Effect of lesions to the supramammillary area of the posterior hypothalamus on atrial natriuretic peptide release following acute blood volume expansion in conscious Wistar rats.

Acute blood volume expansion (AVE) is a potent stimulus for atrial natriuretic peptide (ANP) release. Since several central nervous structures are well known for their involvement in the regulation of fluid and electrolyte homeostasis and in the secretion of central ANP, we carried our experiments on 33 conscious Wistar rats in order to determine if the integrity of the supramammillary (SMA) hypothalamic area is essential for the peripheral ANP response to AVE. We performed stereotaxic electrolytic lesions of SMA in part of the animals. To obtain AVE we administered 2 mL saline/100 g b.m. for 2 minutes into v. jugularis through the chronically implanted venous catheters. Plasma ANP was assayed radioimmunologically. AVE significantly increased plasma ANP both in the intact animals and in the lesioned rats. This concluded that SMA is not involved in the regulation of peripheral ANP release during AVE.

Effect of dopamine receptor blockade on the renal excretory response to acute volume expansion (AVE) in conscious Brattleboro rats.

UNLABELLED: All the studies were performed on chronically cannulated, conscious Brattleboro rats, housed in metabolic cages under standard conditions. The renal excretory indices: diuresis (V), sodium (UNa.V), potassium (UK.V), chloride (UCl.V) and osmotic (Uosm.V) excretion were measured under the following experimental protocol: (1) controls, (2) 2% volume expansion (AVE)-0.9% NaCl i.v. for 2 min, (3) Dopamine (DA) receptor antagonist Flupentixol (FLU) 0.5 mg.kg-1 i.v., and (4) AVE 10 min after i.v. application of FLU. All the indices studied, given as cumulative curves, showed a firm linearity with time during the whole experimental period (5 h) in groups 1 and 2 (p < 0.05), while such a relationship was not found significantly in groups 3 and 4. AVE quickly, strongly and significantly (p < 0.01) increased V and especially UNa.V, UCl.V and Uosm.V. Pretreatment with FLU potently suppressed the effect of AVE on the renal excretion. FLU alone decreased almost equally V and saliuresis. IN CONCLUSION: the DA antagonist FLU blocks the diuretic and saliuretic response to AVE probably by affecting tubular processes.

Interrelation between the renal sympathetic nerve and atrial natriuretic peptide in conscious long Evans rats subjected to sodium restriction.

The renal excretory function and plasma renin activity (PRA) were studied in conscious rats on a low sodium diet (25 mmol/kg) after atrial natriuretic peptide (ANP) infusion (100 ng/kg b.w./min) for 80 min through a catheter implanted in the right atrium. The half of the animals were with bilateral kidney denervation. The rats were housed every day from 8 a.m. to 2 p.m. in individual metabolic cages for urine collection and Na, Cl, osmolality and endogenous creatinine determination. At the last day of the experiments after the ANP infusion, blood was taken from the heart for electrolytes, endogenous creatinine and PRA. The effect of denervation was monitored by measuring of noradrenaline in kidney homogenate. The data indicated that even at low sodium diet ANP stimulates the diuresis and sodium excretion without changing the glomerular filtration rate (GFR). The kidney denervation combined with ANP infusion increased twice the diuresis and four times sodium excretion vs. the control animals. In the same time PRA was decreased by about 70%. We assume that the low sodium diet attenuates the effect of ANP in respect to the excretory function. This inhibitory effect is amplified by the renal sympathetic nerves. The decrease of PRA and possibly the increased activity of renal receptors after the denervation could explain the data obtained.

[Excretory function of the kidney after denervation and the administration of a beta-blockader]. / Ekskretornaia funktsiia pochki posle denervatsii i vvedeniia beta-blockatora.

Osmotic diuresis (15% mannitol, 4.5 ml/hr) was in duced in anesthetized rats. At the end of each of 10 consecutive 10-min clearance periods the following parameters were determined: diuresis, sodium, chlorine and osmotic excretion, GFR (inulin clearance). The animals were divided into three groups: a) controls, b) with bilateral renal denervation (performed one week earlier) and c) with application of beta-adrenergic blocking agent propranolol (Obsidan, Germed DDR) introduced intravenously 0.1 mg/100 g initially and 0.12 mg/100 g sustaining dose during 2 hrs. The experimental results showed an increased sodium excretion in denervated and obsidan--treated animals with no change of the total excreted osmotically active substances. In denervated animals the chlorine excretion was increased as well. The data suggest that, in osmotic diuresis, the renal denervation and beta-adrenergic blocking agents inhibit the tubular sodium transport. The kidney osmoregulatory functions remains unchanged.