R. Di Nicolantonio

Subfornical organ lesion decreases sodium appetite in the sodium-depleted rat.

The effect of subfornical organ (SFO) lesion on various models of ingestive behaviour was investigated in rats. Intake of water after 24 h water deprivation or systemic administration of hypertonic NaCl were not altered by SFO lesions. Intake of food or water after 24 h of food deprivation were not altered by SFO lesions. Intake of NaCl after furosemide-induced Na depletion was decreased by ablation of the SFO. This decrease in Na intake was ameliorated by pretreatment with a low dose of captopril. These results suggest that the SFO is involved in Na intake after Na depletion, but not in water or food intake following periods of water or food deprivation, respectively. The observation that a low dose of captopril can eliminate the decrease in Na appetite which occurred subsequent to SFO lesion suggests that other brain areas may also participate in Na-depletion-induced Na appetite.

THE EFFECT OF CAPTOPRIL OR ENALAPRILIC ACID ON THE Na APPETITE OF Na‐DEPLETE RATS

1. The converting enzyme inhibitors, captopril (SQ14 225, Squibb) or enalaprilic acid (MK 422, Merck Sharp and Dohme), were used to evaluate the role of angiotensin II in sodium (Na) appetite of Na‐deplete rats given a choice of water and 0.5 mol/1 NaCl to drink. Also, the effect of these drugs on taste was evaluated in water‐deprived Na‐replete rats and in Na‐deplete rats given a choice of NaCl, sucrose and water.

Perinatal salt intake alters blood pressure and salt balance in hypertensive rats.

Blood pressure and the rate of excretion of an oral salt load were examined in spontaneously hypertensive rats of the Okamoto strain after exposure in utero and during suckling to a high salt (3% NaCl, wt/wt), low salt (0.1%), control salt (0.8%), or high potassium (1% KC1) maternal diet After weaning, all offspring were given a diet containing 0.8% NaCl. There were small but significant differences in growth rate among offspring groups over the 60 weeks of observation, with rats exposed to perinatal low salt and high salt diet being lighter than those given control or high potassium diet There were positive, significant correlations between body weight and blood pressure in all dietary groups at 8 weeks of age but not 16 or 24 weeks. Rats exposed to perinatal low salt diet had significantly lower blood pressures than the other three groups, which had similar blood pressures. Low salt rats also exhibited an exaggerated natriuresis after a single, oral salt load (0.15 M saline, 1% body weight) compared with the other three diet groups, which were not different from each other. High potassium rats had a reduced kaliuresis and diuresis after the salt load when compared with the other three groups. At 60 weeks of age, rats that received perinatal low salt diet had significantly heavier adrenal glands when compared with the other groups, and the high potassium group had significantly elevated plasma renin concentrations. Thus, maternal electrolyte intake during the perinatal phase may alter body fluid homeostasis in genetically susceptible individuals at maturity.

Sodium Chloride Preference and Recognition Threshold in Normotensive Subjects on High and Low salt Diet

Young adult volunteers were placed on two week periods of high and low-salt diets following dietetic counselling and using normally available foodstuffs. Changes in sodium recognition threshold, salivary and urinary electrolytes and preference for NaCl, NaCl/KCl (1:1) mix and monosodium glutamate were measured during the high- and low-salt diet periods and during two-week control periods with subjects on their usual diet. Sodium preference was defined as the sodium concentration of unsalted tomato juice following ad libitum addition of a sodium salt till the most preferred taste was achieved. Subjects served as their own controls across the dietary periods in a cross-over design. While sodium excretion on the low-salt diet was significantly less than at on the high-salt diet, there were no significant changes in blood pressure, sodium recognition threshold, body weight or salivary electrolytes between these dietary periods. There was a significant increase in preference for NaCl, NaCl/KCl mix and monosodium glutamate on the high-salt diet when compared to the low-salt diet period. In all dietary periods less sodium was added to the unsalted tomato juice with monosodium glutamate than with NaCl/KCl and less sodium was added with the NaCl/KCl mix than with the NaCl. This study demonstrates that relatively short periods of increased sodium intake result in an increase in sodium preference in the absence of changes in salivary electrolytes or recognition threshold.

Captopril potentiates the vasodepressor action of Met‐enkephalin in the anaesthetized rat

1 The transient vasodepressor action of Met‐enkephalin (10–80 μg kg−1, i.v.) in anaesthetized rats was significantly potentiated by the angiotensin‐converting enzyme inhibitor, captopril (2 mg kg−1, i.v.); at this dose, it failed to modify the transient vasodepressor action of the non‐specific vasodilator, nitroprusside (2.5, 5.0, 10 μg kg−1, i.v.). 2 Captopril (2 mg kg−1, i.v.) caused a slow, progressive fall in the blood pressure of anaesthetized spontaneously hypertensive (SH) rats when compared to vehicle‐treated controls. Pretreatment with naloxone (1.5 mg kg−1, i.v.) 30 min earlier failed to alter significantly the hypotensive action of captopril in anaesthetized SH rats. 3 It was concluded that although captopril potentiated the vasodepressor action of Met‐enkephalin in anaesthetized normotensive rats, potentiation of endogenous opioids does not appear to be involved in the hypotensive action of captopril in anaesthetized SH rats.

BLOOD PRESSURE, SALT TASTE AND SODIUM EXCRETION IN RATS EXPOSED PRENATALLY TO HIGH SALT DIET

1. Blood pressure, sodium excretion and salt taste were examined in Sprague Dawley (SD) and Munich Wistar (MW) rats exposed prenatally to either a high salt (2.3% NaCl w/w) or control diet.

PRENATAL HIGH SALT DIET INCREASES BLOOD PRESSURE AND SALT RETENTION IN THE SPONTANEOUSLY HYPERTENSIVE RAT

1. An examination was made of the effect of prenatal, high salt (5% w/w) and low salt (0.1% w/w) diet on the blood pressure and ability to excrete a salt load of mature spontaneously hypertensive rats (SHR) of the Okamoto strain maintained on normal salt (0.8% w/w) diet after weaning.

Captopril attenuates diuretic and natriuretic actions of furosemide but not atrial natriuretic peptide

Atrial Natriuretic Peptide (ANP) exerts a potent diuretic and natriuretic action in rat, dog and man. To test whether these actions of ANP are due to antagonism of the antinatriuretic actions of endogenous angiotensin II, an examination was made of the renal actions of ANP in anesthetized rats with and without captopril pretreatment. Captopril treatment did not alter the diuretic and natriuretic action of a single, intravenous bolus injection of ANP (1000 ng of the 8-33 ANP). Captopril treatment did significantly attenuate the diuretic and natriuretic actions of Furosemide (20 mg/kg ip). This attenuation was not reversed by concomitant, exogenous angiotensin II infusion. These results suggest that while ANP exerts its renal actions independently of the circulating renin-angiotensin system the diuretic and natriuretic action of Furosemide is modulated by a substrate of angiotensin converting enzyme.

Altered uterine environment in the spontaneously hypertensive rat.

1. In order to determine the role of the uterine environment in the development of hypertension in the spontaneously hypertensive rat (SHR) we examined the patterns of fetal and placental growth and the composition of amniotic fluid of SHR and normotensive Wistar‐Kyoto (WKY) rats during the final trimester of pregnancy.

Role of uterine factors in the development of hypertension in SHR.

1. To examine whether the uterine environment plays a role in the development of hypertension in the spontaneously hypertensive rats (SHR), we have compared fetal weight, placental weight, and amniotic fluid composition of SHR and Wistar‐Kyoto (WKY) rats after 20 days of gestation.