Blood ethanol level and physiologic measurements during ethanol-induced hypertension

Increased circulating vasopressin may account for ethanol-induced hypertension in rats

BACKGROUND

Long-term ethanol intake has been reported to evoke both hypertension and increase of systemic vasopressin levels in rats.

METHODS

In this work, we investigated the involvement of systemic vasopressin in the hypertension evoked in rats by long-term ethanol (20% vol/vol) intake for 2 weeks, by systemic treatment with the V1-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP (50 microg/kg). Moreover, plasma arginine-vasopressin (AVP) content was quantified using an AVP radioimmunoassay and the expression of vasopressin mRNA in the supraoptic (SON) and paraventricular (PVN) nuclei was measured using real-time PCR.

RESULTS

Mild hypertension was observed after 2 weeks of ethanol treatment when compared with control animals. Moreover, an increase in both the expression of vasopressin mRNA and the vasopressin blood content was observed in ethanol-treated rats in comparison to the control group. Basal blood pressure levels of ethanol-treated animals were significantly reduced by IV treatment with the V1-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP. However, dTyr(CH2)5(Me)AVP had no effect on the blood pressure of control animals.

CONCLUSIONS

The results indicate that mild hypertension is already observed at an early phase of ethanol consumption in rats. Because the content of circulating vasopressin was increased in ethanol-treated rats and their basal blood pressure returned to control levels after IV treatment with a V1-vasopressin receptor antagonist, it is proposed that increased circulating vasopressin content may mediate the hypertension observed in ethanol-treated rats.

The Effect of Oral Consumption of Perchlorate, Alone and in Combination with Ethanol, on Plasma Thyroid Hormone and Brain Catecholamine Concentrations in the Rat

Literature has reported a controversy concerning the effects of the environmental pollutant perchlorate on pertinent physiological systems. However, no research to date has evaluated the effect of concomitant consumption of perchlorate and an additional environmental contaminant on physiological systems. The present preliminary investigation served to assess the effects of oral consumption of perchlorate, alone and in combination with ethanol, on thyroid hormone and brain catecholamine concentrations in female rats of gestational age. Forty, female Myers' high ethanol-preferring rats were randomly assigned to 1 of 7 groups that received: (1) deionized water, both bottles (2) deionized water and 10% ethanol (v/v), two separate bottles (3) 300 microg/l perchlorate solution in deionized water, both bottles (4) 300 microg/l perchlorate in deionized water and in 10% ethanol (v/v), two separate bottles (5) 3000 microg/l perchlorate solution in deionized water, both bottles (6) 3000 microg/l perchlorate in deionized water and in 10% ethanol (v/v), two separate bottles (7) 0.01% propylthiouracil solution in deionized water, both bottles. At cessation of the treatment period, plasma triiodothyronine (T3) and thyroxine (T4) levels were measured by radioimmunoassay and brain area concentrations of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), and norepinephrine were measured by high performance liquid chromatography. Perchlorate consumption, alone and/or in combination with ethanol consumption, failed to produce significant alterations from control values for triiodothyronine, thyroxine, dopamine, DOPAC, or norepinephrine. The data suggest that the no-observed effect level of perchlorate consumption on thyroid hormone and brain catecholamine concentrations is above the 3000 microg/l concentration in the adult female rat.

Bicuculline sensitive depressor response to ethanol infusion into the lateral hypothalamus

Decreased GABA function in the hypothalamus increases mean arterial pressure (MAP) and heart rate (HR). Since ethanol acts on GABA-A receptors, blocking GABA-A receptors can prevent a decrease of MAP and HR by ethanol in the lateral hypothalamus (LH). Ethanol at 5-30 mM, with or without 25 ng/microl bicuculline, was infused into the LH, and the activity of the site was validated with 100 nmoles of serotonin. Male rats were anesthetized with pentobarbital, and the femoral artery was catheterized to measure MAP and HR. Microinfusion was performed with a 28-gauge cannula placed into the LH. Serotonin increased MAP and HR within 15 sec. Ethanol decreased the MAP by -21.15 +/- 3.92 mmHg and HR by -53.61 +/- 14.95 BPM, at 15 min, which recovered by 15 min after the infusion was terminated. These maximum decreases were produced by 20 mM ethanol giving a U-shaped dose response. The aCSF vehicle had no effect. Bicuculline prevented ethanol-induced changes and had no effect when administered alone. Both serotonin and ethanol have direct effects on LH neurons with cardiovascular function. Ethanol produces this effect through GABA-A receptors.

