Studies on the maintenance of cytochromes P-450 and b5, monooxygenases and cytochrome reductases in primary cultures of rat hepatocytes.

The cytochrome P-450 content of rat hepatocytes declined rapidly over 72 h in culture, due primarily to denaturation to cytochrome P-420. Six different media were investigated for their ability to conserve cytochrome P-450 during culture, and the most successful was a modified Earle's medium. After 72 h culture in this medium, cytochromes P-450 and b5, NADH-cytochrome b5- and NADPH-cytochrome c-reductases were maintained at 40, 100, 35 and 52% of fresh cell values, respectively. Cytochrome P-450 showed differential functional stability during culture with ethoxyresorufin O-deethylation being more stable than either pentoxyphenoxazone O-depentylation or biphenyl 4-hydroxylation. Monooxygenase than did cytochrome P-450 content. This discrepancy was not explained by loss of flavin nucleotides, FMN or FAD.

Prolactin responses to histamine H2 receptor antagonists.

We have compared the effects of cimetidine and SK&F 92994, a new more potent histamine H2 receptor antagonist, on serum prolactin, and also assessed the effect of the H2 receptor agonist impromidine on the response to cimetidine. As previously reported, cimetidine 200 mg given as an iv bolus dose produced a marked rise in serum prolactin, but 50 mg and 200 mg of SK&F 92994 given by the same route had no effect. Iv infusion of impromidine 10 microgram kg-1h-1 failed to modify the prolactin response to cimetidine. It is concluded that the rise in serum prolactin following iv administration of cimetidine may be due to a specific property of cimetidine. An effect mediated via histaminergic pathways within the central nervous system, although less likely, cannot be excluded.

Conjugation of polyamines in mammalian cells in culture.

In cultures of BHK-21/C13 cells (Syrian baby hamster kidney fibroblasts) or 3T6 cells (Swiss mouse embryonic fibroblasts), spermidine and spermine undergo conjugation to a low molecular weight moiety which, under certain conditions, is excreted from cells into the extracellular fluid. A schematic model has been devised to describe the various metabolic processes that may be involved in the control of polyamine levels in mammalian cells and their extracellular fluid.

Polyamine replacement by magnesium ions in BHK-21/C13 cells.

Cultures of BHK-21/C13 cells, whose growth was inhibited by deprivation of serum, were stimulated to grow by addition of serum to the culture medium. Addition of MgCl(2) to the medium, to increase the concentration of Mg(2+) ions by 15mm, 30min before addition of serum, had no effect on the stimulation of cell growth, but inhibited the accumulation of cellular spermidine, so that the spermidine/spermine molar ratio was lower in these cultures than in cultures that had received no additional cations. The increase in the activity of ornithine decarboxylase that occurs 4-5h after serum ;step-up' was substantially diminished by increasing the concentration of Mg(2+) ions, but not of Na(+) or K(+) ions, in the medium by 30mm, 30min before addition of serum, and this inhibition was maintained for at least 24h. Methylglyoxal bis(guanylhydrazone), added to serum-deprived cultures to a concentration of 20mum, 30min before addition of serum, severely inhibited the increase in cell growth. The inhibitory effects of the drug were prevented by simultaneous addition of spermidine to the medium (to 100mum), and were partly prevented by the simultaneous addition of Mg(2+) ions (to 30mm). Mg(2+) ions were particularly effective in overcoming the inhibitory effect of methylglyoxal bis(guanylhydrazone) on the synthesis of DNA. Thus although a certain lack of specificity for cations exists in BHK-21/C13 cells, in that Mg(2+) ions can be substituted for polyamines, particularly spermidine, to some extent, there are cellular processes for which the requirement for polyamines as cations is specific.

Excretion of spermidine from BHK-21/C13 cells exposed to 6-thioguanosine.

The growth of BHK-21/C13 cells in monolayer cultures was inhibited by 6-thioguanosine. Accumulation of putrescine, spermidine, and spermine was inhibited by 6-thioguanosine, and cells incubated in the presence of the drug had a decreased content of polyamines relative to control cells. These effects were more marked for spermidine than for spermine or putrescine. Consequently, the intracellular spermidine:spermine molar ratio was decreased in cells exposed to the drug. Cells, the polyamines of which had been labeled with [3H]putrescine, were incubated in the presence or absence of 6-thioguanosine. More polyamines were lost from cells exposed to the drug than from control cells. The radioactive material excreted was predominantly spermidine, both as its free form and in a conjugated form, even when the cells contained large amounts of labeled spermine. This release of spermidine from BHK-21/C13 cells into the culture medium was a specific response of the cells to alterations in growth potential rather than a consequence of leakage due to cell lysis.

Diminished excretion of polyamines from BHK-21/C13 cells exposed to methylglyoxal bis(guanylhydrazone).

Methylglyoxal bis(guanylhydrazone) (1,1'-[methylethanediylidine)dinitrilo]diguanidine) inhibited the growth of BHK-21/C13 cells in monolayer cultures. Accumulation of spermidine and spermine was inhibited, whereas the accumulation of putrescine was increased. The intracellular spermidine/spermine molar ratio decreased conly slightly after exposure of the cells to 20 micrometer-methylglyoxal bis(guanylhydrazone) for 1 day. Cells incubated in the presence of the drug released less polyamine into the culture medium that did control cells, the polyamine released consisting almost exclusively of spermidine, both free and as a conjugated form.

The use of pindolol in the treatment of essential hypertension: a multi-centre assessment.

A multi-centre general practitioner assessment of pindolol, a beta adrenergic blocking drug, was carried out in 464 patients with essential hypertension. The average daily dose was 21 mg and the average period of observation was 15 weeks. Pindolol was shown to be a safe, effective and well tolerated hypotensive agent. In 227 new cases of hypertension, 148 (65.2%) were controlled on pindolol alone, and in 237 previously treated cases of hypertension 91 (38.4%) were subsequently controlled on pindolol alone. In the remaining cases the addition of a diuretic or other antihypertensive agent was necessary to achieve satisfactory control. The mean blood pressure was lowered from 190/111 mmHg to 154/90 mmHg, a mean fall of 36/21 mmHg. Side-effects were not of a serious nature.