage, a functional AVP receptor mechanism via terminals in the nRVL may be activated to restore normal levels of AP.

The renin-angiotensin system in different stages of spontaneous hypertension in the rat (S H R).

The present study analyzed the concentration of renin-like activity and angiotensinogen concentration (AoC) in different brain areas related to cardiovascular control in SHR and Wistar Kyoto (WKY) animals. Male rats of both strains were studied at 8, 16 and 30 weeks of age. The following brain areas were isolated: anterior, medial and posterior hypothalamus, septal area, periaqueductal gray (PG) and the remaining brain stem; nucleus tractus solitarius (NTS) and the remaining medulla oblongata. Plasma renin activity (PRA) and plasma and cerebrospinal fluid (CSF) AoC were determined. Renin-like concentration was higher in SHR than in WKY in the anterior hypothalamus, PG and NTS at different stages of hypertension development. AoC was also higher in some areas of the SHR brain during different periods. PRA, plasma and CSF angiotensinogen concentration showed significant differences between both strain of rats during the development of high blood pressure. Present data support the possibility that the central and peripheral renin-angiotensin system may participate in the maintenance of high blood pressure in the SHR animals.

Open field behavior and cardiovascular responses to stress in normal rats.

Experiments were conducted in normal Wistar rats with different patterns of behavior to assess the effects of stress on cardiovascular reactivity. One week after weaning and one month later rats were tested in an open field. Animals that did not cross any square in both open fields were classified as HYPOACTIVE. Those crossing more than 43 squares in the first and any in the second open field were classified as HYPERACTIVE. No difference was found in the basal mean blood pressure (BP) or heart rate (HR) between both groups. After a stress (change of cage, electric shock or immobilization) BP and HR increased. The increase in BP was higher in HYPOACTIVE rats. The HR increase was similar in both groups. Therefore, the ambulatory activity in the open field allowed us to separate groups of rats with different cardiovascular reactivity to stress.

Suprapontine ablation in normal and Doc-salt or one-kidney, one-clip hypertensive rats.

The role of suprapontine areas in the acute maintenance of the hypertension in awake Doc-salt (4 weeks of treatment) or one-kidney, one clip (1K-1C) (4 weeks after clipping) rats was studied. Mean blood pressure (BP) and heart rate (HR) were measured before (15 min) and after (2 hours) removing all brain tissues rostral to the pons. After this procedure no change in BP was found in normal or 1K-1C rats. In Doc-salt rats the BP falls (154 +/- 4 to 110 +/- 5 mmHg; p less than 0.001). HR was increased in normal (351 +/- 10 to 446 +/- 20 beats/min; p less than 0.01) and in 1K-1C rats (350 +/- 10 to 485 +/- 12 beats/min; p less than 0.001). Clonidine injected into the cisterna magna in 1K-1C rats after suprapontine ablation lowered BP (146 +/- 6 to 118 +/- 11 mmHg; p less than 0.05) and HR (515 +/- 17 to 400 +/- 33; p less than 0.05). Pentolinium reduced BP after the suprapontine ablation in normal (116 +/- 4 to 63 +/- 5 mmHg; p less than 0.001), Doc-salt (111 +/- 5 to 53 +/- 3; p less than 0.001) and 1K-1C rats (163 +/- 8 to 59 +/- 6 mmHg; p less than 0.001). These data suggest that suprapontine structures have an important role in the acute maintenance of Doc-salt hypertension. In 1K-1C rats the acute maintenance of hypertension depends on a sympathetic activity originated below the lesion.

Effect of transection in the brainstem on short-term maintenance of deoxycorticosterone-salt hypertension.

Sections were made to determine supraspinal areas that participate in the maintenance of deoxycorticosterone (DOC)-salt hypertension. Blood pressure (BP) falls after cuts which severed: (a) the lateral connections between pons and midbrain, (b) the pathways between caudal hypothalamus and midbrain, and (c) parasagittal connections between medial and lateral hypothalamus. No changes in BP were found either after coronal cuts that severed a central area located at: (a) the pons-midbrain edge, (b) above the caudal hypothalamus, and (c) the level of the anterior hypothalamic area, or after parasagittal cuts at the level of the capsula interna or after a hypophysial stalk lesion. These results implicate the hypothalamus in the maintenance of DOC-salt hypertension. The hypothalamus-neural lobe system appears not to be involved in the lowering of BP found.

Evidences against a primary role for the pituitary neural lobe in the development and maintenance of DOC-salt hypertension.