Chronic ethanol ingestion modifies the renin-aldosterone axis independent of alterations in the regulation of atrial natriuretic peptide

Using an animal model, we have investigated the effects of chronic ethanol ingestion on the regulation of atrial natriuretic peptide (ANP) synthesis and release. Male Sprague-Dawley rats were maintained for 6 weeks on a liquid diet of ethanol (up to 20% v/v) as part of a 2% solution of calf milk replacer. Weight-matched controls received an equal volume of ethanol-free solution, and normal animals drank ad libitum. All animals received rat chow throughout the experiment. This model produced physiologically relevant levels of blood ethanol, as concentrations at the time of sacrifice were 171.98 +/- 39.26 mg/dl. Plasma renin activity was significantly elevated in response to ethanol treatment, whereas circulating aldosterone concentration was reduced. No alterations in the plasma or atrial tissue levels of ANP were evident, although we did observe a significant increase in the ventricular tissue levels of ANP from 45.1 to 71.8 ng/g as a consequence of ethanol treatment. Levels of both atrial and ventricular ANP mRNA were not different between alcohol-treated and liquid-restricted control animals, although both groups showed significant increases in the amount of transcript in comparison with rats drinking ad libitum. No significant increases in either arterial blood pressure or heart/body weight ratio were observed for ethanol-treated rats. These results suggest that modifications in the renin-aldosterone axis can occur independently of alterations in the regulation of ANP under the influence of chronic ethanol ingestion.

Role of the sympathetic nervous system in ethanol-induced hypertension in rats

The present study investigated the role of the sympathetic nervous system in the development of ethanol-induced hypertension (EIH) in the rat. Sympathetic nerve activity (SNA) as an index of central sympathetic tone was measured directly from the preganglionic fibers of the greater splanchnic nerve. Four weeks after starting ethanol feeding, and prior to the development of hypertension, SNA of the ethanol-fed rats was significantly greater than that of controls. The increase in SNA was also evident at the early stages of EIH, at 8 weeks, and in fully developed EIH, after 12 weeks of ethanol consumption. Baroreceptor reflex control of heart rate (HR) but not SNA was impaired prior to the development of EIH at 4 weeks. However, at 8 and 12 weeks, baroreflex control of HR and SNA was normal or slightly greater than that of control rats. Because arterial pressure of ethanol-fed rats was significantly higher than that of controls at 8 and 12 weeks, the data suggest that ethanol feeding caused baroreceptor resetting. Pressor responsiveness to phenylephrine was depressed before the development of EIH but was similar to that of control rats following the development of EIH. The data also shows that blood and plasma volumes of ethanol-fed rats at the times that coincided with the pre- and posthypertensive states were similar to those of control rats which suggests that the development of EIH does not involve an increase in plasma volume. It is concluded that an increase in SNA contributes to the development of EIH and that baroreceptor resetting evoked by ethanol feeding plays a permissive role in maintaining an elevated blood pressure in ethanol-fed rats.

Plasma noradrenaline, platelet alpha 2-adrenoceptors, and functional scores during ethanol withdrawal

Plasma noradrenaline and platelet alpha 2-adrenoceptor density (sites/cell using 3H-rauwolscine with and without phentolamine) were correlated with withdrawal score in 23 hospitalized patients undergoing ethanol withdrawal. Control groups for plasma noradrenaline were 25 patients admitted to hospital for elective gastroscopy and 12 laboratory workers accustomed to venipuncture. Controls for platelet alpha 2-adrenoceptor measurements were a separate group of 31 normal subjects with a mean age close to that of the patients' withdrawing from ethanol. Plasma noradrenaline was significantly higher in the patients undergoing ethanol withdrawal than in patients admitted to hospital for elective endoscopy. Twelve laboratory controls had plasma noradrenaline levels significantly lower than either patient group. A significant though poor statistical correlation existed between ethanol withdrawal score and simultaneously determined plasma noradrenaline level. Platelet alpha 2-adrenoceptor sites/cell were reduced in ethanol withdrawal compared with the normal controls. Platelet alpha 2-adrenoceptor sites/cell increased over the first 24 hr of ethanol withdrawal but remained significantly lower than control values. The change in platelet adrenoceptors was accompanied by a fall in mean plasma noradrenaline. Thus, the stress of hospital admission itself is associated with an increase in plasma noradrenaline, but ethanol withdrawal enhances this increase, which is accompanied by and probably causes a reduction in platelet alpha 2-adrenoceptor numbers. These changes begin to return towards normal within 24 hr as the withdrawal reaction subsides.