M. Costales

Increased salt preference in adult offspring raised by mother rats consuming excessive amounts of salt and water

This study was designed to evaluate the effects of an early high-salt environment on the maternal and the young offspring physiology and on the adult offspring sodium appetite. Twenty-five-adult female Wistar rats were pseudorandomly divided into two groups. Twelve animals underwent a partial ligature of their abdominal aorta (PAL). Once polydipsia and sodium appetite (tested by measuring water and a 2.7% NaCl intakes) developed, they were mated. The other 13 rats (SHAM) were sham-operated and also mated. Throughout pregnancy and lactation, water and salt intake of PAL rats was consistently and significantly higher than that of the Sham. On gestation day 20, amniotic fluid and maternal plasma sodium concentration of PAL and Sham rats did not differ. Sodium concentration in the milk of the lactating PAL group was elevated (P < 0.05) on day 20 after delivery. At 0, 10 and 21 days of age, plasma sodium concentration of PAL offspring (PAL-O) and Sham offspring (Sh-O) were not significantly different. At 90 days of age, the salt preference of PAL-O rats was greater than that of Sh-O rats after 7 days of sodium deprivation (P < 0.01).

Changes of blood pressure responsiveness in rats exposed in utero and perinatally to a high-salt environment

We tested the hypothesis that the pressor responses to angiotensin II could be influenced by an early salt exposure. Twenty-five adult female rats were pseudorandomly divided in two groups. Twelve animals underwent a partial ligature of their abdominal aorta (PAL). Once polydipsia and sodium appetite developed, these rats were mated. The other group (13 rats) was sham-operated (Sham) and mated. Throughout pregnancy and lactation, water and 2.7% NaCl solution intakes differed between the two groups of mother rats. PAL offspring (PAL-O; n = 14), and Sham-operated offspring (Sh-O; n = 10), were maintained on a solid diet containing 1% NaCl, tap water and a 2.7% NaCl solution. At 90 days of age, pressor responsiveness to intravenous angiotensin II (50, 100 and 200 ng) was assessed in anesthetized rats. The pressor responses to 50 and 200 ng angiotensin II were significantly greater in PAL-O rats than in Sh-O rats. These results support the hypothesis of a modulation of cardiovascular responsiveness or its underlying mechanisms by an early high salt environment.

Sex difference in polyethylenglycol-induced thirst

The polyethylenglycol-induced thirst in male and female castrated rats has been studied. The polyethylenglycol (PG) increases the water intake more in females than in males. Estradiol benzoate and testosterone P. diminishes the amount of water drunk after PG treatment in the females, but not in the males.

Angiotensin-induced dringking: Sexual differences☆

The dipsogenic effect of Angiotensin-II (A-II) in relation to sexual variables was studied. It was found that Angiotensin-II administered SC constitutes a stimulus which induces more drinking in females than in males. Moreover, the adult females show maximum sensitivity to A-II during proestrus. The males and females castrated at birth, and females androgenized at birth, drink similar volumes of water after A-II SC injection. The pattern of stimulated intake is different in the two sexes, and appears to depend upon the development of the rats.

Thirst changes in offspring of hyperreninemic rat dams

The aim of this study was to investigate the changes in thirst dependence on the renin-angiotensin system (RAS), in offspring of hyperreninemic, hyperdipsic, and natriophilic rat dams. Female rats underwent a partial aortic ligature between the renal arteries (PAL) or were sham-operated (SHAM). At 6 days of age, offspring of PAL (O-PAL) and SHAM (O-SHAM) dams were injected with isoproterenol (subcutaneously, 500 microg/kg body weight) or vehicle. Pretreatment with captopril (intraperitoneally, 50 mg/kg) on isoproterenol-induced thirst was also studied. Plasma renin activity in dams and hematocrit and osmolality in pups were measured. O-PAL had a greater water intake than O-SHAM. However, they responded similarly to isoproterenol or isoproterenol with captopril pretreatment. Only minor differences in hematocrit and osmolality were found between O-SHAM and O-PAL rats after isoproterenol or vehicle treatment. Beta-adrenergic or angiotensinergic responsivity seems not to be altered in offspring of hyperrenimic, hyperdipsic, and natriophilic dams. Nevertheless, other thirst responses of offspring may be critically dependent upon uterine conditions.

Maternal RAS influence on the ontogeny of thirst

Perillan, C., Costales, M., Vijande, M., and J. Arguelles. Maternal RAS influence on the ontogeny of thirst. Physiol Behav XX (X) 000-000, 2006. The main objective of this study was to investigate the effect of an altered ambiance in utero, on the development of thirst mechanisms in the offspring. Female rats underwent a partial ligature of the aorta (PAL), which induces an intrinsic activation of the renin angiotensin system (RAS), thirst and sodium appetite. A second group of female rats was treated with desoxycorticosterone (DOCA) which depresses the RAS. The offspring of these two groups were tested for their responses to several thirst stimuli at 2, 4 and 6 days of age. The offspring from PAL mothers responded like their controls to cellular dehydration (NaCl hypertonic injection) at 2 days of age, and also did to extracellular dehydration by polyethyleneglycol at 4 days. Nevertheless, they responded more to isoproterenol at 6 days of age in comparison to their control group. The offspring from DOCA treated mothers did not show statistically significant responses (in comparison with vehicle injected pups) to hypertonic NaCl at two days nor to polyethyleneglycol at four days. Water intake at 6 days of age after isoproterenol administration in DOCA was statistically enhanced, but not differently from the response obtained from pseudo-DOCA treated pups. In particular, rats developed in a hypereninemic ambiance (O-PAL) during gestation, responded with higher water intake when treated with a strong RAS and thirst activator (isoproterenol) but responded normally to a more gentle and complex stimulus (PG). Therefore it seems that in utero conditions can determine the chronology and intensity of thirst responses in offspring.