The role of the antidiuretic hormone (ADH) in the development and maintenance of the hypertensive state produced by deoxycorticosterone (DOC) and salt in rats is a matter of controversy. The effects of neural lobe lesions that would prevent the release of the hormone to the systemic circulation without affecting the hypothetical release from the hypothalamic nuclei to other areas of the central nervous system was tested. A diabetes insipidus-like syndrome was obtained. But, neither the delay in the onset nor the development of DOC-salt hypertension was modified. This lesion made in rats at 3-4 weeks post DOC-salt did not alter the hypertension during the following 3 more weeks of treatment. These results suggest that the neural lobe would not be essential for the development and maintenance of DOC-salt hypertension in rats.

Further evidence that a beta-adrenergic mechanism regulates water intake: role of the subfornical organ.

The daily water intake was reduced in rats by subcutaneous administration of propranolol. The fluid intake after 24 h of dehydration in nephrectomized animals was decreased by propranolol. In intact rats diazepam did not modify the postdehydration water intake. Propranolol injected into subfornical organ decreased water consumption after 24 h of fluid deprivation but did not change the dipsogenic response to carbachol given in the same structure. These results suggest that a beta-adrenoceptor mechanism participates in the regulation of the daily water intake. After a stimulus such as dehydration, beta-blockade modifies water consumption by a non-renal mechanism. This mechanism involves neither a general depressant nervous activity nor a local anesthetic action and could be located in a periventricular structure, the subfornical organ.

The brain renin-angiotensin system and the development of DOC-salt hypertension.

UNLABELLED: The effect of captopril, given in the drinking fluid, on the development of DOC-salt hypertension was analyzed. Although captopril did not prevent an increase in blood pressure (BP) elicited by DOC-salt, captopril did diminish BP in both DOC-salt and control animals. From the first week of treatment DOC-salt rats increased their fluid intake (FI). At the end of the experiment, captopril reduced this increment (655% to 357%). At the same time plasma angiotensinogen was diminished (-35%; p less than 0.001) and cerebrospinal fluid (CSF) substrate concentration increased (+33%; p less than 0.02) in DOC-salt rats, captopril did not modify these changes. In control rats captopril did not alter FI, depleted plasma angiotensinogen, (-73%; p less than 0.001), did not change the central prohormone and increased plasma renin activity (PRA) (+260%; p less than 0.001). IN CONCLUSION: CSF angiotensinogen concentration changes as previously found in CNS while a clear dissociation between plasma and CSF angiotensinogen was found in DOC-salt rats. In these animals the hypertension was not clearly affected by captopril treatment. However the effect of the converting enzyme inhibitor suggests that the central renin-angiotensin system could participate in the increase in FI.

[A simple system for recording and/or infusion-withdrawal in animals without restriction of movements]. / Un sistema simple para registro, y/o infusión-extracción en animalessin restricción de movimientos.

A low cost system was designed to allow a normally active animal to be monitored unrestrained in experiments using indwelling catheters and electrode leads. It is composed of a motor-rotated plate, an animal-activated switch and a power source. This system automatically compensates the horizontal, vertical and rotative animal movements and prevents twisting or kinking of the catheters and leads.

Surface morphology of the subfornical organ: effects of low and high sodium chloride diet.

Ependymal cells found in the subfornical organ of the rat were counted. Cells covered by small microvilli, small protrusions and smooth cells were frequently found. Also present were cells with long or short cilia, cels with large protrusions and supraependymal cells. High and low sodium diets reduced the number of cells with large protrusions. Microvilli-covered cells increased after a low sodium diet.

Angiotensinogen concentration in the cerebrospinal fluid in different experimental conditions in the rat.

Angiotensinogen is the most important component of the renin-angiotensin system present in the cerebrospinal fluid (CSF) of the rat. Its physiological significance as well as its origin have not been clearly elucidated. In this experiment we have examined plasma renin activity (PRA) and plasma and CSF angiotensinogen concentration under the following experimental conditions in male rats of the Wistar strain: 1) adrenalectomy (Adx) 4 days prior to sample collection; controls were sham Adx animals; 2) nephrectomy (Nx) 48 hours before blood and CSF collection; controls were sham Nx rats; 3) DOC-salt treatment (Cortexon depot, 50 mg/kg.s.c. twice a week) plus saline to drink was given during 4 weeks; controls were intact rats; 4) DOC-salt plus captopril: captopril (100 mg/kg/day) in the drinking fluid was added to the treatment of experimental and control animals of Group 3; 5) two-kidney, two clip hypertension: silver clips placed in both renal arteries 8 weeks before samples collection; control: sham-operated rats; 6) water deprivation: rats deprived of water for 5 days; controls: intact rats; 7) peripheral sympathectomy: 6-hydroxydopamine (6-HODA) injected s.c. from birth until 16 weeks of age, adrenodemedullectomy and adrenal denervation performed at 8 weeks; controls were vehicle-injected animals. Determination of angiotensinogen concentration in plasma and CSF was accomplished by incubation of the samples with excess hog renin. The angiotensin I released as well as PRA were evaluated using an specific radioimmunoassay technique. PRA was significantly increased by Adx, captopril treatment, and water deprivation, and was almost suppressed by Nx, DOC-salt, and DOC-salt plus captopril treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of propranolol on induced water intake and on the subfornical organ surface.

