G. Schmid

Altered cyclic AMP levels in specific cardiovascular brain centers of spontaneously hypertensive rats (SHR)

ZusammenfassungDie Frage nach einer möglichen Beteiligung cAMP-abhängiger Vorgänge bei der zentralen Blutdruck-Regulation wurde am Modell der spontan-hypertensiven Ratte (SHR) untersucht. Hierzu wurden in 36, durch Mikrodissektion gewonnenen, spezifischen Hirnarealen — eingeschlossen insbesondere die primären und die sog. modulatorisch wirkenden höheren cardiovasculären Zentren — die Konzentrationen von cAMP bei erwachsenen SHR mit bereits stabilisierten Bluthochdruck und normotensiven Kontroll-Ratten des gleichen Stammes bestimmt.Bei den SHR fanden sich in verschiedenen Hirnarealen, die in enger Beziehung zur zentralen Blutdruck-Regulation stehen, veränderte cAMP-Konzentrationen. Erhöht war cAMP im Nucleus tractus solitarii, in den katecholaminergen A1- und A2-Zellgruppen der Medulla oblongata, im Locus coeruleus, im Zentralen Höhlengrau (Subnucleus medialis) und in verschiedenen corticalen Arealen (Cortex cinguli, Cortex parietalis, Cortex frontalis, Hippocampus). Erniedrigungen der cAMP-Konzentration fanden sich vor allem in hypothalamischen Strukturen (Nucleus paraventricularis, anterior, ventromedialis, dorsomedialis und posterior hypothalami). Die Daten von weiteren 19 Hirnarealen der spontan-hypertensiven Ratten unterschieden sich nicht von den entsprechenden Kontroll-Werten.Die Ergebnisse zeigen, daß cAMP-abhängige Vorgänge in biochemische Mechanismen der zentralen Blutdruck-Regulation beim genetischen Hochdruck einbezogen sind. Die Areale, die cAMP-Konzentrationsänderungen aufzeigen, stehen — wie neuroanatomische Untersuchungen zeigen — in enger neuronaler Beziehung zum primären Barorezeptoren-Reflexbogen. Vermutlich handelt es sich bei diesen Arealen um auf den Barorezeptoren-Reflexbogen modulierend wirkende Zentren.SummaryThe possible participation of cAMP in central regulation of arterial blood pressure was investigated in spontaneously hypertensive rats (SHR).Cyclic AMP concentrations of 36 microdissected individual brain areas — including primary and higher cardiovascular centers — were measured in adult SHR and compared with those of normotensive control rats of the same strain and age.In the adult SHR, elevated cAMP concentrations were found in brain areas which are in close connection with the central regulation of blood pressure: nucleus tractus solitarii, A1- and A2- catecholaminergic cell groups in the medulla oblongata, locus coeruleus, central grey matter (subnucleus medialis), and certain cortical areas (especially cingulate cortex and hippocampus).On the other hand, hypothalamic cell groups which have been also suggested to control blood pressure, such as paraventricular, anterior, ventromedial, dorsomedial and posterior hypothalamic nuclei, show lower concentrations of cAMP in the SHR than in normotensive controls.Cyclic AMP levels in 19 other brain areas of SHR which seem to be not involved in mechanisms of central blood pressure regulation practically do not differ from the values of normotensive rats.The results suggest that cAMP-dependent processe are involved in the regulatory mechanisms of central blood pressure control. The brain areas which show alterations of cAMP-levels are also distinguished by close neuronal connections to the baroreceptor reflex arc. It is supposed that these areas represent modulatory higher centers capable to affect baroreceptor reflex function.

Technique of continuous collection of parotid saliva in the rat.

SummaryA method is described, which is suitable to collect continuously and quantitatively saliva from both parotid glands in rats under in vivo conditions and which allows to investigate salivary electrolyte composition in relation to flow rate during several hours. This might be of expanding scientific interest in disturbances of transepithelial electrolyte transport in various pathophysiological situations (for instance different forms of experimental hypertension, endstage renal failure and so on).

Glandular adenylate cyclase system in genetic hypertension: age-dependent response to catecholamines☆

The parotid excretion of cAMP was measured in normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) in this study. In addition, adenylate cyclase activity in parotid gland tissue was determined. The cAMP excretion rate was increased immediately after isoproterenol infusion. This elevation was more pronounced in young (6-8 weeks) than in older (16-18 weeks) animals, both in WKY and in SHR. These data demonstrate a diminished cAMP response to isoproterenol application with respect to the age of the animals. This could indicate that there is an age-dependent functional alteration of the beta-adrenoceptor-adenylate cyclase complex. In agreement with the results of these in vivo studies, the stimulation of adenylate cyclase activity of the parotid gland by isoproterenol or fluoride was enhanced in young SHR and lowered in old SHR when compared to their normotensive controls of the same age. One may conclude that the sympathetic activity is enhanced in young SHR, and that the beta-adrenoceptor system is hypersensitive to adrenoceptor agonists. This might contribute to the development of hypertension in SHR. Sixteen to eighteen weeks old SHR showed a diminished cAMP output following isoproterenol application when compared to normotensive control rats of the same age. The reduction of the response to isoproterenol stimulation in old SHR seems to be related to a reduced sensitivity to catecholamine stimulation.

