Nocturnal hypertension in mice consuming a high fructose diet

OBJECTIVE

To investigate the effect of fructose consumption on the light/dark pattern of blood pressure, heart rate and autonomic neural function in mice.

BACKGROUND

Insulin resistant diabetes is associated with hypertension and autonomic dysfunction. There is evidence that the increasing incidence of diabetes may be related to dietary changes, including consumption of high levels of fructose.

DESIGN/METHODS

C57/BL mice, instrumented with radiotelemetric arterial catheters, were fed a control or high fructose diet (60%). Cardiovascular parameters measured were light/dark pattern of mean arterial pressure (MAP), heart rate (HR) and variability (time and frequency domain). We also measured plasma insulin, glucose, lipids and angiotensin II (Ang II) as well as glucose tolerance. In situ hybridization was used to measure brainstem expression of tyrosine hydroxylase (TH) and Ang AT1a mRNA.

RESULTS

Fructose diet (8 weeks) produced an increase in MAP, variance and low frequency domain (14+/-3 vs. 33+/-4 mm Hg(2), variance and 10+/-2 vs. 26+/-4 mm Hg(2), LF, control vs. fructose, P<0.01). The changes occurred only at night, a period of activity for mice. Glucose tolerance was attenuated in the fructose group. Fructose also increased plasma cholesterol (80+/-1 vs. 126+/-2 mg/dl, control vs. fructose, P<0.05) and plasma Ang II (18+/-5 vs.65+/-12 pg/ml, control vs. fructose, P<0.05). Depressor responses to alpha(1)-adrenergic blockade with prasozin were augmented in fructose-fed mice. Using quantitative in situ hybridization, we found that Ang AT1a receptor and TH mRNA expression were significantly increased in the brainstem locus coeruleus.

CONCLUSION

A high fructose diet in mice produced nocturnal hypertension and autonomic imbalance which may be related to activation of sympathetic and angiotensin systems.

Sarin produces delayed cardiac and central autonomic changes

The aim was to evaluate the acute and delayed effects of low dose sarin exposure on cardiac autonomic and brainstem catecholaminergic function in mice. The rationale was to expand our knowledge of the cardiovascular effects of this neurotoxic, acetylcholinesterase (AChE) inhibitor. C57BL/6 male mice with telemetric arterial catheters were injected with saline or sarin (8 microg/kg, 0.05x LD(50); sc, two injections) with blood pressure (BP) measurements made at 1 and 10 weeks after sarin exposure. BP and pulse interval variability (PI) and low and high frequency spectral oscillations were measured using autoregressive spectral analysis. In situ hybridization (ISH) was used to quantify tyrosine hydroxylase (TH) mRNA expression in brainstem cardiovascular centers. Sarin had no effect on blood AChE activity, heart rate (HR) or BP. There was a biphasic response in PI variance, an early increase (+140%) and a delayed decrease (-62%) at more than 2 months after sarin exposure. There were no changes in BP variance. Assuming that increased PI variance is a positive outcome, the short-term response to sarin should be protective. This is opposite for the delayed decrease in PI variance which is associated with adverse cardiovascular effects. There was an increase in TH mRNA in both locus coeruleus (0.18+/-0.05 vs. 1.4+/-0.2 microCi/g; control vs. sarin) and dorsal vagal complex (0.09+/-0.06 vs. 1.17+/-0.03 microCi/g; control vs. sarin). Results show that a dose of sarin which had no peripheral cholinergic effects caused changes in autonomic modulation, a short-term enhancement followed by a delayed impairment in heart rate variability. Sarin-induced cardiac effects suggest a controversial aspect to the use of pharmacological agents which target AChE for management of cardiovascular risk.

