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L Share

Publications and source records attributed to L Share.

155 records · Page 9Linked to original sources
PubMedDate not supplied

The importance of vasopressin in the development and maintenance of DOC-salt hypertension in the rat.

Experiments were performed to determine the role of vasopressin in deoxycorticosterone (DOC)-salt hypertension. In order to determine if vasopressin is necessary for the development of DOC-salt hypertension, rats with hereditary diabetes insipidus (DI) and normal Long-Evans rats (LE) were unilaterally nephrectomized, treated with DOC Pivalate (30 mg/kg . week) and given saline to drink for 8 weeks. A second group of DI rats were unilaterally nephrectomized, but received no treatment. Systolic blood pressure (SBP) increased 40 mm Hg in the LE group (p less than 0.01) but failed to increase significantly in either DI group. Urinary excretion of vasopressin (UADHV) and SBP were measured in unilaterally nephrectomized LE rats treated with DOC and salt (DOC-LE), salt alone (NaCl-LE) and untreated rats (H2O-LE). The UADHV was elevated in DOC-LE (p less than 0.01) and NaCl-LE (p less than 0.05), but only the DOC-LE rats became hypertensive. Finally, the I.V. injection of analogs of vasopressin, which block its pressor but not antidiuretic activity, lowered mean arterial blood pressure 27 +/- 5 mm Hg in 11 conscious DOC-salt hypertensive rats. It is concluded that vasopressin plays a major role as a pressor agent in both the onset and maintenance of DOC-salt hypertension.

Animals↗
PubMedDate not supplied

Pressor responsiveness to vasopressin in the rat with DOC-salt hypertension.

To further characterize the role of vasopressin in DOC-salt hypertension, four groups of unilaterally nephrectomized rats were studied: control rats given no further treatment, rats treated with DOC and given 1% saline to drink, or rats treated with only DIC or 1% saline had similar pressor responses to exogenous vasopressin and angiotensin II. Within the DOC-salt group, two populations of rats were identified: one with normal pressor responsiveness to vasopressin, and one with markedly enhanced pressor responsiveness to vasopressin. Incidence of enhanced responsiveness increased with duration of treatment. Urinary excretion of vasopressin was elevated in the 1% saline and DOC-salt groups after 1 week of treatment, and in the DOC group after 4 weeks. However, the plasma vasopressin concentration was elevated only in the rats treated with both DOC and saline. It is suggested that vasopressin is essential for the expansion of blood volume in the early stages of DOC-salt hypertension, and functions as a direct pressor agent only in the later stages.

Angiotensin II↗
PubMedDate not supplied

Vasopressin release does not contribute to pressor action of enkephalin in SHR.

The effects of injection of a peptidase-resistant analog of methionine-enkephalin, [D-ala2]-methionine-enkephalin, on blood pressure (BP), heart rate, and vasopressin release were studied in spontaneously hypertensive rats (SHR). Intravenous injection of [D-Ala2]-methionine-enkephalin (DAME) increased BP in both SHR and normotensive Wistar-Kyoto (WKY) controls, with a significantly greater increase in hypertensive rats. Intracerebroventricular injection of DAME produced a biphasic increase in BP and an increase in heart rate in both groups. The initial pressor effect was significantly greater in the SHR, Plasma vasopressin levels in SHR were depressed relative to both untreated hypertensive rats and animals given vehicle control injections. Intravenous pretreatment with a vasopressin vasopressor antagonist, [l-(beta-mercapto-beta-beta-cyclopentamethylenepropionic acid),2-(O-methyl)tyrosine] arginine-vasopressin, did not block either component of the central enkephalin response in hypertensive rats. These date indicate that central enkephalin injection does not release vasopressin and that SHR are hyperresponsive to enkephalin. It is concluded that pressor systems other than that of vasopressin mediate the enkephalin-induced cardiovascular effects.

Animals↗
PubMedDate not supplied

Effect of intracerebroventricular captopril on vasopressin and blood pressure in spontaneously hypertensive rats.

In conscious, unrestrained spontaneously hypertensive rats (SHR), mean arterial blood pressure (MAP) increased from a pretreatment value of 150 +/- 4 to 179 +/- 7mm Hg within 10 min (p less than 0.01) following an intracerebroventricular (i.c.v.) injection of captopril (2 mg/kg body weight), and the plasma vasopressin concentration was increased eightfold (p less than 0.01). MAP than fell to 131 +/- 5 mm Hg at 120 minutes (p less than 0.01), and plasma vasopressin concentration returned to pretreatment levels. The initial increase in MAP was due in large part to increased plasma vasopressin levels since this increase was reduced 50% by pre-treatment with a specific antagonist of the pressor action of vasopressin. The reduction in MAP at 120 minutes in captopril-treated rats may been nonspecific, since a similar effect was observed in SHR given an i.c.v. injection of a control solution. In (Wistar-Kyoto) WKY rats, i.c.v. captopril was without a statistically significant effect on MAP, but the plasma vasopressin concentration increased three-fold (p less than 0.01). These findings may reflect an increased sensitivity of the control system for vasopressin release in the SHR.

Animals↗
PubMedDate not supplied

Contribution of vasopressin to hypertension.

The contribution of vasopressin to the hypertensive process has been examined in a number of models of hypertension. Vasopressin is essential for the production of DOC-salt hypertension in the rat, It is likely that vasopressin is required in the early stages of this model of hypertension for its antidiuretic activity and contributes to the later stages of the hypertension as a pressor agent. Vasopressin secretion is increased in SHR, but there may be some differences between the SHR and stroke-prone SHR strains. The pressor action of vasopressin appears to be important in the stroke-prone SHR with well-established hypertension, but not in the young SHR. Vasopressin secretion is greater in Dahl S rats on a high salt diet than in similarly treated R rats. Blockade of vasopressin's pressor activity failed to lower blood pressure in these S rats, unless they were pretreated with captopril. There is insufficient information to determine whether vasopressin has a role in the hypertension in NZGH rats. Vasopressin appears to function as a pressor agent in some, but not all, rats with two-kidney, one clip hypertension. Although vasopressin is not essential for the production of one-kidney, one clip hypertension, it apparently contributes to the hypertension by virtue of its antidiuretic activity. Vasopressin secretion is elevated in partial nephrectomy-salt hypertension, and here, too, it is needed for its antidiuretic action. The question of whether vasopressin secretion is elevated in human essential hypertension is controversial, and its role remains to be determined.

Animals↗