Acute changes in cyclic AMP levels of certain brain areas following intraventricular injection of renin in rats

Actions of the central angiotensin system on brain cAMP concentrations were studied after intraventricular injection of renin. Biosynthesis of endogenous brain angiotensin II was stimulated by 0.1 U renin and the blood pressure was elevated 40 min after the application. Stimulation of the brain angiotensin system affected cAMP metabolism in several brain areas, mostly expressed as decreased cAMP levels. Significant decreases in cAMP concentrations were found in the cerebral cortex, hippocampus, basal ganglia, various hypothalamic nuclei, substantia nigra, central grey matter and in the locus coeruleus. The unchanged cAMP levels in the nucleus of the solitary tract might indicate that intraventricular injection of renin induced an acute blood pressure elevation which is not associated with changes in the cAMP system in the primary baroreceptor area.

Intracellular histidine content of various tissues (brain, striated muscle and liver) in experimental chronic renal failure.

ZusammenfassungBei chronisch niereninsuffizienten Ratten (5/6-Nephrektomie) wurden die intrazellulären Histidin-Konzentrationen verschiedener Organe (Gehirn, Skelettmuskel und Leber) bestimmt. Als Vergleichsgruppen dienten gesunde Kontroll-Ratten sowie sog. „pair-fed“ Ratten, die entsprechend den niereninsuffizienten Tieren eine verminderte Nahrungsmenge zu sich nahmen. Während sich in den untersuchten Gruppen die Plasma-Histidin-Konzentration nicht unterschied, war Histidin im Gehirn der chronisch niereninsuffizienten Tiere signifikant erhöht. Dieser Konzentrations-Anstieg dürfte als urämie-spezifisch anzusehen sein, da die entsprechend minderernährten Kontrolltiere keine Alteration zeigten. Als Ursache ist in erster Linie eine cerebrale Störung des Histidin-Metabolismus zu diskutieren.SummaryIntracellular histidine levels were determined in brain, striated muscle and liver of rats with chronic renal insufficiency (5/6-nephrectomy) and compared both with normal rats and food-restricted (pair-fed) animals. There was no difference in plasma histidine concentration of the three groups whereas in the brain of the uremic rats histidine was significantly increased. Since there existed no alteration of the cerebral histidine in the corresponding pair-fed group, the finding of a raised histidine level in the renal insufficient rats seems to be due to a specific uremic disorder caused by a cerebral disturbance in histidine metabolism.

Rapid alterations in cAMP accumulation in brain nuclei of rats following microinjections of vasoactive intestinal polypeptide (VIP) into the lateral ventricle

The in vivo effect of exogenous vasoactive intestinal polypeptide (VIP) on the accumulation of cAMP in 21 microdissected brain nuclei was investigated 3 and 7 min after intraventricular injections in rats. VIP elicited significant (up to 20-fold) increases in cAMP levels. This effect is region specific varying considerably among the brain regions investigated. VIP dramatically increased the cAMP content of the lateral septal nucleus, several hypothalamic nuclei, the habenula, the midbrain central gray and the locus coeruleus. Smaller increases were observed elsewhere including some VIP-rich brain areas such as the cerebral cortex and the hippocampus.

Participation of Various Brain Nuclei in the Altered Time Course of Genetic Hypertension in SHR Dependent on Changes in Calcium Metabolism

Variations in calcium alimentation influence the development of high blood pressure in genetic hypertensive rats. Different calcium feeding and changes in parathyroid hormone status cause altered cAMP-content in specific brain areas. All animals with high calcium diet show significant elevated cAMP-content in the locus coeruleus, irrespective of parathyroid status. These findings support the hypothesis that elevated cAMP-concentrations reflect an increased depressor activity of the locus coeruleus.

Alterations in Cyclic AMP Concentration and Adenylate Cyclase Activity in Specific Brain Areas of Rats with Inherited Hypothalamic Diabetes Insipidus (Brattleboro Rats)

The concentration of cyclic AMP (cAMP) and the activity of sodium‐fluoride‐stimulated adenylate cyclase was measured in 29 microdissected brain areas of homozygous Brattleboro rats and their Long‐Evans control rats. In ten of the investigated brain areas a decreased cAMP level was measured in Brattleboro rats. It was particularly decreased in the supraoptic nucleus, cingulate and parietal cortex, hippocampus, habenula and organum vasculosum laminae terminalis. Significantly lower cAMP levels were also found in the periventricular nucleus, bed nucleus of the stria terminalis, area postrema and locus coeruleus. An increased cAMP concentration was detected only in the subcommissural organ of Brattleboro rats. In most brain areas, where cAMP was decreased, sodium fluoride‐stimulated adenylate cyclase activity was significantly increased (supraoptic nucleus, parietal cortex, periventricular nucleus, bed nucleus of the stria terminalis, locus coeruleus) or unchanged (hippocampus, habenula, organum vasculosum laminae terminalis). The coincidence of alterations in cAMP concentration and adenylate cyclase activity in brain areas of Brattleboro rats with relatively dense vasopressinergic innervation and/or vasopressin receptor population in control rats, suggests an influence of brain vasopressin on the cAMP‐adenylate cyclase second messenger system.

BAEE Esterase (Kallikrein-Like) Activity in Parotid Saliva of Normal Rats and Rats with Various Forms of Experimental Hypertension (Genuine, Renovascular and DOCA Salt Hypertension)1

A technique for continuous and quantitative collection of parotid saliva including salivary flow rate determination for in vitro experiments in rats is described. Kallikrein-like activity in parotid saliva of rats with various forms of arterial hypertension (genuine, renovascular and DOCA salt hypertension) was studied. Kallikrein-like excretion was measured by its estoerolytic activity using benzoyl arginine ethyl ester (BAEE) as a substrate. The levels of kallikrein-like activity in parotid saliva of normotensive control rats ranged between 2.5 and 4.0 mU/min during salivary flow stimulation with pilocarpine. In all forms of experimental hypertension kallikrein-like activity in saliva was increased two-to fourfold. This increase was not related to the activity of the renin-angiotensin system.