Effects of inhibitors of the renin-angiotensin system on water intake after insulin administration

Male wistar rats drank in a dose-related manner, in response to 1 to 40 U/kg of i.p. insulin. Maximum intakes took place during the first 30 min after i.p. insulin administration, coinciding with the period of maximal drop of blood glucose. Plasma renin activity (PRA) in rats treated with i.p. insulin was higher than in basal conditions or after saline injection. Nephrectomy and adrenalectomy did not abolish insulin-induced drinking. A low dose of captopril (0.1 mg/kg s.c.) did not modify insulin-induced drinking, but a higher dose (10 mg/kg s.c.), or enalapril (0.5 mg/microgram s.c.), significantly increased insulin-induced drinking. Enhancement of insulin-induced drinking by s.c. captopril was not secondary to an increased diuresis. Captopril (50 micrograms i.c.v.) significantly reduced the cumulative water intake after i.p. insulin (20 U/kg i.p.) plus s.c. captopril (10 mg/kg). The blockade of central receptors for angiotensin II with sarile-AII (5 micrograms) significantly diminished insulin-induced drinking. It appears that the peripheral renin angiotensin system is not necessary for insulin-induced drinking but central angiotensin II plays an important role.

Renin Dependence of Insulin-Induced Thirst

The influence of insulin on food intake has been amply studied. However there has been little work on the effect of this hormone in water intake. In 1964 Novin1 reported increased water intake due to insulin administration, separated from its effect on food intake. Booth and Brookover2 (1968), Spitz3 (1974) and Waldbillig and Bartness4 (1981) also found similar results of stimulation of thirst by insulin. Unpublished results by Fitzsimons reveal that i.p. insulin-induced drinking (IID) is abolished by nephrectomy. It could favour the possible participation of the renin-angiotensin system in this phenomenon. Waldbillig and Bartness4 found that i.p. insulin produced neither hypovolemia non plasmatic hyperosmolality, both conditions typified as thirst stimuli. On the contrary, animals presented hypervolemia and hypoosmolality.

In utero extracellular dehydration modifies thirst in neonatal rats.

The main aim of this study was to investigate the effect of maternal extracellular dehydration during pregnancy in rats on the development of thirst mechanisms in the offspring. Pregnant rats underwent three episodes of extracellular dehydration induced by injecting s.c. 15ml/kg b.w. of a 20% wt/vol solution of polyethylene glycol (PEG) in saline. The treatment given on days 14, 17 and 20 postconception is thought to induce endocrine and natriophilic responses similar to those elicited by vomiting. The offspring were tested for their responses to three different thirst stimuli at 2, 4 and 6 days of age. Like the controls, the offspring from PEG-treated mothers responded to beta stimulation by isoproterenol at 6 days of age. However, they failed to respond to cellular dehydration (NaCl hypertonic injection) at 2 days of age or to extracellular dehydration by PEG on day 4. In conclusion, offspring exposed to in utero extracellular dehydration do not respond to cellular dehydration at 2 days of age or to extracellular dehydration at 4 days of age, whereas control pups had already developed an appropriate response to these stimuli. According to these results, it therefore seems that in utero conditions determine the development of adaptive thirst responses in offspring.

Effect of castration and gonadal hormones on insulin-induced drinking

Female Wistar rats in any of the estrual phases have been shown to drink significantly more water than males (p < 0.05), after a single I.P. insulin injection (5 U/kg b.wt.). Sexual differences in insulin-induced drinking persisted after castration when it was made in adult rats (4.6 +/- 1.2 ml/2 h, males = 8; vs. 13.0 +/- 3.1 ml/2 h, females = 8; p < 0.05). On the other hand, when animals were castrated before puberty or when newborn, sexual differences in insulin-induced drinking disappeared. Hence, insulin-induced drinking seems to be a sex-dependent phenomenon that differentiates just before or during puberty since it is abolished by castration prior to sexual maturation. Sex hormone administration in male and female rats castrated at different ages showed a variety of actions on insulin-induced drinking. A pattern emerged showing that androgenized (testosterone treated) rats drank usually less in response to insulin than estrogen-treated rats (independent of their genetic sex). According to the above results, we can conclude that insulin-induced drinking is a phenomenon sensible to gonadal hormones, both by conditioning the differentiation of some physiological structure or mechanisms that underlay drinking behavior in that paradigm and by a direct action on these or other related mechanisms.