Perinatal dietary NaCl level: effect on angiotensin-induced thermal and dipsogenic responses in adult rats

Early free access to hypertonic NaCl solution induces a long-term effect on drinking, brain cell activity and gene expression of adult rat offspring

Exposure to an altered osmotic environment during a pre/postnatal period can differentially program the fluid intake and excretion pattern profile in a way that persists until adulthood. However, knowledge about the programming effects on the underlying brain neurochemical circuits of thirst and hydroelectrolyte balance, and its relation with behavioral outputs, is limited. We evaluated whether early voluntary intake of hypertonic NaCl solution may program adult offspring fluid balance, plasma vasopressin, neural activity, and brain vasopressin and angiotensinergic receptor type 1a (AT1a)-receptor gene expression. The manipulation (M) period covered dams from 1 week before conception until offspring turned 1-month-old. The experimental groups were (i) Free access to hypertonic NaCl solution (0.45 M NaCl), food (0.18% NaCl) and water [M-Na]; and (ii) Free access to food and water only [M-Ctrol]. Male offspring (2-month-old) were subjected to iv infusion (0.15 ml/min) of hypertonic (1.5M NaCl), isotonic (0.15M NaCl) or sham infusion during 20 min. Cumulative water intake (140 min) and drinking latency to the first lick were recorded from the start of the infusion. Our results indicate that, after systemic sodium overload, the M-Na group had increased water intake, and diminished neuronal activity (Fos-immunoreactivity) in the subfornical organ (SFO) and nucleus of the solitary tract. They also showed reduced relative vasopressin (AVP)-mRNA and AT1a-mRNA expression at the supraoptic nucleus and SFO, respectively. The data indicate that the availability of a rich source of sodium during the pre/postnatal period induces a long-term effect on drinking, neural activity, and brain gene expression implicated in the control of hydroelectrolyte balance.

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.

Role of angiotensin II and the subfornical organ in the pharmacological actions of ethanol

AIMS

The current study was designed to evaluate if angiotensin II mediates the hypothermic effects of ethanol, and to determine if the effects of angiotensin are mediated centrally. We also tested the hypothesis that the subfornical organ (SFO) is a site responsible for the alterations in body temperature and aerial righting reflex mediated by ethanol and for the modulation of ethanol consumption in rats.

METHODS

Male Sprague-Dawley rats were used in a series of experiments to evaluate the role of both peripheral and central administration of losartan, a selective angiotensin type 1 receptor antagonist on ethanol-induced hypothermia. Subsequent studies were undertaken in SFO-lesioned rats to evaluate the effects of SFO-lesion on alcohol intake, the thermal response to alcohol and angiotensin, and the aerial righting reflex.

RESULTS

Selective antagonism of the angiotensin II type 1 receptor, administered either peripherally or centrally, attenuated not only the fall in colonic temperature but also attenuated the transient rise in tail skin temperature that was associated with administration of ethanol. The thermal responses to both angiotensin and ethanol were similarly attenuated in SFO-lesioned rats. Likewise the aerial righting reflex, which has previously been shown to be impaired by losartan treatment, was also significantly attenuated in SFO-lesioned animals. Alcohol intake, as determined by a 48 h, two-bottle preference test also revealed that SFO-lesioned animals consumed significantly less alcohol (ethanolic beer) than did controls.

CONCLUSION

Collectively, the results demonstrate that ethanol-induced temperature responses are mediated by the renin-angiotensin system and that this interaction is mediated centrally. In addition, the results demonstrate that the SFO is a site that mediates several neurobiological effects of ethanol, possibly via the renin-angiotensin system.