Area postrema lesions augment the pressor activity of centrally administered vasopressin

Chronic Cardiovascular Effects of Central Vasopressin in Conscious Rats

To clarify the cardiovascular effects of central vasopressin (AVP), a chronic intracerebroventricular (ICV) infusion of AVP was performed in conscious Wistar normotensive rats. Animals were divided into 3 groups: 1) AVP 1 ng/hr (Low), 2) AVP 100 ng/hr (High), and 3) saline (control) ICV infusion. After a 6 day control period, AVP or saline was continuously infused into the lateral cerebroventricle at a rate of 1 microliter/hr using osmotic minipump for 7 days. As a result, a dose-related elevation of AVP concentration in CSF was achieved. Systolic blood pressure in both Low and High AVP infusion was slightly (7-12 mmHg) but significantly higher than that in control. ICV infusion of AVP did not alter urine volume, electrolytes excretion or osmolality, and AVP vascular antagonist injected intravenously failed to affect mean arterial pressure. Furthermore, plasma catecholamines and renin activity did not differ significantly among the groups. Thus, chronic ICV infusion of AVP induced the elevation of blood pressure, which is due to centrally mediated effect of AVP.

Endogenous vasopressin modulates the cardiovascular responses to exercise

The role of brain-stem vasopressinergic projections in the genesis of reflex bradycardia and in the modulation of heart rate control during exercise is discussed on the basis of both changes in endogenous peptide content and heart rate changes observed during exercise. Dynamic running caused an increase in vasopressin content specifically in dorsal and ventral brain-stem areas. Rats pretreated with vasopressin or the V1 receptor antagonist into the nucleus tractus solitarii (NTS) showed a significant potentiation or a marked blunting of the exercise tachycardia, respectively, without any change in the blood pressure response. It is proposed that long-descending vasopressinergic pathways from the hypothalamus to the NTS serves as one link between the two main neural controllers of the circulation, that is, the central command and feedback control mechanisms driven by the peripheral receptors signals. Therefore vasopressinergic input contributes to the adjustment of heart rate response (and cardiac output) to the circulatory demand during exercise.

Endogenous vasopressin and the central control of heart rate during dynamic exercise

The present article contains a brief review on the role of vasopressinergic projections to the nucleus tractus solitarii in the genesis of reflex bradycardia and in the modulation of heart rate control during exercise. The effects of vasopressin on exercise tachycardia are discussed on the basis of both the endogenous peptide content changes and the heart rate response changes observed during running in sedentary and trained rats. Dynamic exercise caused a specific vasopressin content increase in dorsal and ventral brainstem areas. In accordance, rats pretreated with the peptide or the V1 blocker into the nucleus tractus solitarii showed a significant potentiation or a marked blunting of the exercise tachycardia, respectively, without any change in the pressure response to exercise. It is proposed that the long-descending vasopressinergic pathway to the nucleus tractus solitarii serves as one link between the two main neural controllers of circulation, i.e., the central command and feedback control mechanisms driven by the peripheral receptors. Therefore, vasopressinergic input could contribute to the adjustment of heart rate response (and cardiac output) to the circulatory demand during exercise.

Vasopressin receptors in the area postrema differentially modulate baroreceptor responses in rats

This study examined the effects of microinjection of [Arg8]vasopressin (AVP) into the area postrema (AP) on baroreceptor reflex control of heart rate (HR) and sympathetic efferent discharge (SED) in anesthetized rats. Comparable increments in blood pressure evoked by systemic AVP, as opposed to phenylephrine, were associated with significantly greater reflex bradycardia. Similarly, AVP augmented the baroreflex-mediated sympathoinhibition; however, this effect was evident only with the lower increments in arterial pressure (< 45 mm Hg) i.e. following systemic administration of small doses of AVP. Beyond 45 mm Hg there was no further augmentation of baroreflex-mediated sympathoinhibition showing the non-linearity of the response compared to phenylephrine which was linear over a wide range of induced pressure increases. Microinjection of AVP into the AP produced a differential effect on HR and SED responses to baroreceptor activation by systemically administered phenylephrine, the baroreflex slope of HR response was attenuated whereas that of SED was enhanced. Microinjection of the V1 antagonist AVPX (d(CH2)5Tyr(Me)-AVP) into the AP abolished the inhibitory effect of AVP on the baroreceptor-HR response suggesting that V1 receptors are involved in this response. Further, AVPX inhibited the baroreceptor-SED response suggesting that V1 receptors in the AP are tonically involved in modulating the baroreceptor reflex control of SED. Qualitatively similar but smaller responses were obtained following microinjection of AVP into the nucleus tractus solitarii (NTS) suggesting involvement of neural input from the AP to the NTS in AVP-evoked responses in the AP. It is concluded that the AVP receptors in the AP differentially modulates the baroreceptor reflex control of HR and SED.

Alcohol effects on the morphometric development of the subfornical organ and area postrema of the albino mouse

We have studied the development of the nuclear sizes of ependymocytes and neurons of two circumventricular organs of the male alcoholic mouse: the Subfornical Organ (SFO) and the Area Postrema (AP), comparing the results with a control group. The global volume of both centers was also studied. The results show that the SFO, a structure related to the control of fluid balance, responds to alcoholism with an increase of the global volume. This increase could be related to the variations of salt-water balance and/or blood pressure in chronic alcoholism. However, the size of cell nuclei in the SFO is not affected. In contrast, the AP responds to chronic alcoholism like other nervous centres, with a decrease of the nuclear size of its cells. The global volume of AP does not change.