The chronic effect of propranolol on induced water intake and on the subfornical organ was studied. Propranolol reduced water intake postdehydration. It did not inhibit the increase in plasma renin activity due to dehydration or the dipsogenic response to angiotensin II. Propranolol decreased the subfornical organ large protrusion cells. This result suggests that propranolol impairs the thirst not related to angiotensin II. The subfornical organ changes may indicate that propranolol blocks a beta-adrenergic system originating in ependymal cells.

Central connections of the toad neural lobe as shown by retrograde neuronal labeling: classical and new connections.

Iontophoretic deposit of horseradish peroxidase (HRP) in the hypophysial neural lobe (NL) of the toad labeled neurons in the classical neurosecretory preoptic magnocellular nucleus. Further, a number of labeled neurons appeared in the whole extension of the periventricular and medial preoptic nuclei. The latter were continuous dorsally with two other labeled areas known as the bed nucleus of the hippocampal commissure (which appears to be homologous to the subfornical organ in mammals) and the ventromedial thalamic area of Frontera. The possible functional role of many of these afferents to the neural lobe is unknown because all types of neurons were labeled in the projecting zones and, in addition, many are outside of the generally recognized neurosecretory groups.

An uneven distribution of choline acetyltransferase activity in the pituiatry neurointermediate lobe of the rat.

The neurointermediate lobe of the pituitary gland of male rats was assayed for choline acetyltransferase (CAT) activity. Precise microsample punches were obtained from neurohypophysial tissue, pure pars intermedia tissue and from the junction area between them. The level of CAT activity (pmol/h per microgram protein) in the neurohypophysis, pars intermedia and junction area were 0.390 +/- 0.038 (S.E.M.), 0.228 +/- 0.042 and 1.824 +/- 0.268 respectively. These values show an uneven distribution of CAT in the neurointermediate lobe. The hypothesis of a cholinergic system located in the junction area has been advanced.

Evidence for the control of prolactin secretion by hypophysial posterior lobe extracts.

The effect of posterior lobe extracts on prolactin secretion in vitro was compared with that of median eminence, hypothalamic (with and without median eminence) and cortex extracts. The posterior lobe extract clearly inhibited adenohypophysial prolactin secretion, showing a similar effect to that of the hypothalamic extracts. The median eminence extract showed inconstant inhibitory effects, while the cerebral cortex extracts showed no effect. The removal of the median eminence did not modify the hypothalamic inhibitory effect. Although the median eminence has always been considered to be the final common pathway for the control of adenohypophysial secretion, these results suggest that the posterior lobe may also play a physiological role in this control.

The adenohypophysial hormone content of the rat pars tuberalis.

The pars tuberalis of the hypophysis was shown to contain LH, which increases after castration, TSH and a very low amount of PRL. FSH was found after castration.

Involvement of adenohypophysial dopamine in the regulation of prolactin release during suckling.

Dopamine (DA) was measured in the anterior lobe of the pituitary and median eminence from lactating rats. The effect of pup separation and suckling was studied in order to correlate changes in DA levels with changes in serum PRL. In lactating rats separated from their pups, low levels of circulating PRL were found at 2,4, and 8 h. DA levels in the median eminence showed a decline at 2h; at 4 and 8 h of separation, a significant increase was observed. In the pars distalis, the concentration of DA increased with the length of the nonsuckling interval. Suckling induced a rapid rise in serum PRL levels in rats that were separated from their pups 4 h earlier. Under these conditions, a significant decrease in DA levels in the median eminence and pars distalis was observed as early as 5 min after the onset of suckling; at 30 min, the DA levels were still low. In the situations studied (suckling and pup separation), a negative correlation between serum PRL and DA levels in both the median eminence and pars distalis was always found.

Choline acetyltrasferase activity in the neurointermediate lobe of the rat pituitary.

CAT activity was determined in the neurointermediate lobe of the rat's pituitary gland. The level of enzyme activity in the adult rat is of 386.2 +/- 39.1 picomoles/hour/neurointermediate lobe. CAT activity is present in the pituitary gland of the newborn animal and increases with age. In organo-typic cultured neurointermediates lobes CAT decreases progressively and practically disappears after 10 days.