Natalie Alexander

Single and Repeated Environmental Stress: Effect on Plasma Oxytocin, Corticosterone, Catecholamines, and Behavior

Rat studies were done to further characterize an environmental model of stress designated shaker stress (SS). Plasma oxytocin (OT), corticosterone (CS), norepinephrine (NE), and epinephrine (E) were measured before and after 5 or 30 min of SS applied one time or applied 10 times over a 2-week period. The major findings were partial adaptation of plasma E within 30 min of acute SS, adaptation of plasma CS baselines but not responses to chronic SS, and complete adaptation of plasma OT responses to chronic SS. Poststress behavior during chronic SS was affected in the following ways: freezing time habituated, defecation and rearings increased, and grooming and teeth chattering remained relatively constant. The results show that SS produces consistent patterns of hormonal and behavioral responses; some aspects of the patterns are similar to those elicited by other environmental stresses, whereas some aspects are unique to SS. We conclude that rats do not adapt to repeated SS but rather that most hormonal and behavioral defense mechanisms are renewable on a daily basis.

Extracellular oxytocin in the paraventricular nucleus: hyperosmotic stimulation by in vivo microdialysis.

The effect of central osmotic stimulation on oxytocin (OT) secretion from the paraventricular nucleus (PVN) was examined using a newly developed in vivo microdialysis technique. A dialysis probe was inserted into the PVN region and microdialysis was performed in conscious animals. Hyperosmotic solutions were delivered via the dialysis probe, and perfusate and blood samples were collected. OT was consistently detected in the PVN dialysate. Hyperosmotic sodium chloride (1 M) produced a significant increase in dialysate and plasma OT, whereas D-mannitol (2 M) had no effect. These results suggest that (1) in vivo microdialysis may provide a useful technique for the evaluation of neuropeptide secretion from specific brain regions and (2) there are sodium-sensitive cells in the PVN region which respond to increases in extracellular sodium, resulting in an increase in central and peripheral oxytocin secretion.

Enzymatic deconjugation of catecholamines in human and rat plasma and red blood cell lysate

We have developed a method for enzymatic hydrolysis of both sulfated and glucuronidated catecholamines in plasma and red blood cell lysate. Hydrolysis occurs in the course of the radioenzymatic assay for catecholamines. In human plasma, catecholamines are conjugated almost entirely with sulfate while, in rat plasma, glucuronides are the main conjugates of epinephrine and dopamine but not norepinephrine. Rat plasma contains less percent conjugated catecholamine than human plasma. Human red blood cell lysate contains less conjugated catecholamine than plasma, whereas free E in lysate exceeds that of plasma and free NE has same level both in sulfated + glucuronidated) catecholamines and the nature of conjugated catecholamines.

Psychosocial Hypertension in Members of a Wistar Rat Colony

Summary This study was an attempt to induce hypertension in rats by the continuous psychosocial stimuli caused by aggregation. Wistar rats of both sexes were isolated from weaning to 4-5 mo of age. Tail cuff pressures were obtained every other week during the last 2 mo of isolation and up to 8 weeks of aggregation. Two types of physical conditions were used for aggregation: (1) 6 interconnecting cages in a wheel-like arrangement around a central eating and drinking area; (2) a single cage. Two wheels were used each with 24 rats, 12 males and 12 females and 10 single cages, each with 2 or 4 rats of the same sex. Other rats of both sexes remained isolated as controls. Approximately one-third of all aggregated rats of both sexes showed a 15 mm Hg or more average increase of systolic pressure during aggregation; other aggregated rats showed less average pressure rise. Rats in single cages did not fight nor did wheel aggregated females; nevertheless, arterial pressure increased among these rats. Among wheel aggregated males that developed hypertension, those classified as dominant types, by the least number of tail bites, had the largest pressure increases. The frequency of pressure increase was the same in dominant and nondominant wheel males.

A radioenzymatic microassay for simultaneous measurement of catecholamines and their deaminated metabolites.

Abstract A simple and specific assay for measurement of norepinephrine, epinephrine, and their major deaminated metabolites 3,4-dihydroxyphenylglycol and 3,4-dihydroxymandelic acid in plasma has been developed. The assay is based on the conversion of these compounds to their O-methylated derivatives in the presence of catechol-O-methyltransferase and S-adenosyl-[methyl3H]methionine. The formed tritiated derivatives are selectively extracted in organic solvents and isolated by thin-layer chromatography. After oxidation to vanillin they are purified by solvent extraction and measured by liquid scintillation spectrophotometry. The assay is rapid and results can be obtained in less than 3 hr.

Elevated plasma dopamine beta hydroxylase activity in rats with neurogenic hypertension

Abstract Increased plasma dopamine beta hydroxylase, DBH, activity has been cited as evidence of increased sympathetic function in essential hypertension. Here-to-fore, experimental hypertension in animals has been associated with normal plasma DBH activity. This study shows that rats with neurogenic hypertension, induced by sinoaortic denervation, SAD, have elevated DBH activity; the mean increase in plasma DBH measured 3 days to 11 weeks after operation was 74% higher in the SAD group than in the sham-operated, control group. DBH activity showed a positive correlation with arterial pressure. Mesentery DBH activity was inversely related to plasma enzyme activity in SAD rats, indicating sympathetic nerve terminals in mesentery are a source of plasma DBH. We conclude that plasma DBH activity is an index of increased sympathetic function since it is consistently elevated in rats with neurogenic hypertension resulting from sustained central activation of the sympathetic nervous system.

