We investigated the participation of A1 or A2 receptors in the gonadotrope and their role in the regulation of LH and FSH secretion in adult rat hemipituitary preparations, using adenosine analogues. A dose-dependent inhibition of LH and FSH secretion was observed after the administration of graded doses of the R-isomer of phenylisopropyladenosine (R-PIA; 1 nM, 10 nM, 100 nM, 1 microM and 10 mi...

Background: In this study, the effects of three structural analogues of adenosine upon proliferation of human tumor cells were investigated. Previous research showed a cytotoxic effect of adenosine via A3 receptor and A1 receptor and sometimes this effect was receptor independent. The researches showed a differential cytotoxic effect of adenosine and its A3 agonists on cancerous cells, while ot...

The effects of adenosine deaminase and of pertussis toxin on hormonal regulation of lipolysis were investigated in isolated human fat cells. Adenosine deaminase (1.6 micrograms/ml) caused a two-to threefold increase in cyclic AMP, which was associated with an increase in glycerol release averaging 150-200% above basal levels. Clonidine, N6-phenylisopropyladenosine, prostaglandin E2, and insulin...

Hypothyroidism is associated with an enhanced sensitivity of rat fat cells to the inhibitory action of adenosine and adenosine agonists. The sensitivity of the forskolin-stimulated cyclic AMP response of rat fat cells to the adenosine agonist N6-phenylisopropyladenosine is amplified 3-fold by hypothyroidism. Forskolin-stimulated adenylate cyclase activity is more sensitive to inhibition by this...

BACKGROUND In this study, the effects of three structural analogues of adenosine upon proliferation of human tumor cells were investigated. Previous research showed a cytotoxic effect of adenosine via A3 receptor and A1 receptor and sometimes this effect was receptor independent. The researches showed a differential cytotoxic effect of adenosine and its A3 agonists on cancerous cells, while oth...

The purpose of the present study was the identification of A, adenosine receptors in intact rat ventricular myocytes, which are thought to mediate the negative inotropic effects of adenosine. The adenosine receptor antagonist [H]-8-cydopentyl-l,3-dipropylxanthine was used as radioligand. Binding of the radioligand to intact myocytes was rapid, reversible, and saturable with a binding capacity o...

The mechanism of adenosine-induced vasodilation in rat diaphragm microcirculation was investigated using laser Doppler flowmetry. Adenosine (10(-5), 3.2 x 10(-5), and 10(-4) M), the nonselective adenosine agonist 5'-N-ethylcarboxamido-adenosine (NECA) (10(-8)-10(-7) M), the specific A(2A) agonist 2-p-(2-carboxyethyl)phenyl-amino-5'-N-ethyl carboxamidoadenosine (CGS-21680) (10(-8)-10(-7) M), and...

Exposure of cells to adenosine receptor (AR) agonists leads to receptor uncoupling from G proteins and downregulation of the A(1)AR. The receptor levels on the cell surface generally recover on withdrawal of the agonist, because of either translocation of the sequestered A(1)AR back to plasma membrane or de novo synthesis of A(1)AR. To examine the mechanism(s) underlying A(1)AR downregulation a...

Caffeine, a nonselective adenosine receptor antagonist, 7-methyl-1,3-dipropylxanthine, a purported A2 selective antagonist and a 1,3-dipropyl-8-phenylxanthine amine congener (XAC), an A1 selective antagonist, were evaluated for their in vivo selectivity at A1 vs. A2 adenosine receptors. Blockade of the negative chronotropic effect of bolus i.v. injections of 2-chloroadenosine, R-phenylisopropyl...