Stress-induced pressor and corticosterone responses in oxytocin-deficient mice

We used oxytocin knockout (OTKO) mice to investigate the role of oxytocin in regulation of blood pressure, heart rate and stress reactivity (pressure reactivity and plasma corticosterone). Male OTKO and control wild-type mice with carotid arterial catheters were exposed to intermittent shaker stress for 7 days (2 min stressors, 45 times per day). Mean arterial pressure (MAP) and heart rate (HR) were recorded continuously (24 h) before stress (basal), on stress days 1, 3 and 7 (S1, S3 and S7) and 1 day poststress (recovery). Plasma corticosterone (Cort) was measured before stress and 30 min after the last stress on day 7. Twenty-four hour averages of MAP and HR were lower in OTKO mice than in controls (P < 0.0001 and P < 0.005, respectively) with a significant diurnal rhythm. Chronic stress (S1 and S3) produced an increase in 24 h average MAP in OTKO mice, but not in controls. There were no stress-related changes in 24 h average HR values between control and OTKO mice. The immediate pressor responses were analysed during the dark and light periods (19.00 and 08.00 h). During the dark period, stress-induced pressor responses were observed only in OTKO mice (S1 and S3). In the light period, stress-induced MAP increases were seen on all days in OTKO mice and on days S1 and S3 in controls. There were no differences in baseline Cort between the groups; however, OTKO mice showed a reduced response to chronic stress (+298 versus+411%, OTKO mice versus controls, P < 0.005). In conclusion, oxytocin deficiency alters the endocrine and pressor responses to chronic stress, suggesting that the endogenous oxytocin system is important in regulating the stress-induced pressor response.

Rapid neurosecretory and cardiovascular response to osmotic stimulation in conscious mice

Experiments were performed to evaluate the neuroendocrine and cardiovascular effects of osmotic stimulation in mice. Hypertonic saline (HS) was administered centrally or via the blood stream to conscious mice during measurement of blood pressure (BP), heart rate (HR) and plasma vasopressin (VP) and oxytocin (OT). A test of hypovolemia on VP secretion was also performed. Chronic carotid arterial cannulas were inserted for blood sampling, cardiovascular monitoring and vascular injections. Intracerebroventricular (ICV) cannulas were used for central injections. Vascular injection of HS (30 microl, 3.4 M NaCl) caused rapid and transient increases in plasma VP and OT. Plasma VP increased from 5.6 +/- 0.9 to 10.0 +/- 1.0 pg/ml, while plasma OT increased from 1.5 +/- 0.6 to 8.6 +/- 2.4 pg/ml at the earliest time point, immediately after ICV injection. ICV osmotic stimulation produced a rapid and sustained increase in plasma VP, with no change in OT. Plasma VP levels were increased from basal levels of 5.1 +/- 1.5 to 13.1 +/- 4.6, 11.4 +/- 1.5, 12.6 +/- 1.7 pg/ml at 0, 1 and 5 min after injection, respectively. ICV HS also increased plasma corticosterone. BP was increased by both vascular and central osmotic stimulation. Vascular HS increased BP immediately (Delta15.3 +/- 1.7 mm Hg, 0 min) and transiently (Delta-3.9 +/- 4.6 mm Hg, 5 min) while central HS produced a sustained increase in BP (Delta10 +/- 1.4 and Delta9.8 +/- 1.9 mm Hg, 0 and 5 min). Osmotic stimulation produced no significant changes in HR. Acute hemorrhage (approximately 10% decrease in blood volume) increased plasma VP (4.9 +/- 1.0 vs. 8.4 +/- 2.2 pg/ml). These results show the pattern of endocrine and cardiovascular responses to osmotic stimulation in conscious mice. They demonstrate that (1) there are extremely rapid changes in plasma VP and OT; (2) plasma OT is increased only after peripheral vascular hypertonic injection, and (3) central and peripheral osmotic stimulations are associated with pressor responses.