Microdialysis in the posterior hypothalamus: sodium chloride affects norepinephrine release, mean arterial pressure, heart rate and behavior in awake rats.

A microdialysis probe, implanted in the posterior hypothalamus (PH) was used to examine changes of extracellular norepinephrine (NE) in freely moving rats from which mean arterial pressure (mAP) and heart rate (HR) were continuously monitored. Artificial cerebrospinal fluid (aCSF) was pumped through the probe and 10-microliters dialysate samples were collected at 5-minute intervals and analyzed for NE by radioenzymatic assay. High sodium chloride (NaCl)-aCSF solution elicited pressor and tachycardiac responses and locomotor activity coupled with significant increases in levels of dialysate NE. The latter and the associated cardiovascular effects were significantly attenuated by perfusate lidocaine (0.5%). When alpha-adrenergic receptors in PH were blocked by phenoxybenzamine (0.165 M), high NaCl-aCSF released NE but the associated cardiovascular effects were attenuated. In addition, intravenous ganglionic blockade with hexamethonium (25 mg/kg) also attenuated cardiovascular responses during the high NaCl-aCSF perfusion of PH. These results indicate that PH is one of the important areas for central actions of NaCl and that the cardiovascular and locomotor responses produced by central NaCl, in part, depend on neuroadrenergic activity in PH.

Catecholamines and their major metabolites in plasma and cerebrospinal fluid of man

In 36 patients undergoing elective surgery under spinal anesthesia, plasma and cerebrospinal fluid (CSF) concentrations of catecholamines and their major metabolic products were determined. The development of specific and sensitive radioenzymatic assays make these determinations possible. The levels of norepinephrine, epinephrine, and the O-methylated metabolite, normetanephrine, were greater in the plasma then the CSF, although the difference was significant for norepinephrine and epinephrine only (P less than 0.01 for both) On the other hand the levels of both deaminated metabolites dihydroxyphenylglycol (DOPEG) and dihydroxymandelic acid (DOMA) were greater in the CSF the in plasma, but the difference was significant for DOPEG only (P less than 0.01). Although there was a positive and significant correlation between the levels in plasma and CSF of all these compounds, their concentrations in CSF may reflect metabolism of catecholamines in the central nervous system.

Regional and Systemic Hemodynamic Patterns in Rabbits with Neurogenic Hypertension

The hemodynamic basis of neurogenic hypertension was studied in unanesthetized rabbits 10 minutes to 30 days after sinoaortic denervation (SAD). The fractional distribution of 86Rb to body tissues was determined and used to calculate regional blood flow from the value of cardiac output obtained from an arterial dilution curve of the indicator. Sham-operated rabbits served as controls. Increased cardiac output was a major hemodynamic component of SAD hypertension in 69% of the rabbits studied 1–40 hours postoperatively (acutely) but in only 25% of those studied 3–30 days after surgery (chronically). In the majority of the chronic SAD rabbits, increased total peripheral resistance (TPR) was the basis of the hypertension. All SAD rabbits had increased heart rates. Acutely, most high-cardiac output hypertensive rabbits had increased splanchnic resistance with normal blood flow, whereas all of them had low or normal renal resistance with high blood flow. Flows were increased in other major regions. Acutely, in the few high-TPR hypertensive rabbits, resistance was significantly increased in splanchnic tissue, liver, and carcass but not in the kidneys. Chronically, renal resistance was elevated in both types of hypertension. Chronic high-TPR rabbits had increased resistance in all major regions, but, unlike the acute high-TPR group, increased carcass resistance was located in bone rather than skeletal muscle. In the few chronic high-cardiac output hypertensive rabbits, TPR was reduced and regional blood flows were high with the exception of that to the kidneys and liver. Skin received a larger percent of cardiac output in chronic hypertensive rabbits than it did in acute hypertensive rabbits regardless of the hemodynamic basis of the hypertension.

Increased Plasma Vasopressin in Sinoaortic Denervated Rats

The main purpose of this study was to evaluate changes in plasma arginine vasopressin (AVP) associated with arterial baroreceptor deafferentation. Food and water intake of sham-operated (SO) rats was matched to that of sinoaortic denervated (SAD) rats, and blood samples were collected from groups of SAD and SO rats 15 min, 1-4 h, 24 h and 4-7 days after operation. Plasma AVP was 2-4 times higher in SAD than SO rats at each of the times studied during the 1st week (p less than 0.001); at those times no significant differences in hematocrit, plasma sodium or osmolality were found. Three weeks after surgery, plasma AVP was similar in both groups of rats. Mean arterial pressure, measured in additional groups of rats, was approximately 35 mm Hg higher in SAD than SO rats for the first 4 postsurgical hours, remaining about 20 mm Hg higher at the later times. Administration of an AVP pressor antagonist to SAD rats caused a small (8-11%), statistically significant reduction in the elevated pressure of SAD rats during the first 4 postsurgical days. Thus, AVP contributes modestly to the elevation of arterial pressure caused mainly by neurogenic mechanisms in SAD rats during the early postoperative period. Ingestive behavior was monitored in additional SO and SAD rats. SAD rats had significantly reduced food and water intake for 5 days after surgery, however, by day 6 intake was comparable to that of SO rats. Preoperative body weight was not regained until 2 weeks after surgery.(ABSTRACT TRUNCATED AT 250 WORDS)