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.

Pharmacokinetic investigation with 125I labeled T-actemodulin (TAM).

The aim of the study was to label TAM with radioactive iodine and to follow its distribution in different organs of rats. T-actemodulin is a thymic hormone isolated from calf thymus by a new technology. TAM was labeled according to the method of Greenwood and Hunter. Two major peaks were observed on the gel chromatography: The first peak contained the labeled TAM; the second peak contained 125I which was not bound to the organic compound. Additional purification of the first peak was performed on a Sephadex G-75 column, and the eluate was designated as purified peak I. After a radioimmune testing it could be concluded that TAM was labeled successfully and the peak I contained 125I-TAM. Peak I, purified peak I and the peak II were applied to young male Wistar rats. The radioactivity of pancreas, kidney, spleen, adrenals, liver, thymus, bone marrow, testis and thyroid were measured after killing the animals 10 min, 60 min, and 24 h after the injections. The pharmacokinetic study showed that all organs, except for the thyroid have a higher affinity for labeled TAM than for the free 125I. Higher accumulation of labeled TAM was observed in the pancreas, kidney, adrenals and spleen. A specific uptake of labeled TAM in these organs can be suggested. Functional interrelations between thymus and pancreas, spleen, adrenals are discussed.

Morphological changes in pancreatic B-cells after intravenous administration of forskolin.

The morphological changes in rat pancreatic islets were studied after intravenous injection of forskolin (1.5 mg/kg), an activator of adenylate cyclase, to male Wistar rats. A high amount of insulin containing granules was observed on PAP immunostained paraffin sections. Ultrastructural study of islet B-cells demonstrated enlarged perinuclear space, dilated cisternae of rough endoplasmic reticulum and activated Golgi complex with numerous vesicles. The results suggest that intravenous administration of forskolin produces a modest increase of B-cell synthetic activity in the pancreatic islets of rats. It is assumed that forskolin affects pancreatic B-cells via increased cAMP.

A precise radioimmunochemical method for determination of free insulin and insulin bound to serum proteins, including antibodies.

Polyethyleneglycol precipitation of insulin antibodies and insulin-antibody complexes is associated with co-precipitation of part of the free insulin. The recovery of free insulin was found to depend both on the quantity and quality of the antibodies and varied between 94% and 40%. Thus, the concentrations of free and total insulin may be lowered up to 2.5-fold in different sera containing endogenous antibodies. A critical evaluation of these results led to the development of a more reliable method for the assay of total and free insulin, based on individual radioisotopic determinations of the recovery of insulin extracted by PEG. The recovery of insulin added to sera containing antibodies as determined by the present method is within the range of 100 +/1 2.5%. In sera not containing antibodies total insulin concentration was found to be up to 5-times higher than that of IRI and to reach values above 250 muU/ml whereas whereas indirect IRI (i-IRI) may increase over 25 times with age.