Circadian differences in stress-induced pressor reactivity in mice

The objective of this study was to determine the effect of chronic stress exposure on the circadian pattern of cardiovascular responses in mice. Using male C57BL6 mice with carotid arterial catheters, we tested the effect of 7 days of intermittent shaker stress on body weight, food intake, drinking activity, plasma corticosterone, mean arterial pressure (MAP), and heart rate. The stress was delivered automatically for 2-minute periods (150 cycles/min), 45 times/d for 7 days. Plasma corticosterone was significantly increased in acutely and chronically stressed mice, with a partial attenuation in the chronic condition. Stress increased water intake, produced no change in food intake, and significantly decreased body weight (5% change). MAP and heart rate were measured continuously on stress days 1, 3, and 7 and during the basal and recovery periods. Chronic stress did not produce a sustained increase in MAP; however, there was an increase in MAP during the first stress day and a decrease during the recovery period. There was a circadian pattern in the pressor responses, with greater increases seen during the light period (nonactive phase) than in the dark period (+24% versus +11% on stress day 3, light versus dark). The results suggest that a stress delivered during the nonactive phase represents a higher cardiovascular risk.

Case study: melatonin in severe obesity

Nocturnal serum melatonin was measured at half-hour intervals from 6:30 P.M. to 7 A.M. in two sisters, one severely obese 15-year-old and one somewhat overweight 12-year-old. Both, otherwise, were physically and psychiatrically healthy. In the severely obese sister, there was a significant increase in the serum melatonin mean level, a delayed phase-shift, and a delayed peak. Also, her overnight urine melatonin and its metabolite, 6-hydroxymelatonin sulfate, were significantly higher. Could there be a relationship between dysregulation of the pineal gland and severe obesity?

Nocturnal serum melatonin profile in major depression in children and adolescents

BACKGROUND

In major depression, biological rhythm disturbances in sleep, appetite, and mood suggest dysregulation in neuroendocrine functions, possibly in the pineal gland. In this study, pineal gland function was examined by measuring nocturnal serum melatonin levels during both wakefulness and sleep in depressed children and adolescents.

METHODS

Twenty-two youths aged 8 to 17 years primarily with major depression were compared with 19 controls. Blood samples were drawn every half hour from 6 PM to 7 AM. Nocturnal serum melatonin levels were measured by radioimmunoassay.

RESULTS

The overall nocturnal serum melatonin profile from 6 PM to 7 AM was significantly higher (mean +/- SD, 0.18 +/- 0.14 nmol/L) in the depressed group than in the controls [mean +/- SD, 0.15 +/- 0.10 nmol/L, F(1,26) = 4.37, P < .05]. In dim light, when the subjects were awake, no difference existed between the 2 groups. After lights-out, from 10 PM to 7 AM, the melatonin profile rose in both groups; however, the depressed group had a significantly higher increase (mean +/- SD, 0.24 +/- 0.14 nmol/L) than the controls [mean +/- SD, 0.18 +/- 0.07 nmol/L, F(1,26) = 4.93, mean square error = 0.11, P = .04]. Post hoc analysis showed a significantly higher melatonin profile in depressed subjects without psychosis (n = 15) than in depressed subjects with psychosis (n = 7) or in the controls.

CONCLUSIONS

Measuring the overall nocturnal serum melatonin profile during darkness may help to differentiate children and adolescents with major depression without psychosis from those with psychosis and from controls.

HLA type and the genetic risk for type 1 diabetes mellitus

One hundred twenty-nine type 1 diabetic children and 176 non-diabetic siblings from the Louisville referral area were HLA typed by microlymphocytotoxicity technique. DR antigen frequencies were compared to frequencies for the Southeast USA population. Frequencies of DR3 and DR4 were significantly increased in both the diabetics and their unaffected siblings relative to the general population and DR2 was decreased. Forty-six percent of diabetic children possessed both DR3 and DR4 antigens while only 7% had neither. The findings are consistent with those in other geographical areas and give strong support to the role of DR3 and DR4 antigens as markers for diabetes susceptibility genes.